Thoughts on MoPar Flatheads - 3

[grey beard]

Rear Main Bearing Seals

Engines built before 1951 used a rear main seal that incorporated a flat metal flange with three screw holes in it. These seals required removal of the flywheel to allow replacement of the top half. Later flathead engines used a different neoprene seal design that could be rolled into place in the top half by loosening the crankshaft, much as you would in replacing a top rear main bearing. The two types of seal are not compatible reciprocally, due to block casting differences.

Timing Chain/Gear Lubrication

Engines built before 1951 use a pressurized oil nozzle of about 1/16-inch diameter to lubricate the timing chain and components. This tube protrudes from the block above the center of the crankshaft gear and points downward, and has a small bracket attached by one screw to the front of the block. The oil is sourced from the front oil passage leading from the main galley on the left side of the block to the front camshaft bearing.

This system provids positive lubrication to timing components and is very nice . . . . . . as long as it stays clean and free from sludge. It was abandoned in later production in favor of an oil slinger disc placed behind the crankshaft timing gear that supposedly slung oil up and onto the chain. Since the slinger lives above the normal oil level in the oil pan, it can operate only when the engine is running. In this writer’s humble opinion, the earlier pressurized system was far superior, and was discontinued only because of the poor quality oil available at the time and the difficulty in getting the block hot enough for this oil component to get warm enough to keep sludge from forming. It would be interesting to compare timing chain wear between two otherwise identical engines, to observe which of the two systems really provides best lubrication and least wear.

Connecting Rods/Caps

Somewhere around 1951 again, a change was made in connecting rod and cap design on the 218/230 engines. Earlier engine design used a special very thin-wall lock washer that sat in a relief on the cap to retain the rod nut. Later engines dispensed with this relief area and used a flat boss on the cap and instead of the thin lock washer used a split lock nut with several small perforations in the top half. What is interesting is that both rod types carry the identical casting number.

The two rod cap types each require use of the correct fastener, and cannot be mixed or matched. If you have the earlier type rods, you must use the lock washers and nuts. This writer has been unsuccessful in finding a vendor source for these washers. They are quite easy to loose on disassembly, especially if you don’t know they are even there. When installed, they are not visible due to the recess in which they sit. And they are hard to find when they are dropped. Ask me how I know. It goes without saying that rod caps can never be interchanged on connecting rods.

Oil Pans – Oil Leaks

The front of the oil pan area on these engines presents a small challenge for first time restorers. There are several places from which oil can leak, all of which will show up at the front pan area. In order to understand the nature of the situation, it is necessary for the reader to have seen the individual parts.

The front of the oil pan has a wide cork gasket which rides against an aluminum saddle, designed just for this purpose. The aluminum saddle is held in place by two machine screws, and must be removed before access can be had to the front main bearing bolts, for they are partially covered by the saddle.

The engine timing cover gasket must seal the cover itself, the front of the block and this aluminum saddle on which rides the oil pan gasket. It is at the juncture of these three pieces of metal – block, timing cover and aluminum saddle, that oil leaks can easily arise if proper assembly is not observed. This might be a good place to mention that the timing cover has one bolt on the passenger’s side that enters the cover from the rear of the block flange, in direct opposition to all the other cover bolts.

In addition to this area of potential leakage is the front main oil seal that sits in the timing cover and rides on the crankshaft pulley. Always check the seal area on these pulleys for wear. It is not unusual to find a definite groove worn into the pulley seal area from seal lip and dirt wear at this point. A worn pulley will cause a new seal to leak. Speedy sleeves are available, as are “trick” seals that ride on a new and different spot on the pulley to avoid the worn groove spot.

This writer also likes to incorporate a good sized magnet inside the oil pan on reassembly for attracting any wear metal pieces that may get into the crankcase. Old flat speaker magnets are perfect for this purpose. Never throw one away. An ounce of prevention . . . . . .

Miscellany

Engine assembly involves using many bolts that thread into water jacket passages. This is true for head bolts, manifold bolts and a few of the upper timing cover bolts as well as the three water pump bolts. It is important that these bolt threads have some form of waterproof sealer used on them. Clean, tight threads can still leak fluid past them if not sealed. There are no shortcuts to cleanliness that work here. Never use or hang a dirty part on a rebuilt engine.

Engine reassembly is fairly critical work. It cannot he done in a less than clean environment. With all the engines I have ever overhauled, I spent about two hours of parts cleaning time for every half hour of assembly. Fasteners and related block thread holes must be completely clean. The only way this writer has been successful at this task is to use thread taps and dies on each individual part. I have cleaned head bolts on a wire wheel grinder to the point that they shined, yet when the threads were chased with a die, a pile of dirt and carbon showed up on the vise. Do not worry about removing metal with a tap or die. If you are using the correct size, the threads will not be damaged.

MoPar flathead engines were manufactured with very low compression ratios, even for their day. This engineering was based much on the octane levels of fuel available to the public. Flatheads respond very nicely to an increase in compression ratio. This can be accomplished quickly and cheaply by milling material from the bottom of the cylinder head. Doing this will also assure that the head surface is true and free from warpage, as well as offering an opportunity to increase compression and engine performance.

Unleaded fuel offers no problems to these engines, in this writer’s opinion. They certainly do NOT need high octane fuel. Using it in flathead engines will not be beneficial in any way, contrary to the opinions of many. Valves and seats are already of superior quality from the original manufacturer. Just make sure when you set initial engine timing that the engine does not ping or preignite under load.

On the subject of engine timing, here is one often ignored area of performance – the distributor. Distributors have two timing advance mechanisms incorporated in their design – vacuum and centrifugal. The vacuum advance is visible on the outside of the distributor and can easily be tested by mouth or vacuum pump. If it doesn’t leak it will be okay, as long as the distributor breaker plate moves freely inside the cap.

Centrifugal advance units are harder to see, for they are underneath the breaker plate that holds the contact points and condenser. These mechanisms are usually trouble free, but may wear over time. Short of removing the distributor and having it tested on a stand, the only way to test a centrifugal advance unit is with an advance-type timing light and a knowledgeable mechanic. Specs for both vacuum and centrifugal advance units are available with other tune-up data, and of course are a requirement before checking either advance unit. Suffice to say that lots of flatheads are weak in these areas. When one performs well, it is usually a sign that both systems are functioning correctly.

This still leaves the issue of initial timing, which refers to the relationship of the engine to the distributor, and is adjusted by turning the distributor in the block while the engine is running, with the use of a timing light. Power timing, advocated by a few, aids little with these engines, unless you are a performance buff. If such is the case, have at it . . . .

dte

[PatS....]

Thanks alot, Dave. Lots of great info there for someone like me who rarely has an engine apart as far as I do now. Right now, I'm chasing head bolt holes and next is installation of the pan and front cover, so this is good info for me.

Thanks again for taking the time to share your knowledge.

Pat

[Guest garydcle]

Thank you for your flathead posts.

I need to replace the rear main seal on my 75. I understand the flywheel will have to be removed to replace the top seal. Is there a special procedure for this? My reference material stops at 1935. I am going to have to use a modern shop to do this work and would like to have everything on hand that may be needed. I have two cork strips that I hope are the seals and a pan gasket set. The 2 side sections and 2 heavy cork strips for the front and rear. Any advice or guidence would be welcome.

Thank you

Gary Cleveland