On my 92 pickup (3vze) after a year of problems I finally got a valve job, two polished freshly machined cylinder heads! After putting everything back together, aligning the crank to TDC and the two cams to the marks on the dust cover and the dist cap at 1130 lined up with #1plug, and then turning the engine around two full cycles and everything still be aligned properly I tried turning the engine over and it sounded horrible!! I couldn't figure it out b/c I was sure it was all aligned. I opened it back up and the left cylinder was off three teeth. I had tightened the tension pulley after putting the spring on. My second time aligning everything perfectly I did not tighten the tension pulley b/c I noticed in the book it doesn't actually say to tighten that bolt. The very first time I turned the engine over the spring stretched really far and the timing belt jumped.

So I think its obvious why the timing belt slipped the second time, b/c I didn't tighten the tensioner bolt, but why did it slip the first time when I had tightened that bolt? What do I do? Replace the spring? The spring is 1/4" longer than the specs say it should be. I can't even get the thing to start and idle so I can correctly time it, it slips so quickly. Where do I go from here?

 

I also don't understand, if you are supposed to tighten the tension pulley, why there is a spring? just to get it the right tension, then you lock that down with a bolt. I would think they would use a more solid mechanism to achieve perfect tension then a spring.

 

Toyota changed to a hydraulic tensioner in 93 probably for this reason. You can upgrade but you have to install the later fan bracket to do so. If you don't want to upgrade I would suggest a whole new tensioner.

 

If your tension spring is 1/4" longer than it should be, replace it. It sets the tension, then you rotate twice, and lock the bolt down tight, thereby ensuring the belt is evenly tensioned around all pulleys. If your spring is too long, the belt doesn't see the right tension, and slips under load. The hydro tensioner is an upgrade, but with millions of the sping tensioners out there, they aren't that unreliable.

 

So were thinking the 1/4 too long is why it's slipping? Why didn't it slip forever ago then?

 

Because when it was installed umpteen thousand miles ago, the spring was 1/4" shorter, setting the correct tension, then the bolt was tightened. So the belt ran until it was replaced.
That's a part of why belts and chains have a service interval of 60/70/80/90 or however many thousand miles. They stretch, increasing the possibility of slipping, as well as general wear from many millions of rotations.