could be distributer but also could well be timing gear/chain. More likely the last if it has some mile on it.

 

How many miles is on the engine? I wouldn't think the distributor is worn enough to cause the problem. Are you using a timing light? Are you checking the timing before and after adjustment to make sure it is out of adjustemnt? You might check for a vacuum leak. If the dist. gear pin has sheared than that would cause the timing to get off but it would probably quit running after a short period of running.

Take the dist. out and check for bushing wear, check the inside of the cap is the rotor making contact with the cap or terminals inside the cap. If the engine has high mielage or has been driven somewhat hard and if the cam gear is plastic, the cam gear might have sheared all the teeth.

 

Make sure your hold-down clamp is actually doing its job. If not, your distributor will "walk".

 

My motor has 75,000 miles on it.

I use a timing light each time, timing set at 8 BTDC one time, next time I check it may check out at around 10 BTDC when I put the light on it.

The truck will run better if I advance timing to around 10, but after a while it will end up showing different setting with the timing light.

Thanks,

80 Chevy C10

 

To repeat MHenricks, are you using a timing light to verify the timing change or do you just think it's changing because it seems to run better when you move it for a while. The easiest method I use to check a distributor for wear is to hook up a dwell meter (most decent automotive multimeters have a dwell setting) and watch for any eratic changes in the dwell while she's running. A good distributor should hold the dwell pretty stable, if your readings jumping around that means the distributor is toast.

 

Hey we posted at the same time . Also just tightening down the hold-down clamp can shift your timing a degree or two.

 

To check for timing chain play remove distributor cap and watch rotor while moving crankshaft back and forth with a socket on the front crank bolt. When you reverse crank direction the time it takes for the rotor to start moving is how much play you have in your chain.

 

I am verifying timing changes with a Light.

I have a Dwell Meter, but did not think to get it out and try it - Thanks for that idea!

The Hold Down Bolt is kinda' sticky, I may be allowing Distributor to move.

Thanks for helping, I am glad I found this forum!

80 Chevy C10

 

Pull the cap off the dist. then turn the engine over by hand. watch the rotor. is there a time lag before it moves? Is it a large lag? This will indicate a timeing chain issue.
Let us know!!
Slider in Wa.

 

I had a distributor doing something similar and it was the bushing starting to seize up and the distributor was actually moving in the clamp till it finally seized completely and spun the distributor to where it would not run at all.

 

If the distributor is actually advancing itself (from 8 btdc to 10 btdc) I would check the centrifigul advance for proper operation (broken spring etc.). After I set the timing and tightened the hold down, I would check it again immediately.

 

I checked my distributor with a dwell meter today, dwell is erratic.

I tuned crankcase over and did not notice much of a lag in movement of ignition rotor while cap was off.

Lookin' like I might have to spring for a new distributor!

I appreciate all advice received!!!

Thanks,

80 Chevy C10

 

When checking for play in the chain, bring the engine to TDC on the balancer. Remove the distributor cap and move the balancer the opposite direction until rotor movement is detected. Check how many degrees the balancer has moved before the rotor moves.

 

How many degrees would you allow before you condemned the chain? Is there an industry standard?

 

I would say nothing much over 2 to 3 degrees for an every day passenger car engine. But I like it tighter on a street performance engine and even tighter on a strip engine.

You have to figure what you are losing when the chain has the cam following exactly and you let off the fuel then increase fuel pressure again. The valve timing and ignition timing floats momentarily and then is shocked back into alignment. Talk about spark scatter! Losing a lot of horsepower there.