C-3 70 ls-5 distributor questions Vacuum Can

[Duke W.]

Re: C-3 70 ls-5 distributor questions Vacuum Can

Those specs look identical to the 1115201 that was OE on many earlier engines, but never available in service or consolidated early on. That's one of the "problems" with VACs from a judging standpoint - some were never available as service parts.

As you can imagine, a 15.5" VAC is not suited to an engine that only idles at 14-15" unless it has ported vacuum advance. A 12" VAC would be more suitable with full time advance. Idle vacuum will keep it "locked" at full advance at idle. It complies with the "two-inch rule" by providing full advance at no less than 2" below typical idle vacuum.

A 15.5" VAC will not be locked at your idle vacuum. The result is that idle spark advance will be lost, which reduces idle speed/vacuum, which causes more timing loss. It's a positive feedback loop that desabilizes the idle and can cause the engine to stall.

This is how my '63 327/340 behaved until I replaced the 15.5" 201 VAC, with a 8" 236 that the 12" idle vacuum could keep locked on full advance at idle - a "design error" for sure, but one that was easy to fix once I understood the problem.

Duke

[Duke W.]

Re: C-3 70 ls-5 distributor questions Vacuum Can

Those specs look identical to the 1115201 that was OE on many earlier engines, but never available in service or consolidated early on. That's one of the "problems" with VACs from a judging standpoint - some were never available as service parts.

As you can imagine, a 15.5" VAC is not suited to an engine that only idles at 14-15" unless it has ported vacuum advance. A 12" VAC would be more suitable with full time advance. Idle vacuum will keep it "locked" at full advance at idle. It complies with the "two-inch rule" by providing full advance at no less than 2" below typical idle vacuum.

A 15.5" VAC will not be locked at your idle vacuum. The result is that idle spark advance will be lost, which reduces idle speed/vacuum, which causes more timing loss. It's a positive feedback loop that desabilizes the idle and can cause the engine to stall.

This is how my '63 327/340 behaved until I replaced the 15.5" 201 VAC, with a 8" 236 that the 12" idle vacuum could keep locked on full advance at idle - a "design error" for sure, but one that was easy to fix once I understood the problem.

Duke

[Jim T.]

Re: C-3 70 ls-5 distributor questions Vacuum Can

Mark since you have the distributor out, this would be a good opportunity to take it apart and replace the lubricant in the upper cavity. If it has never been replaced since new, you will probably not find any lubricant, just some dried caked stuff. A read of excellent information at www.tispecialty.com will help in the procedure. Lubrication of the tack drive gear will save it from destruction.

[Jim T.]

Re: C-3 70 ls-5 distributor questions Vacuum Can

Mark since you have the distributor out, this would be a good opportunity to take it apart and replace the lubricant in the upper cavity. If it has never been replaced since new, you will probably not find any lubricant, just some dried caked stuff. A read of excellent information at www.tispecialty.com will help in the procedure. Lubrication of the tack drive gear will save it from destruction.

[Mark Z.]

Re: C-3 70 ls-5 distributor questions Vacuum Can

Great article. Was going to adjust end play but totally forgot about the upper bearing lube.

[Mark Z.]

Re: C-3 70 ls-5 distributor questions Vacuum Can

Great article. Was going to adjust end play but totally forgot about the upper bearing lube.