BB distributor shaft question

[Werner R.]

i bought a used distributor from a crook in california [the only crooked dealer i have encountered in 5 years]for my BB. i do not know if the shaft is for a 390/400 engine or if it for a 425/450 engine. can anyone tell me how i can look at my unit and see which one i have?? is there a code on the cam portion?? anywhere else?? can i tell by the shape of the cam??
werner

[Gene M.]

Re: BB distributor shaft question

Werner,
I am assuming you are questioning the distributor shaft that has the mating gear to the cam shaft. If this is true, I don't think there is any differences in any BB or SB distributor main shafts assuming it's tach drive. There is an odd number tooth gear on all assemblies, but it's relative pin position may be different for various assemblies but will still function. Is the gear mis registered to the pin? If so you can reposition it by removing the pin and rotate gear 90 degrees and reassemble. There are after maket oil pump drive shafts that have steel collars in place of the GM plastic one.

[Werner R.]

Re: BB distributor shaft question

gene, the reason i ask is that i have been told that the high performance BB's use a different shaft, and the long island catalogue lists two different shafts, leading to a different advance curve. as far as i know, i have the distributor drive gear installed correctly.
thanks for the response.
werner

[Gene M.]

Re: BB distributor shaft question added

The centrifical cam for the ignition points can be removed and changed. Sorry I never noticed if there is a P/N stamped on them. I would suggest setting up the distributor and alter the advance curve by changing weights and springs. The stock set up comes in a little slow. I never mic'd the cam to see if there is any differences. I've altered the curve more by grinding a little at a time on the weights (trial and error) to get more performance.

[Wayne M.]

Re: BB distributor shaft question

Werner -- as of '67, there were about 15 different shafts/w weight cams; also around 5 different (8-bump, for points) cams and as many cams w/weight bases for TI shafts. And that's just for C2's. Haven't even mentioned the variety of weight springs available.

Most of these components have 3-digit numbers or numbers w/letters codes, but to tie these parts to a factory original distributor, you'd need a bona-fide unmolested unit, or the original design blueprints, to compare.

Maybe if you post the part # of the distrib that you have, members could post what they think should be the appropriate parts.

[Terry M.]

Re: BB distributor shaft question *TL*

Werner,
There is a difference in the auto-cam, that is the portion at the top of the shaft which controls some parts of centrifugal advance. I am told there is a number on the underside of the auto-cam. I have never looked personally, and am relying on the information from others. I'm sure Joe Lucia or Bill Clupper can shed more light on the issue.

[Joe L.]

Re: BB distributor shaft question

Terry and Werner-----

Yes, the only difference in any of the 62-74 Corvette distributor shafts is the auto-cam brazed to the top of the shaft. In combination with the weights and springs, this device determines the centrifugal advance characteristics of the distributor.

Some of these auto cams do have a 3 alpha-character code stamped on them. Usually, it's on the bottom, but I've seen it on the top, too, once-in-awhile. Sometimes, there is no code, at all. For current aftermarket "2-sizes-fit-all" auto cams/shafts, I don't think that there is any code, at least, any code that relates to the original codes.

The original shaft for a 1966 Corvette with L-36, without K-19 and without K-66, was GM #1966992. Unfortunately, this number is found nowhere on the shaft. Also, any code stamped on the auto-cam is not a derivative of this number since the same auto-cam may have been used on other, non-Corvette distributor shafts.

I believe tht Dave Fiedler of TI Specialties has a developed a decoding of these auto cam ID numbers and he may be able to help you. However, if there is NO coding on the cam that you have, this is not going to be of much help. He might be able to tell you which code you need, assuming that the one for the 1966 L-36 application ever used a code, at all.

[William C.]

Re: BB distributor shaft question

Unfortunately, in today's world, the only way to obtain a stock curve is using a distributor machine and the OEM curve specs as a guide. Differences exist in the cams at the top on the main dist shaft, the location and length of the slot that the pin drives, a myriad of springs and surprisingly, only about three sets of weights. With some exceptions, almost any of the tach drive units can be configured to match your desired curve with a machine and a little work, occasionally with swapping a few parts.