140 distributor advance question

D Slater · Feb 11, 2012

Want to determine the original advance rate of a symbol AB distributor used in a 140 in 200 distributor RPM increments? I-T manual that covers a 140 may have it but I have none, or any information source. Thanks for any help.

nosih · Feb 11, 2012

22 degrees

randy hall · Feb 11, 2012

dave, in my blue ribbon serviceman's handbook it says high idle 22 degrees btdc for the a b symbol distributors and 1 degree at 400 rpm's. and after serial number 103 556 they used a t symbol distributor and it was 14 degrees btdc at high idle and 1 degree atdc at 400 rpm's. that's all i have, randy

D Slater · Feb 11, 2012

Randy its a 22 degree max at the crankshaft. Was looking for the in between degrees to compare to others. Most times information will have the distributor RPM and degrees of advance listed at 200,400,600,800 or more if the engine RPM is higher. Advance springs for that distributor advance are almost twice as much as some others I think are close. Thanks

Janicholson · Feb 12, 2012

That is an interesting issue. It might never have been published. One way to do it would be to take a set of new springs in a good or rebuilt distributor and put it on a distributor machine. (or a degree wheel on a smooth running tractor with a good timing light) and make a graph.
Spring rate might be a component. The expensive springs could have coil pitch variability to allow non linear change in tension. I would think that max advance would be located at the top of the power curve at rated RPM. and thus reach an early plateau and be full from there to high idle. Just guessing. Jim

Owen Aaland · Feb 12, 2012

Timing lights with retard adjustment have made the job much easier. For any RPM you just dial in the light to flash at TDC and read the degrees of advance on the light.

mkirsch · Feb 13, 2012

Unfortunately that doesn't do you a whole lot of good if your original springs are shot, and you are trying to save money by scavenging springs from a different application.

You don't have the original springs to measure the advance curve.

I'm with Owen on this. I sincerely doubt that the advance curve has ever been published for these distributors.

In the past, I've read that you could buy a set of GM advance springs that had three different sets of springs for tuning. You'd use one of the sets, I can't remember which, and it would be a perfect fit...

Jim Becker · Feb 13, 2012

I've seen intermediate advance curves for the older distribuutors. But the AB version is newer than the list. The T distributor on the later 140s was shared with some of the LP engines, 300 - 650.

D Slater · Feb 16, 2012

To posters thanks. Found the answer for AB symbol distributor RPM and degrees. 5 degree at 400, 10 at 600 and 11 at 800 or higher RPM.

140 distributor advance question

D Slater

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nosih

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randy hall

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D Slater

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Janicholson

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Owen Aaland

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mkirsch

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Jim Becker

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D Slater

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