I recently changed the timing belt and water pump on my 1987 S4 Euro. However, now I'm having some problems. I'd be really happy to hear some answers to the questions below from those who have more expertise.

1) The tensioner leaks oil. Apparently it comes from the rubber boot. I did not change the boot because it appeared to be in satisfactory condition. I have tightened the boot clamp as tight as it will go but it does not help. When I fill oil through the fill screw, it will start dripping out from the boot area. I guess there is a little oil in there but it cannot be filled until the bleed screw starts to drip because it starts dripping from the boot area before that. My question: What happens if I keep driving without oil in the tensioner? What damage can this cause? Going back to replace the boot is a major operation...

2) In heavy load situations (i.e. foot to the floor, RPMs above 4000) the T-belt warning light sometimes comes on. Can this be caused by lack of oil in the tensioner (dampening action of tensioner is lost) or does it mean that my belt really is too slack?

3) I did not have any official belt tension measurement tools but instead used a method I read about on the web (apply a force of 15 kg to the belt, measure belt deflection, it should be 22 mm when the tension is correct). However, I am not totally convinced that I got the tension right with this method. Is there a way to check if I'm even in the right territory? I tried comparing the tension in the belt between the right cam sprocket and the water pump to the tension in the segment where the tensioner operates. How should they compare? About the same, or should one be tighter than the other? On mine they felt about the same.

4) Belt tension is supposed to be measured with crank at the TDC mark. Does the position of the camshafts matter (as they rotate at half the speed of the crank, they can be in one of two possible positions when crank is at TDC)? To me it seemed there was a slight difference in tension depending on the camshaft position.

Best regards,
Niklas Kampe
Finland, Europe

 

The timing belt and tensioner system is critical to the life of your 928. If it fails on a 32-valve engine, catastropic damage is virtually certain. This damage can cost thousands of dollars to repair.

The timing belt tensioner should be rebuilt EVERY time the timing belt is changed. Rebuilding takes less than fifteen minutes and costs less than $10 US.

The tensioner serves two purposes - to maintain the proper tension on the belt, and to dampen the fluctuations and vibrations of the belt. The tensioner does NOT automatically adjust the tension, so the tension must be periodically checked and reset using a tension gauge.

The tension is set using either of the official Porsche gauges, or the the currently-available aftermarket gauge developed by Jay Kempf and sold thru the 928 vendors for about $60 US. I would not trust the life of my engine to anything other than a proper tension tool.

The belt tension would change due to heat expansion of the aluminum block and heads - the metal grows more than the fabric and rubber belt, loosening the tension - if it were not for the bimetallic Belville conical washer stack in the tensioner. As these washers heat, they change shape just enough to maintain tension on the belt. The oil in the tensioner transfers the heat from the block to the washers - if there is no oil, the heat transfer is much less effective, so the tension will loosen as the engine warms.

The oil also serves to dampen the fluctuations and flapping of the belt. If there is no oil, the fluctuations can become quite violent. The oil also lubricates the tensioner, and if there is no oil, the wear can be severe. The tension costs over $600 US, versus less than $10 to rebuild.

The tension must be set at TDC compression - that is, with the crank and the cam sprocket markings aligned by manually turning the crank in the proper direction. (You must NEVER turn the engine backwards!) The valve springs will push quite hard on the camshaft lobes, and if the tension is set at the wrong place, it will be wrong. The proper location ensures that the belt slack is all at the tensioner.

Your engine appears to be at serious risk.

 

Hey Wally, doesn't the tensioner release tension on the belt with temp increase? As the block expands, I would think that the belt would get too tight. I believe that the curved bi-metallic washers tend to flatten out with higher temps, and thus maintain the proper belt tension as the cams get further away from the crank due to heat expansion.

I had my belt fail last month (no major damage as I caught it before it slipped!) due to this and I believe it's due to the belt overtightening as the engine comes up to temp. If I'm misguided, please explain as I thought I found the reason for my failure.

BTW, It's a must to rebuild the tensioner as Wally said. A friends 87' belt light came on and while checking it out, found the tensioner on it dry as a bone also. There were 15k miles on the belt, replaced by the local dealer, whom I have lost all faith in now. (missing alternator bracket bolt, radiator drain plug siliconed in, wiring harness tie-wrapped instead of clamped, and several other things!) I called them and asked if they rebuilt the tensioner as part of the belt replacement. I think that you already know the answer. (didn't touch the water pump, pulley's or anything else!)

The first time I did my tb, I purchased the real tool and it's easily paid for itself by keeping my 32 valve alive and kicking.

Good luck!

Dave

 

Your cost and time in proper belt care is vital to the life of your car..I have recently replaced all the oil in my tensioner and have found it to have about half the oil. Previous owner and shops never touched the tensioner as far as I could see. Not as much as I would have liked but then running with no oil inside sounds like a disaster waiting to happen.. I will be very sure to rebuild my seals on this tensioner once time comes to replace my t-belt. Checked my belt at lest 8 times in the corse of changing the fluid in the tensioner..cant see any oil leaking out so all looks good. David.

 

Thanks for the info. Since my tensioner does not seem to seal well enough to hold oil inside, has anyone tried filling it with grease instead? I recall somebody suggesting this on the web. Anyone tried it? Or perhaps thicker oil might help?

 

Your just going to have to go back in and rebuild the tensioner. Why risk the life of your engine on unproven shortcuts. If you did the belt the first time then you already have the steps down so going in this time will be faster. Buy the aftermarket belt tensioner. It is worth it for the peace of mind not to wonder if you got it right. Good luck!

<img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />

 

&gt;&gt;Hey Wally, doesn't the tensioner release tension on the belt with temp increase? As the block expands, I would think that the belt would get too tight. I believe that the curved bi-metallic washers tend to flatten out with higher temps, and thus maintain the proper belt tension as the cams get further away from the crank due to heat expansion.&lt;&lt;

Absolutely correct - good catch!

Senility is an UGLY thing ....

 

Quess I'll have to take it apart again then... <img src="graemlins/crying.gif" border="0" alt="[crying]" /> Could someone please outline the procedure for rebuilding the tensioner so that I get it right this time round. Is this the way to do it:

- remove tensioner
- remove rubber boot clamp and rubber boot
- pull out piston
- thoroughly clean everything
- fit new O-ring to piston
- push piston back into tensioner
- fit new rubber boot and boot clamp
- attach to block with new gasket
- set belt tension
- fill tensioner with oil

Last time I did not replace the rubber boot and that's what is leaking now...

 

Pretty much correct.

The plates (washers) go in specific patterns, so make sure that they are correct. They will be in groups of 5 plates, with either 7 or 8 sets. They go like this:

((((( )))))((((( )))))((((( )))))(((((
or
)))))((((( )))))((((( )))))((((( )))))(((((

Be very, very careful installing the tensioner on the block. It is all too easy to damage the gasket or move it so you get an oil leak - everything has to come back off if this happens.

Easiest way to fill the tensioner is to use a pump oil can (trigger type) with three feet of plastic hose that fits the oil can and the bleeder screw.

You fill from the top screw, closer to the fender, until oil runs from the lower, inner screw.

 

Just to add to the fray, rebuilding is cheap and effective. Upon taking mine apart it was coated with thick ugly grease, took me ages to clean it all up.

An interesting modification was made to the tensioner in 89 (according tp PET), the spring which makes the electrical contact between plunger and casting with the tensioner rollers was replaced with a more run of the mill wire with terminal contacts.

I hear rumour (nothing more) that it is possible for the old spring type contact to break and eventually wear through the belt.

Chris

 

Hi Niklas,

If you really can't face taking all the front off the engine, it is just possible to remove the tensioner from the engine without doing the whole bit. All the 5 fixing bolts for the tensioner are accessable from outside the timing cover.

You will have to remove the air pump from its bracket, though.

I 've removed the tensioner on my car like this, and replaced the boot. I first turned the engine to TDC with the timing marks lined up. As the LHS camshaft (looking from the front of the car) will turn as soon as the belt tension is lossened, I locked it into place with a spanner on the flats of its nut. Release all the tension in the belt by slacking off the tensioner bolt, remove the contact for the cambelt tension light if your car has one, then remove the tensioner.

Do fit a new gasket, and as said before be very careful when re-fitting not to damage it. I made sure it stayed on the face of the tensioner by putting a couple of small dabs of Blue Hylomar gasket glue.

It's now perectly oil tight, oil is essential !

Wally and co. have said all the other important bits. Do invest in the Jay Kempf tension tool, it's excellent !

Good luck.

John

 

Thanks for the tips, John and Wally. I'm happy to hear that not all of the front of the engine needs to be torn down I guess I'll start trying it today.

 

Let us know how it goes, if its any consolation I just got mine all my engine back together after the timing belt change, runs like a champ except ...

got back from the test run and gear oil was leaking from inside the timing belt cover !!!! It holds fine until the engine runs ... I replaced all the seals etc .. so got to go back in.

Your not alone.

Chris

 

I removed the tensioner yesterday evening. It was not too much work, I removed the air pump and A/C belts that were in the way and after that it came off pretty easily. I also removed the distributors and upper T-belt covers so that I could check the timing marks and tighten the belt afterwards. Took about two hours, including some problems getting the air pump loose from the tensioner bracket.

The tensioner rubber boot had cracked which explains why it didn't hold oil. It must have cracked during installation or tightening of the belt.

I noticed two suspicious things when I removed the tensioner:

1. One of the four bolts that hold the tensioner to the block was missing. Some previous mechanic lost it? Have to get a new bolt there.

2. I did not remove the center T-belt cover so I cannot see the whole tensioner arm, only the tensioner roller. When I tried to wiggle it sideways (i.e. towards the block and away from it), it moves a LOT (like half an inch or something). How much should it be allowed to move in that direction? I would assume that the belt pushes it to one of the extremes of its travel, as there is nothing that centers it on the belt? Could the bushing that goes to the pin on the water pump be worn?

 

The tensioner arm is pivoted on two nylon bushings that both act as bearings and electrically insulate the arm so that the tension warning system will work. Sounds as if you really need to replace those bushings.