Re-torquing Cylinder Heads

[onevoice]

Originally Posted by Steve@Rennsport

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.

Steve
How do you recommend heads be retorqued? Put a wrench on them and just see if they move at the recommended setting? Loosen, then retorque? In a certain order?
I have ARP's in my 3.6, would there be a difference in engines with or without head gaskets? I am due for a valve adjustment, is checking the nuts every time I adjust valves a reasonable schedule?

[Steve@Rennsport]

Originally Posted by onevoice

Steve
How do you recommend heads be retorqued? Put a wrench on them and just see if they move at the recommended setting? Loosen, then retorque? In a certain order?
I have ARP's in my 3.6, would there be a difference in engines with or without head gaskets? I am due for a valve adjustment, is checking the nuts every time I adjust valves a reasonable schedule?

Its pretty simple: just check each nut (in the prescribed order), only being VERY gentle so you don't pull them up too far. Do NOT loosen them.

Head gaskets or sealing rings will not change anything here.

I use an electronic torque wrench now that both vibrates and beeps when it hits the set value so I can see where the fastener is set at, but I used to use a split-beam wrench which worked just as well (lacking that one feature).

I would check them more often than the 10K valve adjustment if it were my own car.

[keynsham1]

Just as a final update, when I rebuilt my engine, I fitted steel studs to the lower row. Nothing special, but it is not a racing car and I only drive on the road so it has been rebuilt completely standard apart from this. Around 75% of the studs needed to be tightened. A few of the lower ones were tightened by as much as 1/4 turn. This was after about 400 miles from rebuild when they were properly torqued down, so my recommendation is that retorquing is necessary after a rebuild for these engines!

[911 tweaks]

great info here... i am surprised no one is saying they are using supertec head studs... if so, please chime in on your experiences... thx

[Ronnie's.930]

Originally Posted by Steve@Rennsport

I use an electronic torque wrench now that both vibrates and beeps when it hits the set value so I can see where the fastener is set at . . .

So do I - a Snap-On Techwrench . . . am forever spoiled by that thing!

[theQuicker1]

If you hear a snap that sounds like a bolt breaking (hopefully just breaking loose), what should you do?

I was checking that all the head bolts were properly torqued after adjusting the valve clearances. Then I heard a very disturbing noise.

[Neil Harvey]

I would assume you used Loctite when fitting the studs???

You probably broke the Loctite. I would also assume the whatever you were using to check (torque wrench) it snapped as well when the Loctite broke loose. Your only way forward is to hope that this has happened and to re tighten the nut to whatever "way" you did before.

If this is indeed the case here, this is the perfect lesson, not to use Loctite when installing head studs. If you do insist on using Loctite, you have to tighten the head nuts before the Loctite cures. If you then decide to re check the nut, expect this to happen.

Studs should go into the case with a good anti friction grease, and once the nut is tightened correctly, it will not come loose. If they do, its down to poor assembly procedures.

Care needs to be taken when tightening the head nuts, and never taken for granted. Tighten to "seat" the head, allow to rest for awhile, then loosen in reverse order, re seat and rest again. Then do 90°'s or your desired torque value. This is assuming you have checked the bores and washer platforms in the head to make sure they are not deformed.

[Walt Fricke]

Well, this started as an oil leak, probably from the #3 (that is the rear cylinder and closest to the hot air blower up top).

Leaving aside a leak starting up in the cam tower area (and checking there to be sure the rocker shaft hardware is tight and the shaft is where it should be - flush on the narrow end. The intakes are easy, but the exhausts are a PITN - unless mid-way into an oil change so the sump and tank are empty, you need to jack the car up on one side as far as your jack and jack stands will go before you remove the valve cover, and even then have rags on the heat exchangers/headers. And then do the other side.

The cylinder to case seal is by the copper gasket. I suppose this could have been mangled during a rebuild - hope not, as you have to remove the cylinder to put a new one in. You might be able to spot if this is the only likely source of the leak. Since it is fairly easy, you ought to use brake cleaner and rags etc to do a thorough cleaning and de-oiling of this whole area. Then go drive, and then reinspect to get a better idea of where the oil is (and is not) coming from.

The other common leak source in this area is case through bolts. They are sealed with rather delicate O rings, and it is easy to pinch/damage them when installing and torqueing. Some of the through bolt passages have oil under pressure in them, so are potent sources of leaking if the O ring seal is defective. Not a gusher, but an irritating leak. I can't recall offhand just which of the many through bolts have oil pressure in their passages. On sees pictures of these bolt heads all goobered up with silicone by guys who have tried to stop these leaks. But those are a place to clean carefully and later check.

Some oil leaks you can just live with half way to forever. Others are too much, though it is expensive (in time, if not mechanic money) to fix many of those.

And by all means retorque - Nothing to lose, but it was good to be reminded NOT to loosen first - this isn't like the initial install at all.

In one of the interminable discussions about CV joint bolts etc, someone contacted the Nordlok or the like after market fastener maker and discussed things with an engineer there. He was told that torqued fasteners "relax" a bit after the initial tightening. Relaxing would mean stretching a little, which would translate to having a lower torque value when measured some hours after first being torqued. I can't say I know enough about metallurgy - in fact I know very little - to understand how at the molecular or crystal level this could happen (ferrous materials stretched below their elastic limit shouldn't permanently elongate, though rod bolt makers give you a little extra relaxed length when deciding if you can reuse the bolts, so maybe this is involved). Any way, this would support a reason, or another reason, to do at least one retorquing of the head nuts.

I've got ARP head studs on one engine, and Supertechs on another, and Raceware on yet another. Only the SC had stock studs, one of which broke a year (or maybe more? - I found it in October of '18). I like the bullet head of the ARP because it makes getting the washers and nuts on easier, but Henry has a lot of experience, and customers are pretty quick to bring up problems to aftermarket manufacturers. I suspect Steve is happy with the Porsche studs he uses, so has no reason to try anything else on a customer engine.

Someone suggested using Loctite on the head studs. Porsche does or did that on the case end, and I don't see that as being a likely problem if it is Blue. It will help keep the stud in place when next the heads are removed for whatever reason, especially if the nut end has gotten a bit corroded. But never on the head barrel nuts. If the stud stretch has been lost, Loctite won't keep the nut from loosening further.

The first aftermarket head stud maker was Raceware. His spiel was that he had chosen an alloy which closely matched the expansion characteristics of aluminum. Then ARP came out with one, and of course they have pretty good technical smarts too. The Raceware guy lambasted them for using a material which wasn't the right expansion match. I have Raceware on my 2.7 race motor, and it never had loose head nuts despite being flogged (and blown up a couple of times). But I'll have to remember to recheck the torque on my ARPs.

[Eagledriver]

Originally Posted by theQuicker1

If you hear a snap that sounds like a bolt breaking (hopefully just breaking loose), what should you do?

I was checking that all the head bolts were properly torqued after adjusting the valve clearances. Then I heard a very disturbing noise.

Not to worry. I’ve heard this noise before as well. It’s just the sound of the nut moving on the stud. After a time the nuts get slightly rusted to the studs and make a loud noise when they break free. Usually you hear it when you tear down a 30 year old engine, but it can happen when tightening as well.

-Andy

[mikedsilva]

Interesting leak.. I have a VERY similar leak on a fairly fresh motor. It doesn't always leak, but tends to leak after the car is stopped and sitting overnight. Same spot too.. under the front of the left bank, cylinder 3.

Looks like it is the oil return tube where it exits the cam tower. I can 'just' see a small pool of oil around the tube base (heat exchangers are in the way)... Not really sure why it's leaking. New tube, new green o-rings. I have ordered a replacement collapsible tube (never used these before).. will hopefully get to change it out tomorrow.

[cmovic]

Replying to this thread since it has somewhat recent activity. Hopefully it's the "right place."

I got the "better plan to retorque your ARP head nuts" advice from my mechanic when I rebuilt my SC engine in 2004. Since then I've done it every few years/couple thousand miles. It's pretty much the same three nuts on the driver's side and two on passenger. All on separate cylinders, one top row, remaining four on lower studs.

This year I checked them after 1 year and 1500 track miles. Same set loose as last time so I'm starting to make plans to pull my engine and swap out the head studs. Before I head down that rabbit hole again is there anything else to try? I'm guessing no but would rather not spend the time and money before exhausting the alternatives.

Thanks!

[ahh911]

To re-stress the importance of checking head studs for looseness after rebuild.

No oil stains/weeping till about 5000 miles after top end but didn't look into it until today. Noticed at cyl 6 between head and cylinder. Where's this coming from? Pulled the top off, all okay, pulled the bottom off, 3 were loose, cylinder 6 was very loose. All rockers shafts in place and bone dry, camshaft wear looks good. I'm at ~ 12000 Miles now.

Steel head studs x24 w red locktite, clean assembly, new barrel nuts and washer all around (zinc plated OEM german I think?), optimolly ht, torqued to the 32nm spec following the Dempsey sequence.

I'm so pissed that I didn't check at 600 mile run in when I pulled the covers to check the valve clearance. I was afraid to disturb them, how silly. Today I set the torque wrench to 22nm and when they're loose, they're loose, you'll know. ughh.
Phil

1981 SC stock u.s.

[winders]

How do you check the torque of head studs when you used red loctite on them?

[ahh911]

Originally Posted by winders

How do you check the torque of head studs when you used red loctite on them?

No, red loctite was used only on the case end and I'm pretty sure they are perfectly stuck in there as it was a very thorough and clean job with new loctite on installation and they did not turn upon torquing as I'd marked their orientation, the barrell nut end had optimolly ht per bentley if I recall on threads and lightly under the barrel nut, that is a suspect, also curil-t under the case to cylinder gasket, I question that as well, they may have not fully squished down, don't know of course, So re torque not an issue as loctite not present near nut, I have yet to do it fully, just tested at 22nm, and zing it turned and finally clicked.

I'm so dissapointed that I didn't respond earlier to the oil seepage. Every interface every joint is absolutely dry,, then I see this weepage at first and was very curious, thought it might be the headstud, read around, didn't make sense, well I'm pretty sure it's that, something simple like this can ruin a perfectly good job, leaving well enough alone is not always the correct action, I should have re-torqued them to 32nm at the 1000 mile inspection, though for this car it's not specifcally instructed to do so, now there's 12k miles on it with who know how long this s8at has been going on for. Especially used new washers and barrel nuts for this area too, just to prevent this sort of thing, well there you have it, slick new washer barell nut and optimolly ht between nut and washer per bentley i believe, sounds like a recipe for a slip to me, but surely there are hundreds who have not had them come loose.
Phil

[H-viken]

Originally Posted by 911 tweaks

great info here... i am surprised no one is saying they are using supertec head studs... if so, please chime in on your experiences... thx

I have those, but haven’t started the engine so no feedback yet

[ahh911]

Originally Posted by H-viken

I have those, but haven’t started the engine so no feedback yet

Original spec for the 3.0l sc was 33nm. Supertec looks like ~41nm, roughly 30% more. The exrtra torque alone would be helpful, but I was reluctant to go that way.
If it had come with the bottoming "thread cleaner/tap" as an option for a few bucks more, I might have gone that route, maybe I should have called.
Phil

[Henry Schmidt]

Generally there is no need to re-torque head studs on air cooled 911 engines. If the nuts come lose, there's a reason.
Over heated engine
Studs pulling from the case (generally a function of excessive heat)
Machining error on heads
Too many base gaskets (stacked base gaskets cause excessive movement during expansion)
Cylinder height inconsistency
Head studs/nut material (we see ARP studs coming lose regularly)
And of course, mechanic oversight.

[Henry Schmidt]

Originally Posted by ahh911

Original spec for the 3.0l sc was 33nm. Supertec looks like ~41nm, roughly 30% more. The exrtra torque alone would be helpful, but I was reluctant to go that way.
If it had come with the bottoming "thread cleaner/tap" as an option for a few bucks more, I might have gone that route, maybe I should have called.
Phil

Supertec head stud kits use a completely different design. The torque specification is based on years of testing. Higher torque values create better clamping numbers. The trick was to find a number that offered the clamping force we wanted but didn't compromise the cylinder integrity [IE: ovality]
Our studs are longer for deeper thread engagement, a material that offers greater stability than most other stud on the market, they have a finer thread at the nut end to promote a more accurate torque, they use a serrated flange, 12.9, 12point nut to prevent changes in clamping force and because it uses these nuts, installation height is no longer an issue.
This combination allows the assembler to install the head studs after the cylinders are in place. This creates a simpler installation of piston and cylinder combination.
To date [some 750+set] we have never seen or heard a complaint. That does not mean people haven't have problems but most were a lack of common sense.

BTW: We do stock the proper forming tap for those who want the order one for $ 26.00. We list the proper tap in the installation instructions and it is readily available on line.

[ahh911]

[QUOTE=Henry Schmidt;11533108]Generally there is no need to re-torque head studs on air cooled 911 engines. If the nuts come lose, there's a reason.

Over heated engine: Nowhere near red, or even middle, did piss around at McD's drivethrough after a long drive on a very hot day, still had vacuum retard hooked up, heat went about 20 degrees above top of the box, so between 90 and the box edge roughly, wouldn't have called it hot, but I remember that one as ugh ohh. In u.s. talk, around 85F out and 5k rpm highway stretching.

Studs pulling from the case (generally a function of excessive heat): Not likely

Machining error on heads: Possible, but only touchup on mating surface, machinist insisted they are all even, I don't think I had the means to check it to high accuracy, I may have but the other note book is downstairs.

Too many base gaskets (stacked base gaskets cause excessive movement during expansion): No one gasket

Cylinder height inconsistency: Possible, flipped dial gauge run on inner edge cyl 5 6 to less than .1Thou between them all around, cyl 4 had hight inconsistancy on nineties of 0 -.1 -.2 -.2 thou relative to cyl 5 and 6, d delta that I recorded. 3 exhaust headstuds looser than the rest, one on each head, the one closest to the front of the car for each head. Looking at the drivers side this afternoon.

Head studs/nut material (we see ARP studs coming lose regularly): Possible, zinc plated oem german brand nuts/material I believe, I can confirm if anyone cares, probably unlikely unless others chime in and the regular steel head studs from Pelican.

And of course, mechanic oversight: Not other than already mentioned.


Today for right side so far:
Bought a new digital torque wrench, checked against my other ones to make sure nothing was completely out of wack, torqued all the exhausts to 33 Nm. The optimoly ht sure still provides a slick movement.. If this happens again, I'll back out the nuts that are loose a touch, then hit it with brake cleaner to remove the ht from between the nut and the washer, hopefully.. Original torque was 32 Nm with a wrench I checked at the time to higher and lower torque against very new wrenches, it checked.

Update on other side:

Left Side, cyl1,2,3 all tight at 22Nm, this is where I get nervous again, there is no oil at all on that side and all the studs seem tight. If I crack one at 30Nm and not the others, things get a little screwy, then I crack them all up to 33Nm, so here, my gut tells me to leave it. This side had more cylinder height variation then the other side, so probably not cylinder height difference that caused cyl 4,5,6 to loosen the exhaust nuts. Should I check the torque a little higher? Originally torqued to 32Nm. Tried 25 Nm tight, that's a wrap for this side.

Henry didn't mention case spigot height. I remember being upset because I didn't measure that height. Next time I'll find a way to measure relative between the 3 spigots.

To rule out any major damage, compression test post tightening of E4,5,6. All 6 cylinders between 160 and 165, original alusil/rings. All plugs look better and more consistent than any other car I've ever owned, light grey with a touch of brown. It's parked in it's "maybe" last time till spring spot in the garage

81sc stock

Phil