Bob Barry
08-12-2002, 05:19 PM
I cured the debilitating engine knock that contributed to my decision to not travel to Ouray.
The pinging began after I replaced the distributor, but it had some before, especially starting up from a stop after a long highway run.
It would occur whenever I used more than 1/2-throttle, and come on worse as the revs rose. Even with the adjustable timing, backing it down to 0ºBTDC wouldn't completely eliminate it.
The EGR valve was working, and the thermostatic switches that limit its operation were letting it work when it needed to.
The fact that the ping was somewhat tied to engine speed pointed me toward the mechanical advance. I pulled the vacuum advance unit and the magnetic pickup plate, and discovered what was causing my pinging.
The Duraspark distributor, like most units, uses centrifugal weights and two springs to control the mechanical advance. The way it is set up, however, is to use a light spring that is stretched tight and a heavy spring that has some slack in it: the light spring controls the advance until the slack in the heavy spring is taken up, after which the centrifugal weights are working against the heavy spring.
Well, the A1-Cardone distributor I got from Advance Auto had a LOT of slack in that heavy spring, so the light spring was letting a LOT of advance come in before the heavy one slowed things down. The heavy spring was a silver-colored unit, but was lighter than the brown-colored spring usually found in 360 distributors. This was feeding too much advance into the distributor, causing the ping.
I replaced the silver spring with the brown spring from the original distributor, and took out some of the slack by bending the tang one end wrapped around out a little more.
I also figured out how to adjust the vacuum advance. It is adjusted through the vacuum-nipple using a 1/8" allen-wrench, which engages a hex collar just inside the fitting. Turning it clockwise actually *loosens* the spring inside it, which makes the vacuum advance come on sooner. I bottomed it out all the way clockwise, then backed it off two turns counter-clockwise (you can back it off much more, but beyond two turns the spring becomes so stiff that the diaphragm will never move under engine vacuum). I tested it out, and adjusted it to 1.5 turns out, which is still rather conservative, but I want a margin of comfort in the timing curve.
Results: With the adjustments I mentioned above and the initial timing set to 12ºBTDC, I couldn't get it to ping, even lugging the engine and accelerating hard up a long hill in 95ºF weather with the A/C on.
I could probably quicken the advance curve a bit more by putting more slack in the heavy spring or by loosening up the vacuum advance diaphragm spring a bit more, but first I want to make it up Mt. Washington without any pinging.
[ August 16, 2002, 09:34 PM: Message edited by: Bob Barry ]
The pinging began after I replaced the distributor, but it had some before, especially starting up from a stop after a long highway run.
It would occur whenever I used more than 1/2-throttle, and come on worse as the revs rose. Even with the adjustable timing, backing it down to 0ºBTDC wouldn't completely eliminate it.
The EGR valve was working, and the thermostatic switches that limit its operation were letting it work when it needed to.
The fact that the ping was somewhat tied to engine speed pointed me toward the mechanical advance. I pulled the vacuum advance unit and the magnetic pickup plate, and discovered what was causing my pinging.
The Duraspark distributor, like most units, uses centrifugal weights and two springs to control the mechanical advance. The way it is set up, however, is to use a light spring that is stretched tight and a heavy spring that has some slack in it: the light spring controls the advance until the slack in the heavy spring is taken up, after which the centrifugal weights are working against the heavy spring.
Well, the A1-Cardone distributor I got from Advance Auto had a LOT of slack in that heavy spring, so the light spring was letting a LOT of advance come in before the heavy one slowed things down. The heavy spring was a silver-colored unit, but was lighter than the brown-colored spring usually found in 360 distributors. This was feeding too much advance into the distributor, causing the ping.
I replaced the silver spring with the brown spring from the original distributor, and took out some of the slack by bending the tang one end wrapped around out a little more.
I also figured out how to adjust the vacuum advance. It is adjusted through the vacuum-nipple using a 1/8" allen-wrench, which engages a hex collar just inside the fitting. Turning it clockwise actually *loosens* the spring inside it, which makes the vacuum advance come on sooner. I bottomed it out all the way clockwise, then backed it off two turns counter-clockwise (you can back it off much more, but beyond two turns the spring becomes so stiff that the diaphragm will never move under engine vacuum). I tested it out, and adjusted it to 1.5 turns out, which is still rather conservative, but I want a margin of comfort in the timing curve.
Results: With the adjustments I mentioned above and the initial timing set to 12ºBTDC, I couldn't get it to ping, even lugging the engine and accelerating hard up a long hill in 95ºF weather with the A/C on.
I could probably quicken the advance curve a bit more by putting more slack in the heavy spring or by loosening up the vacuum advance diaphragm spring a bit more, but first I want to make it up Mt. Washington without any pinging.
[ August 16, 2002, 09:34 PM: Message edited by: Bob Barry ]