william_b_noble

ok, we have here a real WTF situation - perhaps one of you folks has encountered this before and can offer some thoughts -
1. the car - 1987 944S - the 16 valve kind
2. the situation - replaced front seals (crankshaft and balance shafts), which involved removing the old timing belt, tensioner, the pulley and sprokets on the crank, replacing the seals and putting it all back together. no problem, right?

WRONG ---- put it back together with new tensioning roller and new belt. Set tensioner to minimum position to install, and belt would not fit - about one or two teeth two short.

So, what have I done:
1. removed new belt and new roller, replaced wtih original belt and roller - the original combo is too short.
2. verified proper belt (1 inch wide) with proper number of teeth. verified proper part number on new and old roller.
3. removed drive sprocket from crankshaft and reversed it - didn't think this would matter, and it didn't - still too short. Note that the manual for the regular (8 valve) cars shows a sprocket on the crank that has a flange, and the flange goes away from the engine and towards the balance shaft drive sprocket - I had speculated that I might have reversed this and the belt might be riding on the flange - well, the sprocket in my car has no flange, so reversing doesn't matter.
4. checked part number on original sprocket - it is cast with the
part number 944-105-125-05. So, just to be safe, I look up in PET 6 (and
also in the PDF you can DL directly from Porsche), and (it's MG1, SG 2) you
find this part, item 14 on the exploded view, and the part number is
944-105-125-06. -- ok, minor WTF, but this sprocket was on the car and working, so it couldn't have grown or something.
5. took tensioner to my milling machine, enlongated the adjustment slot by about 3/16 inch - put it all back together again - that helped, but belt is still too tight if I force it on.

So, this makes no sense - I noticed nothing amiss when I took it apart, so I am pretty darned sure the tensioner was not bottomed out at that time. I have not removed the head nor the sprocket on the cam shaft - only the sprocket on the crank and the tensioner. Didn't mess with water pump either. Old parts don't fit, new parts don't fit, and they are too close for it to be something really stupid like putting the tensioner in wrong (after all, it goes over those 3 studs - you can't put it in off by a "tooth" or something like a distributor on a 38 plymouth.

So come on guys - someone must have a theory on this - I realy don't want to just mill the slot a little longer and make the problem disappear, though I may have to. (oh, and I notice that the S has a different tensioner too than the regular cars - wonder what the difference is?)

william_b_noble

oh, one more point - if I force the belt on and start the car, it runs fine - but no way am I risking breaking the belt on this car - I need to get the tension right

Mighty Shilling

the only thought I have is that the old belt stretched... a lot...

william_b_noble

not a chance - I measured both, and I tried putting the old belt back and it is also too short.

Serge944

Are the teeth fully seating in the sprockets? I actually had a "Flenor" brand belt where the teeth were just slightly off and after each tooth, the belt would become more and more strained to fit in the teeth. Eventually, it didnt even go into the pits at all.

Also, the 16v engines use a different tensioner sprocket than the 8v. Verify that you didn't purchase the wrong one.

xsboost90

do you have an 8v belt?

Team SSR

It's been awhile since I tensioned my S, but I believe the tensioner roller is cogged (has teeth)... in which case it would be possible to leave it loose between the crank drive pulley and the tensioner which would effectively leave your belt 1 tooth "short".

Jay W

I just put a belt on my S. While I was putting the tensioner back on the car, it had to be in a position where the tensioner roller had to get past the water pump pulley and another pulley. Then when I went to put the belt over the cam sprocket, the belt was too short. So then while the tensioner is on the car and tightened down, I re-released the adjustment nuts on the tensioner and was able to compress the tensioner just a little more. After that I was able to slip the belt over the cam sprocket. You may also be attempting to put on the belt over the cam sprocket incorrectly. I have found that if I force the belt over a small part of the sprocket and then try to push the rest on, it gets jammed. I usually try to slip the belt evenly over the whole sprocket at the same time, that way it slips on properly without jamming up. And lastly, if you are not using a flywheel lock to hold the crank at top dead center, then after you get that belt on and before you turn the engine, make sure both the top and bottom marks are still on. I had an 8V car that while I was slipping the belt on, the crank moved and I didnt know it until I had already turned 1 revolution by hand.