Distributor advance limit bushing question

[Duke W.]

I've been working on a friend's single point distributor, and it had no limit bushing. He ordered one from Standard and it's brass and slips over the pin with a clearance fit, so there's no way that it could be retained without a C-clip, which the pin has a provision for.

IIRC the OE limit bushing was nylon or rubber and had enough interference fit to stay on the pin without a c-clip. Is this correct? It's been so long since I disassembled a single point distributor, I can't remember. Also, the IPB does not show a retainer clip for what they refer to as a "sleeve" that fits over the limit pin.

As a temporary measure, I installed a piece of rubber tubing over the pin, but I don't think that's a long term solution as the rubber will eventually degrade and disintegrate.

This particular distributor, which is banded 1111196 ('67 L-79) has been through quite an ordeal. The non-original spec VAC was not suited to the engine's manifold vacuum characteristics, which was an easy fix. The perplexing part was that centrifugal was limited to about 16 or 17 degrees. A 196 distributor should have 30.

Upon disassembly no advance limit bushing was evident, and after some head scatching the owner noticed a hole drilled opposite the OE advance slot on the cam assembly, and further analysis indicated that the pin was indexed in this hole rather than the OE advance slot, which is why the total centrifugal was so low.

So my temporary rubber limit bushing and the OE slot are now yielding 25 degrees centrifugal, which is fine because the engine has a high overlap cam, and I want to run high initial timing (13-14) along with the 8" VAC to obtain about 30 deg. total idle timing, and 38 total WOT timing, which the engine seems happy with - no detonation.

You never know what you will find when you disassemble a 40 year old component.

Duke

[Joe L.]

Re: Distributor advance limit bushing question

Duke------

The bushing to which you refer was once-available from GM as a seperate part. However, it was discontinued in May, 1991. This bushing was definitely an interference fit on the vacuum control plunger rod and was manufactured of some sort of plastic. However, I don't think that it was rubber or nylon. It had a resiliency to it that was "rubber-like" but it was very durable.

[William C.]

Re: Distributor advance limit bushing question

I have been known to cannibalize swap meet distributors to obtain little items like these, and there seem to be at least three types, a black "rubber" version, a brown version similar to a round piece of fiberboard, and a white-ish "plastic" version, all interference fit.

[Duke W.]

Re: Distributor advance limit bushing question

Thanks guys. I guess my memory is intact as I recall the bushing was some sort of interference fit "hard rubber" or other organic material, definitely not brass or any other metal.

We can probably find a c-clip to retain the brass bushing, which should be very durable.

Duke

[Joe L.]

Re: Distributor advance limit bushing question

Duke------

I would say that the brass will work perfectly and will last for as long as anyone is going to need it to last. By the way, the original outside diameter of the GM bushings was, nominally, 0.25".

[Clem Z.]

i soldered the brass ones on,can't fall off

and detonate the engine

[Duke W.]

Re: Distributor advance limit bushing question

Thanks for the OD info. That will be useful as the owner is considering a change to the 300 HP cam, so I will want to reduce initial timing to 6-8 and get closer to the original 30 degrees centrifugal from the 196 distributor.

The rubber tubing is definitely larger than 0.25" OD when stretched over the pin, so it's limiting centrifugal advance to less than 30 degrees, which is okay for the current configuration, but we'll install the bronze bushing with a c-clip after the cam change, and I can turn the any difference in bushing diameters into an estimate of what the brass bushing will give us compared to the OE bushing.

Duke

[John G.]

Re: Distributor advance limit bushing question

The Accel advance curve kit I used in my single point distributor rebuild came with a brass bushing. This bushing was an interference fit and seemed to fit tight enough so as not to cause a problem with coming loose. A pair of pliers were used to drive the bushing up onto the bent 90* vacuum actuator rod end. The original stock factory bushing appeared to be of black tubing origin, or something similar.

I don't remember seeing a retainer groove on the vacuum rod actuator end? .. Probably should have been wearing reading glasses! .. Clem's mention of soldering the brass bushing to hold it fast sounds good.

[John H.]

Re: Distributor advance limit bushing question

The centrifugal advance limit bushing goes on the pin from the top of the mainshaft that protrudes down through the slot in the weight plate; there's no bushing or limiting device on the vacuum advance actuator rod.

[John G.]

Re: Distributor advance limit bushing question

Big OOPS ..! .. My apologies. That is correct, John. I don't know why I 'remembered' the bushing going on the actuator rod? .. Thanks for posting the correction . .

John

[Joe L.]

Re: Distributor advance limit bushing question

John------

Somae, but not all, of the Delco vacuum controls did include a pre-installed bushing on the end of the plunger rod. Attached is a photo of an NOS GM #1115357 vacuum control which does have the pre-installed bushing.

Incidentally, the bushing used on the lower pin in the autocam was the same bushing as that used for the vacuum control. It's a bit tighter "interference fit" on the autocam pin, though.

[John H.]

Re: Distributor advance limit bushing question

Joe -

What was the application for that vacuum advance unit?

[Joe L.]

Re: Distributor advance limit bushing question

John------

This particular one is used for

1965 passenger car with 396 except L-78

1965 all models including Corvette with small block except L-79, L-76, L-84

1966 passenger car with 396 excpt auto trans

1969-70 all models including Corvette with 300 hp

1971-72 many applications; mostly small block with lower performance

There are several other vacuum controls that use the bushing, though. It is not unique to the 1115357. This just happens to be the one I have that was the easiest to lay my hands on.

[Clem Z.]

i have seen quite a few GM distributors with

this advance limiting bushing on the vacuum advance can.

[John H.]

Re: Distributor advance limit bushing question

Thanks, Joe