Dwell questions

[Scott1953]

Hi,

I checked my dwell for the first time ever yesterday and found it to be 56*. I adjusted it down to 40* and the car feels like it's running stronger. Would that be the case or is it all in my head? I couldn't time it because i don't have a light yet but i hooked up a vacuum gauge and it was steady at about 22 in/hg. I tried turning the distributor to see if it would go higher but it wouldn't turn and it felt like i was getting a little shock so I stopped for now. So,what would dwell being so far out affect? I don't know much about this aspect of the car and my manual doesn't give me much help.

Scott

[Plymouthy Adams]

dwell will affect the timing..what makes the electronic ignition so great..no points to wear and close up that in turn changes the timing...

[greg g]

The dwell is the time the points are open, and that is the time that the coil builds its charge. If the dwell is shorter, less charge accumulates, there for less is available when the points close and fire the coil, Less spark, shorter or weaker spark = less engine efficiency.

If you are getting a shock, you need to look at your wires, make sure the boots are in good shape, there is no carbon tracking across the cap to the dist body.

There is a secondary fastener for the distributer clamp that lets you reposition it for a bit more or less rotation of the dist when adjusting the timing.

[Scott1953]

Thanks guys. So I went from 56 to 40. this essentially shortens the amount of time the points are open right. so my guess is that spark intensity wasn't the problem. How would the dwell affect the timing? Could that be why it seems to run better?

[Merle Coggins]

When your dwell is longer, due to a too small points gap, that means that they close sooner and open later. The "open later" is the point that changes the timing, since the coil fires when the points open. This effectively retards the ignition timing.

Merle

[Rusty O'Toole]

Dwell is the time your points are closed. Typical settings would be breaker point gap .018 to .022 inch = dwell of 34 1/2 to 38 degrees ( from 1949-52 repair manual).

The points gap gradually closes as the rubbing block wears down. This increases the dwell time.

When you reduced the dwell, or opened up the points gap, you also advanced the timing a few degrees. This is why you are supposed to recheck the timing when you change the dwell or replace the points.

In your case it sounds like the timing is spot on or close to it. If the car starts easy, runs fine, and the vacuum is at its highest point, and there is no knock or ping it must just about perfect.

It doesn't hurt to give the points cam a little grease. Just a tiny dab half the size of a match head. They used to sell special grease for ignition points, don't know if you can get it anymore. If the points have a red felt square, a couple of drops of oil.

[Scott1953]

Thanks guys. I now have another question that will cause some to chuckle, but what does it sound like if the engine is 'pinging'.

Also, would the condition of the points/timing before i made the change cause the engine to run hotter than it should?

Scott

[Dodgeb4ya]

Your timing is too early (advanced) because of your dwell adjustmen-assuming the dwell is correct.. Thats why you need to now check timing with a light to see where it's at. Or if you know what you're doing adjust by sound/feel and or a vacuum guage.

[TodFitch]

Your timing is too early (advanced) because of your dwell adjustmen-assuming the dwell is correct.. Thats why you need to now check timing with a light to see where it's at. Or if you know what you're doing adjust by sound/feel and or a vacuum guage.

I once tried to adjust the timing and mixture by sound/feel. Ended up burning the valves on that D200's 318 V8. I've stuck with doing it by the book since then.

[Dodgeb4ya]

With todays fuel you still might have to deviate from the factory settings for correct drivability!

[Rusty O'Toole]

Pinging is a kind of dry rattling sound. It is most likely to occur just off idle on a heavy load. To test your car try driving up a gentle hill in second and give it full throttle at 10 or 15 MPH. You will hear it then if you are ever going to. When you hear pinging back off the gas right away or you could damage the pistons.

There is an old trick called "power timing". This means, doing the above test and advance the timing little by little until you get just a trace of ping. That is the setting that will give the best power and economy.

[Scott1953]

Rusty,

Your description seems to fit what i'm hearing pretty well. I would have never thought to describe it that way though:). I notice it when in third and trying to accelerate hard, from maybe 30 or 35 mph up. I haven't gone ever 40 because the sound was bothering me and I thought it could be bad.

Scott

[Scott1953]

I would advance the timing by rotating the distributor clockwise correct?

Scott

[Tom Skinner]

Scott,

To advance the timing adjust the Distributor in the opposite direction of the rotation of the rotor - thus in your case Counterclockwise - most likely.

Tom

[Rusty O'Toole]

If you are getting ping you need to retard the spark in other words back off a little.

Here is a trick. Just look at the vacuum advance can, they always point in the direction of advancing the timing. In your case you will want to turn it the other way. Just a touch. A couple of degrees will make a difference.

You might want to mark the position of the distributor with a crayon mark or a bit of masking tape. In case you lose the adjustment you can go back where you started. Loosen the clamp then tighten it up just snug. You want to be able to turn the distributor but have enough resistance it will not move by itself.

Adjust, test, repeat until the ping disappears or until you have just a trace under hard accelleration then don't accellerate that hard when driving. Finally snug the clamp down.

This may be better than using the timing marks because the timing marks often move on old engines due to the rubber in the vibration damper deteriorating.

Once again Chrysler was ahead of the game by allowing positive measurement of TDC through a hole in the #6 cylinder head. If you want to be pernickety you can check your timing marks with a screwdriver down the hole.

[Plymouthy Adams]

or you can do it the fast and simple way with the proper timing light..by setting your base line idle..disconnecting and plugging your vacuum to the dist...rev the engine per specs for max centrifical advance at stated rpm..what you are looking for here is the timing not to shoot above the limits...then with thes established you can connect the vacuum to the advance and ensure at x rpm the vacuum advance advances the diming to number of degress it is supposed to...base line + centrifical + vacuum advance...a timing light with advacne dial is needed or at minimum a timing tape that is for the correct size damper and run some 40 degrees of advance. Simple technique and one I performed just today.

light throttle ping as attributed to slight increase in road grade is a by product of too much vacuum advance..you are not at the point of throttle plate opening to lose vacuum and the engine load in the advance state causes the ping. This is adjusted by the adding removing the washers on the spring inside the vacuum canister. If you try to adjust this light throttle spring out by altering your base line timing you are not doing the engine justice and you will suffer performance loss..if you alter the base line..you alter the mechanical and the end result is that you have clipped the total vacuum advace to the point of no ping but on the lower end of the scale when vacuum is not present (WOT) you engine is not going to perform as well due to being retarded..

[Scott1953]

Tim Adams,

I read and respect your posts regularly.

I plan on buying a proper timing light and once I have it in my possession i will re-read your last post but until I can put a little 'hands on' knowledge with your words they are a little confusing to me. It's OK though, I will get it eventually. I appreciate all the answers guys and I will report back after I get a timing light on it.

Scott

[greg g]

Timing that is to advanced at idle can caue hot running. Its always better to be a little retarded than to0 advanced. Take a look at the post regarding scored cylinder walls.

put 5 or 6 washers in an empty metal coffee can and shake it. Pinging is actually some of the sound coming from a diesel engine. They fire through compression basically squeezing air fuel charge till its ign temp rather than introducing a spark. But those engines are designed to deal with those pressures. Gas engines are not. If the spark is too early it fires the cylinder while the piston is still tryig to compress the chage fighting the upward motion of the piston. This ca verpressure the assembly.

[Plymouthy Adams]

Tim Adams,

I read and respect your posts regularly.

I plan on buying a proper timing light and once I have it in my possession i will re-read your last post but until I can put a little 'hands on' knowledge with your words they are a little confusing to me. It's OK though, I will get it eventually. I appreciate all the answers guys and I will report back after I get a timing light on it.

Scott

Scotty..read this if you want..gives you a bit of information on the Advance Timing Light and its use. You can source other online articles on adjusting the vacuum advance cannisters..from the old style like the flattie uses with washer which continued to be used for many years forward to the last of the vacuum advance cans where you adjust with an Allen wrench..(usually a 3/32) These have since disappeared with ECM and distributorless ignition..but as long as this hobby is left to survive..we will always be in need of these tools/parts and the hands on to put it all together

http://www.tradervar.com/DC%20Power%20Timing%20Light%20CP7520_english.pdf

[Don Coatney]

I posted this information in another thread.

The centrifugal advance curve is set by spring tension and counter weights. On a P-15 centrifugal advance should pull 3 degrees advance @ 400 RPM's and be full in 9 degrees @ 1300 RPM's. The vacuum advance is set by adding/removing shims to adjust spring pressure on the diaphragm. On a P-15 the vacuum advance should pull 2 degrees of advance @ 6 3/4 inches of mercury and be fully advanced 10 degrees @ 14 inches of mercury. The vacuum advance comes into play only while accelerating. Once at speed it does nothing. Many Mopar flathead 6 industrial engines do not have a vacuum advance on there distributor as they run at a constant governed speed. If you replace a vacuum advance unit it is very important to use a vacuum generator as pictured below to adjust the shims to the prescribed range for your engine.

[Don St Peter]

Dumb question

[Don St Peter]

I have a dumb question. How does one check and set "dwell angle" on the original flathead 6 in my 40 Ply P-9.

Thanks in Advance

Don

[Plymouthy Adams]

Don..the point gap and the dwell angle are the one and the same..it is only the manner in which you view/set it that differs. The dwell angle is the number of degrees of rotation that the points are closed..and you will need a dwell meter to view this electrical reading..this ensure that the points are closed long enough to ensure saturation and open long enough to also ensure collaspe of the coils field to generate a spark. That is why point systems require frequent tune up and replacment/adjustment of the contact gap..as the breaker cam wears or the point contacts erode..the dwell changes, that effectively degrades the actual capacity for the coil to generate a high voltage charge and thus it also alters the opening of the points that in turn shifts the time of fire thus resulting in timing error..

[woodie49]

One thing that I have found is that my dwell meter, which is for 12 volts, gives me a very inaccurate reading for my 6V system. I think when I bought the dwell meter a year or so ago and tested the dwell, it registered something like 56 degrees, which should be pretty impossible. I assume the theoretical max could only be 60 degrees, given a six cylinder, and that would be points closed all the time, so the car wouldn't start.

When I tried to gap the points to acheive the appropriate dwell, I think they were way too far open and, of course, I had the adjust my timing (with a vacuum gauge) to compensate. I was able to do so, and the car ran OK, but a little hotter than usual and not as much get-up-and-go.

I finally decided I would just gap the points properly and adjust the timing (I usually use a vacuum guage and then test with a timing light, I am generally a little before TDC).

So, from all this, I decided that a 12 volt dwell meter (at least mine) is inaccurate for a 6V system.

You might want to recheck the point gap and make sure you aren't having the same issue. If so, you are probably running pretty far advanced in your timing.

[Don Coatney]

I set my dwell on the work bench using an electric drill and a 12 volt power supply. If I recall I ended up with 46-48 degrees with my dual point setup. That is 10 degrees more than a single point distributor dwell.