bouncing timing line
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Most likely a sticky [mechanical] advance mechanism in the distributor. It could be the harmonic balancer, but usually, when the rubber joint breaks down, the line just 'wanders' around. If you have an electronic ignition, it could also be a bad electronic module.
Thread Starter
Instructor
Joined: Apr 2011
Posts: 151
Likes: 1
From: Cedar Springs MI
I don't think an 81 has any mechanical advance stuff. I looked and there were no springs at all.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
Any mechanical issues are there whether your connector is plugged in or not.
If it only acts that way when the computer connector is unplugged, then I would probably look toward the ignition module.
If it only acts that way when the computer connector is unplugged, then I would probably look toward the ignition module.
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Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,352
From: Santa Ana CA
This is how it's fixed. You should be able to find something on the web on checking it with a feeler gauge.
http://www.jegs.com/p/Moroso/Moroso-...48771/10002/-1
http://www.jegs.com/p/Moroso/Moroso-...48771/10002/-1
Racer
Joined: Oct 2008
Posts: 278
Likes: 5
From: illinois
I believe "toddalin" has a good point. I have a 71 points distributor converted to a pertonics(spl) electronic ignition. Had the same timing bounce. I remove the distributor and checked the shaft to gear for end play. Measured 60 thousands way out of spec... Bought the shim kit and got the gap to within 10 thousands..No more bounce.. my 2 cents.
Mike
Mike
Drifting
Joined: Sep 2006
Posts: 1,986
Likes: 21
From: Columbus MN
The timing on my '80 was all over the place too. If there is vertical slop in your distributor, bouncing up and down advances and retards your timing because of the diagonal cut distributor gear teeth.
To check for vertical slop, just grab the rotor or shaft and pull up a few times. If you are able to move it more than 1/16", then you have too much vertical play. You fix the problem by adding gear shims. Vendors (such as Moroso) sell HEI shim kits. Be sure to get the gear shim kit, not the shaft shim kit.
That worked wonders for my car.
To check for vertical slop, just grab the rotor or shaft and pull up a few times. If you are able to move it more than 1/16", then you have too much vertical play. You fix the problem by adding gear shims. Vendors (such as Moroso) sell HEI shim kits. Be sure to get the gear shim kit, not the shaft shim kit.
That worked wonders for my car.