Technical distributor moving? 350 sbc

Hi all.. im having an odd thing here.. after i clamp down the dizzy, fires right up - after a few seconds the whole body moves! and yes its tight.. no way I can make it budge by hand.

Possible the driven gear is shimmed too tight down on the cam? the dizzy that came out had shiny wear marks on the gear.. the block was machined too much during an align job and I had to put in a tighter chain - im thinking the dizzy is now too tight on the cam because the center lines are tighter (cam closer to block basically).. is there a way to check clearance/backlash between the dizzy and cam?

Possible?

 

The cam and distributor are located relative to each other, by two holes bored in the block. Those holes can't move.

Is the oil pump drive shaft bottoming out?

 

The clamp bolt is too long, bottoming out before its really tight?

 

Besides the clamp bolt being too long, it's not uncommon for the clamp to flex and flatten out when clamped down, allowing the dist. body to turn while running and driving the oil pump. Besides checking into these, I'd pull the dist. and verify the shaft is free to turn without binding.

 

I had a similar problem once with a Unilite, the bushing below the breaker plate had some kind of varnish buildup and once I removed the varnish and lubed the shaft. I never had the timing change again. Once the engine was hot, the timing would change and the car wouldn't start. I couldn't move the dist. by hand but once that shaft started to seize up, there was enough torque to move the dist. and change the timing.

 

Put a washer under the hold down bolt.
Always the EZ-est and cheap-est first!
6sally6

 

Can you pull up on the distributor shaft and detect any play at all?

 

I'm for lubricating the distributor first, then followed up by some of the other suggestions made here second. Certainly couldn't hurt.

 

thanks guys - good info as usual!! I removed the gear bushing and removed a thick shim from the gear.. i never checked the "lash" at the rotor once it was tight.. but it has a little wiggle room on the shaft after removing the shim and the timing is staying put it seems..

The clamp is thick and angled down, VERY tight - no way I can even make it budge after locking it down, i tried..

that explains why the prev gear was so worn - dunno how 2 distributors would have the same issue- maybe the problem will re-appear.. fyi i had a used nylon cam gear and it was pretty worn. I tried a new set and it was just as bad (well maybe a tiny bit better) - put on a used cloyes double roller and way better.. makes no sense- im sure the cloyes was a reduced center chain..

I should have taken the time to check if the cam gear jumped or dizzy.. anyway hopefully i wont have any more issues! not a fan of half dropping a well sealed oil pan to get timing cover off over and over -

thanks for the replies - u guys sure are the bomb. HAMB is my favorite forum hands down..

Ive slapped so many chevies together and then this comes and hands me a few slaps - just when you think you got a grip on things another rabbit jumps out at you!

 

Check to see if the base of the distributor base is pinching gasket tight to the intake manifold when clamped with a thin feeler gauge, could be another cause for it bottoming out against the gear.

Nylon distributor shim kits available with .030, .060 and .090 shims to raise the base away, allowing you to clamp it with out binding the gear.

 

Thats exactly what i didnt see previously, after i removed the shim i couls see the oil squishing out of the gasket thanks yes a good way to eyeball - i did check shaft play after and it had some wiggle room downstairs so hoping it holds up

 

I have had that problem before and found the bushing on the distributor shaft would seize up when engine got hot and turn the whole distributor.