Rob Edwards

Stopped by Greg’s yesterday, he shared this timing belt failure with me. Here are three pictures of a failed timing belt.

Question: Based on the pictures below, what’s your reconstruction of the sequence of events?

Pic 1. Side view of failed belt-



Pic 2: Longitudinal view of failed belt. Note the length of the complete loss of teeth.



Pic 3: Closeup of the bottom ‘curve’. The curved portion now holds itself in that position….



So whatcha all think?

Answers and additional pics to follow…

danglerb

Orientation of the belt, break on the 5/8 cam side or tensioner side would help, but I will guess it broke at the 5/8 cam. Wow, missing a LOT of misc teeth besides the stripped portion.

5/8 cam locked up, maybe issue with the chain to the exhaust cam?

Charley B

Broken spider.

Leon Speed

No oil to the heads, cams froze on both drivers and passenger side, the crank gear stripped off all teeth.

Landseer

looks like a pattern developed on that last rotation, gotta cipher on this a bit..

ptuomov

Your subsequent photos will surely give us the answer. But I'll play, for entertainment value to others.

One possibility is that cam sprocket somehow chipped a tooth or teeth, or was worn down to a sharp edge. There must be a lot of worn out sprockets out there nowadays when the new set of Porsche cam sprockets costs about as much as a running used S4 engine. The sharp sprocket edge(s) started cutting off teeth of the (bastard L-pitch HTD) timing belt one by one. As more teeth were cut off, the belt started skipping. Once it skipped enough, the valves hit the piston and the valvetrain seized. Crankshaft still rotated and the sharp sprocket teeth really dug into the belt. The belt was like a ribbon curved by pulling it over a scissor blade (forgive me as I can't explain this analogy in English.)

Or any of million other explanations. For example, installing old-style square tooth sprockets with new style HTD belt, and then going thru the above sequence.

supercedar

Looks like Murphy went south for the winter! Maybe I will start my TB/WP now

Mrmerlin

I am with Aryan on this we had a GT that had the oil port get blocked in the head the cams seized the belt then sheared the teeth off at the crank,
given the distance the teeth are removed its from the crank sprocket

Lizard928

With the teeth missing it was a very old belt.

Obviously the crankshaft kept spinning.

As to what caused the total failure, it could be age causing tooth degradation, worn gears, siezed cams, frozen waterpump, frozen tensioner roller, broken spider, the list goes on.

My money from what I see is that it was an original belt that had never been changed and the belts teeth were letting go and a few too many fell off and crank just spun.

Tom. M

I bet if you look at the base of each "tooth" on the belt there will be micro cracks. And Im betting those cam gears were probably sharp enough to slice your finger..

Ducman82

lack of money caused the motor to go in to a frenzy and start eating its self.

Rob Edwards

This was from a 95 GTS.

76FJ55

I'll venture to speculate the failure was initiated at the oil pump gear. that is the only way I can see having teeth stripped off the belt on both sides of the crank gear location for that approximate length. I haven't figured out what drove the 3rd tooth shearing pattern. the pattern appears to be continuous even past the areas that do not have the missing teeth, as you can count in groups of 3 and when you hit the next section of missing teeth it will line up with the previous 3rd tooth. I'll give it some more thought and post if I come up with any additional ideas.

Tom in Austin

a '95 GTS? Hate to see that repair bill ...

Leon Speed

What brand is the belt?