Hi, Any idea's on a problem I am having with my mechanical advance. My 1971 Stage 1 has a HEI . The motor has a pretty radical cam with roller rockers, and a MSD box. The cam is radical enough that I need and have a vacuum canister for my power brakes and not that still much power at all. My mechanical advance does not seem to work. It works fine set at 8-10 initial and advances to about 30 -32 with the vacuum line connected .When I disconnect the vacuum it will only advance a hair, giving a blip up when I let off the rpms. My buddy who is a Tin Indian Man and a trained mechanic in his former life went over the distributer, adding new springs tore it down adding a dab of grease were needed is a bit stumped.The weights seem to go forward by hand nicely and return well. We even shaved a little off the underside of the blue HD rotor just in case it was binding on it. The only problem he said he saw was the bushing on the shaft may be worn a little because it had a tiny bit of play. What can be causing this problem. Thanks for your help.
It is almost surely springs that are too heavy to allow the weights to move at lower revs... Try removing the weights, and wrap a little piece of wire around their little stem to keep th weights from flying off entirely and check the timing as the rpm's are increased (with the VA disconnected and plugged).
Frank might be on to something. Is it possible that the weights are almost fully open at idle? So when you set the base timing, your actually setting it with full mechanical advance? That is one explaination your not getting any difference in readings. What RPM does the car idle at? Just to diagnose the problem, try putting on a super heavy duty set of weight springs. The ones that look like front coil springs:grin: Then hook up your light and see if you get mechanical advance out of it.
Thanks guys, I do have heavy springs on it now but,I didn' think they would be a problem since I assumed heavy springs would still work and only allow advance later and return quicker. I will try the weaker springs.
From Dave Ray (IgnitionMan), who read this question. "I would get your mechanic to check for a few things. Check to make sure the center and weights are installed correctly for the distributor rotation, as they will mount either eay. Reversed, they won't allow advance with some few weight/center combinations. Bound up mainshaft to reluctor. Even if the reluctor turns free when the engine is stopped, heat can bind the reluctor to the shaft when the engine is running. No end play in the distributor. This binds the reluctor up, and stops the mechanical advance. Set end play to between .016 to .022, NO TIGHTER. Worn center plate/weights and weight pins. Look closely at the sliding faces of the center plate and weights, they can wear very severely and stop the advance, as can the pins. Also check the pin holes in the weights to make sure they are still round, and not elongated. If the weights and center are aftermarket types, from a "curve kit", remove them and go back to stock parts. The poster is correct in the fact that even with the heaviest springs, the mechanical advance should actuate and return, depending on the rpms it takes to move the weights against the spring pressures." If you wish to ask Dave questions, he is a moderator, with his own ignition system section, at buickthunder.com Regards, Milton
Dave and Milton Thank You. I just spoke to my Poncho friend and he agreed he didn't think about the rotation for the Buick when he had it on the bench.
Dennis, It sure does make a person think there is a lot of over-moderation here, doesn't it. Lets see if this one gets pulled. Regards, Milton
