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Old 09-19-2012, 10:17 AM
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Originally Posted by sbnova View Post
Hi I am having a problem I hope someone out there can help with. When timing my sbc the timing mark on the dampener jumps all over covering at least 8 degrees. I cannot get an accurate base timing done. What can be causing this. I have a 510 lift cam, stock double hump heads, a holley 750DP,headers, and 10-1 compression.
Vacuum advance disconnected and line plugged, right?

Is the timing mark steady above idle? If so, first thing to check is the mechanical advance for smooth operation and that the springs aren't allowing the mechanical advance to come in and out at idle.

Other possible causes:

loose outer ring on the damper
worn timing set
excessive distributor endplay
damper/crank key/keyway that is worn or loose
loose damper bolt
a crossfire will cause this, but you should see a bigger jump in timing

BTW, if the damper is a loose fit on the crank, this will also eventually shear the key. The damper needs to be a tight press fit on the crank in order for it to do it's job correctly.

Good luck.
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