Technical Tips Technical Tips
Every owner should have a copy of the factory service manual for your P15 or D24. Even though you may not work on the car it provides your mechanic the information to service and maintain your car. You can bet he won’t have information in his shop covering a car from the forties or fifties! For owners who do wrench on their cars this page covers some common issues (and uncommon) issues you may come across.

Lug Nuts

Lug nuts on your vintage mopar don’t follow the righty-tighty, lefty loosey rule! Lug nuts are tightened in the same direction as the wheel rolls forward. Lug nuts set up this way as a safety feature! The idea was any momentum transferred to the lug nut from the wheel turning would always be in direction to tighten the nut. Remember, on the drivers side wheels you turn counter clockwise to tighten the lug nut (Lefty-tighty!) It you look closely on the lug bolt or stud you will usually see a "L" or "R" stamped on the end. So when you are doing a brake job, don’t get the drums mixed up. More importantly if you are having the tires serviced be sure to warn the shop about the reverse threads as they have probably never seen a car with lug nuts like this. Also request they do not reinstall nuts using an air gun. It is very easy to strip a reverse pitch thread in the wrong hole using an air gun. If they use a manual torque wrench it is pretty hard accidentally damage a fastener.

Valve Adjustment

Proper valve adjustment is critical for quiet and efficient operation of a flathead six and is the first line of defense against burned valves. Compared to overhead valve engine the flathead is a very simple design. A tappet follows the contour of the cam lobe pushing a valve up and open at the appropriate time. The only adjustment is the clearance between the tappet and valve stem. Accurate adjustment can only be made while the engine hot. To complete the job you will need a valve gasket set, set of go/nogo feeler gauges, pair of tappet wrenches and a pair of gloves to protect you from burns on the exhaust manifold. While the valve covers are readily visible from the top of the engine, don’t attempt this job from above the manifold. Instead raise the right front on a jack stand and remove the right front tire. Inside the wheel well is an access panel approximately 3 feet wide and 18 inches high. Remove the bolts holding the access panel. When removed you will have straight on access to the valve covers. Start the engine and bring it up to operating temperature. After the engine warms up, stop the engine and manually turn it over to Top Dead Center (TDC). Verify piston #1 is in firing position by checking the position of the distributor rotor. If should point around 7 o’clock. If it points to the 1 o’clock position, you have piston #6 in firing position. Manually turn the engine one full revolution and you are ready to start. Remove the valve covers and use the following sequence for the order of the valves to adjust.

Exhaust valve clearance .010
Intake valve clearance .008

Stage A, #1 and #6 at TDC, #1 in firing position
Stage B, #1 and #6 at TDC, #6 in firing position
To move from Stage A to B, manually turn the engine 1 revolution.

Stage A – Adjust #1 Both valves, #2 Inlet valve, #3 Exhaust Valve, #4 Inlet valve, #5 Both valves.
Stage B – Adjust #2 Both valves, #3 Inlet valve, #4 Exhaust valve, #5 Inlet valve, #6 Both valves.
Using the two tappet wrenches you can use one hand to adjust the tappet, leaving the other hand free for the go/nogo gauge, The go/nogo gauge has three steps cut into it. If the adjustment gap is too wide, you will be able to slide it to the third step. If the gap is too narrow only the first step will slide between the valve and tappet. What you want is the middle step to fit snugly. Adjust each valve as specified in the adjustment sequence. It is better to err on the side of too much clearance versus not enough. Too much clearance may result in a slightly noisy tappet, while too little may burn the valve. After you finish the adjustment, reinstall the valve covers with the old gaskets. Bring the engine back up to operating temperature and you will notice the engine is much quieter. Sometime you will need to readjust a single noisy valve. Just make sure it is fully off the cam lobe and totally closed. If everything is OK remove the valve covers and install the new valve cover gaskets (780-469) with sealer. When re-tightening the valve covers don go overboard. They just need to be snug, letting the gasket and sealer do the work. Too tight distorts the sheet metal cover and usually results in leak. Reinstall the access panel and tire and you are back on the road. Properly adjusted valves result in a quiet running engine and help protect against damaged valve train components. If you have done the job right it will be difficult to tell if the engine is running from five feet away because it so quiet!
Evr-Dry Kits
Evr-Dry kits are rubber boots enclosing the spark plug and wire, creating a waterproof enclosure. Looking at the hood you will notice a seam alone the center of the car, directly over the spark plug wells on the cylinder head. Rain often seeps in the seam and drips onto the plug wires, often filling the shallow plug wells recessed in the head. When you try to start the spark plug wires are shorted by the water. Also water drips onto the distributor cap with the same result. Evr-Dry kits keep the plugs and connectors watertight. The kit consist of a small metal lipped cup which sits under the spark plug, rubber boots to cover the top of the spark plug and distributor cap terminals, new plug wires and brass connectors. Installation is a simple 30 minute job. Separate the new plug wires by length. After removing the spark plug, place the metal cup under plug and screw the plug back into the head. A Plymouth Product Information Bulletin indicates you should remove the spark plug gasket. The metal cup acts as a washer and correctly positions the depth of the plug electrode in the head. Next remove the old plug wire from the distributor. Push the new plug wire through the Evr-Dry boot, and install the brass sparkplug terminal. Depending upon the terminal design, you may need to strip the plug wire back a 1/2 inch, then crimp the terminal in place. If you have one a die crimper will provide a better connection. Push the terminal onto the spark plug and mount the boot on the top edge of the metal cup. It is now watertight. Feed the other end of the new plug wire through the distributor wire guide mounted on the side of the coil. Push on the smaller distributor rubber boot. Finally install the brass distributor terminal and re-insert the plug wire into the distributor cap. This simple and inexpensive add on will guarantee easier starting in wet weather year round. Evr-Dry Kits are available from Robert's Motor Parts. One installation issue has been reported. After installing Evr-Drys and plug wires the car would refuse to start or run poorly with a bad ignition miss. Every time this was tracked down to a connector on the plug or coil wire not seated properly in the distributor cap. The problem is often the brass terminals. They use a small spade point pressed into the center plug wire conductor. However this terminal design has nothing to hold the terminal to the plug wire except the sides of the cap as you slide it in. If they are slightly off center the spade point loses contact with the center conductor. A simple fix is replacement plug wire terminals form NAPA. The design allows you to securely crimp the brass terminal to the wire. You may want to consider discarding the terminals in the Evr-Dry kit and use the more secure NAPA terminals
Hard Starting Hot Engine
One of the most common complaints is hard starting when the engine is hot. Usually the starter will just grind away but won’t fire. After about 10 minutes  the engine cools down and starts immediately. Generally the problem is blamed on vapor lock which is the fuel getting so hot in the fuel line it vaporizes or builds pressure and floods the carburetor bowl. The culprit is heat specifically from the exhaust manifold. The Chrysler engineers addressed the problem by adding a fuel pump heat shield mounted to the top of the fuel pump. Often this equipment has been lost or modified over time, causing the problem to reoccur.
  Missing Fuel Pump Heat Shield Fuel Pump Heat Shield The flat heat shield is installed between the pump and manifold. It is held in place with a bolt on the manifold and tall bolt to the fuel pump. It is common this part was not reinstalled when the fuel pump was replaced. If it is missing reproductions are available from Paul Taylor Industries, PO Box 618, Arroyo Grande, CA 93421 for reasonable cost.
Second, is your heat riser system working correctly? If it is preheating the fuel mixture all the time it will just contribute to your hard starting problem. The heat riser section has information on how to service and maintain the unit.
How far is the fuel line from the exhaust manifold? If it is less than one inch from the exhaust manifold, replace the line. Relocate it away from the exhaust manifold. Do you have an aftermarket fuel filter installed on the line? This is not a good location as it provides more area to absorb heat. Factory fuel filters were installed at the carb inlet away from the exhaust manifold. NEVER use a plastic inline fuel filter. Under heavy engine load the temperature will get high enough to melt the outside of the filter case, allowing fuel to be sprayed directly onto the hot engine.
Next check the carburetor float and make sure it is correctly adjusted and the needle valve is not worn.  It the float valve is out of spec it can make the carburetor easier to flood. If you still have problems after checking these items you can try a couple inexpensive modifications. Insulate the fuel line with a small rubber hose split in the middle, wrapped the length of the steel line. Insulation products made specifically for this purpose are also available from aftermarket suppliers.
Hard To Start When The Engine Is Cold?
On cars with a manual choke there is a specific starting sequence you need to follow:
Pull the manual choke out 3/4 to 1 inch.
Pump the accelerator once or twice.
Then hit the starter button.
When you pull the choke out it doesn’t set the throttle on the fast idle ramp until you step on the gas once. At the same time a spring snaps shut the choke butterfly. This will insure easy cold engine starts.
Crankcase Ventilation System
The crankcase ventilation system on your flathead six is simple to check and maintain. Its job is to clear the crankcase of unburned fuel and moisture to prevent sludge forming in the crankcase oil. This is accomplished by bringing in fresh air through the oil filler cap and tube. Under the exhaust manifold a downdraft tube creates a vacuum as you drive down the road, pulling gases and moisture out of the crankcase.
The recommended maintenance includes cleaning the filter in the filler filter cap with kerosene. Perform this with your oil changes. After it dries, re-coat the filter material with engine oil. Go easy with the oil, 5-10 drops is fine, or you will be wiping it off your distributor and oil filter for the next thousand miles. Make sure the orientation of the cap is correct. The open filter area should face the rear of the car. The maintenance instruction decal should be visible on the side of the filler cap. The keyway in the oil filler cap fits over the ridge pressed in the oil filler tube. Turn the oil filler tube so it allows the correct orientation of the oil filler cap. If the open filter area is facing forward, the engine fan will blow more dirt and dust into your oil. You may need to adjust the two flats springs inside the cap for easier removal. When everything is set up correctly, the cap will come off easily without pulling the oil filler tube out of the block.
Last check the downdraft tube under the manifold. Even though most illustrations show the tube positioned vertically, a Plymouth Service Department flyer stating "It is important that this pipe (ventilator outlet pipe) be returned to its extreme rear position... If this is not done and the ventilator pipe is left in forward position, dust will enter the engine oil pan, causing rapid wear of moving parts." This extreme rear position maximizes the vacuum effect created by they air moving past the tube, thus pulling the gases out of the crankcase. Make sure the tube is not damaged or partially blocked by oil sludge. It is attached to the block by one bolt and is easily removed for cleaning or repair.
  Factory PCV System
Chrysler also supplied an optional positive crankcase ventilation (PCV) system. Originally used on some truck models to waterproof engine, it was a dealer installed factory option. A tube draws fresh filtered air from the air cleaner into the oil filler tube. The oil filler tube is sealed with a removable locking cap. The down draft tube is replaced with a tube that goes to a metering valve on the intake manifold. This draws moisture and blowby back into the engine via vacuum into the intake manifold to be recycled. Factory installations for the factory kit are available on the Downloads pages and parts can still be source to assemble a working system.  Keeping your crankcase ventilation system correctly operating will improve the life of your oil and general engine life. Just remember to check it with each oil change.


Water Distribution Tube

The water distribution tube provides a vital function in cooling your engine. It directs cooling water directly form the water pump to the upper block and valve area. Generally it is removed for inspection when an engine is overhauled, and replaced as required. However, in my experience, many production rebuilders do not perform this repair because the tube is rusted in place and difficult to remove. Failure to replace a rusted out water distribution tube will certainly lead to hot spots in the block and future problems.
Water Distribution TubeReplacement water distribution tubes are readily available from many NOS suppliers, manufactured in either steel or brass. Be sure you order a tube for a your engine block. Two versions are used, one for 23” and the other for 25” blocks. Access the tube by removing your water pump. If you are doing a rebuild, access is straightforward. If you are trying to do this in the car you will need to drain the coolant, remove the radiator, fan and water pump. Looking at the block face, it is the "D" shaped opening on the left, almost in line with the valves. Using a hook formed from 1/2 inch steel rod, insert the hook and catch one of the slots cut into the upper edge of the tube. This is not an easy repair to do with the engine block in the car. If you are really lucky, a sharp pull should break it loose and the tube will slide out. I you are like the most of us, it won come out. Next step is to liberally apply a lubricant like Liquid Wrench or motor oil along the edges of the tube. I flip the engine block upright, and this allows the lubricant to run down the sides of the rusted tube. Let it soak for a while and give the hook another try. If you are having trouble getting the hook to stay set in the tube hole, try squeezing the edges of the tube together with a pair of vise grips. You can generally collapse the tube sides inward 2  3 inches and this provides a firm grip for the vice grips. A small slide hammer can be hooked on to the vise grips and a couple swings on the slide hammer pops the tube out. Still no go? Take a piece of 1/2 wide flat bar stock and gently drive it into the block between the thin straight side of the tube wall and the block. Again, use plenty of lubricant like Liquid Wrench or motor oil. You are trying to break loose the rusted tube wall from the block. Usually the tube collapses inward a bit, making it easier to remove. Drive the bar stock in 6-8 inches, then try the vice grips and slide hammer. If this doesn’t work, try driving the bar stock in a little deeper until you can finally remove the old tube. I have used this technique on four different blocks with success. If it is not moving, be patient and let the oil soak overnight. Give it a chance to loosen up the rust bond between the tube wall and block. Another trick is to remove the manifold and manifold studs. Penetrating oil can be applied through the holes directly onto the sides of the rusty distribution tube for the entire length of the tube.
If you are really unlucky, the tube will break and only a section will come out. I have not had this happen, but have seen it mentioned in the service manual. Slightly sharpen the edge of the bar stock so you can catch and lift the remaining tube pieces away from the block side and again lubricate well. I think you will need a stronger hook to catch the remaining tube pieces. In my experience it was very easy to pull the hook out of the 1/4 inch rod stock when trying to pull the tube. A heat formed hook would be the way to go. If you are doing a rebuild, cleanup is easy. When they hot tank the block it will remove the lubricant from the water jacket. It the block is in the car, rinse well with a soap solution, then flush the water jacket until the water runs clear.
  Tube Installed
Installation of the new distribution tube is straightforward. Inspect the block to make sure the water jacket is clean. If not flush and clean. The new water distribution tube is slid into the opening and then the front D shaped edge gently peened over to hold it in place. Reinstall the components you removed and refill with appropriate coolant.

Convert Or Keep The Faith, 6 or 12 volts

A common thread on the forum is the conversion of the original 6 volt system to a "modern" 12 volt environment. While such a project is technically feasible, it’s a good idea to review the objectives and issues of a 6 to 12 volt conversion. The first question is why. Common answers include "the lights are dim", "faster cranking to start easier" or " I want install an updated music/nav system". Some owners feel a 12 volt system is "safer and more reliable" or "easier to jump start if the battery is dead”. Lets look at these issues and balance it against your challenge if you decide to convert. Personally, I’m in the "keep the faith" school of staying with a properly maintained 6 volt system. Conversion has a whole set of issues and may reduces the show and resale value of your car. Starting when these vehicles were built, headlights were bright and the weather in 1948 was just as cold today and the cars started. And a poorly maintained 12 volt system will be just as problematic as a poorly maintained 6 volt system. Dealing with the core maintenance problems of the 6 volt system will often eliminate the reason for contemplating the switch to 12 volts. So lets look at the potential impacts of switching from 6 volt positive ground to 12 volt negative ground. First the good news. Six volt systems required greater amperage for the same load as 12 volt systems, which means the wire gauge currently installed is larger than what you would find on a modern 12 volt system. So you won’t need to rewire provided the existing wiring harness is in good condition. However, a deteriorated wiring harness is probably the most common source of electrical problems. Fifty plus years of thermal cycles have left the rubber and cloth insulation rotted and cracked, and connectors rusted and corroded. Only a new wiring harness will fix this problem. If you don’t fix it the higher voltage potential of 12 volts will create a greater hazard and potential for fire. If the wiring harness is not in top condition, replace it. Next check your battery cables. What is the condition and gauge. The most common cause of slow cranking is using a 12 volt cable on a 6 volt system. They will not have the capacity to deliver the correct amperage to the started and it will turn slow. Six volt cables should be 00 gauge to provide best service. Next you will need to switch all light bulbs including: headlamps, front and rear running lights, brake lights and turn signals. Then the turn signal flasher and dash indicator lights. Finally all dashboard illumination lights, hi-beam indicator and inside courtesy lights. Equipment changes include: battery, regulator, generator, coil, horn relay, horns and starter solenoid. You will probably need to fabricate or buy a mounting bracket for the alternator and appropriate belt(s). Voltage reduction devices are required for non-resistive loads like the interior clock, radio, fuel gauge and heater motor (or swap out the motor for a 12  volt unit) I have seen several types of voltage reduction devices, ranging from resistors to sold state devices. Pricing range is $5.00 to $15.00, depending upon amperage. It is unlikely the ammeter could be used unmodified. Technically, the starter motor would need to be replaced, but do to the short duty cycle you probably can get by with the existing 6 volt unit. Now if your P15 had been manufactured with a negative ground system, you would be pretty much finished. However, P15s are positive ground, which makes the conversion much more interesting. Devices which are on a voltage reduction device, such as the stock radio, may require positive ground for operation. If would be impossible to isolate these devices from chassis ground (I.E. "float" the grounds) and any such devices would require replacement with a negative ground device. Stock radios are most difficult because of the required antenna ground and typically require a radio shop to convert them.
After making all these changes, how is it going to be more reliable? The alternative approach is to fix what is wrong with the existing 6 volt system. Then look at few options to satisfy the objectives mentioned at the beginning of this article. First, replace the battery and battery cables with the correct sized parts. The battery tray will hold a Group 2 battery. If you are going with a wet acid battery, most battery suppliers do not stock this size and they will try to sell you a smaller battery. Have them order the correct battery or better, replace it with one of the new dry cell Optima type batteries. These put out over 650 amps, while the smaller 6 volts cases are in the 350 to 400 amp range. As mentioned earlier make sure you have 6 volt battery cables. You can bet somewhere along the way the cables were replaced with 12 volt cables. You will probably need to order the correct cables as auto parts stores don’t stock them. Another option discussed to switch to 8 volt battery while staying with positive ground. This will provide a slightly higher cranking speed and brighter lights at the expense of bulb life. There is also the potential to damage stock radio equipment. In addition, an automotive electrical shop will need to adjust the voltage regulator/generator so the battery will fully charge. The 8 volt units are special order items but generally available, especially from battery suppliers who deal with agricultural equipment.
Dim lights are caused by poor connections, usually a bad ground, deteriorated wiring harness or an incorrectly installed 12 volt bulb in your 6 volt system. Verify the condition of the wiring harness, perform proper maintenance on the connectors, junction blocks and grounds and verify the correct bulbs are installed. The single most common cause of dim tail lights is someone installed a 12 volt bulb! Check the Downloads page for 6 volt bulb information. The condition of your wiring harness is the crucial link in the chain. If you wiring harness needs replacement, changing over to 12 volts will not improve anything except the potential for a fire. If the rubber insulation is broken or cracking, replace the harness. YnZ Parts of Yesterday (909-798-1498) or Rhode Island Wiring are quality sources for a new harness. My personal experience with mass market "mail order" suppliers is they do not provide the correct wiring gauge for a 6 volt system, so shop carefully.
Connecting a modern sound system is problematic, but not impossible. One option is have the unit modified adding FM Stereo and aux capability to the AM unit while maintaining a 100 percent stock appearance. Another option for an iPod or CD use a 6 to 12 volt DC inverter. You will need to insulate the unit from chassis ground and run separate circuits for the hot and ground from the inverter to the unit. Don’t use speakers that have a common ground with the speaker leads and frame ground. Your speaker grounds need to "float". You should not use a 12 negative ground device requiring an antenna connection as the ground will cause a short. Even better, keep it simple. Buy a portable CD/iPod player.
A properly maintained 6 volt system is neither intrinsically more or less reliable than a 12 volt electrical system. The systems condition is what determines if is safe and reliable and proper maintenance is key.
If you decide to covert to 12 volts, search the forums for additional background info. For example one P15 owner made the switch to 12 volt system started by using a homemade harness. The generator was replaced with a 60 amp Chrysler alternator which bolted to the original generator bracket. An external voltage regulator replaced the stock 6 volt regulator. The original oil and temp gauges, being non electrical, required no changes. An inline voltage reducer was used on the fuel gauge. The original amp gauge, to date, has not caused any problems. It was wired only into the charging circuit. Nothing else runs off of the amp gauge. Also upgraded was the electrical service by adding a fuse panel with nine fuses. The radio and clock were upgraded to 12 volts. The heater motor was exchanged for a 12 volt motor with the same dimensions and shaft size. Turn signals were installed and the original brake light is used as a "third brake light". This P15 owner would definitely do this conversion again as the car was very easy to re-wire and he has minimal issues post conversion.
Installing Valve Guides
If you are doing a valve job or full overhaul pay close attention to how the valve guides are re-installed. In the factory service manual one sentence warns exhaust valve guides are mounted reverse from the intakes valve guides (P15 Service Manual. Page 149.) It is not even mentioned in the D24 Service Manual! For exhaust valves install the counter-bored ends upward. This provides better heat shielding. Intake guides are mounted counter-bore down. Most machine shops are not familiar with these engines anymore and you need to warn them about the correct installation procedure.  In the image the lower valve is #6 exhaust guide.
Valve Guides

Oil Leaks
Let me count the oil leaks: seal on the timing chain cover for the crankshaft vibration damper, seal on the transmission extension for the parking brake drum and the seal on the pinion for the rear end. Makes working under the car a messy job. Replacement of these seals is pretty straightforward, but often time consuming. Because of this, be sure to do the job right by repairing both the seal and shaft surface. Otherwise you will be re-doing the job in the near future. For example, the crankshaft seal behind the vibration damper is the source of oil that blows all over the bottom of the engine. After you replace the seal check the sealing surface of the crank hub. It should be smooth with no traces of grooves or roughness. Usually you will see a groove cut by the old seal. Repair procedure for this damage use to be to braze new metal to build up the surface, then turn the hub down to the correct diameter. Good luck on finding a shop that knows how to do this type of work. Enter "Speed Sleeves". Today, you can use a speed sleeve, a very thin steel sleeve which is pressed over the damaged shaft area. This provides a factory finish for the new seal to mate against. They work great and most engine rebuilding shops have the equipment to correctly install them. They will also work on the your parking brake drum and rear end pinion seals. Installation on these parts is definitely a task to job out to your machine shop. They require a special press to install. Also the machine shop will have (or can get) the proper sized sleeve for the part to be repaired. Once completed, you can be assured you seal repair job will provide years of leak free service.
Rear Axle Lubrication
The factory recommendation is every year or 10,000 miles. However, before you perform this maintenance you might want to take little extra time find out what is really going on behind your brake backing plates. It could save you an expensive on the road breakdown. And it is one of those jobs you only need to do once, then maintenance is easy. In working of three different cars, I have seen quite a range of axle bearing conditions. One car had no grease behind the bearing and only a small amount in the bearing. Another had at least 4 different types of grease, all stratified into multi-colored layers. The top layer was white lithium grease, inappropriate for the job and leaking past the outer seal onto the brake shoes. The third had packed grease, probably from 1948, as it required quite a bit of effort to dig it out. The point is you don’t know what previous owners have done good or bad. Take the time to pull the axle bearing and check the axle inner seal and bearing race. Also check axle vent to be sure it is not clogged with dirt or old oil.
Once you have the axle pulled, clean out all the old grease on the bearing and recess behind the bearing. Recoat the recess with a layer of grease, and repack the bearing. Use the correct grease for the job. Make sure the filler plug on the bottom side of the axle is a bolt and NOT a zerk fitting. If you use a zerk fitting you can over-pressurize the bearing, causing the seal to fail and spread grease to the brake shoes. Write down what kind of grease you used and put the information in the glove box. Next year or 10,000 miles later you will be glad you did.
Temperature Gauge Sender Unit Replacement
By Jim Leman
Temp Sender
Replacing the temperature gauge unit on your P-15 is a service best undertaken when you are in a patient mood. As with most jobs requiring work under the dash, this task will test your patience. You will want to replace a broken or defective temperature gauge sending unit because without it you will lack information of a critical aspect of engine operation, water temperature. Temperature gauge sending units fail for various reasons, often from kinks or breaks in the capillary tube. This tube is inside a coiled outer protective wire shield running from the sender bulb to the gauge unit itself.
Replacement units can be purchased from any well-known Mopar parts suppliers, both those who market through catalogs, the major old car publications, the Mopar car club periodicals and occasionally they can be found both used and NOS as swap meets. Expect to pay from $100 to more than $200. Inspect the unit carefully, especially the sender capillary tube for kinks and breaks. Test the unit before you install it in your car. Fill a glass or cup with water heated to a predetermined temperature, say 180 degrees, and insert the bulb unit into the liquid. The gauge needle should begin to move slowly and settle on or very close to the gauge face temperature marking that corresponds with the known temperature of the water. If the gauge is working right, lets head to the garage. Get to know the project. Open the car hood and place your fender blanket and tools on the driver’s side fender or bring your tool cart to your side. Hang your shop light so it illuminates your work area brightly. Disconnect the battery ground. Drain the coolant by opening both the radiator and block petcocks. If you don’t coolant will run out onto your clean shop floor when you remove the old temperature bulb from gland nut in the side of head.
Gland Nut
You will find this gland nut in the left (drivers side) of the head nearest the firewall. The bulb sits inside a tapered, threaded part known as the radimeter gland nut. The nut is a threaded into the head. To remove the old nut, use a little penetrating oil to ease your effort. Loosen it and back away the retainer and then slide the bulb carefully free of the nut. Clean all threads. To reinstall, reverse this procedure. When the retainer is tightened against the gland nut, it will secure the bulb and prevent coolant from leaks. Use thread sealer for insurance.

Getting set up: Here’s a helpful hint on positioning yourself for removing the gauge unit from the dash. Position yourself in the passenger compartment like slat, head and torso under the dash with legs and feet over the back of the front seat. Before you get into position though, first pull the throttle knob out full. This will depress the accelerator pedal. Place a rag or old tee shirt over the pedal to provide a cushion for the back of your head when you’re in position. Make sure you get all your tools in position first too. Hang a shop light (I prefer the cooler florescent type) so it illuminates the underside of the dash. Having two lights carefully positioned will help to eliminate or reduce the harsh shadows you’ll get under there with just one light in action. Position the tools you’ll need on the floorboard or on the front seat where you will be able to reach them when in position. The tools you’ll need include a flashlight, a long shaft slotted screwdriver, preferably a magnetized one. Leave the beer in the house.

Clearing a path: You might want to remove some underdash clutter before you start. First, remove the headlight switch. The knob removes by inserting a narrow slotted screwdriver blade into the slot on the underside. This frees the knob from the shaft so you can remove the panel nut and slide the switch free from the other side. Bag any hardware removed and label it. You may want to use tape to tape up the switch or let it dangle free. I also found it almost impossible to access the gauge without removing the speedometer unit first. The speedometer is held to the backside of the dash by a few screws across the top and bottom of its housing. When these screws are removed and the speedometer cable removed from the unit, you should be able to jostle the unit free and clear. Place it were it won get damaged. Now, with your long-shafted magnetic slotted screwdriver, find the retaining screws in the back of the gauge and remove them. Keep the screws in a safe place. Unfortunately, the gauge doesn’t pop free, but it too requires plenty of jiggles and a little cussing to convince it to come free of the dash. Try moving the unit up slightly and to the left (as you view it under the dash) to clear the edges of the housing frame. If it doesn’t come free after a few minutes, sit up in the drivers seat, reach up with your arm under the dash and take the unit in hand. Move it to understand how it comes free of the dash glass and how you must move it to free it from the housing. Remove the unit. You’re almost done! To install the new unit, first remove the clip from the firewall grommet through which the sender wire will travel. From inside the car, with the gauge, wire and sender bulb carefully resting on your floorboard or accelerator pedal cushion, carefully push the new sender bulb through the grommet. (A lubricant like ArmorAll here eases the penetration). Now, from engine side, carefully pull the bulb clear of the grommet and with sufficient slack that it touches the gland nut head. Go back inside the car and get into position again. Carefully pull the wire and gauge unit up and through the confusion of wires and stuff behind the dash. Just as you removed the old unit from the dash, install the new one. Use care when feeding the gauge face back into its housing so you don’t damage the delicate needle. You may need to make a paper gasket for the unit first and install it on the gauge face where it mates to the housing. When the unit fits into its housing, insert and tighten the retaining screws you had carefully set aside. Reinstall the speedometer, headlight switch and any other components or wires you may have removed. With the gauge in the dash and capillary tube through the firewall, insert the sender bulb into the gland nut in the head carefully securely. Use some sealer on the retainer nut and tighten against the gland nut. A firm snug and then a nudge is sufficient.

Finishing up: Refill the radiator with coolant and restart the engine. Check often for coolant leaks at the gland nut and both the radiator and block petcocks. Keep an eye on the gauge. I t should begin to move as the coolant warms, and it should stop when the coolant reaches the temperature allowed by your engines thermostat. Replacing the temperature gauge on your P-15 takes a little time, but you can do it yourself.
Static Ignition Timing
The classic Catch-22. Your trying to get your flathead started. The engine is not running so you can't check the timing with a timing light. However you suspect the reason the engine won’t start is because the timing is set incorrectly. The solution is easy, static time the ignition.
You need a cheap neon indicator, the kind you use to check your household wall outlet. First turn the engine over by hand until the timing marks line up at top dead center (TDC). Pull the distributor cap and verify the rotor is pointing at the cylinder #1 plug tower on the distributor cap. Usually the rotor is pointing around 7:00 o’clock. If not, it means cylinder #6 is in firing position and you need to turn the engine one full revolution. One way to be sure of the firing position is to pull the front valve cover off and watch the lifters. If cylinder #1 is TDC, both valves will be closed. As you continue to turn the engine manually, the exhaust valve will open. Once TDC is set, pull the plug wire off plug #1 and hook up one lead of the neon tester to the plug connector. Connect the other neon lead to a solid ground, such as the coil bracket. I use short jumper wires with alligator clips to secure the connections. Reinstall the distributor cap, and loosen the locking bolt on the distributor so it will rotate. Turn on the ignition. Rotate the distributor fully clockwise until you hit the stop. Then slow turn counter-clockwise until you see the neon tester flash. When the light flashes you are set for TDC. Tighten the distributor lock bolt. The advantage of starting with static timing is neither the vacuum or centrifugal advances are in use. By the way, this procedure is similar to one discussed in the Plymouth Service Manual in the Ignition System section. The service manual setup uses the ignition point circuit instead of the plug wires and a six volt bulb is used instead of a neon test light.
Road Timing
A reader recently shared a story from his grandfather about the red neck method of road timing a flathead. One guy drives in circles in an empty pasture while the other guy is holding on for dear life under the hood with screwdriver in hand. The reader had seen photos of this in a local diner, and indicated you don't really grasp the hilarity of the situation until you see it, complete with several barking dogs in pursuit of the vehicle in question! Road timing, a common practice for flatheads, need not be a danger to life and limb. The procedure is discussed in the factory Service Manual in the Ignition System section. You "road time" when you advance the ignition timing up to 4 degrees BTDC. Usually this makes the car more responsive. You know you have advanced the timing too far when the engine starts to ping or knock under load (i.e. out on the road). Then you retard the timing a couple degrees. Best news is you don’t need a helper holding onto the hood!
Head Gasket Replacement
In car removal and replacement of a head gasket on a mopar flathead is a straightforward job. The following guidelines can help minimize the frustrations. You will need to determine the reason for the failure of the old gasket. Common causes are warped heads or blocks, improper torqueing during the previous installation or overheating the engine. Carbon buildup on the pistons can also increase engine compression, blowing out the gasket. Usually the cause can be determined until you pull the head. First step is to drain your engine coolant. Many of the head bolts pass into the water jacket and coolant will spill onto the pistons if the radiator is full. Remove the head when the engine is cold. Working on a warm or hot engine will usually warp the head. After removing all the head bolts, lift the head straight up. Don’t drag it off the block as it may damage the valves. The head weighs about 40 pounds and a helper is a good idea to assist in getting it out of the engine compartment. Examine the old gasket and if it has failed be sure to get all the old pieces. Now is the time to scrape the carbon off the pistons and valve seats. Next, chase all the bolt and block threads with a tap and die. Use plenty of oil when cleaning the threads You will know they are clean when you can thread the bolt by hand. That will ensure the torque reading is accurate when you reassemble. Unlike modern engines you can safely reuse your head bolts. Verify all your head bolts are in good condition, not stretched or twisted. If any are eaten away from corrosion or rust replace them. With the head off check both the block and head with a steel straightedge and feeler gauge. The straightedge is placed across the head. Sight along the straightedge to detect any warpage. Slide the feeler gauge between the head/block and straightedge to determine the amount. No factory specs are provided for maximum allowable warpage, however Stockel's provides the following general guidelines. Warpage up to .003 in any 6 inches or .006 overall is permissible. Beyond that the head/block needs to be milled up by a machine shop. Reinstalling a gasket on a warped head or block usually fails in a very short period of time. If the head and block are ok, place the new head gasket on the block and visually check every bolt and coolant hole for proper alignment. It is easy to get the gasket turned over the wrong way. If your head gasket is copper on both sides use of a sealant is optional. I have never had a gasket fail when installed with the correct sealer. Newer replacement gaskets may have copper on only one side and should be installed dry. The hardest part of this job is placing the head back on the block without knocking the gasket out of alignment. A good trick is to make a set of guides using three head bolts. Cut the heads off and with the gasket in place, screw two of the guides into the block by cylinder #1 and one guide back by cylinder #6. When you lift the head back onto the block, align the bolt guides to the cylinder head holes. Let it slide down and into position. This way the gasket will stay properly positioned. Again an extra pair of hands is helpful for lifting the head over the fender and back onto the block. Start a couple head bolts, then remove the guides. At this point everything is aligned and ready for the remainder of the head bolts. Head bolt threads which pass into the water jacket should be coated with gasket sealer. Make sure you have an accurate torque wrench and follow the correct torque sequence. Start in the middle and move in an expanding circle outward (See the shop manual for details). Make at least three passes to bring the bolts up to torque, such as 25 foot/pounds, 45 foot/pounds, and then the final 65 foot/pounds. After everything is reassembled, refill the coolant and start the engine. Bring it up to normal operating temperature (160 degrees). After the engine is warmed up, shut it off and make one more pass with your torque wrench at the recommended 65 foot/pounds. If your engine has a history of water leaking at the head gasket, you can try a radiator sealer product after replacing the gasket. Usually a leak indicates a warped head or block and while this solution is a hack, many times it will keep an engine in service until a proper repair or replacement is made. Interestingly, I have seen some manufactures of head gaskets for hi-performance V8 engines now recommending the use of a radiator sealer product as part of the installation instructions when using their product.
Bypass Oil Filter
One option found on almost all flathead mopars is a bypass filter kit. The factory version was a Mopar Oil Filter Kit available in two versions, replaceable cartridge filter inside a filter housing (Mopar # 1123-152) or a non-cleanable canister (Mopar # 861-028). The first type is more economical to operate as all you need is a replacement filter. They are readily available from suppliers such as NAPA. Installation and operation is unlike today's full flow oil filters. Numerous other manufacturer’s such as AC or Purolator also offered aftermarket versions. These are "bypass" filter systems, which means they only filter and circulate oil through the filter when a specified oil pressure is reached. Below that pressure the oil filter circuit was bypassed by a valve in the oil pressure relief valve. It is a good idea to verify the kit is correctly installed. Filters have line connectors which are stamped "Inlet" and "Outlet". The inlet is plumbed to the oil galley on the side of the block. They would put it under pressure to fill the filter case. The return line (Outlet) goes to the fitting on top of the oil pressure relief valve. In the P15 Parts List manual, page 174, is a drawing illustrating a standard installation. The Plymouth Service Manual ('46-'54) on page 153 provides an explanation of how the filter works. When the oil pressure relief valve is closed the oil pump fills the oil line and oil filter. The relief valve blocks oil flow FROM the filter to the crankcase. When the oil pressure is greater than relief valve spring tension, the valve starts to open. Excess (clean) oil then returns form the filter to crankcase. The relief valve opens a passage for the oil to flow from the filter to crankcase. Because the filtering operation is dependent upon proper and timely operation of the oil pressure relief valve, the quantity of oil cleaned is substantially less when compared to a modern full flow filter. The size of the oil line is approximately 25% of what is found on a modern filter so the volume of oil when the pressure relief valve is open is also much lower. While filtering may longer than a modern full flow spin on filter, the level of filtering is much higher than a full flow. Because of this they provide excellent protection for your engine's components.
Fluid Drive
Fluid Drive was a $25.00 option available on the Doges, DeSotos and Chryslerss. Besides the cool looking Fluid Drive script on your rear deck, what did you get? Fluid Drive is a torque converter, that is, it converts engine torque and transfers it to the transmission via a fluid medium. The idea is simple. Imagine two electric fans facing each other. If you turn on one fan the air pressure created will cause the blades of the facing fan to spin. In this example, the fluid medium is air. The Dodge Fluid Drive works in a similar manner. The torque converter coupling is bolted to the flywheel. Inside the torque converter coupling are two "fans" facing each one another. The entire torque converter is filled with a special fluid. As the engine turns one set of fan blades (called vanes) is driven, forcing the fluid against the vanes of the facing unit. This causes that unit to turn which drives a standard clutch and pressure plate assembly. The power is then transmitted down the drivetrain to the rear wheels just like the standard drivetrain. The advantage of Fluid Drive is there is no direct mechanical connection between the engine and drive train. This translates into a very smooth power transfer and resulting smooth ride. It also provides some unique and interesting features. For example, to shift into gear you would put the clutch in just like a regular three speed. However if you are idling at a traffic light you can let the clutch out and the car won’t stall! That’s because at idle not enough energy is being transferred from the front vanes to the rear vanes. As you step on the gas the pressure increases and the rear vanes start to spin, transferring energy to the drive train. You would then shift gears like a normal three speed. You can also start in any gear. For example, you could start in third, even though the acceleration would be slow. In some ways, Fluid Drive is like a very simple automatic transmission. The units are essentially maintenance free. The only service requirement is to maintain the correct level of fluid in the torque converter coupling. A special access port is located on the passenger side floorboard on the side of the transmission hump. Remove the access door and bell housing cap. Turn the engine over until the filler bolt lines up. It is a good idea to stuff a rag around the opening so you can drop the filler bolt in the flywheel housing. The service manual recommends using a magnetic socket for the same reason. Be very careful as you fill the unit. Any spillage will always find its way to your clutch disk! After filling, make sure the filler bolt is secure with no leakage. The factory fluid was a Mopar #10 Fluid Drive fluid. Unfortunately this is no longer available. The original fluid was an ISO 32 (10W) with an anti-wear additive and an anti-foam additive which was needed to break up the foam which develops as the vanes turn in the torque converter (Fluid Drive Coupling). The non-foaming characteristics are critical because if air bubbles form the fluid will compress and power can not be transferred. Today, two replacement fluids are readily available. Automatic transmission fluid (ATF) is an ISO 32 fluid. However DEXRON ATF contains a seal swell additive which may swell old seals in Fluid Drives and cause a failure An alternative ATF fluid is Ford Type F fluid. It does not contain the seal swell additive. The best replacement is Universal Tractor Fluid #134. This is an ISO 32 fluid with all the properties of an automatic transmission fluid for wear, heat dissipation, and anti foam. Available at most NAPA stores in 1 and 5 gallon quantities. Obviously if you have a farm/tractor supply outlet nearby they will have it. Universal Tractor Fluid #134 has other positive characteristics including added shear strength for moving bevel cut gears under high loads similar to what is found in the old Fluid Drive transmissions. Many of today’s modern manual transmissions use the #134 fluid, not a gear lube, as the factory fill. The biggest repair problem with Fluid Drive is seal leakage where the transmission input shaft mates into the housing. Any leakage will quickly ruin the clutch disk. Repair kits are available but difficult to find. So are experienced repair personnel. Using the correct replacement fluid can go a long way in extending the service life of your unit. Otherwise the units are factory sealed. Carburetors used on Fluid Drive cars are different than the non-Fluid Drive models. The Fluid Drive adds some drag on the engine and a dashpot is used to slow throttle closing, thus preventing engine stalling. The adjustment of the dashpot and replacement of Fluid Drive seals are addressed in detail in the factory service manual. Lastly the same manual three speed transmission (Type C) is used on both Fluid and non-Fluid Drive applications with one part change. The Fluid Drive transmission has a slightly longer input shaft to accommodate the greater depth of the coupling. The shafts can easily be replaced making a standard 3 speed into a fluid drive version and vice versa.
Converting Original Tires Sizes to Modern Equivalents
Original sizes are 100 series aspect ratio, that is, the section width equals height from rim to tread. So, a 6.50-16 is nominally 6.5" wide, 6.5" high on a 16 inch rim. To determine what modern tire size is needed do the following calculation: 6.5 inches X 2 (tire height) + 16 inches (rim height) = 29" tall tire. The closest modern equivalent to the 100 series is a 85 series aspect ratio tire. Match up the tire tread width and tire height to the 85 series tire specifications and you will see what choices are available. Usually they will run in the range of a 205 to 225 size.
Cooling System Check List
Most 218/230 flatheads use a stock 160 degree thermostat and will run all day long in the 160 170 degree range. I have driven a P15 across the California desert in 100 degree weather at 60 m.p.h. and the water temperature climbed to the 200 degree range. These vehicles have large radiators with sizeable coolant capacity so overheating is not a common experience. In fact, I have found them to be a bit on the cold hearted side. So if you are seeing temperatures above the 170 degree without extenuating circumstances such as towing or climbing hills, your engine is telling you something is wrong. Ignoring the warning signs will almost always lead to engine damage ranging from burned exhaust valves to a cracked block or head.
Phase 1 are quick checks for common problems with easy fixes. Break out the tools and plan on a Saturday for Phase 2. Phase 3 are those really tough problems that unfortunately are usually expensive to fix. Good news is they don’t occur very often.
Phase 1
Low Coolant:
Check the engine oil to see if any coolant is leaking into the oil. It will appear white on the oil.
Check all hose clamp and hoses for leaks.
Loose, worn or incorrect fan belt
Ignition timing too far advanced
Radiator cap missing or defective: P15 and D24s use a non-pressure cooling system. If you use a pressurized cap you will probably damage the radiator as it is not built to handle the higher pressure and it may push the water temperatures up.
Coolant mix: Just use the amount of antifreeze required to protect your engine from freezing in your area. Additional antifreeze actually reduces the waters ability to transfer heat. Remember water is more efficient that antifreeze for heat transfer.
Phase 2
Faulty reading temperature gauge, check against another gauge.
Defective water pump, leaking seals or impeller rusted, impeller shaft broken. Wiggle the fan, check for leaks around the front shaft.
Clogged or inoperative thermostat, installed incorrectly, wrong thermostat
Clogged radiator
Clogged block
Clogged, missing or rusted out water distribution tube. The water distribution tube plays a critical role in cooling the upper block and valve system. Cool water from the water pump is directly pumped into the water distribution tube, reducing the temperature in the valve area. The tube carries the water to the #6 cylinder area. It then travels on down the block water jacket.
Soft radiator hoses: Hoses which collapse under suction when hot, especially the lower return side hose from the radiator.
Missing or bent fan blades
Carb heat riser valve stuck in open position
Phase 3
Wrong water pump installed
Carbon buildup on the head causing high compression
Cracked water jacket in the head or block
Leaking head gasket, coolant level is always low.
Leaking freeze plugs, coolant is always low.
Metallic ping from the bell housing
Occasionally after driving for 15 or 20 minutes I would hear a metallic ping from under the floorboard. The frequency would vary with engine speed. However nothing seemed wrong with the engine or transmission. When I stopped and restarted sometimes the noise would go away, sometime not. Finally I tracked it down to the starter bendix. While driving, the bendix gear would vibrate and move toward the flywheel ring gear, sometimes enough to make contact and create a metallic ping. When I would restart the bendix gear moved back from the ring gear. Cleaning the bendix gears fixed the problem.
Erratic Idle Speed
Ever come to a stop sign and have the idle speed vary between 650 RPM and 950 RPM for no reason ? The fix was having at least 1/16 inch of free play in the manual throttle cable on the dash. If you don’t have any free play as the engine moves on its mounts it can tension the throttle cable, changing the idle.
Whistle During Deceleration
When coming off a freeway off ramp one afternoon a loud whistle started in the engine compartment. I couldn’t duplicate the condition standing still so it went on for weeks. I finally discovered tightening the two carburetor mounting bolts stopped the vacuum leak at the gasket between the carburetor and intake manifold. This only occurred during deceleration when the throttle plate was closed.
Mysterious Mis-fire
Driving home from work one afternoon my P15 suddenly developed a misfire and the smell of burning rubber. Opening the hood revealed the Evr-Dry sparkplug boot on cylinder #3 was melting along with the plug wire connector. I limped home on 5 cylinders. The next day I started the engine up and heard a loud rhythmic popping sound. Opening the hood revealed the ceramic top of plug #6 moving up and down like a valve! I pulled all the plugs and 3 of the 6 Champion JY45 had separated where the ceramic insulator went into the metal casing. The #3 plug was allowing hot gas to blow up and melt the plug wire. I replaced all the plugs with AC 45s and the car ran great again. If you use Champions you might want to inspect them a regular basis as the plugs all looked normal before they suddenly failed, with no rust or other obvious physical damage. Broken Plug

Clunky Clutch

For years after I got my P15 the clutch pedal would always make a loud "clunk" when you pressed it down. Clutch operation was fine, and throwout bearing free play was on the money. Adjusting the clutch overcenter spring did nothing to get rid of the noise. Finally, while replacing a master cylinder, I tore down the pedal assembly and clutch torque shaft. The balls of the torque shaft ride on spherical shaped split bronze bushings. On one side half of a bushing was missing. The clunk was the pivot ball rattling inside the remaining bushing. NAPA had replacement bushing inserts for about a buck and I was back on the road with a smooth and quiet clutch pedal.