So there has been alot of questions about bent valves from timing belt failures.

 

It's been my experience that if the belt breaks, it surely bent valves.

 

But sometimes, if the belt just skips a few teeth, things are okay.

 

Example :  this '06 forester started running incredibly rough about 10k miles after the owner did his own timing belt replacement.  Pulled the covers, and found this

 

IMG_2926 by Dans Subaru, on Flickr

IMG_2925 by Dans Subaru, on Flickr

 

He had striped out the lower idler hole, and it had walked funky out of the hole and forced the belt against the inside of the cover until it shredded and it had skipped 2 teeth on the passenger and 4 teeth on the drivers side.

 

After tapping the lower hole deeper, and installing a longer bolt to hold the idler, I installed a new belt and did a compression test.  165+ in all cyls.  Lucky SOB

 

So if yer belt has skipped, don't go immediately tear the engine down.  Worth a compression test first.

4 teeth and still fine? oh wow, now thats pushing it.

yeah, 4 teeth is about 22.5 degrees of cam rotation.  So 45 degrees of crank.  

 

That puts the piston about halfway below TDC when the intake should be just begining to open, and the Exhaust should be just fully closed.

 

I think the threshold is around 35~45 degrees of cam, 70~90 degrees of crank where you get valves open when the piston hits TDC.  

 

I suppose one could look up the Cam degree profile and make a pretty accurate assesment of just when valves begin to hit.

Yep worth a check - Ive had one lucky one so far. Broke at idle and he tried to restart multiple times.

Edited April 27, 20187 yr by idosubaru

side note - the belts are TOUGH