Timing Belt Tensioning - "Clarks" / Mine

[rodkahle]

I already posted this on Rennlist after somebody wanted the procedure from the "Clark's Garage" website, so I though I'd repeat it here. Plus I added my own from checking the timing belt tension on my 1987 951 awhile back.

“Clark's Garage” website

Initial Tensioning on Belt
1) Pre-tension the camshaft belt by turning the tensioning roller eccentric nut (thin 24 mm or thin 27 mm open end wrench) counter-clockwise until the belt can be twisted 90° using the thumb and forefinger. This should be checked at the midpoint between the cam sprocket and the crankshaft sprocket.
2) Tighten the tensioning roller locknut to 45 Nm (33 ft-lbs). Apply counter-torque to the tensioning roller eccentric nut while tightening locknut to prevent altering the belt tension.

NOTE: Originally, this was the only method of tensioning used on 928’s and 924’s. I know of several shops that have never purchase Special Tool 9201 and use this method on 944’s as well. However, it is very risky and I strongly recommend checking the belt with the factory tensioning gage.
3) 1987 Model and Newer Cars with Spring Tensioner:
* Release the spring tensioner by loosening the locking nut and locking bolt near the spring end of the tensioner.
* Tighten the locking bolt and locknut to 20 Nm (15 ft-lbs)
Checking and Adjusting Belt Tension (All Cars)
Yes, all cars. While some people contend that the tension does not need to be checked on cars with spring tensioners, I would disagree. From experience, I've found that spring tensioners vary from car to car and will not apply the same tension consistently when the spring is released. The spring tensioners seem to get close enough to the 2.7 ±0.3 spec for a used belt to be of little concern. However, the spring tensioner WILL NOT tension a new belt to within the tolerance for a new belt (4.0 ±0.3) unless the spring is released, the engine is rolled a degree or two, and then the tensioner is tightened down. The problem is that since spring tensioners tend to vary, you don't know exactly how many degrees to roll the engine. That's why it's important to check the tension using Special Tool 9201.
1) After the camshaft belt has been pre-tensioned, remove the flywheel lock if installed.

NOTE: Do not install starter until crankshaft bolt is installed and torqued as the flywheel lock will need to be installed again
2) Turn the engine clockwise two complete turns and align the mark on the camshaft sprocket with the alignment tab in the window on the distributor housing (TDC). Verify that the crankshaft is also at TDC by checking the "OT" mark in the window on the bell housing.

3) Turn the crankshaft 10° counter-clockwise. This is approximately 1.5 teeth on the camshaft sprocket.

4) Check the belt tension using Special Tool 9201:
* Pull the lock pin on the tool to release the tension roller.
* Align the drag needle with the gage needle.
* Install the tool on the section of the cam belt between the cam sprocket and the cam belt idler roller. Make sure that the tool's tensioning roller is on the toothed side of the belt.
* Push the tensioning roller against the cam belt until the locking pin on the tool engages.
* Read the tension on the dial.

Tension specs:
New belt - 4.0 ±0.3
Used belt - 2.7 ±0.3

5 a) Adjusting tension on cars with eccentric roller tensioners:
* Adjust the belt tension by loosening the tensioning roller locknut and turning the tensioning roller eccentric nut (thin 24 or thin 27 mm open end wrench) counter-clockwise and tighten locknut. Apply counter-torque to the eccentric roller when tightening locknut to prevent altering torque.
* Repeat the steps above until the cam belt tension is within the specified tolerance. Torque tensioner locknut to 45 Nm (33 ft-lbs).

5 b) Adjusting tension on cars with spring tensioners:
* Release the spring tensioner by loosening the locking nut and locking bolt near the spring end of the tensioner.
* Using a pry bar or other suitable tool, manually compress or release tension on the spring as needed. While holding in position, tighten the tensioner lock nut/bolt to 20 Nm (15 ft-lbs).

NOTE: The intended tool for this purpose is the balance shaft sprocket pin spanner (P9200). The spanner pins fit into two holes on the front of the spring tensioner body.

* Tighten the locking bolt and locknut to 20 Nm (15 ft-lbs).


Balance Shaft Belt Tensioning (All Cars)

1) Determine the amount of belt tension required for the type of belt you have.

Old style belt (15 mm wide) - 2.7 ± 0.3
New style belt (18 mm wide) - 3.5 ± 0.5

2) Loosen the locknut on the balance belt idler roller and move it away from the balance belt. It should not come in contact with the belt while checking the tension or during tension adjustment.
3) Check the belt tension using Special Tool 9201:
* Pull the lock pin on the tool to release the tension roller.
*Align the drag needle with the gage needle.
*Install the tool on the section of the balance belt between the lower and upper balance shaft sprockets.
*Adjust and recheck the belt until the tension is within the specified limits.

NOTE: If you have someone to help you it is possible to adjust the belt tension while the tensioning gage is installed. However, the tension should be checked again after the tensioning roller locknut is torqued.
4) When the belt is set at the proper tension, tighten the locknut to 45 Nm (33 ft-lbs). Apply counter-torque to the tensioning roller to prevent changing the belt tension.
5) Adjust the balance belt idler roller such that the clearance between the roller and the belt at the lower balance shaft sprocket is 0.5 mm. This can be done with Special Tool 9207. I normally use a 0.5 mm feeler gauge. When properly adjusted, torque the locknut to 45 Nm (33 ft-lbs).
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Timing Belt tension check on 1987 951

1) Remove plastic engine guard plate from bottom of car
2) Remove the distributor cap
2) Remove the belt cover – 7 bolts with 10 mm socket
3) Remove camshaft sprocket cover – 3 bolts with 10 mm socket
4) Turn crankshaft CW (as viewed from front of engine looking towards rear of car) to TDC; verify by (a) lining up notch on flywheel with slot on bellhousing (seen from bottom of car), (b) seeing "OT" in window (seen from top of car between engine and firewall), (c) notch on camshaft sprocket lining up with notch on cover. The camshaft sprocket will turn one revolution for every two revolutions of the crankshaft – 24 mm socket
5) Loosen top two bolts on automatic tensioner; the one on the left is the "pivot", the one on the right inside the slot is the "position lock" (can see tensioner spring behind and to the right) – 13 mm socket
6) Use a small pry bar or large screwdriver to push the bottom of the tensioner towards the right (compressing spring). Take care to put the pry bar behind the belt roller and not on it. Hold in position and tighten "pivot" and "position lock".
7) Turn crankshaft CCW a very slight amount to release tension from "front side" of timing belt (section of belt that leaves the top of camshaft sprocket at 2 o' clock). Do this from the top side of the car so you can verify that the timing belt does not jump off the camshaft sprocket. You will hear a loud "click" sound when belt tension releases.
If the belt does slip on the camshaft sprocket, then slide belt off and reposition camshaft sprocket so its mark lines up with the notch on the cover.
8) Loosen top two bolts on automatic tensioner to allow it to again push against timing belt. The bottom of the tensioner will move towards the left due to the spring expanding. If the belt feels too loose, then give the tensioner a gentle nudge because it may not pivot freely (due to inherent friction?). A properly tensioned belt can be twisted approx. 45 – 90 degrees using the thumb and forefinger, checked between the camshaft sprocket and crankshaft sprocket. It is best to check at the midpoint of the belt section if possible. This is on the "front side" or section of belt leaving the top of the camshaft sprocket at 2 o' clock.
When my belt was new the "position lock" bolt was positioned approx. halfway in the slot.
For my used belt the "position lock" bolt was positioned approx. ¾ of the way towards the left in the slot.
Also make sure that the timing belt is in the center of camshaft sprocket and others.
9) Tighten top two bolts on automatic tensioner.
10) Turn crankshaft CW two full turns and verify TDC position as in step #4.
11) Check tension on timing belt; if it still feels loose (more than 90 degrees of twist) then repeat step #5 - #10.
12) Repeat step #9 and #10 at least two more times.
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Previous Rennlist or Pelican post for what it's worth

I have set both the belts up by hand for years. On the 944, I always set the timing belt to about 45 degrees of twist for the longest run of belt. The balance shaft belts run loose, and I have always set them to just below 90 degrees of twist on the longest span.
Some people may not agree with this method, but once you have done a few of them, it is okay. You would be surprised at the number of shops doing it this way. At least it will give you a basis from which to check the tension of the two belts.
If you over tension the balance shaft belt, it will start to make a lot of noise.....the real reason it is set looser than the TB.
Remember, if the balance shaft belts comes off, it can get underneath the timing belt, causing it to lose drive, resulting in belt failure, and ultimately valve and piston damage. Better to set it a tad bit on the tight side, then back it off. Also, the belts will seat in over the first 100 or so miles, so it is always good to go back and re-check them

[dasMafia]

so, since this may well possibly be WAY beyond me....

what does a shop charge for this work... lets say it is new belts water pump and all the labor?

i live in the midwest, so likely low-end for the labor.

thanks!

[dasMafia]

for that matter, anyone know where I can find a good independent shop...

I'm in Lincoln, Nebraska... Omaha is fine too.

anyone know of a list somewhere???

[SoCal Driver]

Exactly what is:

Tension specs:
New belt - 4.0 ±0.3
Used belt - 2.7 ±0.3

There must me some reference as to what these numbers refer to as in pressure or movement.

Lets have some one to one scans of all sides of the Porsche tool.

I still think this can be done accurately with a less expensive set up.

[AFJuvat]

Well, I can take lots of close up pictures of the tool for you, but unfortunately there is no "scale unit - Nm/Ftlb scale on it anywhere.

The calabration bar (P9201A) is supposed to be a constant 4.0 scale units - I imagine with enough math or under lab conditions you could figure out what 4.0 scale units equate to.

Das Mafia - a timing belt job (replacement) should run around $300 or so. Why are you changing your waterpump, is it leaking or howling? A waterpump will add at least $250 to the job.

AFJuvat

[ChrisBennet]

Originally posted by AFJuvat
Das Mafia - a timing belt job (replacement) should run around $300 or so. Why are you changing your waterpump, is it leaking or howling? A waterpump will add at least $250 to the job.

AFJuvat

AFJuvat,
I thought it was standard operating proceedure to replace the pump and belts at 60K? The reasoning being that the pump won't reliably make it to the next 60K belt change (120K). What is your take on this?
thanks,
Chris
944S2

[kenny]

most folks replace the belts every 30K although the factory says 45K. The feeling is that belts are cheap compared to head work -- especially the 'S' head.

Time is a factor too and I hear folks talking about 5 years or so for belts (timing and balance).

I would think that water pumps would be good for 90K or so (three belt changes at 30K ea.) but again there is the time thing. Also, if the pump seizes, it will take out the belts -- which is bad! There is some judgement needed. Mine was done at 40K (not sure why) and I did the belts at 80K. I figure I'll do the pump at 110K which would only be 70K on the pump (unless it starts whining or leaking before then).

[AFJuvat]

Well, there are 2 schools of thought - replace it or leave it until it needs fixing.

Generally, the waterpumps are pretty good - especially since most of them have been updated to the newer version. IMHO, if you keep up with your scheduled maintenance and take the time once a month or so to crawl under the car and take a look to see what is going on; I say it is perfectly fine to let your waterpump alone.

Also - know your car - know what temps it operates at and what is "normal" - if you start getting strange behavior, investigate

Obviously if it is leaking or making noises, it should be replaced promptly.

In the older style pumps, they could if they completely siezed, snap your belt - this is becomeing much less likely with the pump upgrades. Statisticly, you have a better chance snapping a belt from a siezed roller than a bad waterpump.

thats my 2¢ worth - others will chime in saying how it should be replaced every 60k - FWIW I have an 85.5 with an original waterpump - 125K miles

AFJuvat

[SoCal Driver]

Originally posted by AFJuvat
Well, I can take lots of close up pictures of the tool for you, but unfortunately there is no "scale unit - Nm/Ftlb scale on it anywhere.

The calabration bar (P9201A) is supposed to be a constant 4.0 scale units - I imagine with enough math or under lab conditions you could figure out what 4.0 scale units equate to.

AFJuvat

OK. I would also request that a metric scale be place along the measuring axis so that I might be able to do the "physics".

Thanks In Advacne

[kenny]

SoCal,
I don't think that this is going to work the way you're thinking. The gage goes around and the knobs essentially try to displace the belt from straight -- the gage measures the difficulty in moving the belt. I have been thinking about this though and believe that I have come up with a cheap way of doing this if someone with the gage and time wants to give it a shot next time they have their car appart.


IS EVERYBODY READY!!

OK, here's the theory. I think if a straight-edge (or maybe even a tensioned string) was placed on top of the belt between the cam gear and the first pully it comes to (long span where you usually put the gage). If a known force (postal scale with maybe 4 or 5 oz etc.) were to applied normal to the belt (pull down), then the displacement from the staight-edge (zero) to the new deflected location could be measured.

Keeping the load constant and varying the tension in the belt, a plot of gage tension vs belt deflection could be made. Then, when someone wants to tension their belt they just put the staight edge on the belt, load it up with calibration force and then check the deflection!

I think this would work and still yield an accurate tensioning of the belt. Whether or not there is sufficient room remains to be seen.

[Lawrence Coppari]

Kenny:
The method would have to specify the position of the camshaft or whether the crank has been 'backed off' 10 degrees. The tension varies depending on where the cam is in its rotation.

[rodkahle]

I was thinking of trying to get the same measurement when I did mine awhile back. However there was not very much room in there. In fact I recall that you would have to remove other stuff, maybe a lot, just to get to the other pully opposite the cam sprocket. You still may not have room to make reliable/repeatable measurements.

It's a good idea but I have not seen where anybody really did it after searching both Rennlist and Pelican. Somebody that is pulling their engine or radiator would have the easiest time of making the measurements. Hopefully someone will remember to do it.

[SoCal Driver]

Kenny,

You've got the right idea. I think I can do it with a straight edge and a digital gram scale. Possibly far more accurately than the mechanical Porsche gauge.

Yes you do have to "unload" the belt -- rotate the engine a couple of times with just the timing belt on. These procedures would be developed once the tooling is finalized.

[kenny]

Lawrence,
Of course -- this is just the 'tensioning' portion of the procedure.

And I'm not saying you wouldn't need three or four hands!

[John_AZ]

From the beginning.......If the timing belt has the words "Nicht Krimpt" -do not crimp, on the belt should you do the thumb/forfinger twist or will this stress the belt and cause a premature failure?

What is the opinion on changing the crank bolt once it has been removed for seals ect. Does this bolt stretch like the head bolts and its just additional insurance to replace it?

[kenny]

Yohann,
twisting the belt does not a crimp make -- crimpping would be folding over on itself -- like kinking a hose. Twisting causes torsion which is a different kind of loading; plus, the tension in the belt prevents the 'kinking' of the belt.

I haven't heard of any crank-bolt problems

[dasMafia]

belts and a water pump for $550??? that is sooooo cheap! (from 500+ just for the belt on my old integra).

thanks a bunch guys...

and this was for my information... still waiting to finalize the deal on the car...

black 88 944 8v WOOOOOHOOO!

[fletch944t]

Okay, here's some history and theory on timing belts and water pumps. This is going to be long, so bear with me.

When 944s first came out, there really was no factory recommended service interval for timing belts. It was left up to the discretion of the individual shops as to when the belts should be checked and when they should be replaced. There was also no "tool' in the beginning. 944 belts were tensioned in the same fashion as 924 and 928 belts were tensioned - using the twist method. In fact, this method is still described in the 924 and 928 Chilton's manual. Yes, the belt should not be crimped if it is going to be reused. And, Kenny is absolutely correct. The twist method does not fold the belt over onto itself so it does not crimp the belt.

Because many shops did not do an inspection/tension after the initial belt stretch and because inspections were often not done with consistency, a lot of 944s which were still under warranty started experiencing timing belt failures. So, Porsche was forced to adopted a position on timing belt intervals. Initially, Porsche decided that belts should be retensioned before 1800 miles, inspected every 15,000 miles, and replaced at 30,000 miles or three years. Some shops still adhere to the 30,000 mile replacement interval even though Porsche later changed the interval to 45,000 miles for the 944 and 60,000 miles for the 968. This still includes the initial retension before 1800 miles and a checks at 15,000 miles. In talking to the tech reps at PCNA, they also referred to a little known Porsche recommendation which calls for annual inspections after the first two years. Since the belts have a tendency to dry rot if the car is not driven regularly, this is Porsche's way of covering their rears is the timing belt fails before it reaches the required inspection interval.

So, the bottom line is:

1) Initial retension before 1800 miles.
2) Inspect and retension if necessary every 15,000 miles.
3) Replace every 45,000 miles for 944s every 60,000 miles for 968s.

Additional guidelines (from me):

1) If the car does not reach 15,000 miles within 18 months, have the belts inspected and then annually thereafter. Reason - I've seen belts break on cars as early as one year when they weren't driven at all.

Now, for water pumps. It's extremely unusual for a water pump on a 944 to last more than about 100K miles. In fact, it's normally the initial tension after a timing belt replacement at 90K miles that ultimately does in the bearings on a water pump. Of course, how a car is driven, weather conditions, a lot of things play into the longevity of a water pump. However, use 100K miles as a thumbrule. So, I always recommend replacing the water pump at the 90K mile belt replacement. I do so because the pump isn't going to last much longer anyway and since your already doing belts, it saves you 4 hours labor. The question was asked, "Why not wait until it starts to give you trouble?" Well, the reason is that often the first sign of trouble is often when the water pump locks up. When it does, it will often destroy the timing belt before you even realize the water pump has locked up and then you have a real mess.

One thing that hasn't been discussed is rollers. A failed roller or tensioner can take out a belt as easily as a locked up water pump. When you have the belts inspected at 15,000 miles, have the rollers removed and spun by hand to see if they are making any noise. If they do have them replaced. Also, any rollers that haven't been replaced by the 90,000 mile belt/water pump service should be replaced at that point.

All this may sound a little extreme to some folks, but I came to these recommendations through email discussions with Jim Pasha, phone calls to PCNA, and through my own personal experience.

Although I'm on the road a lot, I still work on 944s on occasion. And, although the recommendations above may sound a little extreme, any one who brings their car to me for maintenance and follows the above recommendations (religiously) will be warranteed for life against a timing belt failure - period.

BTW, I'll do timing belts for $160 labor plus the price of parts and water pump for an additional $160 labor plus the price of the parts.

Regards,
Fletch

[41V]

Fletch944t:

so how do you tension/retension? twist or 9201?

[Britwrench]

Fletch, I agree with everything you said. However, I was at the factory on a month long training course when the 944 was introduced and they did have that tool for belt tensioning then.
They also, as you said had more than a few problems too.......