have you ever set your timing then 3 weeks later after a few good launches its moved a few degrees....sometimes more then a few. my clamp is tight but i have been told sometimes the dizzy can bottom out down on the bottom near the oil drive rather then were it is meant too on the manifold with the seal and the dizzy can torque/spin enough to ruin your timing position. the difference is only minute but can be enough to cause the problem. have you ever had it happen or think its possible?

i ahve been told to install 2 gaskets under the dizzy to lift it enough that it hopefully can torque down properly. ill do it in the next week or so and see how it goes.

 

May want to replace the dizzy clamp. Your clamp may have weakened or has been bent in such a way that tightening the dizzy bolt doesn't apply enough pressure to eliminate shaft movement.

 

The outer ring on your balancer could also slip. Its a good idea to mark the pulley to rule that out.
The centrifugal and vacuum can also be another source of the change.

 

good points dwwnchs and jim but i have to rule them out....balancer is a romac so no way that can slip. clamp is billet alloy and i have done it up tight. im still sticking to the dizzy bottomng out

 

If the timing is "slipping" and can be brought back to the correct setting with the balancer marks still where they were supporsed to be ie, 10 degrees is still 10 degrees on the balancer, then the dist. is slipping. This is physically moving.

When you put the dist into the manifold without a gasket, does the collar lay flush with the top of the manifold??

If not, just tightening the clamp is putting serious pressures on the drive gear and pickup and will eventually wear them down.

If it is, then I would put in the plastic spacer shims (they come in .030, .060 etc) they sell and then a gasket for sealing. Two gaskets will compress and the same thing will happen.

If it is flush, the clamp may be bent from the years and does not put the pressure on the dist collar.

 

I too bought a really nice clamp and ended up having the same problem. No matter how tight I made it (the dizzy was stable and not moving) after a while the timing would be off. Finally decided to try to stock clamp again and haven't had any problems with it since. Wasted money on the nice clamp.

 

First check if the distributor gear isn't bottoming on the oil pump shaft. Some clearance is necessary between these two parts ( about 0.02 to 0.04" ). Otherwise you can destroy a good oil pump pretty fast...
But I would prefer metal shims instead of plastic ones. They never crack or compress.

 

All good suggestions ... & romac / rollmaster stuff is really sturdy & robust ... but ...

... a romac damper can slip. Suggest you don't assume any part's failsafe simply because it's widely-accepted to be top quality.

I'm not certain it slipped ... but suggest you should verify.

 

You might also check the internal mechanism in the dist. There are parts that need to move freely...any binding due to lack of lube and/or corrosion can cause that same problem.

 

Thats why I suggest a simple mark on the pulley to match the mark on the outer ring of balancer. One quick glance rules out slippage of the outer ring. "Never be fooled again"

 

I suggest you also check the gap between the dist gear and shaft. I bought a new Accel dist and found the timing "walked". Pulled and checked the play and it was 60 thou! Shimmed to 12 thou (Aluminum housing) and problem went away.

 

okay thanks everyone. ill get onto all these things that you have mentioned in every reply . ill play with it today and get back to you.

 

Could the distributor clamp be on upside down?

 

This is a valid point.
I leave my dist just loose enough to move if the shaft binds in the housing.

Better too retime if it catches, instead of snapping.

More than one person has had a dist shaft snap.

Might check the dist bush and that it is not gummed up.

 

oh dear 76.... the clamp is up the right way. i havent had that many beers yet.

12 month old msd so shouldnt be any binding or corrosion. be back soon to see what i find.

 

I think 71 is on to something and you might read on.

EDIT. . . I didn't see that it was a MSD distributor, I'm not sure how the shaft is made but this might still be something to check so I've left the original post below.

Boy, this brings back a horror memory for me! My 1979 when it had only 12k miles decided to do this exact same thing! I would set the timing, drive the car and it would change. I instantly went to the balancer and it’s a good idea to check this first! I did not waste time checking it; I just yanked it off and installed a new one.

I then set the timing, drove the car and it changed again! What the ????. I checked the clamp, checked, double checked and triple checked everything! Never in my mind did I ever think what was wrong would actually be the cause! It was the distributor!

I pulled the distributor out of the car and looked at everything real close! I pulled the shaft out and on first glance it appeared fine! I put the shaft in a vice and low and behold I found my problem, I could turn the upper plate ever so slightly! This is the plate at the top of the distributor shaft that is supposed to be made to the shaft. It was loose on the shaft and it was turning! New shaft solved the problem!

What was happening was when I would hit the throttle hard, the upper plate would move ever so slightly and change the timing instantly.

I hope this helps, and you should also check the balancer but. . . Check it before you remove it!

Willcox Inc.

 

Hi gingerbreadman. A points dizzy or breakerless??

 

ok guys i have sent everyone on a wild goose chase. i better explain from the start. 3 months ago my dizzy did spin under high rpm and the symptomes were exhaust backfire at light throttle. i rectified the timing and put on the billet clamp i have now.
so just recently when my car started to stumble at high rpm i jumped to conclusions and thought the same thing had happened again as it seemed such a similar feeling. i took on everyones advice and went out to the garage today, put the light on my balancer and guess what- its on 12 degrees exactly where it is meant to be so DAM its not timing.
i then checked my idle mixtures which is 4 point on my demon 750 and oh oh they had somehow screwed out to 2 full turn. one of them was 3. i put them all back in to 1/2 of a turn from lightly seated which is where i like it and WHAMO i go for a drive and HELLO BOYS IM FLYING AGAIN. i must have been fowling the plugs at every lights and then stumbling on the next run. it now goes like a dream but dont worry , ill be back here in a week with some new problem im sure.im going to smash a heap of them tonight now..beers that is

 

usually you only have to turn the cap 1/2 (rich) to open a beer.....now you know!!.....