inconsistent Factory Head Stud install height 136-137mm

[Dauner]

Hi everyone,

1989 911 3.2 engine rebuild. Replacing the dilivar exhaust studs with steel today. Decided to measure the factory intake studs to verify the highly published 135mm height from boss to top of stud. The original factory installed studs vary in height from 136-136.5mm, with none of them at 135mm.

Should i install at the 135mm per conventional wisdom, or copy original intakes that are 136-136.5mm?

Thanks,

Mark

[Dauner]

Quick update. I installed both a new stud and one of the original dilivar studs and with them fully installed and bottomed out, height is around 136.5, so Porsche must have changed the bore depth so factory could just bottom out?

New steel studs identical length to originals.

Unless someone thinks something fishy going on I'll just install to full depth, measure, and move on.

[shamrok]

I’ve read tighten to full depth, then back it out half a turn, which is what I ended up doing. If you’re sticking with the barrel nuts, you’ll get more hex driver into the nuts (which can strip) then if you have them out more. If you’re switching to 12-pt nuts, it really shouldn’t matter.

[Neil Harvey]

Exactly right. Do not bottom the studs out. And, if you do decide to use locktite, make sure you torque the head nuts before the locktite has a chance to cure. If you will install the head sometime later, do not use locktite. Just some good grease.

As for an installed height, there is no set height. Install one stud, fit the base gasket you will use, one cylinder and one head. Fit a head washer and the nut. Just seat the nut, don't need to torque it, and make sure there is a couple of threads showing out above the nut face. If not, wind the stud out. If too much, wind the stud back in. If the heads have been surfaced all the same height, you should be able to do this measurement once and set the studs all to this height. Job done.