Arp Main Studs... At What Point Should They Be Needed?

[GTRNUR]

Ive been thinking about the need for running aftermarket main studs instead of the standard bolts, and at what point aftermarket is really needed.

Researching engine failures, it seems very rare that a bottom end failure occurs except through oil surge related issues. And even then the failures occur more on rod journels than on the mains.

Id like to know if anyone has ever had a failure due to the main bolts stretching or letting go?

[Keeper]

was going to buy main bolts for the crank cradle off the boys at Chilton, he called a couple ppl and said at 400kw i wont need them, they just distort the shape of the bearings

[Beer Baron]

anything up to 350rwkw and I wouldn't bother. after that they are worth looking at depending what else is going into the build and how much power you're ultimately after.

[doo doo]

Remember that main studs will pull the crank bearing surfaces out of round (higher tensioning) requiring re- machining, which is a little more complicated than normal tunnel boring with the RB26 due to the one piece cradle cap apparently, ask a reputable machine shop about it.

[T04GTR]

if your after less than 900hp and not reving past 9k dont bother

[GTRNUR]

Thanks for the feedback there guys. Kind of a mixed bag of responses. I follow doo doo about pulling the mains out of round. It makes sense.

Does anyone shuffle pin (Hollow dowel around the main studs) the girdle to the engine block, or is that considered overkill?

So it seems that nobody has managed to break a girdle or crank other than by having a bearing spin or a rod thrown. So just using good head studs is where ARP bolts seem to be really needed to stop the head lifting. And 1/2" seems the go there if your going custom.

I cant help but think about what those RIPS guys do with RB30's and standard main bolts...

[Piggaz]

I have them in my car. Tomei 2.8 stroker, GT block running anything up to 1.9 bar through twin RS's revving no more then 8300RPM. 12000 KMS and no issues Although mine are Jun main studs.

[GTRNUR]

I wonder if people are using the factory torque specs for tightening the arp studs down on the cradle, or do ARP recommend a higher tension?

The whole point of a bolt is that is has a designed in degree of elastacity so that it can stretch a little under load, and while an arp bolt can be tightened to a higher tension its not necessarily a good thing that it is. The possability that it could distort the block for example.

So if a bolt is tightened to factory specs results in the factory designed in level of block distortion, but the bolt can also handle considerably more stress (from the engine bottom end taking a 9000+ RPM pounding) before it stretches beyond safe limits then that is possibly the way to go.

The last engine I assembled used carillo 5/16th WMC5 conrod bolts, and for curiosity sake I torqued them to spec in stages and measured the bolt stretch to see how it related to the applied torque tension. The results were:

30ft-lb - 3 thou

35ft-lb - 4 thou

40ft-lb - 4.5 thou

43ft-lb - 5 thou

45ft-lb - 5.1 thou

46ft-lb - 7 thou

Normal 5/16th arp 2000 bolts only go to 28ft-lb and have the same bolt stretch of 7 thou. ARP 8740 were something like 24ft-lb.