Alright, I bought a 95' Monte Carlo 3.4 DOHC with 138k for $300 not too long ago, certainly not a bad deal. It needed a timing belt at the time (belt that was on had broke), so I went and bought the belt, and the two idlers and the tensioner. I had a bud of mine do it the first time-because I did not feel like tangling with that mess. He installed the belt and the pulleys, car started up and ran fine. I drove it and didn't get very far until the timing belt jumped teeth and the car started running like utter trash. Got it towed home, and i figured the saying "if you want something done right, do it yourself" was a good idea. So i dived in, reset the timing marks, checked over the belt and saw no damage. Checked over the pulleys, saw nothing. So I put the belt on and put everything back together. Car again ran great. And it has since been my daily driver for about 4 months now, no problems. Out of the blue a few days ago, the belt jumped again. Got the tow, ripped it apart again, reset everything and checked everything--all looked okay. My question is what could be causing this? The only thing that wasn't replaced was the hydrolic tensioner that applies tension to the tesnioner pulley itself. Now, the tensioner itself was missing the entire rubber boot at the end, you could see the shaft and everything. But was like that when we pulled it off, and it still seems to apply tension. I would have replaced the hydrolic tensioner but I could not find one anywhere. Do you guys think that hydrolic tensioner is the cause of the jumping? Need to get this problem situated because constantly going back in there and redoing the timing is not fun.
Thanks!

 

I can tell you this much back when I was working for the local chevy dealer we wouldn't dare time those 3.4 dohc engines without replacing everything, including that tensioner.

 

Having owned two of the bloody things (I used to be REALLY stupid), I second aero's comment.