720 Stalls, Won't Start after Timing Chain Replacement

[gone2long]

Hi again,

 

Recently changed the timing chain, adjuster etc. on my 1979.5, 720 4x4. The truck ran better, but after driving it a few miles, it would stall at idle then become difficult or impossible to start. I had to set the distributor as far clockwise as she will go, in order to avoid this problem, but does anyone know the cause? The compression is low, so could this be the cause? Worn valves, or what?

 

Planning, as a minimum, to replace the rings in the near future, but wondering if the above indicates other issues I need to look at.

 

Regards to all,

 

G2L

[izzo]

It ran fine then now doesn't.  Strange

 

 

What was the compression test readings?  You may have set it a tooth off, either chain wise or oil pump spindle location wise.

 

Once you got all done, did you reset your timing to see what degree it was running at an idle?

[gone2long]

Hi,

 

The engine didn't run fine originally, as it had the same stalling when hot, not starting problem, and you could hear the chain rattling around.  After the new chain, we timed it, rebuilt the carburator, and it ran fine for a while, then the stalling etc., problem began again, and adjusting the distributor stopped it.

 

Don't remember exactly the timing setting, after replacing the chain. Should have made a note of that.  Compression readings were down around 75.  After injecting some oil in each cylinder to seal the rings, it went up to 90 - 95.

 

Any other ideas you could throw at me would be appreciated. 

 

Regards again,

 

G2L

[izzo]

That's pretty low compression.  That says your rings are bad, but also the valves probably need rebuilt.  Valves need relapped at the very least, probably new seals too just for cheap insurance...

 

Its old and tired.  Bad compression will make it harder to start I think. 

 

 

I don't know if just a set of rings will do the trick.  You will have to check the bore in various places with a MIC to see whats going on. Feel down the cylinder and see if there is a ridge towards the top. If so you will probably have to bore the cylinders, new bigger pistons, correct rings, hone, etc... 

[datzenmike]

Check valve lash. Tight valves can cause low compression too. Do this on a hot engine.

Set timing to 12 degrees.

Set carefully to TDC turning in a clock wise direction only. If you over shoot back up and try again... 10 times if you have to. Get it right.

Look through the top hole in the cam sprocket and you should see this if the cam timing is correct...

 

The notch in the back of the sprocket should be just below or to the right of the horizontal line. This is why the TDC must be carefully set. If it is not as pictured it will need adjusting. The cam out of time will screw up everything.

.