Phil Silano

How much wear is allowable on cam sprockets? If any?

I took all the drive belts off the car this morning, one at a time, trying to find a noise from the front of the motor. No joy.

Then took off the timing belt covers. That belt is flapping around and the tensioner roller is bouncing like crazy, 1983 16V motor.

This is my first 928 belt, how much movement should a properly tensioned belt have?

The bigger question, at least from a new parts perspective, is the sprockets. There are obvious signs of wear on the cam sprockets and the oil pump sprocket.

The teeth are actually worn down on all three and the cam sprockets have wear on the face of the teeth also. At least 1/64 of an inch.

My first impression is to replace them but would like a second opinion.

Dave H.

correct your first impression would be...

Big Dave

Replace the worn sprockets, and then get a belt tension tool to make sure you have the belt tensioned correctly. It should NOT be flopping around at all.

Once you have the new gears and the belt tensioned properly, rotate the engine by hand and watch how the belt travels over the gears. I'd be concerned that you may something bent if the belt is that loose... you'll be looking for the belt to stay on the same spot on the gears through several rotations of the engine.

PorKen

The cam gears wear quickly once the annodizing is worn off. The (steel) crank gear is likely worn too, put a straight edge over the teeth, and look for cupping.

Worn gears will loosen the tension on the belt, so that's likely why it's flapping, but there may be tensioner/pivot arm/pulley issues too.

Mrmerlin

since your this far count on doing the whole job. This includes
New water pump,
A new set of water pump bolts (I believe there are 13 of them and they are NOT all the same)
New crank timing gear drive sprocket ( replace this even if it looks good they wear out, as they turn 2 times as fast as the cams)
New cam pulleys (2)
New Oil pump drive sprocket (make sure its steel) Remove the oil pump shaft woodruf keyway before removing the radial seal)
New Oil pump O ring seal
New oil pump radial seal
New cam shaft front seal (2)
New cork rear cam shaft seals(2)
New front main seal
New tensioner rebuild kit ( to rebuild the original tensioner)
New cam belt idler roller
New idler roller pivot bolt
New Timing belt
Thread sealant to seal the bolts a few razor blades to remove the old WP gasket.
Since your replacing all of the drive sprockets ,make sure you get the new style HTD (hi torque drive) they are curved teeth instead of the old style square tooth, if that is what you have now?
Also pay attention to how the timing marks are so you DONT put the crank shaft pulley on backwards, mark this before you remove it. Get some PB blaster for the water pump bolts and be gentle with the old bolts so you dont strip them/shear them off I have had luck heating the bolt heads and spraying PB on them a few times and let the WP sit for an hour or 2 while the PB soaks in. Lastly get a manual and a tensioner gauge. YOU can do this repair yourself if you take your time and verse yourself on the proper proceedures There is also a good how to manual for timing belt replacement do a search.
You will also need a way to remove the front crank pulley bolt this requires a 27mm deep socket and if you have an impact gun you can sometimes get it off but a flywheel lock is preferred. Also remove the radiator to make acess easier , I am sure others will chime in here but thats off the top of my head

oups59

Replace them. I did mine last year.

marton

Like they all said; if the teeth are shiny on the alloy gears (like cam sprockets) then it is replacement time.
For the steel gears like the crank sprocket and some oil pump sprockets (some oil pump sprockets are alloy) check the wear and look out for sharp edges. Best practice is to change all but who can afford best practice?

Good luck

marton

Phil Silano

Thanks for the info and advice. The PO made a real mess of this one.

Here are three initial condition pictures.

The next three show the wear on the cam and oil pump sprockets. The belt was so loose I took it off by hand.

The tensioner arm and the tensioner itself are an absolute mess. The hole in the arm for the pivot pin is oblong (see next picture) and the tensioner was full of crud. There was no gasket behind the tensioner, just red silicon. I guess all the oil just leaked out over time.

I’m not even sure it’s the right one. The number on the housing is 928 105 541 4R (there is 1 602 also shown below this number). I can’t find this number in PET.

So far I'm planning on doing the following;

new belt
new/used sprockets (all 4)
rebuilt tensioner and gasket
new/used pivot arm
new pivot bolt and bushings
new tension roller
new idler roller
new cam and main seals
water pump and bolts

What am I forgetting??

This should be an interesting project next weekend.

ROG100

The number on the tensioner is the casting number so not a lot of help.
However it looks to be correct.
Most of the tensioner and parts will clean up, however check the inside bore for corrosion as there was no oil in there.
When you take the washers of the plunger use a tie wrap to keep them in the correct order.
I use a small ultrasonic to clean the parts.
How does the oil pump gear look?
Roger

ROG100

On the pivot arm the hole does not look oval, were there any bushings in it?

Hilton

Hi Phil,

Having just been through this, I'd also add bearings for the lower idler assembly (under the crank sprocket).

You can buy the whole assembly from porsche for >$100, or just grab two 6201RS bearings and press them in place of the original ones.

Here's a photo of the rollers nuder the crank.. as you can see, one of them has no wear at all, so I just swapped them round (after replacing the bearings).


Also, I didn't do it, but am regretting it now.. but replacing the oil pump seal and having a check of the pump to make sure its ok is relatively painless while you're in there. I'll be doing this next time (didn't want to keep my car in pieces over the holiday vacation, and waiting for parts to Australia can take a while). While you're replacing the oil pump sprocket, remove the shim that's on the spindle behind the woodruff key. I found a post from Bill Ball that mentions this a few years ago.. the newer steel sprockets have a raised bezel that compensates for it, and there's a technote from Porsche to remove the shim when updating the sprocket.

Here's pictures, of the shim behind the key (right before I removed it), and also of the two sprockets.. the old aluminum one is on the right looking very worn, and the new steel one on the left with the slightly raised center that negates the need for the shim.





Lastly, do you have access to a Porken timing tool? If you're removing the cam sprockets, then chances are the valve springs will move the cams slightly. Being able to reset the timing after fitting new cam sprockets is invaluable for peace of mind, as well as the satisfaction of knowing your car is running at factory spec Borrow a tool from a nearby 'lister if you can, or buy one if he has any left.

marton

How did you get the cam belt covers off without taking off all the other stuff??

Where the tensioner meets the motor you should ensure the motor has a nice flat & smooth surface so you get a good oilseal.

Marton

Mrmerlin

dont forget to replace the oil pump O rind outer seal and the Radial seal. Or see post # 5

marton

I do not think Phil's car has these, it was only on the later models.
Also first time I heard of one showing signs of wear; was your TB correctly tightened before the change?

Marton

Hilton

Ok.. I wasn't sure on the lower -idler, I know some model years only have a single one, and I bow to your experience of pre-32v cars in saying there isn't a single one even

My timing belt was slightly loose.. I had wear very similar to Phil's on my sprockets - I could feel a noticeable ridge on them and they were all very shiny (all 150k mile original). I'd guess the belt was originally too tight - the PO's maintenance records showed a TB change was last done in '99 and re-tensioned in '00 - I did 300 very paranoid km's total since buying the car before changing the TB, to get to emissions tests, registration inspections etc.

After replacing everything around the TB (except the oil pump seal) I'm now much more relaxed and rev-happy driving the car