C3 distributor shaft cam

**Joe L.** · February 9, 2018, 04:56 PM

Re: C3 distributor shaft cam

Originally posted by Dean Berto (64374)

Rebuilding my 70 distributor. The original distributor shaft is in very usable condition with only one exception and I would really like to reuse it. The shaft cam, brazed to the top of the shaft, has two posts that locate the mechanical advance weights. One of the posts extends underneath the cam and serves to limited the travel of the advance. That post has some kind of sleeve on it made of plastic or some other kind of fairly soft material that increases it's diameter just a little thereby limiting the mechanical advance a few degrees. That sleeve has deteriorated on mine so would like to fabricate another to bring it back to new dimension. Question is what is the diameter of the original post with the sleeve? Or what is the bottom post dimension on a new shaft? Or is it even worth worrying about?

Dean------

The sleeve was 1/4" OD, 3/16" ID. GM #1961234 but long-since discontinued.

**Dean B.** · February 9, 2018, 07:40 PM

Re: C3 distributor shaft cam

Thanks for the specs Joe. Was guessing it was about that size but no way to know for sure. Have any suggestions as to what to make the sleeve out of? Always to easier to ask someone who has already been there rather than to "reinvent the wheel."

**Paul O.** · February 9, 2018, 07:45 PM

Re: C3 distributor shaft cam

https://www.corvettecentral.com/62-7...-sleeve-271026

**Dean B.** · February 9, 2018, 07:53 PM

Re: C3 distributor shaft cam

Awesome! Will order one. Should have bought one in 1974....listed at 20 cents from your local genuine Chevrolet dealer. Thanks for the info.

**Tom G.** · February 10, 2018, 06:33 AM

Re: C3 distributor shaft cam

You could take a piece of shrink tubing,, snip it to length,, slide it over the stud and apply heat. Quick and easy.

**Timothy B.** · February 10, 2018, 10:44 AM

Re: C3 distributor shaft cam

Originally posted by Tom Gerhard (7991)

You could take a piece of shrink tubing,, snip it to length,, slide it over the stud and apply heat. Quick and easy.

I agree, you can also buy one of those advance kits and use the brass sleeve supplied with the kit exactly for this purpose.

You may also have some fun trying different spring combos, your car may run better.

**Duke W.** · February 10, 2018, 12:25 PM

Re: C3 distributor shaft cam

Originally posted by Dean Berto (64374)

Rebuilding my 70 distributor.

What 1970 engine configuration, and has it been modified in any way especially "lower compression ratio"? The spark advance map specs are in your CSM and AMA specs.

Post them.

Depending on the OE specs it may be advantageous to not install the bushing. As long as you have the dist. out for overhaul, why not "blueprint" it and optimize the spark advance map.

Search the web for my 2012 San Diego National convention tuning seminar. Also search this site for a thread started by my circa 2012 "L-79 distributor blue print overhaul". The same applies to any Delco single point distributor. The only difference between engines is the spark advance map - VAC, centrifugal, and initial timing.

Duke

**Dean B.** · February 10, 2018, 01:10 PM

Re: C3 distributor shaft cam

Engine configuration is LS5 survivor that is completely original with exception of vacuum spark advance which was replaced many years ago, stamped MS 360-12. Pulled the distributor to check out tach wobble at lower rpm and found quite a bit of play in side gear, about .130". Have a plan to take care of that issue, installing new bushings for drive shaft, so looked like the spring post bushing was the only issue to get it back to original specs. Read quite a bit from many sources about the spark curve and seemed the consensus was that the factory original was hard to beat for a low yearly mile casual driver. Most recommended keeping the original shaft to maintain the original mechanical advance curve of the shaft cam, even going to the extent of removing the original cam and brazing it back on to a replacement shaft if the original shaft was beyond reuse.

Had the car for 39 years now and just recently got a new burst of interest in it....almost like the first few months after I bought it. It's just a really fun car! New to NCRS so hope I'm not igniting a can of worms about spark advance curves, etc. Truly appreciate all input, especially while the distributor is all apart and waiting for parts and am open to advice from those that have been there done that.

**Duke W.** · February 10, 2018, 01:39 PM

Re: C3 distributor shaft cam

Originally posted by Dean Berto (64374)

Read quite a bit from many sources about the spark curve and seemed the consensus was that the factory original was hard to beat for a low yearly mile casual driver. Most recommended keeping the original shaft to maintain the original mechanical advance curve of the shaft cam, even going to the extent of removing the original cam and brazing it back on to a replacement shaft if the original shaft was beyond reuse.

New to NCRS so hope I'm not igniting a can of worms about spark advance curves, etc.

I can lead the new horses to the trough, but it's up to them to take a drink.

Duke

**Dean B.** · February 10, 2018, 02:04 PM

Re: C3 distributor shaft cam

Duke, found your presentation from the 2012 National. Looks like you really did your homework on that one, excellent presentation with lots to digest, thanks! Will be fun to dig into it and see what I can do. Will also check out the thread you mentioned. BTW, been called lots of things but never a horse....at least it's a new horse. That's kinda a compliment compared to other things people have said. Thanks!

**Timothy B.** · February 10, 2018, 02:10 PM

Re: C3 distributor shaft cam

Dean,

Welcome to the forum, sounds like your car is very nice. Just install a new centrifugal stop bushing and check to make sure the tach cross gear has not wore into the distributor housing.

**Joe L.** · February 10, 2018, 03:11 PM

Re: C3 distributor shaft cam

Originally posted by Dean Berto (64374)

Engine configuration is LS5 survivor that is completely original with exception of vacuum spark advance which was replaced many years ago, stamped MS 360-12. Pulled the distributor to check out tach wobble at lower rpm and found quite a bit of play in side gear, about .130". Have a plan to take care of that issue, installing new bushings for drive shaft, so looked like the spring post bushing was the only issue to get it back to original specs. Read quite a bit from many sources about the spark curve and seemed the consensus was that the factory original was hard to beat for a low yearly mile casual driver. Most recommended keeping the original shaft to maintain the original mechanical advance curve of the shaft cam, even going to the extent of removing the original cam and brazing it back on to a replacement shaft if the original shaft was beyond reuse.

Had the car for 39 years now and just recently got a new burst of interest in it....almost like the first few months after I bought it. It's just a really fun car! New to NCRS so hope I'm not igniting a can of worms about spark advance curves, etc. Truly appreciate all input, especially while the distributor is all apart and waiting for parts and am open to advice from those that have been there done that.

Dean------

The GM #1115360 is the correct vacuum control for your application. It might not be the best, but it is the correct one.

**Duke W.** · February 10, 2018, 03:20 PM

Re: C3 distributor shaft cam

Originally posted by Dean Berto (64374)

Duke, found your presentation from the 2012 National. Looks like you really did your homework on that one, excellent presentation with lots to digest, thanks! Will be fun to dig into it and see what I can do. Will also check out the thread you mentioned. BTW, been called lots of things but never a horse....at least it's a new horse. That's kinda a compliment compared to other things people have said. Thanks!

Thank-you for taking my comment in the light-hearted context that was intended. Be sure to read the chart on emission controlled engines. Welcome to NCRS and I hope you consider joining your local chapter. You'll make some great new friends.

Duke

**Dean B.** · February 10, 2018, 08:53 PM

Re: C3 distributor shaft cam

Thanks Duke, plan to join the local chapter, Central California. Have already met many of the members and they are all top notch and have been a great source of information in the last few months. Have participated in many blogs and learned a long time ago to always take things light-hearted or just ignore them as the other way quickly turns to the dark side and is not productive for anyone. This site from all that I have seen is great and you should all be proud of it!

C3 distributor shaft cam

C3 distributor shaft cam

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