Paul902

I had my left hand heat exchanger off this weekend in order to assess a few oil drips from the lower valve cover gasket. At one of the 6 mounting locations, I removed the nut along with the stud that goes into the head. I replaced it "as is". Next time I'm in there, should I use some thread locker on the engine end of it to prevent the whole stud from coming out in future? Alternate method?

Garth S

It really doesn't hurt anything if the stud releases with the nut - it's just a PITA: Med blue loctite may help, but considering the operating temp at the exhaust, the stuff may be long disintegrated between visits ....

Re stud installation, note that they are only lightly hand tightened into the block: often, the easy way to do this is to double nut the stud - and snug it into place at something considerably less than the torque spec for the nut once the manifold is in place.

Paul902

They must be tightened into the block at nominally a bit more than the torque on the nut, no?

For this double nut plan, are you saying to do that to seat the stud, then remove one (or both) nuts before mounting the manifold. Sorry, I think I'm missing the obvious.

Garth S

The strength of a stud, and its ability to cope with differential thermal expansion are signifigantly comprimised if it is threaded in so deep that it either bottoms on a blind hole - or torques against its shoulder ( usually the latter .... which places all the stress against the last thread before the shoulder = broken stud in service).

If using locking nuts on the stud to hold the exchanger in place, then threadlocker is a good idea to install the stud into the head: installation should be not much more that finger tight, sic., " by hand".

The 'double nut" is locking two nuts together on the outer section of the stud so that it can easily be threaded in - but not overtightened: once the loctite sets, two wrenches break apart the 2 nuts, and spin them off.

Then, install the exhaust and torque to spec ... this creates an evenly dispersed torque over the stud and female block threads .... and minimizes breakage: it does, however, cause some studs to turn out with the nut on dissassembly. Personally, I far prefer that issue than trying to have nuts welded on to broken studs so they can be extracted

Paul902

Got it! thanks.

neunneundrei

I replaced several studs a while ago and I believe the Porsche manuals indicated the amount of thread (or the height that had to protrude) for the studs, rather than any torque of the studs themselves.

I'll see if I can dig up the info and I'll post it.

neunneundrei

Not sure if this will help, but here's the word from the p-car shop manual on installation of the studs:

"Fitted with Loctite 270, protruding length 23 - 0.5mm. Screw studs with unmarked end into cylinder head (exhaust side)."

Paul902

Thanks for the follow-up, Enrico! excellent.