924Board.org

[JasonO]

Hope everyone's doing good?
Just had a major freak out
Lifted bonnet today just checking stuff over, there is a bit of very fine black shavings around the cam-belt pulleys both top and bottom, Not sure what to make of It.
I changed the belt myself about 3 years ago, mileage has been minimal maybe 2-3 thousand Kilometers max. I'm not sure If this is just started recently........surely I would have noticed It? but stranger things have happend.
In regards to tension I can just twist It 90 degrees half way between the top and bottom pulleys.
I have had no cam cover but sourced one and It's repaired/Repainted and ready to fit.
The teeth are worn 3/4 way through on the Inside
Obviously Ill stop using the car for now.
Any Ideas or advice before I just replace It and watch VERY CLOSELY to see what happens?

[ideola]

WOWOWOWOWOWOW, very very lucky. This is why I don't like the cam belt covers, you'd not have seen this with one on!!!

Never seen that before, only thing I can think is poor quality belt to begin with, perhaps already beyond age when you put it on???

I only supply Contitech belts. Do you know what brand it was???
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erstwhile owner of just about every 924 variant ever made

[JasonO]

I cant remember the brand off hand but I'ts a reputable one.
I Brought It as a kit inc a new tensioner which was slightly different than the old one (needed a longer bolt),
Could well have been sitting about In the store for who knows how long.
kit was specified for a V.W but I cross referenced It on this forum I believe.
Pretty glad I saw this today

[Rasta Monsta]

Very odd. I'd suspect damage to either the cam gear or crankshaft gear.

Less likely alternative, binding camshaft.
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Fasteddie313]

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80 Turbo - Slightly Modified

[morghen]

Wow!
You're so lucky to have spotted this in time.
Dont even crank the engine anymore.

My advice is change both cam and crank gear as well as the tensioner before you put a new belt on.
You may have gotten a bad belt but not likely that they wear like this.
I suspect there is something wrong with one of the gears.
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https://www.the924.com

[Rasta Monsta]

[Mike9311]

I saw this and wondered why?? ...then searched "cog belt tooth shear", since this looks like shear at the base of the teeth.

Pretty nice explanation here at this link below. Some of it obviously does not apply. That leaves belt quality/profile, tension, and alignment according to the doc. I am also assuming cam rotates as its supposed to be i.e. normal load for the belt

Also +1 on the no cover. Nary has there been a better reason not to have one

http://www.pfeiferindustries.com/troubleshooting/timing-belt-tooth-shear.html

Edit: Added this link. See page two. Interesting side view of stress distribution.

http://www.sdp-si.com/D265/PDF/D265T003.pdf
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

[RC]

Belt is / was too tight, considerably so.
Then as engine warms and expands it becomes much too tight.

That 1/4 turn BS is BS. more like 180 - 360* for a man.
Try it on a hot engine,not running, then see how lose the belt is cold.

Better yet, buy a tension gauge. The Krikit gauge is a cheap but accurate tool, set for a minimum reading.
_________________
World`s quickest 924 2L slushbox

[Carrera RSR]

[Mike9311]

[JasonO]

So i got a new belt and Installed it this afternoon, turned over by hand all fine...fired up and ran gave a few revs all good so far.
I checked all the teeth THOROUGHLY there is no burs, nicks or odd protrusions so to speak that I can detect, I checked the tensioner over no visible problems there, on a note the last belt sat "just" over the edge of the top cam, this new belt sits much better been flush with the front edge.
I tensioned the belt so I can twist It about 100 degress...( just past 90) a little more If I get really tough on It. I had the last one so I could just turn 90 warm.
I'm Still very wary.
The engine Is quieter now seems that worn old belt made a bit of noise.

Can I get some Actual confirmation about tension ( Is It even super important)

All the advice above Is pretty awesome above and beyond as always thanks!.
Tomorrow Ill look over It all again.

[Johann]

Belt tensioning is an art more than a science

If you can hear the belt wining when the motor is warm the tension is too high. With a warm and cold engine you should not be able to hear any wining from the belt.

Turning the belt 90 degrees is a good way of measuring, but make sure that you can twist it up to 90 degrees with relative ease. To go past 90 degrees should require more effort and the tension should build up very quickly.

[JasonO]

I wish they would publish tensioned frequency

the belt Is tensioned to 112 hertz at the moment, I am a musician by trade.
No fancy gear needed.

[Mike9311]