I have a jumping spark when checking timing ( vacuum disconected ). I would say +/- 2 or 3 degrees.

where to look at ?

What kind of engine big block or small block?

I had the same thing happen with my big block and I installed a 1/2" split collar on the distributor shaft just about the intermediate oil pump/ distributor drive gear. This holds the drive gear down and keeps the distributor from moving up and down which changed the timing.

400

I didn't get what exactly you made

whats that SPLIT COLLAR?

BTW I didn't have that fail when I rebuilt the engine.

recently rebuilt the dist ( new bearings and the plastic collar ) but dunno remmeber If I had that fail before make the job on dist.

could it be the block bearing to the oil shaft some worn ? original was aluminium. Broken once and replace for a brass one, used but did look perfect...

maybe using a shim washer between oil shaft and block bearing will save that too ?

Buut why I suddenly would need to make that ?

Quote:

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I didn't get what exactly you made

whats that SPLIT COLLAR?

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A split colar is a metal ring that is cut in half and has 2 allen screws to tighten the 2 halves together on a shaft. One half has the holes that allow the screws to fit into. The other half has holes that are drilled and tapped so the allen screws can be screwed into.
This colar should be placed just above the notch on the distributor shaft that would go into the top of the distributor/oil pump drive gear. The purpose is to stop the distributor shaft from moving up and down when the engine is running, so positioning the colar is very important. I installed mine loosely but snug, to the low end of the shaft. Then put the distributor in and tightened it down all the way. then removed it again and tightened the collar in place. Then reinstall and set timing. Some guys have used a heavy piece of reenforced fuel line to accomplish the same thing. But this would have a tendancy to move over time.