Timing Jumping

[Michael H.]

Re: Timing Jumping

I never switched this wire out when I switched out the spark plug wires because it was not shielded but what I also noticed was a bit of spark from the neg distributor wire to the coil. It was jumping across to the base of the distributor.

Thanks Steve. Good to hear it's corrected. I think we all learned something here.

[Clem Z.]

Re: Timing Jumping

shimming the clearance down does help eliminate spark scatter cause by the uneven motion of the oil pump that is driven by the distributor.

[Michael H.]

Re: Timing Jumping

shimming the clearance down does help eliminate spark scatter cause by the uneven motion of the oil pump that is driven by the distributor.

Yes, that's true Clem. And, in addition, there are more things besides the oil pump that cause the timing to get very strange at higher RPM near the torque peak at WOT.
The flexing, or twisting of the crankshaft at high load/RPM, can cause a lot of cam timing changes that also affect the distributor. The slight change in speed/RPM of the front of the crankshaft that occurs, loads/unloads the timing chain and the slight change in velocity also affects the distributor.
GM engineering did a lot of research on this in the late 60's and I think Yunick was involved too.
In the end, it was concluded that no cam driven distributor/ignition system would ever be free of this problem and the only solution was a crankshaft triggered electronic system.

Fortunately for us, this doesn't have much to do with our old restored cars because most of us never buzz the motors up past 4000 RPM anyway. Well, maybe just occasionally.

[Clem Z.]

Re: Timing Jumping

Yes, that's true Clem. And, in addition, there are more things besides the oil pump that cause the timing to get very strange at higher RPM near the torque peak at WOT.
The flexing, or twisting of the crankshaft at high load/RPM, can cause a lot of cam timing changes that also affect the distributor. The slight change in speed/RPM of the front of the crankshaft that occurs, loads/unloads the timing chain and the slight change in velocity also affects the distributor.
GM engineering did a lot of research on this in the late 60's and I think Yunick was involved too.
In the end, it was concluded that no cam driven distributor/ignition system would ever be free of this problem and the only solution was a crankshaft triggered electronic system.

Fortunately for us, this doesn't have much to do with our old restored cars because most of us never buzz the motors up past 4000 RPM anyway. Well, maybe just occasionally.

chevys new NASCAR engine the R-07 has the distributor up front like a f--d to eliminate the twisting of the cam shaft causing timing to move around. since they use a dry sump oil system spark scatter from the oil pump is not a problem

[Gary B.]

Re: Timing Jumping

I have seen harmonic balancers slip so the timing mark was way off and the engine just wouldn't run right using the mark. I had to set the timing by ear until the balancer was replaced. I have never seen a harmonic balancer jump around, but it could happen. Also, have you checked for vacuum leaks, this would cause a jump.

[Paul Y.]

Re: Timing Jumping

I've seen this type of thing when a timing chain is loose and the gears are worn. Be sure to let us know when you find it. Paul