tveltman

Here's the bad news...

http://i733.photobucket.com/albums/w...o/DSC00417.jpg

http://i733.photobucket.com/albums/w...o/DSC00417.jpg

http://i733.photobucket.com/albums/w...o/DSC00422.jpg

Super-loose T-Belt and cam about a half crank revolution out of time. My guess is the valves are shot? Can anyone tell me otherwise?

The other side is about the same timing-wise, and obviously the belt is loose there too. My dad said that he thought he could pull the belt off as it is right now, no need to slacken the tensioner, so my guess is that's what did it. Somehow the tensioner must have crapped out, which is strange because i cleaned and lubed it and replaced the seals as per the manual.

Bill Ball

Ugh!

You don't know if the valves are damaged until you either pull the heads or do a compression check. I would figure out why the belt is loose, remedy that if it isn't too catastrophic and then do a compression check. BUT you are probably right in your suspicions.

Lizard928

yes if that picture was taken with the engine at TDC you do have bent valves in both banks.

Find the source of why the belt is loose BEFORE fixing.

tveltman

So the thing to do is reset the timing to the correct position, then tighten the belt and do compression check?

Bill Ball

That's the Reader's Digest version. You are probably going to have to pull the center cover to see why the belt came loose.

Before you do that, you can look at the tensioner adjustment bolt and see if by chance it backed out. It's right under the air pump poking out of the side of the center cover. 17mm head. It should have a lock nut. If that's not it, then the center cover has to come off.

tveltman

Why did porsche bother cutting eyebrows into the face of the pistons if they won't actually protect against a valve collision?

Tampa 928s

I'm not sure why you don't pull the front covers off and do it right. If your valves are damaged and the belt tensioner assembly is obviously damaged or incorrectly installed you need to do it anyways. Taking shortcuts is not the way to go. I thought it was a timing issue but you may have saved it if you stopped and did not keep turning the motor over. Good luck!

LT Texan

Valve relief are usually there to ensure a min piston to valve clearance is maintained during normal piston and valve movement, not to ensure pistons and valves cannot collide in all circumstances.

Mrmerlin

who installed the belt??
How much experience did they have??
Was/ Who rebuilt the tensioner?

tveltman

Well, failure is all on me. My father and I have rebuilt engines in the past (including his '72 454 corvette), and I read up on it and followed the factory manual procedure to the letter. I double checked everything, and I don't understand why it failed, and it *had* to be a failure and not an installation error because I drove the car around the block a bunch of times, ran the engine on jack stands countless times, and it ran like a top. The only thing that I can think of is that the tensioner adjustment bolt must have been slowly backing off, but IIRC there is a locking nut that should prevent that from happening.

To answer the previous post about rotating the engine, I had no reason to believe the engine was out of timing since the car had previously been running fine. I remember reading about fuel computer failure exhibiting hard start/loss of power/rough running symptoms and (evidently) I erroneously concluded that it was a fuel computer issue, and the valve noise was a result of me previously pumping lots of oil on the ground when I forgot to reconnect the oil cooler line (yes, i did replace the lost oil). I planned on nursing it home, thinking it was a fuel computer issue, so starting the engine (as I did several times) in this case would have contributed to the valve damage. When I finally had it towed home and investigated the problem, I discovered that it was almost certainly a timing issue, not a fuel computer issue, but having run the engine several times, I didn't think turning the engine over by hand would do any more damage than had already been done (and I still think this). The only question comes from why the tensioner failed. I put in the 90-weight gear oil, the new seal, the gasket, and the boot, just as the manual said, and the engine ran fine for a while. Maybe I'm a born loser, maybe the car is cursed, or maybe I'm a moron. I'm willing to accept all but the first explanation, though as I said, I was extremely careful, and this isn't my first bit of engine work, nor is it even my first 928 engine (I had dismantled an old '82 engine prior to this, I found the car in a junkyard and bought it sight-unseen for 200 bucks. The engine ended up looking pretty good with no scoring or anything on the cylinders, and I'm planning on reassembling it and selling it off as-is).

As a point of interest, I assume that when I redo the valves, I should replace the valve guides and guide seals while the heads are out, yes?

Mrmerlin

B4 any other work is carried out i would first want to know why the belt system failed.
Until this is determined other work should not be performed.
I am sorry to hear of the belt failure, if you can post some pictures of the belt in its installed condition it would be helpful for diagnosing the system, this will of course include removing the center belt cover

tveltman

pictures will be posted. As for "not doing it right", that's not what I'm about, I'm simply trying to plan out what my next moves will be, and what parts I need to buy.

Tampa 928s

I had my tensioner nipple **** sideways after tighten it it drained the fluid and the adj bolt backed off and the belt loosened. I did not see it after it was all on, one place to look. Before you take it apart look why it did that, could be the idle pulley or the bolt is bent.

tveltman

Bolt backed of, despite the locking nut (and is now finger-loose). Perhaps I didn't make the nut tight enough, or maybe it somehow rattled itself loose...
http://i733.photobucket.com/albums/w...o/DSC00427.jpg

Here's a pic of the passenger side. As I said, it's loose too.
http://i733.photobucket.com/albums/w...o/DSC00430.jpg

Here's a shot of the tensioner idler
http://i733.photobucket.com/albums/w...o/DSC00429.jpg

All-in-all, pretty messed up

Mrmerlin

I am not convinced that running the engine for less than 5 miles would let this bolt back out, it usually has loctite on it from the factory, and once its close to the correct tightenss will be very hard to turn,
please look for other things like a worn WP shaft. Or possibly a stretched belt , or maybe you didnt tension the belt correctly in the first place .