Oil pump stud (tensioner) question.

[CPorsche]

I had the water pump stud that holds the tensioner on an 85.5 944 break. The stud is an m10x1.5. I think it is around 100 mm long.

The belt was properly installed and tensioned using the Arnworx tool. Have done many over the years and this is the 2nd stud I have seen break. I have talked with a couple of friends that have worked on many 944's professionally and they have experienced the stud breaking. One guy said I can tell you exactly where it breaks and that is where the stud comes out of the block and the thread ends. That is exactly where both the ones I have seen broke.

I have wondered if the bolt fatigues over the years. Would a harder rating work better? I think the stud is an 808 hardness.

If anyone has experienced this and has a good solution please post. I don't think Porsche has this part available new.

[944 Ecology]

https://www.fastenal.com/products/details/0349286?term=stud+m10x1.5

[Rasta Monsta]

http://www.clarks-garage.com/pdf-manual/eng-04.pdf

[smokintr6]

Originally Posted by CPorsche

I have wondered if the bolt fatigues over the years. Would a harder rating work better? I think the stud is an 808 hardness.

A harder rating makes for a more brittle bolt, and is not likely to help. In cases like this, a SOFTER bolt that's more ductile would be desirable as long as the strength requirements can still be met.
The same reasoning is why you don't often find exotically hard bolts in suspension systems... in the event of an impact you'd rather the bolts bend a little, than to have them break off and lose a wheel.


I've had a timing belt stud break in exactly the manner you're referencing. Looking at the clarks garage procedure it looks like hes recommending replacing them every belt change.... interesting.

[CPorsche]

Would a threaded rod cut to the correct length be as strong as a stud?

[kevingross]

My concern with a threaded rod is the quality (and source) for it. Studs, like bolts, have rolled threads, not cut threads. Be sure the source is a reputable manufacturer.

[peteb]

Hi all,

There is a Porsche TSB (1-8701) that calls for checking the torque of the shoulder nut under the tension roller every time the cam belt tension is adjusted. It goes to 32 ft-lbs. Applies to all models through 1986.

Per Porsche "failure to ensure proper torque may cause breakage of the stud". Makes sense to me. If the shoulder nut is not tight on the pump, the stud will wiggle as the belt turns and break after a while.

I would check the torque of the shoulder nut. If it has been loose I would consider replacing the stud. Otherwise, it should last forever.

Peter

[jderimig]

Originally Posted by peteb

Hi all,

There is a Porsche TSB (1-8701) that calls for checking the torque of the shoulder nut under the tension roller every time the cam belt tension is adjusted. It goes to 32 ft-lbs. Applies to all models through 1986.
Peter

My 84 does not have a shoulder nut.....

[v2rocket_aka944]

^^ there exist a number of different variants, using different nuts based on which oil pump your car has. minor revisions.

that said i've never seen one of these studs break.

[Waz951]

I encountered this issue but not due to a stud failure but because I changed from a spring tensioner block to a earlier eccentric. I made a post about what I did on my blog Dave951: Oil Pump Eccentric Tensioner Stud and Collar Nut