Two weeks ago I had to have my truck towed. The starter was bad. With the new starter the truck would not start. Pulled the distributor cap and found a lot of metal shavings in the cap and the rotor had soot on it. Set truck to TDC and the rotor was not pointing to #1. The chain and guides looked fine. Replaced distributor, checked valve lash, and the truck started fine and ran fine until Thursday. I say fine but I had heard some spark knocking, but only a few times. On Thursday the truck would not start again. I had it towed home suspecting the timing had jumped again and was concerned the timing chain was the problem.

The timing is off again, way off. The chain has about 90K miles on it. Again the guides and chain look fine. The chain link is still where it should be on the cam gear. I will be replacing the chain. Besides the chain, is there anything else that could cause the timing to jump? The distributor drive gear looks ok to me.

 

What did you find? If there was metal shavings IN the distributor I would suspect a problem there first. Especially since you said the mark on the timing chain is where it is supposed to be and it looks ok. Is the shaft loose or the gear spun? What about the drive gear on the end of the cam? How does it look? Is it tight? Teeth look ok? Weird one for sure.

 

Just a thought, if you are relying on the timing mark on the harmonic balancer they have a rubber ring between the inner and outer pieces that is known to separate allowing the outer ring with the mark on it to walk around.

 

Even though I thought my distributor drive gear looked ok, I didn't have a frame of reference since it's the only one I've ever seen. The teeth on it have wear and it seems to be uniform. Also when stabbing in the new distributor it took force. So I thought the gear was ok. That is until I saw a pic of one in another yotatech thread. Mine is very worn. I just picked up a new distributor drive gear from the dealer this morning. Of course I figured it out after I pulled the timing cover. Now I'm trying to decide whether to replace the chain (90k on it) which is tight and the guides are ok.