cylinder head tightening with aftermarket studs

hey guys so as the topic states, when tightening a cylinder head with aftermarket studs, many people have indicated that after correctly tightening the head to the manufacturer tq settings, you have to let it sit for a couple hours for the studs to settle and then re-torque it to get best clamping. can anyone say if this necessary or not?

Studs, or bolts, don't 'settle' but there is a potential for the gasket to compress slightly more - shouldn't hurt and falls in line with the old "have a cup of tea and retorque" method from back in the day.

Thanks, will keep that in mind

In re-torqin, would it be recommended to back off the nut a bit and then re-torque the nut or just re-torque from where the nut is?

Normally this is something that's completed after the engine is heat cycled a couple of times. It's more critical on engines that use a composite gasket as these compress more than a MLS style gasket. It's a process we used on any of the high boost drag engines we built, even though we were using MLS gaskets. You'd be surprised how much additional movement you'd get out of the studs to achieve the correct torque.

To re-torque the head, each stud is backed off until it's loose and then torqued back to spec. This needs to be done one at a time - i.e don't completely loosen all the studs and then tighten them all back down.

awesome, thanks for the info andre

By loosen, I would just crack them back - that initial release when undoing the fastener - the aim being to remove the static friction from 'sticking' the fastener and allowing a smooth movement as the fastener is re-torqued.

But different people have different views.

Yes Gord, that is the aim. If you just try to torque the fastener up without loosening it first, you have the break away torque to overcome before the fastener moves. It's possible that the break away torque may actually be higher than your target torque in which case you're not going to achieve much.

I have seen issues with the nut / washer sinking into the head spot face; this was with ARP studs & washers. We machined oversize washers which solved the problem. I believe ARP have now upper the washer diameter for that application, but something to keep in mind when using aftermarket studs or bolts with higher torque/clamping force.

Good point - most good hardware suppliers will also carry high tensile washers which 'might' be an option.

I've used them in some plant applications but can't recall if they were actually larger OD or not - because they are an industrial product, probably a good idea to make sure the surfaces are polished, or at least cleaned up, for consistent torque.

[edit] Ah, Ii see ARP have a range of OD sizes for each ID - may be worth checking out for you chaps - maybe order at time if getting ARP bolts/studs.