Truck keeps getting out of timing

[Skunksmash]

Me and a buddy have been working on his 86 5.7L 2wd Automatic, and from what we can tell, it keeps working it's own way out of time. About 2 months ago, he truck started running badly, and we figured out that it just needed to be timed. He had a timing light and we must have set it correctly (according to his Chilton repair manual) cause after we finished it ran very smoothly. The problem was fixed, for about a month. Then it started running badly again, so we rechecked our work, and found that it was out of time again. So once again, we timed it and it ran fine. Now about another month has gone by, and yeah you guessed it, the truck has worked it's way back out of the proper timing. What could be causing this? He drives the truck to work and around town, but it does not see any abuse. He is a fellow enthusiast and is working to improve the truck, and i know he is not hot rodding it or off-roading it or anything. We checked more than once to see if we had left anything out or done anything wrong, but we could find nothing. Any thoughts on what could be causing this? I seem to remember hearing that a bad harmonic balancer could do something like this, but i am not sure as to the validity of that.

[enaberif]

Sounds like its time for a new timing belt.

[frogman68]

How is the bolt ? Is it loose ? could be simple as the threads are too far gone (from being over torqued)

Try some loctite on it this time..

[choptop]

Check the cam gear on the end of the distributor.

[Skunksmash]

Gear seems to be ok, and the bolt also seems to be ok. I guess he will have to replace the timing belt then. If that does not work, then maybe i can talk him into getting a brand new MSD dizzy lol. However at this time i would like to ask if we may have left anything out here. I mean, is there anything else that yall can think of that might be causing the problem?

[enaberif]

Gear seems to be ok, and the bolt also seems to be ok. I guess he will have to replace the timing belt then. If that does not work, then maybe i can talk him into getting a brand new MSD dizzy lol. However at this time i would like to ask if we may have left anything out here. I mean, is there anything else that yall can think of that might be causing the problem?

Try this with the bolt.

Tighten it down enough so its tight but you can move it with your hand.

Then keep moving it. See if it becomes loose over time.

[VileZambonie]

Do you have the hold down clamp on upside down? What's this timing belt business?

[choptop]

Doesnt have a timing belt. If the timing chain were jumping a gear, it wouldnt be as easy as retiming it. Bad things can happen when the chain goes out. Either the distributor is moving, or the gear is spinnig on the shaft. How far out of place does it get before you have the problem. Do you have to pull the distributor and retime it, or just turn it a litle. Hang in there friend, you'll get it sorted out.

[eventhorizon66]

What's this timing belt business?

I thought you of all people would know.  All DOHC 350s came with timing belts.

[enaberif]

Bah I came from driving imports for the last few years.. just one of those things.

[eventhorizon66]

Bah I came from driving imports for the last few years.. just one of those things.

Just pickin' on ya

[Skunksmash]

I was saying belt but i meant chain. You know what we were talking about...

But it just barely moves. Well, it moves enough to get out of time but we really only have to twist it to get it back to correct, we don't have to remove it. Although we have removed it to check that little gear as a member here suggested. The gear wasnt missing teeth or anything, and did not look to be messed up... but i know there are things that can happen to metal that the eye can't always see. But anyhow, we will be replacing the chain this weekend and all that good stuff, i will report back in about a month in this thread to say if it fixed the problem or not.

[choptop]

I am not sure that changing the timing chain is going to help. If all you are having to do is turn the distributor a little bit to get it back in time, it aint the chain. The chain doesnt slip a little. If it slipped one tooth, you would have to turn  more than just a little bit, plus, if it even ran after the first time, it's wouldnt run the second time. If the distributor housing itself isnt turning at all, and you are sure, then the distributor gear may still be a culprit. I have had to pull the distributor and scribe a make on it, and rerun it to find it. Now, that is how I found it the first time, the proper way is to make sure the pin that holds it on the shaft isnt sheared. Its a tight fit, and a sheared pin, just makes it stiffer, and not possible to turn by hand. My first one looked like the pin was still there, but when I discovered the scribe mark had moved, and tried to pull the pin, is where I found out I had done it the long way around.
   I am wondering if you may be having an electronic problem. An 87 should be fuel injected, and the computer controls the timing after the first initial setting. I dont know what it is to be set at, (this is where Capt,Vile, and the rest of the guys jump in) but some have a spout that needs to be unplugged, timing set at 0, and the spout reinstalled. It really doesnt act like a timing chain. If it where to move that much, by this time the valve train would be so far out of whack, it wouldnt run right anyway.

[VileZambonie]

If the distributor is turning it's not tight enough or the shaft is starting to seize up. Valve timing is not ignition timing so don't bother with the chain. Once you set the timing make a witness mark and see if the distributor is physically moving.

[Blue 82]

the centrifical advance weights might be sticking
take off the rotor and make sure the weights are not flopping around or binding/sticking

check the vacuum advance cannister with a mityvac
http://www.ronshomeandhardware.com/ProductDetails.asp?ProductCode=188870&click=1014