PorKen

Come for the stock tensioner, stay for the flexplate clamp (, HVAC system, crankcase venting, ...).

Sander_Baas

Hello,

I made a movie of how the belt runs over the stock tensioner and roller. (now that I have the centre cover off anyway. (sorry for my bad camera skills I’m not a pro )


It’s not so clear on the movie but the belt actually runs extremely nice over everything. I thought because off all the stories here about flapping belts etcetera it would flap all over the thing but the belt stays nicely in line and the idler pulley does not even get touched, only a tiny tiny bit form throttle down to idle.

I could see the tensioner damping the belt, it moves in and out so the little spring on top also does its work, and maybe together with the oil in the tensioner. (although the oil is not under pressure... maybe together with the washers in the tensioner, there is a damping possibility...)

I really think the stock tensioner is a fine thing. The other item PorKen lists I don’t know yet about, no experience with it yet.

@ Bilal928S4, I did not replace those bushings, maybe I will when I have it now off again. I don’t understand what you mean with the pulley needs to be centered on the bearing. It’s just a piece like this that you put in and fix with the circlip. I don’t see how this needs to be centered.

@ 928porschemangreg, I have all the covers off, they are still as clean and undamaged as last time I had them off

@ Dfrhodes, Good one I will check when o have it off again, although I don’t know how that could cause this sound.
now that I have the covers off and used the stethoscope Its clear to me that the sound comes from the big roller

So when the big roller is delivered i will replace it.
Best regards Sander

WallyP

Ball and roller bearings are normally very well made (at least in advanced countries), but infant mortality can still happen...

PorKen

The stock tensioning system, in good condition, works well enough.

However, I suggest you take another look just after the engine has been started for the first time in the morning.

Or running at 4-5K rpm. (Or running at 5K when cold. )




Note that any time the timing belt touches the idler pulley, the belt is uncontrolled.

Ideally, the belt should always be flat between the 1-4 cam sprocket and the crank sprocket.

Sander_Baas

@PorKen,

The engine was stone cold. Revd it up and remained smooth. (no clue till how high since i was not in the car ) but i also would not like to rev my engine till 5K when cold..

Have the roller off now. Looks in perfect condition offcourse , hopefully this was/is the problem...

Bill Ball

Damping of belt vibration is performed by a valved piston inside the tensioner that controls the flow of oil between two areas on either side of that piston, similar to valving in a shock absorder. This appeared in MY83. The stacked conical bimetallic washers flatten when heated, compensating for heat expansion of the block and heads.

I would carefully check the functional condition of the plastic bushings mentioned. With the belt loose, there should be no rocking play at all in the tensioner arm on its pivot shaft. If there is, the bushings are worn and this allows the arm to "****" at a slight angle, throwing off the geometry of the main roller.

Leon Speed

Yeah you'll have to talk to my wife about that. She's the German side of the family, I'm the Dutch side

Don't have any, but if you're renewing, go with an upgraded compressor, less chances of leaks.

Regarding the main roller, is it spaced with a circlip? I see you have a Contitech belt. Many people experience belt stretching after break in with a Contibelt. This changes cam timing but more importantly can cause a loose belt. It is recommended to use a Gates belt or an original Porsche belt (which is also Gates). Letters in the belt should face towards the front. One more thing, the top of the Oetiker clamp on the tensioner bellows is facing the front of the car, this way it can interfere with fitting the timing belt cover.

Sander_Baas

Hey guys,

I don’t know any more, I replaced the big roller but made no difference.

Then I thought since it comes after a warm up of 5 min it needs to be something that changes over time/temperature. So maybe the oil pump (viscosity change of the oil due to warm-up)
took out the stethoscope and listened to the oil pump. Not clear that is comes from here. The sound is equally strong almost where ever I listen on the engine

Than I checked the tension of the belt again, this one was a bit on the high side of the Kempf tool. So to rule out it could be the tension I decided to put it on the lower side of the Kempf tool window.

Interestingly the engine was now already more quit from the startup.
But not for long because after a warm up it came back, but softer.

Actually during idling I don’t hear it any more but if I ref it up a bit you hear it again.

Then I switched off the engine and felt the belt, seemed more tight to me, so measured it. And I was more than a window “length” more tight, so way over the “max”

So I think the sound is tension related, somehow the tensioner does not want to “shorten” good with the temperature change of the engine. I will check if there is still oil in it soon, but would like to ask you guys is this normal. I understand the tension will not be constant, but this is also a bit much maybe. Anyone did cold and warm tension measurements before?

Any input is welcome, although I know PorKen will say I need to take his design (I am interested in all the stuff you measured an calculated PorKen, if you want to share any you can send me a message)

Thanks,

outbackgeorgia

Did you measure tension at TDC?
Dave

Sander_Baas

Yes TDC of Cil1.
All according to the procedure

Sander

Sander_Baas

I came across this thread:https://rennlist.com/forums/928-foru...m-vs-cold.html and found it interesting that here the opposite was measured.
You would say the whole block of aluminium grows more than the washers shrink...

Im a bit confused, all the imput is welcome!

John Speake

When you changed the belt did you take the tensioner apart completely and check it wasn't jamming and there weren't any ridges inside ?

The random changes of tension you are getting are certainly cause for concern !

Sander_Baas

Yes i took the whole tensioner apart, cleaned it really good and replaced the rubber ring in the tensioner and the boot at front.

Think i just have to take it apart again, Anybody knows if i can check the working of it when its not on the car?

Thanks,

Sander_Baas

Hey guys,

It has been quiet from my side for a while, had some issues with the neighbors and working on my car on our private parking (always tricky in a city) so had to search for a working place.

Now found one not far with all the tools I need, and the car now stands on a lift which makes the working so much easier.

And I had an holiday to Italy, But yesterday I worked on the car again with a friend.

And I found the Problem!

After fixing the tensioner so it cannot leak any oil out any more, the tension of the belt stayed the same, Warm or cold engine. But this did not fix the sound,

Then we decided to try different tensions, from low to high. No difference.

Then we placed the old big roller back (the one that was on the car when I bought it). No difference.

Then we listened everywhere where possible with the stethoscope and the sound was still the strongest at the big roller. So maybe it is the washer that fixates the axial movement of the belt on the crankshaft sprocket (very close to the big roller so any sound can easily be heard there) , replaced it. No difference.

Then we decided to try the old belt to see if that made any difference, and the sound was gone!

So indeed as mentioned here before Continental belts are no good. (I had a Conti one)

Now ordered a Gates belt and hopefully than it will also stay quiet !

So this one is SOLVED. If anybody ever has any weird sound from his timing belt, check if you have a Conti one on there and replace it for a Gates belt!

All you guys thanks for the advice on this one!

Best regards Sander Baas

Bill Ball

Technically, it isn't "solved" until you install the new Gates belt and the sound is gone.

I had one not so good experience with a Conti belt (losing tension at 25K miles - that should NOT happen), so I avoid them as well. I have heard a quite similar moan on a few 928s, tracked by heater hose stethoscope to the crank area at the idler rollers. I never resolved it but it seemed to be inconsequential - perhaps the idler bearings, but they seemed good and the belt should rarely contact the idlers anyway. I recall if I put slight pressure on the belt between the oil pump and crank the noise stopped. One of them had a Gates belt. Awaiting your report after the Gates is installed.