Re-torquing Cylinder Heads
 

I have recently completed a full rebuild of my 911SC 3.0 engine. I have since done around 300 miles and I have an oil leak which seems to be coming from the base of the cylinder under the heater motor (number 3?). I have never got around to rechecking the torque on the head studs and so I am hoping that this is the issue and a check and re-torque will solve the problem. Would I expect an oil leak from the base of the cylinder if the torque setting is low?

Torquing the heads has to do with clamping pressure, cylinder to head or cylinder to case, if the clamping isn't there, there is a possible leak.
Bruce

Generally I don't think they get re torqued. They usually hold. I haven't retorqued any of mine. The other place you may have a leak is in the valve rocker seals. May pay to have a very close look.
Alan

I know it is a general practice to retorque the head stud nuts and perform a valve adjustment at 1500 miles after rebuild but I believe that is more part of the break in process. I am about 400 miles into that number and so far I am in good shape. If you torqued everything the way it is supposed to you should be fine. I suspect you have an issue with either a bad gasket/seal or maybe something got pinched during the reassembly and now is showing up as leaking. Hopefully you will not have to re-drop your engine to address whatever it is. Please keep us posted to whatever you discover.

Hmm, I forgot - these engines have head gaskets (the 930 doesn't - pulling the heads tomorrow). I have had a gasket slip out of place when inserting the head. I guess that might show up as a bad compression number.
Alan

I used to think that they didn't need a retorque, but after finding several that did, I check them whenever any seepage between heads and cylinders is present. May not be loose after 1000 miles, but after a year it's possible.

1100 miles. Three needed retorquing. And that was observed by applying torque and getting rotation before reaching the desired torque.

Some engines don't, some do need retorquing. Asking for guidance based on someone not having too, is a little risky.

It would seem prudent to always check, because it's not really hard to do, and you'll know the answer.

Loose studs lead to head leaks. And that is really bad in the long run.

Experience says check it.

Why not use some loctite

Torque value changes would have to be accounted for.

The need for re-torquing depends on what head studs you use.

:) :)

That's interesting to hear you say that Steve, I always thought the need to retorque the head stud bolts was more due to the break in process and was a product of heat cycling. What is your position on ARP hardware?

I have factory steel head studs top and bottom. New washers and nuts. Permatex anti-seize paste used during assembly. Curil-T on the base gaskets.

During assembly I Torqued in three steps 7, 15, and 24 ft-lbs following the Porsche recommended sequence. Making sure the cam turns freely after each round if torque. I then retorqued to 24 ft-lbs after 15-20 minutes. Always observed some rotation to reach the check torque. So it is possible the anti-seize and/or Curil-T is squishing out, or the base gasket and/or the CE ring are compressing.

For my earlier post, I checked the torque just before starting disassembly, after running 1100 miles since the previous rebuild. The observed angle of rotation to retorque was pretty small. About 5-10 degrees of rotation before I reached the set torque on my wrench. Small, but non-zero motion on three of the 24 studs. May need to wait a little longer before I recheck the torque.

We will not use their head studs; the rod & flywheel bolts are just excellent.

What problem with ARP Steve - I put em on my 930 recently, but have it apart at the moment. In case I need to change them...?
Regards
Alan

A lot of people like the 993TT almost fully threaded head studs best. If you use only factory Porsche parts they are the best but they are expensive.

ARP head studs are good too. They may have different expansion rates than dilivar head studs during heat cycles but they work. Never heard of anyone having a problem with them.
The ARP installation instructions says to put them at 38 foot pounds in two or three steps with ARP fastener assembly lube on the threads for the nuts. It's a good idea to check torque on them while you can during valve adjustments.http://forums.pelicanparts.com/uploa...1454186648.jpg

Hi Jim, Yes got all that. Quite happy with them at the moment. No issues. So curious as to why Steve has issues with them. FWIW I only torque them to 30 ft/lb. And no issues/leaks so far.
Regards
Alan

I'd be interested in hearing Steve's opinion on that too.

Kevin Jeanette who is the most talented and experienced Porsche race mechanic, fiberglass fabricator, and body and paint expert I know and he told me the 993TT studs are best.
He said ARP are good too when I told him I have them.

He told me torque the the 993TT headstuds to 36 foot pounds. His motor inside the Swap Shop 935 won the Daytona 24 hour race in 1983 and I used to work for him so I trust what he says.
I have ARP in mine because I got a good price on a full set 9 years ago and installed them at 38 ft lbs like the instruction sheet says.

Jim - I just posted couple of pics of the Porsche factory museum 935 (at the track) on 930POTD.
Regards
Alan

Hi Alan,

We used ARP head studs for several years following the original Dilavar debacle. While none of them ever failed, we found loose head nuts after several thousand miles (some even were finger tight and/or sitting in the lower valve covers).

These simply do not expand & contract at the same rate as the cylinders, causing leaks and damaged sealing surfaces if not addressed in a timely manner.

FYI, we do check (and re-calibrate if necessary) our torque wrenches twice annually.

Despite the expense, all we will use are the 993TT Dilavars on all engines from 3.0 on up to assure long-term durability as these have been very durable since 1996. 2.7's and smaller can still use steel ones provided Case Savers are installed.

Just my experience so others may have different ones. :)

If one has ARP studs, I would recommend checking them fairly often.

Thanks Steve.
I guess I am going to have to build that into the maintenance schedule. At the moment, the engine doesn't stay in long enough to warrant it. But hopefully this time :-)
Jim - you better get that torque wrench out.
Regards
Alan