I checked my timing a couple weeks ago after I noticed some knocking. It was at 18* advanced. I normally set it to 14*, so I set it back. Today I noticed the starter hesitate after it was warmed up so I checked the timing and it was back at 18*. I tightened the retainer snug enough so you really have to muscle it to make any adjustments. Do I need to torque it down more or could there be another issue. The distributor is a GM HEI out of a late 70s Cutlass and probably original. Mine is a 71 Cutlass with a 455. l had this distributor on my 350 before I swapped the motor.

 

It should be tight enough that it cannot move.

 

Bolt threads become worn after extended use over time - 52 years = an extended time. Are you using the original bolt? A bolt swapped from another engine? Whatever the case, bolts do NOT last forever.

 

Really shouldn't be able to move it when clamped but if it was moving itself I think it would move toward retarding??? the timing, could be wrong though. I'd pull the rotor and clean and lube the weights and check the vacuum advance for sticking/binding.

Match mark the distributor housing as an index to rule out movement.

 

This. You need to tighten the bolt more than what you’ve been doing.

 

It is also possible the outer ring on the balancer is moving.

 

You can purchase a brand spanking new bolt and hold down for $15. They sell them because they wear out. They wear out. They sell them because they wear out. You could continue tightening the bolt until either the bolt breaks, the threads strip (further), or you spin the bolt. That always makes it more fun. Did I mention they sell NEW bolts AND hold-down plates?

 

And…. If the new bolt isn’t tightened sufficiently the same situation can occur.

 

Here's the new bolt and clamp Norm mentioned.

https://www.inlinetube.com/products/inl11282

I imagine there's a torque spec for the hold down clamp, but I just always make it snug. I've never had trouble with the distributor timing shifting once I tighten it. Good luck.👍

 

Bushings wear out in distributors also, can cause all sorts of timing issues. Also as mentioned could be your balancer is slipping, but if you say spark knock is gone and then comes back timing probably is changing, I personally never had a problem with the bolt/retainer but anything is possible.

 

Could mark the body of the distributor to verify that it is actually rotating, so you can rule out the other components mentioned in earlier posts.

 

That would only be apparent if you put a timing light on it. The balancer marks moving would have zero affect on the way it runs AFTER being set.

Obviously if the timing mark isn’t where it’s supposed to be and set the timing, the timing won’t be accurate.