ignition advance, not model A

[dave11]

Wondering how excessive ignition advance affects engine performance. The engine in this case is a 31 Pylmouth that has a centrifugal spark advance. In a modern high compression engine if the ignition advance is set too far before top dead centre the engine starts to ping under load. However in these low compression engines I have never heard one ping. There is obviously a point of deminishing returns?.The other indicator of too much advance is when starting the engine kicks back on the starter. The question is in a low compression engine can exessive ignition advance harm the engine ?

Dave

[katy]

The question is in a low compression engine can exessive ignition advance harm the engine ?

Definitely

[2manycars]

Years ago I had the timing too far advanced on my B engine, and it ruined the rod bearings.

[Tom Wesenberg]

I was riding with a guy that had his Model A ignition too advanced. When he filled with gas and his gas gauge started leaking he panicked and floored it to get home. Within 3 miles his engine locked and the pistons were melted.

Even a low compression engine should give off a knock when it's timing is too far advanced. My Model A temporary engine had junk blocking coolant flow around the rear cylinder and the hot cylinder made the engine ping with the slightest throttle. Once I got the block cleaned out the ping went away.

[Mitch//pa]

Yes is also my answer...

Tom your story made me chuckle. Lol

[BILL WILLIAMSON]

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Generally speaking, if a centrifugal distributor has around 30 degrees of smooth, even, advance, you're probably OK to GO.
Bill W.

[Mitch//pa]

Originally Posted by BILL WILLIAMSON

Generally speaking, if a centrifugal distributor has around 30 degrees of smooth, even, advance, you're probably OK to GO.
Bill W.

I believe he was talking about over advancing the base timing..I could be wrong

[tbirdtbird]

improper advance (too much) can kill any motor regardless of compression. The fire wants to be lit soon enough that the maximum cyl pressure occurs at about 13° ATC
Any sooner and the engine will be fighting itself and will self-destruct.
Timing may be the least understood component of any engine, and the most difficult to get exactly right. It is way more complicated than something as simple as say CR; and ideal timing actually changes quite a bit with load, temp, fuel, chamber design, porting, cam, are the pistons proud of the deck (a really bad idea in a flathead), etc. Some of these you can control some you can't. In truth, the timing we end up with is a compromise of many conditions

[dave11]

Thanks guys for sharing your thoughts / knowledge. On a model A (at least my model A) if you advance the spark via the hand lever too far the engine is not happy, and performance is compromised. Although I have never heard it ping, the fact that I run 92 octane fuel may affect this.
On my Plymouth if I time the engine as per the service manual, it runs OK at slow speed but it doesn't like higher RPMs. If I advance the distributor initial timing it runs excellent, although at times it will kick back on the starter. I guess the proper route is to pull the distributer and have it bench tested to see what the maximum mechanical advance is. I was hoping for a quick diagnosis.

Dave

[Mitch//pa]

You can check the Operation of the advance and total advance by using a timing light with the advance / decrease feature

[George Miller]

To fast timing or to late timing both will hurt your engine. It really needs to be right.

[Terry, NJ]

Yes! And what's right at 1200 RPM is not right at 2400 RPM. The "Set it and forget it!" mentality is not right.
Terry

Originally Posted by George Miller

To fast timing or to late timing both will hurt your engine. It really needs to be right.

[ursus]

I am not familiar with how the Plymouth centrifugal advance is set up, but on the Ford Model B the mechanism can fail to fully advance is there is too much wear in the shaft or the mechanism is impaired by an accumulation of dirt and grease. A worn shaft might impair the normal advancement because the axial spin becomes more of a loose oscillation than a tight rotation.

[dave11]

The 31 Plymouth ignition advance is a bit different than most. The distributor has a mechanic centrifugal advance, but also the distributor has an external vacuum operated diaphragm. This diaphragm supply line is ported below the throttle plate on the carburetor, so at an idle it has no movement (distributor is in the retard position) as soon as the throttle is opened the diaphragm receives vacuum and the distributor moves to the advance position. This advance is in addition to the centrifugal advance.
It seems weird.
I would like to measure the amount of advance with a timing light, but the Plymouth doesn't have any timing marks on either the flywheel or the crank pulley.

Dave

[kenparker]

I think I wrote about this when it first happened to my coupe, but don't remember perzactly. Some of you understand that.

Le Coupe began running badly while at a Hillclimb in early November. I shut her down and spent the reat of the day watching. Time to go home an it is a 25 mile trip from Hillclimb site to home. She started out fine, running smoothly as I motivated thru Mineola, Texas. Out on the hwy west of town - 4 lane- U S 80 - I opened up the throttle running about 55 in 4th gear ( Overdrive). After 1 mile she began running rough, smooth out then get even more rough. All of a sudden as I was crossing the bridge over the Sabine River there was this loud fuphuff and the cabin filled with oily smelling smoke. Shut off ignition and coasted across bridge. Open hood and could see nthing but oily film everywhere.

OK< by now passerbys had stopped to help. Turn key on as hit starter. Running as smooth as she could on three cylinders. Take a chance and se if I could get to the side road that goes to Van. One of the passerbys stayed with me until I turned off. Running on three and very low powere but getting home , then fuphuff again. More oily smelling smoke.

Number 4 spark plug has already been unhooked. This time I pulled the Plug on number 4 and number 3. # 3 was as dead as #4.
By now I am 15 miles from home on a very deserted country road and it is 1 hour before dark. No cell servise in this nechk of the woods.

Did you know a model A can get you home on two cylinders. Very slowly and took ofer a hour.

Upon disassembly of engine here is what I found. #4 Piston was destroyed 9 see pictures). Number three was overheated and the center was depressed.

Problem - For several years out on the open hwyway at speeds over 50 mph I woud pull the Spark Lever all way down to gain that little bit of extra horspowere. Ran beautifully and sounded Ok. But upon inspection and using the NU REX Timing checker it was running at over 35 degrees advance. The 35 degrees and subsequent preignition was slowly blowing a hole in Number four and soon to be number 3.

[kenparker]

oops I messed up - here are the pi ctures of number 4 piston.

[Mitch//pa]

Mark the crank pulley and timing cover at TDC Then use the light..

[dave11]

I suppose one could measure the circumference of the crank pulley divide by 360 to find the distance between degrees, then file a mark at tdc and at 30 degrees, and verify with a timing light. Will have to ponder this option apposed to pulling the distributor and have it bench tested.

[Mitch//pa]

You only need the TDC marks ... The timing light will tell you how far it advances
You need to use a timing advance type light ...

[Rex_A_Lott]

Originally Posted by dave11

The 31 Plymouth ignition advance is a bit different than most. The distributor has a mechanic centrifugal advance, but also the distributor has an external vacuum operated diaphragm. This diaphragm supply line is ported below the throttle plate on the carburetor, so at an idle it has no movement (distributor is in the retard position) as soon as the throttle is opened the diaphragm receives vacuum and the distributor moves to the advance position. This advance is in addition to the centrifugal advance.
It seems weird.
I would like to measure the amount of advance with a timing light, but the Plymouth doesn't have any timing marks on either the flywheel or the crank pulley.

Dave

Not that much different than more modern cars, in theory.
Do as Mitch says, mark it at TDC and then check the timing @ Idle. Pull the vacuum line loose from the manifold and the suck on it while its idling and see if the timing changes. This will verify that the vacuum advance is working or not.
With the vacuum line still loose, rev the motor up and see if the timing advances. This will tell you if the centrifugal advance is working or not.
These are just some quick and dirty checks that will tell you if its completely hosed or not. Its not going to take the place of a nice known setup on a distributor machine, so that you know how many degrees of vacuum advance and how many degrees of centrifugal you are getting.
Good Luck!