found what killed my timing belt...

nynor · 02-21-2005, 10:13 AM

and its doing it again.

check out the pictures. the first is damage to the top front edge of the belt. the second is where the belt is somehow hitting/rubbing the plastic timing belt cover. any ideas? i checked the tension, which is why i found the damage, tensions are good.

bluebullet · 02-21-2005, 10:18 AM

is there anyway you can trim down that section of the cover? sandpaper or something? Or what about getting a new piece from the dealer?

I thought I read somewhere that early 944s had problems with the cover rubbing the belt in some places. Is that the area?

SoCal Driver · SoCal Driver's Garage

As the back cover controls where the front covers locate check the back cover for proper attachment. The belt location fore and aft is also controlled by the flange on the tensioner pulley. Check it's alignment too.

A loose cam gear will let the belt creap out also.

nynor · 02-21-2005, 12:57 PM

found another problem, thanks to my good friend stan...

the tensioning pulley has a SHARP edge all the way around the front edge, teeth and galleys. i think that is doing the worst damage.

cam gear is solid. i believe that the back cover is located properly. however, when i first put it back together, i ran it for about a hundred miles before i figured out that i had left a bolt that holds the back timing cover to the cam housing. i wonder if that did some of the damage. what is odd, i didn't notice the damage when i put the bolt back in, as i had the timing cover and cam cover off.

nynor · 02-21-2005, 12:58 PM

also, i think the gear at the crank is pretty worn. don't know if this would cause the damage. no nicks, just worn. can't wait to take that apart.

SoCal Driver · SoCal Driver's Garage

The flange on the timing belt tensioning pulley has to be on the back (engine) side.

The flange on the balance belt tensioning pulley is on the front side.

nynor · 02-21-2005, 02:09 PM

yep, that is how it is.

SoCal Driver · SoCal Driver's Garage

Wonder if the water pump is straight. Some rebuilts are out of square.

Moneyguy1 · 02-21-2005, 05:55 PM

Worn cogs will destroy a belt because the teeth no longer seat properly.

Britwrench · 02-21-2005, 06:46 PM

Looks like the belt was loose. Even if you say the tension was correct the most likely place for the belt to rub is exactly where it did and usually only when cold.

Run the engine without the outer belt cover and see what is going on.

nynor · 02-22-2005, 06:01 AM

well, i'll be swapping out the tensioner and that crankshaft sprocket (or whatever its called).

water pump still looks and feels good. i think i'll replace the idler while i am at it.

Porsche-O-Phile · Porsche-O-Phile's Garage

I would also strongly recommend updating that assembly to the newer style water pump with the belt guard; this was covered in a Technical Service Bulletin and I've done it to my early 944; it's additional peace of mind. . .

nynor · 02-23-2005, 07:44 AM

well, i now feel like i know what is REALLY going on:

my pulleys are simply worn. they seemed functional, but then i checked some new ones out at the shop. i think they are so worn that they are staying square with the block and are probably causing a lot of vibration. so, all the pulleys and tensioners are being replaced this weekend.