jon928se

I would say studs everytime, irrespective of wether they are designed to yield or not and wether they are replaced every time or not.

For one reason. Studs are screwed into the block with no load on them. Bolts are screwed into the block with load on them. There is lots of chance that the bolt threads could gall against the alu threads in the block while being tightened and damage the threads in the block = mucho problemo.

GregBBRD

Possible, except I've done many, many of these engines and never had a head bolt pull the threads or gall them.

The blocks that get Nicasil coated get bead blasted and then "soaked" in acid before they plate them. When they come back, it takes hours (ask Rob Edwards) to clean the grey "muck" out of the head bolt threads, before we can put them back together. We have to run thread chasers multiple times down each hole to get them ready to accept hardware. They don't even have problems with bolts....so I don't worry too much about this.

Rob Edwards

Yeah, like half a day. Still have bad dreams about it, and what you did to that poor shirt with the ATF.

New bolts on my motor. I have the old bolts, which I had replated so they're good as new. Anyone want 'em?

SeanR

I'm glad you guys hang out here, such an amount of information.

So, let's say that I'm building a 5.0 block, stock internals, for boost. Do you all suggest using studs or sticking with the bolts?

GregBBRD

Aside from the fact that "boost" and "928" should never be used in the same thought process...

With a boosted engine, you want to have really good "clamping"...hot or cold....or the head gaskets will have a tougher life.

New head bolts will do that...they have to be very elastic to stretch as much as they do and not yield.

Mike Simard also has done the calculations so that the material he makes his studs out of "stretches" enough to clamp the head gasket properly when the engine is both hot and cold.

Pick one.

GregBBRD

Try and picture what his face looked like...as he looked down the blower nozzle to see what was happening at the bottom of the stud hole. I think we had to play "seeing eye dog" and guide him to the bathroom, as I recall.

I was going to mention not to do this....but somehow got distracted.

ptuomov

Why not? Too much hp/$ for your taste? ;-)

blown 87

Sounds like he got a face full of crud.

SeanR

Thanks for the info. I know what you did there, and for some reason I agree.

S4ordie

I'd rather end up with a face full of crud from Greg's shop than Rob's shop

blown 87

Good point, and Yuck, just the thought of that.

Formula94lt1

What I am getting out of all this is replace them, whether they are bolts or studs, with either stock parts or Simard's parts. If stock bolts or studs then torque 20nm followed by 3 series of 90 degree turns, seems to be the proper way of doing this. I'm sure Simard has his own way of using his studs.

Correct?

Trying to bring all of this together in an unconfusing manor. Thanks guys!

Formula94lt1

Yes, no?

Hilton

Sounds like replacement is mandatory to me - check the workshop manual and tech bulletins for the correct torquing spec. I vaguely recall some 928's require three 90 degree turns, some only two, depending on studs/bolts/heads.

blown 87

I am going to start replacing bolts on all the head jobs we do at the shop, not just on the ones that call for it.

What I am getting out of this is that you can not get the clamping force that the engineers wanted when using old bolts/studs, regardless of the method used to tighten them, IE simple torque or torque plus degrees.

I have only had two comebacks on head gaskets in the last 17 years and we have done countless ones, if I had to guess the number is over 200, but I wonder if the two that I did have problems with were related to using old bolts.

One was a Toyota R-22 and the other was a Nissan something that I can not remember, this does not include any kind of supercharged cars with tuning issues, those do not count IMHO.