'31 Buick 60 Mechanical Advance Question

[Str8-8-Dave]

So I guess I was in too much of a hurry while overhauling a model 660-E Delco Remy distributor which is used on 60/80/90 series 31 Buick straight 8s.  When I took the weights and springs off the mechanical advance and then removed the breaker cam I didn't realize there were 2 different size holes in the base plate on the distributor shaft that an advance limit pin on the bottom of the breaker cam rotor can be assembled into which would result in a difference of how much mechanical advance is built into the distributor.  The larger hole had the number 32 stamped near it, the smaller had the number 81 stamped near it.  The Specs and Adjustments manual explains the initial advance is 11-1/2 degrees BTDC and the mechanical advance then puts in another 20-1/2 degrees for a total of 34 degrees of advance when the engine is running fast enough to use fully advanced spark.  Playing with the base plate and the cam rotor I estimated when the pin is inserted into the larger hole the breaker cam rotor can be rotated around 10-11 degrees which, since the distributor runs 1/2 crank speed, actually provides 20-22 degrees of mechanical advance. 

 

Does anyone actually know which of the 2 holes, the larger or smaller hole, the advance limit pin should be assembled into?

 

Thanks in advance...  literally...

 

Dave

 

 

[Bloo]

Do your weights go on the right way in either hole?

 

Both holes look offset the same way, suggesting one of them might be for reverse rotation rather than limit. Is that an optical illusion?

[Str8-8-Dave]

It's definitely an optical illusion.  Those holes are exactly 180 degrees apart and equidistant to shaft center.  Weights do go on right way in either hole but when you assemble the breaker cam rotor with the pin in the other hole the amount of advance travel is greatly reduced because the other hole is probably 2/3 the size of the hole I chose to assemble the pin into.

[Str8-8-Dave]

Now then Bloo- I have a little egg on my face.  I installed the distributor I re-worked, the one I asked the question about the advance holes and am still comfortable I have the breaker cam advance limit pin installed in the correct hole because the breaker cam can be rotated with the weights, springs and breaker plate all installed.  Later I took the distributor apart that came with the car and the holes were like you said, NOT 180 degrees apart and the holes were the same size on the rotor plate.  I tried getting the pin into the second hole with the weights installed and that didn't work, probably for the reason you suggested, second hole is likely for a reverse rotation distributor and a different set of weights.   I'm not so sure either that I got the limit pin to go into either hole with the weights installed, it may be the weights were not in place for the second hole. 

 

I hope you will accept my acknowledgement of my mistake and my apology for doubting what turned out to be good advice from you.  Your willingness to respond to technical questions like the subject one is worth more to me than whether I was right or wrong.

 

Dave