Jim Demas

To my horror... I had the balance shaft belt tension loosen unexplainably... and partially chew the belt. This was not at all what I expected to find when I removed the belt cover and was planning to do a belt change. We are not talking about a light loosening... it was really loose. And for your reference... torque on the nut when belt tension was checked last was correct.

This meant that either the crimped nut on the stud (had been a new Porsche sourced nut) lost its ability to hold the tensioner... or the whole thing (tensioner, nut, and stud) slipped due to the stud turning in the aluminum housing into which the stud goes called the gear carrier... part #944.101.042.03 (this gear carrier also incorporates the balance shaft housing "nose" and also holds the power steering pump).

I double-nutted the stud... painted reference marks on the housing and stud... and applied torque to the stud... and sure enough... it moved with approximately 12-15 ft lbs! Hardly enough to maintain the torque of the nut on it at 33 ft lbs (45 Nm).

At this point I knew I had a big problem. The stud was not firmly fixed into the gear carrier... and tension would change yet again if not fixed immediately. Now.. since the stud is threaded on the outside (to allow its nut to be threaded onto it)... it has no thread that you can see where it goes into the gear carrier. This presented a very scary situation as the gear carrier is a very expensive part to buy. Was the stud press fit into the gear carrier with splines on the inner part of the bolt to control any possible rotation of the stud... or was the stud, in fact, threaded in this area as well... but just not able to be seen? I debated what to do... since the last thing I wanted to do was to turn the stud more and to chew the gear carrier even more internally if there were splines... but I realized that in any event I had a problem. The stud was turning... could not be left this way... and I either had to get it out to re-secure it... or I had to buy a new gear carrier (or find a way to repair it). The turning stud had to be fixed... period.

So... since I knew from the small bit I turned the stud and saw it loosen that I was not feeling any more resistance as if something was binding... this "should be" primarily a very good good sign (more on this in a minute). On this basis... I decided that I would take the calculated risk and turn the stud more. I did... and then turned it more... and more... without seeing any threads. Now I was getting I was getting antsy... and thinking that perhaps my calculated risk could be a misjudgment... but I knew that I had not experiened any other difference in torque in doing so (a good sign)... so there was no binding (the only was this could have been fatal is if the internal area was so stripped that any potential splines already destroyed their anchor points in the housing and the stud turned pretty freely). But I had no choice now but to continue... and all of a sudden... I saw threads! I had calculated right... the stud was threaded... and could be removed. Whew!

The stud is in fact threaded into the gear carrier (it is not press fit with splines). It also had thread-locking compound on its threads from the factory. So this means that either they did not apply enough thread-locker... or the thread-locker had now failed and could not secure the stud from enjoying any rotation. This is a scary proposition for any owner of a 968/951/944 series car!!

On further examination... the stud threads into this gear carrier... but does not bottom out in the hole (hole is deeper than the threaded portion of the stud). This means that the stud cannot be torqued into the gear carrier... instead, the stud depends ENTIRELY on the thread-locking compound for its retention and stability.

So now comes the tough part... which Loctite thread-locking compound to use. The reason this becomes an issue is as follows... I performed two tests last night with two different clean M10 bolts (same size as the stud)... with Loctite 262 (red, permanent). Neither of these set up and hardened sufficiently that the nuts could not be removed. The Loctite did not harden fully as it should have.

Why? Well... it could be because the bolts and nuts are plated in various fashions... and the materials being joined affects the ability of these anaerobic thread lockers to set up. Now you might ask... is the stud and aluminum gear carrier the exact same material as the bolts I tried? No... but here's the rub... they MAY ALSO be "inactive metals" as these bolts may be... which means that the Loctite 262 will also not set up fully when joining these!

The stud is certainly plated... which makes it an inactive metal. Therefore... for the Loctite to set up properly... it MUST join with an "active metal" component. This means that the gear carrier would need to be (as Loctite describes it) "commercial aluminum" (such as copper content e.g. 6061)... if the thread-locker is to set up properly. If it is "anodized aluminum" or "pure aluminum" according to Loctite... then the gear carrier would be inactive metal... and there would be an inactive metal stud going into an inactive metal gear carrier... and the Loctite will not set up fully! (query... is this why the compund failed?). Oh... and if the suggestion is to remove the plating on the stud... this has met with poor results in these situations according to Loctite.

Needless to say... I don't want this stud to come loose!

**** So...
1) has anyone either reinstalled or replaced this stud in the gear carrier?
2) if so... what Loctite did you use?
3) has it endured the torquing/untorquing of the tensioner nut on the stud to 45Nm (33 ft lb) without having the stud rotate AT ALL?

Thanks for any feedback.

-- Jim

RajDatta

Jim, not sure if it helps but I had a similar problem with one of my cars. I must have gone through 5-6 differenet retensions until i narrowed it down to the lower balance shaft housing hadving a hairline crack. I swapped it with a housing from a dismantler and have no had any problems since.
I was going through the same situation, the nut would remain torqued but the stud would turn. I hope you find a solution. Let us know which way you go.
Raj

Jim Demas

Raj...

Funny thing you mentioned a crack. I also checked very carefully for this. In my situation... this is all a failure of the thread-locker. The gear carrier is fine.

Thanks for your relaying your experience. I'll keep you posted on what I do with Loctite. ... after I figure out if it will work. Jeez.. Porsche does not even say that the bolt is replaceable... so, of course, there is no mention of what thread-locker they used.

Sure wish I had an idea of what kind of aluminum is used in the gear carrier... per Loctite's requirements.

-- Jim