Arbitrator

I know this topic comes up frequently, so I've done my research. Still, I have questions that don't seem to be directly addressed anywhere, so they are probably obvious to everyone except me.

I have a 1986 951 which had a new timing belt installed about 2k ago by the PO. I'm due for re-tensioning.

I've been following the PelicanParts and Clarks guides: get the car up, remove the PS and AC belts, remove the timing belt covers, put the engine at TDC for adjustment. Straightforward. My questions pertain to a couple of specific things in the Clarks guide ( http://www.clarks-garage.com/shop-manual/eng-10.htm )

1) Do I need to perform the pre-tensioning procedure, given that this is a re-tensioning? Or can I just turn the engine to TDC, turn 10 degrees, and proceed with tightening the eccentric roller until the spec is met?
2) (The doozy) Do I target the "used" tension value (2.7), or is this still considered a "new" belt (4.0) for the first adjustment? And then would I target the "used" value when I re-check at 15k? (I'm planning to do the next timing belt at 30k or 3 years.)
3) There's a slow coolant leak, and the PO did not do the water pump with the TB, so I think the WP may be overstressed. I'm considering replacing the WP. Would that change the answer to #2?

I have a flywheel lock, balance shaft lock tool, and special tool 9201, so I think I'm set if I need to do the whole procedure.

Thanks in advance for your help!

Black51

IMHO, this method is way over complicated. I've only tensioned the belts by feel, and haven't had any issues. If I were you and since you have the special tool, and once you tension the belt correctly, feel the tension the on the belt by hand and remember it. After that, I would just do it by feel. These belts are due to be changed every 3 years anyways. So really, unless you set the belt waaaaaay too tight, it won't break in the span of 3 years, not mention wear out the rollers prematurely. It's really not rocket science though. Plus, it's never a bad idea to visually check the belt once or twice a season, regardless what method you use.

To answer your questions:

1) No. The pre-tensioning is only done with a new belt. this is the aforementioned 'tensioning by feel' method. That is done just to get the belt close to the target tension. So yes, you can just go straight to the TDC + 10 deg. and so on...
2) Your belt is now used, and 2.7 is the target for a used belt. the 4.0 is for a brand new belt because it will stretch. If all goes well, when it comes time to retention the belt, you should be pretty darn close to 2.7. Of course, re-tension accordingly.
3) Honestly, if you're taking the belt off, just put a new belt on. Then you don't have to worry about it for another 3 years. In this case, you will be setting the tension with the special tool to 4.0.

numbskull

When RE-tensioning or RE-placing I always use the flywheel lock. Insurance. Also make sure balance belt is in spec.

Humboldtgrin

86 block. I tension the belt with the engine running. Just be carful. Too loose or to tight it will whine.

numbskull

That sounds crazy to me ! I can't imagine my big hands ever doing that but unless you are joking or own special tools that lock position .. no sweat.

Arbitrator

Thanks all for the answers -- particularly Black51. And for not laughing at my "is it new or used??" question. I swear it was bothering me for days.

And yes, flywheel lock will be used. I'll figure out later where I can cut corners, but the first time, I'm dotting my t's and crossing my i's.

Ski

The simple hand method works pretty well and no whine if you trust your feel...

The tension on the belt, grabbed with thumb and forefinger: if flat is 0 installed, 1/4 to you twist is 90° - the belt when twisted should get tight about 70-75° and not want to go much past that. It should not go full to 90. Rotate a couple of time, try it again. yeah I've done several in my time, and even had the P Car tool. I was witin .2-.3 on proper tension. I quit using the tool and never had an issue.

KevinGross

I agree with Black51's advice. On 3), you will of course have to retension at 1 to 2K miles. But if there's coolant leak, time to replace the pump.

With respect to Clark's fantastic how-to, as well as the factory manual, I don't agree that the automatic tensioner should be released, retightened, then done. It's not accurate enough, and their springs do go off with age, debris, etc. I follow the original method even with the automatic tensioner, indexing the tensioner using the balance shaft tool sprocket (it has holes for this) to achieve the target tension as measured with the factory tool. Porsche introduced the automatic tensioner because too many of their dealer techs were not tensioning belts properly, ignoring the tool for example, and they got tired of warrantying the result. Of course this is not relevant to your '86, but give me a soapbox...

Good luck!

ekoz

I just use the by feel method as well. Of course I change about every 3 years and use the arnworx tools. Its really not that big of a deal after you have done it several times. Not sure if Vans video clip of 1, 2 or three shows the tensioning procedure but I have had good luck with his method.


https://www.youtube.com/user/vsvenso...ry=timing+belt

neunfünfeins

I share the same sentiment.
Granted I have yet to do a 944 TB (soon), but I have done a number of other VAG TBs (including the older TDIs that drive the mechanical injection pump = added TB load) over the course of ~25 years, and I just don't see what is so "special" about this setup compared to any of those. And those were all done by an approved twist method.
VAG TBs also aren't called for to be retensioned, and I've never had, nor heard of, a problem resulting from one stretching too much between replacements. Conti and Gates are both VAG OEMs as well. I don't understand why Porsche would have had so many warranty issues.

With the 944 routing, there is a significant amount of belt wrap around the sprockets that to me makes this setup more robust and far less likely to slip any teeth, than what I'm used to. I would guess that with all this tensioning hysteria there are more 944 TBs running around out there that are too tight rather than too loose. Maybe once I actually dig into the job I will realize something that makes me change my outlook, but so far I don't think so.