[Cloud9...68]

I wrote on this as part of another thread, but I thought I may get a better response if I start a new one, so here goes:



I think my balance shaft belt may have skipped a tooth. The car has developed a significant vibration that starts at 1200 rpm, and stays rough, but doesn't get any worse, as I rev it up. It does this whether the car is driving in gear, or if I rev the engine from idle, so it doesn't appear to be a driveline issue. Assuming it is the balance shaft belt, and I'll check the alignment asap, using the straightforward-looking procedure described in the manual, could somebody please explain step-by-step how to realign the belt? While the manual's description of the alignment checking procedure is very good, its description of how to reinstall the belt is summed up beautifully in the following brilliantly exhaustive, yet magnificently eloquent narrative, and I quote ... ahem ... "Fit the toothed belt."



To help fill in what the manual leaves to the imagination, I have a few questions:



- Is it possible to simply loosen the tensioner and wrestle the belt back to the right setting, then re-tension, or do I need to remove the belt, align the shafts, and reinstall the belt?



- What kind of special tools do I need?



- Speaking of special tools, what about the infamous 9201 belt tensioning device, which I understand costs about as much as a new Cayman? Is it absolutely necessary to use this tool, or are there other ways to assure proper tension?



- This tooth skipping business seems to be a fairly common problem. What causes it? The PO replaced the belts about 16,000 miles ago, and I had the variocam pads replaced about 3000 miles ago, so the belts are well broken in, but far from old, and should have been re-tensioned as part of the variocam pad replacement procedure. I would have thought this would have given me protection against this kind of thing. I wonder what happened?



Thanks in advance.

Partial Post: Please Login or Register to read the full post.

[pickwick]

It's pretty easy to loosen the tensioner and rotate the lower shaft while the belt stays stationary to "unskip" the tooth.



The 9201 has been discussed to death here and elsewhere, with no consensus. I use a Kricket, get repeatable results, and am happy with it. I measure to get the same number (plus or minus 1 or 2) five times before I'm convinced I've done the measurement right.



A very small amount of adjustment change at the tensioner makes a big tension difference; expect to tweak it four or five times to get it right. And if you tighten it, measure, and then tighten some more, the measurement changes, so you have to use full tightness every time. I use a breaker bar (my torque wrench doesn't fit) because the time I just used a wrench it loosened after several miles.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Well, I took the belt covers off this weekend, and found that the source of my vibration is unambiguously the balance shaft belt, which has at least 20 teeth sheared off. So of course the alignment is miles off - or a good third of a rotation of each of the shafts, anyway. One question - I was told by both the mechanic who worked on the car before, and Chuck from Paragon, that it should be possible to remove and replace the balance shaft belt without having to remove the front pulley, which would eliminate the need to use the flywheel lock. Is this true? From Pickwick's answer to my original post, it seems like this might be possible. Thanks.

Partial Post: Please Login or Register to read the full post.

[flash]

can be done - pretty tough to keep it at TDC though - because of the back and forth tendency as you tension the belt, you may have to wrestle with it a couple of times to get it right



bad idea to only do the one belt though - with 16k on the belt, you're already half way there - i'd change it again and be sure both were fresh - were these gates belts (oem brand) or aftermarket?

Partial Post: Please Login or Register to read the full post.

[sayporsha]

This guy has decent tools at reasonable prices. His website has a good tech section covering the procedure, too:

http://www.arnnworx.com/



You do not want to take any chances with these belts. I recommend a timing AND balance shaft belt replacement, and yes, you do have to remove the pulleys to do it right. Don't forget to replace the water pump and rollers/tensioners if questionable.

Partial Post: Please Login or Register to read the full post.

[sasilverbullet]

If some teeth are sheared - check all the rollers - you will probably find some that are bad.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Thanks for the inputs. I'm concerned as to how this could have happened, but for now, I'm assuming it was caused by the fact that I never checked the tension of the belt after having the variocam pads replaced about a year and a half ago, so the belt must have gotten pretty loose. Pretty dumb of me to never have checked it. <img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" /> The one roller I can turn right now feels perfect. But I'll take a close look at the others once I get the belt off, and replace any that are questionable.



I found a mechanic in town who has a flywheel lock which he'll "rent" to me for 20 bucks. A new one from Paragon costs $107 plus shipping (and tax for me, since they're in Texas).

Partial Post: Please Login or Register to read the full post.

[bob blackwell]

Compare the price from Sunset Imports, they may be cheaper in the long run. (www.porscheparts@sunsetimports.com) Sounds like you can make good use of one for the future. Good luck, Bob Blackwell.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Well, I think I have another clue as to why my balance shaft belt went kablooey (well, thankfully, not completely - it sheared off a bunch of teeth, but did not snap) - when I got the old one out, and compared it to the new one I ordered from Paragon, I found that the new one is about 3.5 mm wider than the one that was in the car! The new one is about 18 mm wide, and the old one is 14.5 mm. My suspicion is that the new one is correct, because the old one had quite noticeable gap (about 1-3/4 mm) one each side between the edge of the belt and the edge of the rollers. So it mush have been wandering side to side on the rollers over time, putting strain on the belt. The new belt fits snugly on the rollers, width-wise. Does anybody know the spec for balance shaft belt width? I'll take a look in the manual, but I was wondering if anybody knew offhand. Thanks.

Partial Post: Please Login or Register to read the full post.

[flash]

bingo - common mistake - the 944 belt was narrower - same thing happened to me - thankfully i caught it before it made a mess



the tension spec is also tighter with the new belt - there was a memo on this sent out by porsche



i believe the old tension spec was 2.7 +/- .5 and the new one is 3.5 +- .3

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

Yeah, I'm sure it was wandering all over the place on the sprockets before finally giving up its ghost. Not tightening it when I was supposed to didn't help, either. Can't wait to see how much smoother it runs, between this and the new engine mounts, once I put it back together this weekend.

Partial Post: Please Login or Register to read the full post.