C2 66 300HP centrifugal advance

[Randy S.]

Re 66 1111153 dist 66 300 HP MT

I have been mapping my distributor and been unable to get the 30 deg @5100 centrifugal advance as spec'd by AMA standards. I get 24 max. I pulled the distributor and saw no mechanical issues to prevent full advance. The number on the cam is 84 and number on bottom of weight plate is 514 CCW

Can anyone identify these as correct for a 1111153 distributor?

It looks to me like the limit of centrifugal advance is controlled by the cam and the leg portion of the weights. Wouldn't changing springs control only the rate of advance?

Is the final 6 deg significant?

Randy

[Mark G.]

Re: C2 66 300HP centrifugal advance

Randy -

Search the archives for "distributor advance limit bushing"; there should be pictures too. It seems to me that the bushing reduces the advance range from 30 degrees to 24 when installed.

Mark #35760

[Joe C.]

Re: C2 66 300HP centrifugal advance

Randy,

The bushing on the autocam pin is called a "limit bushing", but I am honestly at a loss to explain whether or not that is a correct term. It may be more properly referred to as a "bushing" or "friction reducer". I do not know what it is referred to on a GM distributor exploded view..........it may simply be referred to as "bushing".

My distributor's maximum centrifugal advance, like yours, is NO LONGER controlled by the "limit" bushing. Last year, while checking my total advance, I found that it went to 36 degrees at the limit, with the nylon bushing glued in place! At that point, I adjusted the heels of my advance weights so that they contacted the autocam to provide NO MORE THAN 27 degrees centrifugal advance. This is three degrees more than specified for my 1111069 distributor, but the engine tolerates it w/o detonation; the total centrifugal advance can be adjusted to any value you desire, by simply bending the mild steel flyweights. I have my initial set at 12 degrees. I have springs installed which allow full advance @ 2000, rather than the specified 2350. The engine tolerates this, as well. There is now a gap of about .060 between the bushing and end of the autocam slot when the weights are fully deployed (heels contacting the autocam).

Your distributor may well be "as-built". I can't say, from the part numbers that you listed, but chances are that something may have been changed at some point in time. Then again, maybe not! Bottom line is, bend the heels of the weights so that they act as the stops.........possibly as they were meant to be. Besides, I'd rather have the steel weights acting as the "limit", rather than a plastic (nylon) bushing, which will wear out/flatten with use, and/or dislodge if not glued in place.

Joe

[Randy S.]

Re: C2 66 300HP centrifugal advance

Mark and Joe,

I did not see a limit bushing on my advance limit pin. I found the picture Mark referenced ( posted by John Hinckley).
Interesting that you say the weights can be bent to effect a greater limit. I will try that.

Randy

[Timothy B.]

Re: C2 66 300HP centrifugal advance

Randy, My 1967 300HP 1111194 distributor has a weight base with 530 CCW and I believe this indicates centrifugal advance 30 degrees. My 63 has a weight base with 724 CCW and is a 24 degree distributor, I have checked both and they are very close. If I am correct than 519 CCW would indicate 19+- degrees and removing the bushing may yield 24. Sounds like someone was there before and changed the weight base cam but I think 24 is good so you may want to experment with lighter springs to bring the advance in quicker and set initial at 12 or set total WOT timing at 36 and see where the initial falls.

I did this on both cars by removing the springs, starting the car, slightly reving the motor and set total. Use the balancer to measure the 36 degree mark. Turn to 12, mark the balancer and repeat two more times and this will give the 36 mark you need. Start engine, rev to advance weights and set 36 mark at the TDC line on tab of timing cover. If you have dial back light it's much easier. Tim