Replacing my cam cover today to finish the 'fix all of the air leaks from crispy air hoses' project (Because last week I pulled a bit on the breather snoot on the left cam cover and pulled it out, it didn't look very airtight anyway). New cam cover (jaguarclassicparts) has gaskets installed and new bolts. Seemed great.

So I removed old one, put new one back in place, then hand tightened everything. Started to torque with the torque wrench set to 10.2 Nm (notional range 9-11 Nm) with bolt in sequence 1, it turned and turned with almost no torque (probably 2-4 Nm at most), disturbingly (already hand tightened to ~1, let's say). Then it sheared off.

I could say I drilled out the bolt, but actually put a small divot in it and turned it back out fairly easily. Okay, what the heck? So, figuring it was just a manufacturing defect, I replaced that bolt with one from the old cam cover.

Second time, I was even more careful than the first, hand tightening the first round. Then hand tightening again hard in the appropriate sequence with a socket before torquing. Bolts 1-4 went fine, then bolt 5 sheared off.

Dug the second bolt remnants out while again trying to avoid getting metallic bolt bits everywhere, again.

So, something is very amiss. Torque wrench appears to be working properly and is clicking over at what I think should be around 10 Nm. All of the bolts hand tighten and there's no particular resistance with the threads in the holes. The threads in the holes also look fine.

I'm uncertain on how to proceed. I could drop the torque to 9 Nm and try again, but an apparent factor of safety of 1 Nm out of 9 Nm on a bolt seems absurd. And I'm tired of digging broken bolts out that don't torque to more than a few Nm.

So, fundamental question, has the torque spec changed at some point on new parts without it being apparent? Do I have the wrong torque spec? Or do I just have a set of crappy bolts?

 

I would go back to the old bolts. As some of the new bolts are ok, I would guess there’s some inconsistency in the batch. Don’t risk it.

Is it possible to bench check the new bolt to 10Nm?

 

Good idea, appreciate it! Proof check before spending time drilling into my engine...

 

I'm in the middle of this now. I strongly suspect leaks from the cam covers. At the very least I want to eliminate this possibility.
The cam covers are on the work bench and I'm going to clean them and reinstall. I'm thinking that the torque of 80-97 inch pounds doesn't seal well enough and I don't want to overtorque the bolts so I'm going to use a little high temp RTV to help them seal.

 

That's worrying. I'd expect Heritage parts to be better than that - especially at ~$300 a rinse pop

Agree with David to re-use the originals. I'd also be having a serious whinge at Heritage. Torque 9-11 Nm is what's called for and what I followed without problem.

The clamping force for the cover is through the rubber isolators, so these bolts only need to be tight enough to nip the spacers against the head. Higher torque won't increase that.

 

Yes, it's inexplicable that these fail at this torque for this application.

Update, two of the first three of the new bolts I 'proof tested' to 10.2 Nm failed (now four out of eight placed under torque). Now having achieved zero confidence in these bolts, I'm in the process of cleaning the old ones. I did test a couple of the old ones, and they didn't fail and don't seem fragile.

Note already in to our friends at Heritage.

Updated Update: Never mind, torque wrench fragged, unclear why. I borrowed another one and, pitted against each other, my settings are off by more than factor of over 2 in this range.

Updated Updated Update: Second (good) torque wrench made short work of it. Everything back together, seems solid, and fuel's a trimming.

 

Oops

 

Also going through the same process. The lower left corner bolt on the right cam cover is a bear to access and I somehow manage to cross-thread it putting it back together. I'm planning to re-tap it although I'm not sure I have enough room to get in there. I might end up have to use some RTV if I have no other choice.

 

Yikes, that's a difficult location. Good luck with it.

 

Yeah, even with the coolant tank removed I wouldn't want to have to tap that. It's enough "fun" just to get the bolt in.