[scenturion]

Hi everyone,

I bought my 968 back in August and will be attempting the timing belt on it this weekend.

This is my first classic Porsche, but I have owned a number of 90's BMWs prior.

My 968 is a 1994 Coupe in Iris Blue.

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[94SilverCab]

Welcome,

 

There is another Iris Blue 968 in your area (DS)

 

Enjoy the site,

 

Jay

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[Roboman]

Welcome, plenty of good information to be had here, and good luck with the belt change ...

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[Waylander]

Welcome

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[ds968]

Welcome ! Iris blues rock !

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[Rap]

Welcome. Enjoy your ride!

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[scenturion]

Thanks everyone! I did the belt change and I feel like it has more vibration now. I am going to take the timing covers off and check the alignment marks this coming week.

 

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[Waylander]

Its nearly always the bottom balance shaft out of bonk, this is due to the marks in the same place on the pulleys but the bottom one uses the other keyway, very easy to get it wrong


Get it checked before you do to many miles, the vibrations can crack the oil pickup pipe

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[scenturion]

Thanks. I didn't remove the sprocket and the pictures confirm the O is in the square box, but it may be off a tooth since it was hard to see down there.

I'm really hoping I can just remove the accessory belts and fans and don't need to take out the radiator and coolant hoses again - that G40 coolant is expensive!

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[Waylander]

get the covers off and if the under tray is off you can see the marks with a mirror,

 

the top is normally 1/2 a tooth off when the bottom is right

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[scenturion]

I don't know how it happened, but the balance shaft belt went from the picture above to this:

 



 

It's clocked correctly now and the car drives great again!

I noticed that the idler shows uneven wear. (its only been 6 miles between new belt/idler and this photo)

Do I need to have the idler deflect the belt more?

 

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[Roboman]

Hi Scenturion ..... if after realigning the balance shaft you have replaced the belt as per your diagram with red arrows, then the idler-to- belt gap to the right of the top red arrow is much too large.

 

The gap between the idler, and the belt as it passes over the lower balance sprocket, should be about 0.5mm, yours looks more like 0.5".

 

So the idler has been set too high and may be pushing hard into the belt above.  Hence, I suspect the skid marks on the idler face.

 

There's probably more info on here but I didn't spot it using the search.  So maybe see Clark'sGarage.com and site search to "balance belt installation", then click link E10 .... scroll to bottom of instructions, pausing to see diagram of balance belt routing with cam belt auto adjust installed.  For some unknown reason the balance belt idler is shown as a blank circle but not labeled, but you know where it is.

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[scenturion]

Yeah, I couldnt really get the idler to seat right. It's both slotted and eccentric. The only way it would be within 0.5mm to the surface of the belt on the lower sprocket was if it was far to the left of the sprocket center.

It actually barely presses into the upper run of the belt, it doesn't look like it deflects the belt at all but I cant fit a shim between the belt and the idler.

Maybe the spacing between the idler and the belt on the lower sprocket is what allowed the belt to skip?

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[Waylander]

Hi

 

you have tightened the belt with the lower tensioner in the wrong direction, that's why the gap is so big, the long run of the balance belt should deflect 1mm, the gap to the lower pulley should be .5, this stops the belt jumping teeth on the bottom balance shaft, as in you picture it already has.

 

the balance belt is so what appears to be slack that the placement of the tensioners and rollers is critical

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[scenturion]

Yes, I just figured that out!

I didn't realize that the tensioner could be tensioned in the wrong direction. It needs to be "out and down" instead of "out and up".

 



 

I'll dig back in and fix it this week. Thanks for confirming!

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[94SilverCab]

Pardon my stepping in here. This section is "Introductions", if you have technical questions, please move to a technical forum.

 

Carry on,

 

Jay

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[Waylander]

Sorry Jay

helping out then realising its in the wrong place

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[Roboman]

Ditto, got swept along .....

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[94SilverCab]

Yep, no worries...

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