Acorn nuts on cam covers

The 2" thick Jaguar E-type book of what’s there and how to do pretty much everything, states that the acorn nuts on the cam covers should be “fully tightened.” I’ve always believed that it’s possible to do some damage to the covers if this advice is followed.

Anyone have any practical/actual experience that the bona fide Jaguar advice, is wrong?

Certainly the nuts on the ribbed covers can be over-tightened to the point that the cover cracks. Mine came to me that way.

Wow, thanks Geo, I think that pretty much sums it up!

There is probably a service bulliten that specifies the torque…7ftlb comes to mind but cant remember where from…if we take the term “fully tighten” to mean keep going till you cant go any more then your covers will by wrecked…therefore yes the manual is wrong

Using a properly annealed copper washer do them all up to 4lbft. If they leak go to 7lbft.

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Context is everything… Here is the relevant section of the manual:
The “tighten fully” comment is in the context of the “but do not tighten fully” at the end of the previous paragraph. I would suggest that “fully” in this context is around 4-7lbft based on standard torque charts… :grinning:


That sounds like pretty irresponsible advice. I wonder how many cam covers had to be replaced under warranty?

It seems like it to me, hence my question…I thought perhaps Jaguar had engineered a limited movement in the nut which when fully tightenedgave the correct ampount of force. Doesn’t seem so!

Probably none under warranty. Only would happened later when they were removed for whatever reason

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You also need to be aware that if you have used replacement nuts that they dont bottom out befor they tighten down…and if you have removed/replaced your studs that they are set to the correct height…this applies to head studs and acorn nuts as well

Tables show the standard torque for of a 1/4-20 Gr5 nut is 6lbft, and for a 1/4-28 is 7lbft. As I highlighted in my earlier post, the word “fully” in the manual is not saying over-torque the nut (as most do), but has to be read in the context of the previous paragraph that instructs the use not to tighten the nuts fully until the rev counter generator and plug have been fitted to the rear of the cam covers. 7lbft is not a lot…

David, I quite agree. I am not sure how the term “fully tighten” became to mean “bottom out.” If one was to fully tighten a head bolt, I do not believe one would interpret that to mean bottom out the head bolt. I believe it would be interpreted to torque to the spec.

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So you know for a fact this was their mechanism for setting the acorn nuts to the correct torque?

In the case of headbolts, big ends etc the literature provides torque guidance, however for the acorn nuts on the cam covers it only says to tighten fully. If they’d wanted it tightened to a given torque I believe they would have said so. However, I do feel that tightening them until they stop, is undesirable. Thanks to everyone for their input.

Hi Les…no thats not what i was saying…some after market Acorns do not have as much depth of thread as originals…so could bottom out on the stud befor they actually tighten the cover down

Nothing wrong with the manual considering it’s a high performance sports car.

You would be assumed to have calibrated your in-built forearm ‘torque gauge’ by wrecking spindle nuts on your bicycle and various fasteners on your moped or scooter before taking the lids off a DOHC torque monster. Note that they don’t explicitly state ‘righty tighty’ or ‘loosey lefty’ anywhere either. :smiley:


The first reference in the text, "but do not tighten fully " seems to be about initial installation. Makes sense…seems to mean: put the cover on, put the acorns on…and tighten em all evenly and just to kinda make firm contact on the surfaces. The end reference “tighten fully” depends what “fully” means doesn’t it. Since we now can’t know what the Factory author meant…experience and common sense will tell us that “fully” means the additional amount to the first “not tighten fully” instruction, that is now needed and no more…so what is that amount: it is logical to (yes assume) assume that amount fo this “fully” is to make a sufficient seal with the surfaces (if surfaces are in excellent condition) , and not so much as to compress one part too much or to crack the metal of the cover, or damage the threads. If at that point there are no leaks…then the acorn is “fully” tightened. Why do any more. Experience seems to show that 4-7ft lb may do it.

In Jaguar works recon,we did 9 ft said,make sure cam studs are fully down so dome nuts don’t bottom out. Always anneal or use new copper washers. Over tightening will cause leaks due to distortion/ cracking. If cam cover off,always check face is flat.

I’m not that familiar with the fasteners being discussed, but I sure don’t like the looks of that cracked cover! I know you guys value originality, but I’d probably change that scheme to the O-ring and flat washer idea. You need a 1/16" thick O-ring with an ID that fits the stud and a flat washer with an ID that matches the OD of the O-ring – meaning 1/8" larger than the stud. Set O-ring around the stud, set the flat washer around that, and tighten the domed nut just until it sits hard on the flat washer – which means it has already compressed the O-ring plenty to achieve a reliable seal. The O-ring serves as a lock washer and will prevent the domed nuts from loosening.

The OD of the flat washer doesn’t matter. So if you wanna do it right you can use copper washers with the same OD as the original washers. With any luck you won’t be able to see the O-rings and the assembly will look exactly original.

The engine just might get too hot for normal O-rings. It’d probably be OK, but if concerned you can get Viton O-rings. If you burn those up, you’ve burnt up your engine.

O-rings sound like a needless complication. It is so much easier to use the proper copper washers and sealant. Just smear a thin coat of sealant on both sides of the washer, you don’t need much, and slip it over the stud. When you tighten the nut it spreads the sealant evenly between the cover and washer and washer and nut. Wipe any excess that squeezes out with a paper towel and you have a leak free cam cover. The sealant is invisible and doing it’s job. That’s how I always did mine and I never had a leak there.