Muscle car question

I have a 396 Corvette engine transplanted in an old pickup that I use for a daily driver/grocery getter. I haven’t converted to HEI distributor yet but I am using a point and condenser upgrade by Petronics (Which works amazingly good and I recommend it). Anyway, I have to reset the timing about every 7-8 days because the distributor retards itself. Can anyone tell me why this is happening? Is the timing gear worn out or is it just a simple hold-down replacement issue?

Is the dwell staying stable? if your point gap closes it will cause the timing to retard.How hard is it to move the distributor housing(should not be easy)?

The Petronics system eliminates the points, condensor, etc. So there is no dwell to worry about.


I’d get some chalk and mark the relationship between the distributor shaft and the engine block. Then when it does it again, you can see if the distributor itself is moving or if it is something internal. I’d suspect that unless the hold-down bolt hole is stripped or something and you can grab it and turn it by hand that you’re looking at a new distributor. Now might be the time for the HEI conversion!

As I recall the OEM hold down resembled a piece of 1/4" diameter wire of hardened steel. It was brittle and prone to breaking. After market hold downs that were more substantial used to be available.

So much helpful input, seems like Norms dizzy isn’t the only thing that’s retarding itself around here.

The chalk indexing is a good way to determine if the dist is rotating on you. If it is, check the clamp. It’s easy to install some of them upside down and they really don’t hold properly then. I’ve seen that one done more than once.

I had an 68 chevelle ( straight 6) that did something like this. It turned out that the distributor shaft was two pieces pressed together. The two sections became loose and the top section of the shaft twisted in relation to the bottom section.

The ignitor gets it timing from the distributor lobes. If the ignitor’s trigger arm (or, whatever you want to call it) rubs on the distributor cam lobes, the trigger arm could be wearing and changing the timing. Also, if the screw which holds the ignitor allows the ignitor to move, timing could change.