You are correct in that they are fine if you use don't torque them down too tight and break them but they are hollow for venting gearcase pressure and a solid bolt will cause that pressure to pass through the bearings and seals.

 

I think that these bolts are made so that they break if over torqued to prevent crushing of the bearing and causing it to swell into a barrel shape and reduce the ball clearance.
If the small hole that is visible is all that goes through the bolt then the material selected is the cause of the failure when over torqued.

Bearings will not last long with reduced ball clearance.

The use of the wrong bolt material and torqued to the specified setting may crush the bearing whereas the correct material will stretch and not load the bearing too much using the same torque setting.

 

First off if you have two bolts made of two different materials with different elasticities and you torque them both down to the the same spec, they will exert the same amount of force on the surface they are being applied against. You might have to turn one more than the other and the amount of stretch may be more but if they are both tightened to 25nm they are exerting 25nm of holding force. Second, yes you want to make sure you don't crush the races but you're talking much higher torque specs before you need to worry about that and unless common sense escapes us all, people know you don't keep cranking on a bolt that holds down a bearing. If you don't, you shouldn't work on your car.

 

On and off on both cars a couple of times now without a problem... You need use some common sense with these, as they are hollow... Not just a bolt you want to attack with a breaker bar....

 

I agree my last statement is a bit erroneous, but torque is dependent on many variables and the same torque can apply different forces on the bearing, a lubricated thread will exert more pressure, a material with greater friction will exert less pressure and so on. So the correct material, formed to the correct profile and finish is required so that the specified torque gives the safe end load.

Tubes are notoriously weak when end loaded and crush relatively easily, a ball raceway that is buckled will not last too long. If you can break a bolt like this using a strap wrench I would suspect that the bolt is meant to fail before the end load was too great for the longevity of the bearing.

The smaller bearing used on this pulley could possibly require less torque on an OEM bolt to prevent distortion than when used on the OEM bearing. It all depends on the new cross section and ball raceway depth.

 

My concern is that my bolt has been in and out many times. And I'm aways worried about weakening
the bolt. I do use a torque wrench, but it is an old style and I'm not really sure how well calibrated it
is anymore. If I'm torqueing a bit more than I should I'm concerned with twisting the hollow end. I'm
not worried it is under torqued, as it hasn't fallen off in several years of use. But, it would be some
bit of a comfort factor to have a replacement. I'd try to find a replacement myself, but I know notthing
about metallurgy.

Sincerely,

 

You need to remember that when you change the variables, you change the outcome. I was talking about different materials in like situations. If you really want to get crazy, you can say that using loctite on a bolt with a high enough RMS could be just hand tight. At the end of the day, this bolt needs to meet 4 conditions, it needs to be the right thread size and pitch, the correct length, be hollow for venting gearcase pressures and have a tensile strength high enough for the recommended 25nm torque plus 20%.

Actually, tubes are tremendously strong when end loaded and actually crush with much more effort than a similar square or other broken straight plane support. This is why we have round supports for bridges and the like. What I think you're trying to say is the tensile strength of a tube isn't as great as that of it's solid core variant. This would be correct. Just for argument sake though, if I had an M6 solid and an M12 hollow, the M12 would stretch less and fail with significantly greater force. That is unless it's walls were only as thick as tin foil.

This was already taken into account and is why the bearing spacer is made from aluminum and not stainless.

 

Tremendously strong..... yes, but they bulge out, not in, as out is the stress relieving direction. In some structures the bulging has no effect on use and is ignored.

Out of interest the ID of the hollow M12 would be 10.4mm to have the same cross sectional area.

Aluminum is often used for ease of machining and cheapness.There should be no drawbacks in this case though.

 

Just wanted to 1) bump this thread and 2) check if there was any status updates.

Understand that is has not quite been 2 weeks yet, and this will take some amount of time... but you
did say you were "going full steam ahead in a few days". So, was just wondering if the ship has left
the port and if any torpedos have been seen in the water that need to be d*mned.

Thanks

 

As of right now, everything is going right on schedule. Materials were ordered by the machine shop last week and they are planning on machining them on the 17th or 18th with assembly and QC happening after that.

I'm not going to litter this thread with daily updates but when the machine shop finishes them up and they are ready to ship, I will update the thread.

Take care

 

Thanks for the update Rudy. PSK has arrived! I think I will try to get before and after dynos

 

Thanks for the update Rudy. We appreciate the work/time you've put into this. BTW, I don't think
anyone is looking for daily updates. You'll note that I waited 14 days before inquiring. However, a
little info every couple of weeks might not be too onerous or litter the thread, should this work get
back burnered or if problems arise.

 

I was busy last weekend with the holiday so I didn't post about the materials being ordered in and with the thread being bumped, there really is no reason to post when they show up with them coming in end of this week or the next. I'd rather just wait until the pulleys are finished up with machining and then post as they are being QC'd and ready to ship. I do appreciate your patience though and I apologize if what I said came off the wrong way.I certainly would update if there was anything that drastically changed delivery wise but I don't foresee that happening.

Take care

 

Rudy you know I'm no doctor, that means I have no patience.lol
couldn't resist doing that to you. jim

 

Rudy, We are all good. I, for one, really do appreciate your work on this (did I say that before ).
And, no worries. Patience is not an issue, as I know this process takes time. I waited an awful long
time for an LSD to be delivered, and made hardly a peep during that time. I can wait for this, too.
Best wishes and happy trails.

 

I keep hearing this pulley referred to as the "Karmen pulley". So, who is Karmen?

 

Mine was off and on 7 times no problems... then it snapped while retorquing it on #8. Chrysler and Mercedes stated its not supposed to be taken off and dont even sell the bolt seperately from the complete supercharger assembly(approx $2000) If you want to keep torquing and straining the same bolt go ahead but id much rather a new bolt and not have to worry about tapping and removing the half that threaded in

 

Same reason at Erbert's and Gerbert's they sell a Narmer and a Gerf. It's just a name the manufacturer chose at random so this would be identifiable as a specific pulley like the "Code3" etc.


Not looking like it's going to happen with one with rolled threads like I was trying to have done. So it's off to the machine shop to see what a few of them will cost with cut threads. For this application, don't think it will be an issue but it was originally made with rolled threads so I figured I'd try to keep it that way.

 

Well, if you strain metal enough, yes, it will break...that is a lot of on and off right there. Twice in 5 years...soon to be 3 time's on the coupe.

 

Any word on shipment?