Lock tabs on 4.2 bearing caps

Assembling my engine, finally, and just noticed that the bolt heads are round and the lock tabs are worthless. The engine shop said to use just 30wt oil in the bolt threads and no loctite. Any guidance on this. Thanks

I think Locktabs are softer than washers so perhaps you should omit the locktabs? But I am sure an expert in this will comment!

Dennis 69 OTS

First time I’ve seen cap screws used on main bearing caps? Why not replace them with the correct bolts and use the lock tabs?

NO soft metal lock tabs: if you must, use proper hardened washers.

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Are those bearing caps iron or aluminum? If they are iron, you can use no washers at all. If aluminum, you should use a flat washer – and a fairly thick, hard one, thick enough to not get dished when the bolt is tightened. You should not use the lock tabs at all, regardless of what bolt heads you have. Lock tabs are verboten these days, as it’s now known that they are too soft and squish, allowing the bolt to effectively loosen without turning.

Jaguar stopped using lock tabs over 40 years ago. Use hardened steel washers as per Jaguar XJ6 S1 parts book.

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Hmmm. Looking at that photo, now I understand why the bearing caps have that nasty notch. It’s where the lock tabs sat! We recently had a thread showing replacement bearing caps that were oodles stronger and a couple of photos were posted of OEM caps fracturing right at that notch.

Ok, so I got my orig “kit” from Welsh which included the cap screw, hardened washer, and lock tabs. So, if I’m omitting lock tabs, am I using locktite?

I wouldn’t use loctite here. Just torque to spec. The bolts are long enough to provide some “stretch” so they won’t come loose.

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Never, ever use Loctite on a main bolt or rod bolt.

Always use a light oiling, unless the fastener supplier explicitly specifies their own moly lube, as ARP do.

Who is the manufacturer of these bolts? Did they include a torque spec, or are they just considered direct replacement fasteners.


They are cast iron, as with all XKs.

I think they are considered direct replacement. Torque in manual is 73 or 78. I can’t remember off the top of my head. My machinist said to toss the tabs and just use the flat washer they came with. All torqued down now and on to the Piston assembly. This is much better than building Legos.

What is your opinion on torquing with clean dry threads after chasing?
I’ve always understood that to be the correct practice.

Some manufacturers do specify a dry or oiled thread Torque, but Jaguar has always specified “dry clean” as you say.

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You can use loctite 242 with clean, dry threads. It shouldn’t alter your torque readings.

I’m not sure about the manufacturer of these. I don’t think they are ARP but that is what went in my engine, no lock tabs. You’re just supposed to use the provided moly and torque to 90 IIRC. Did the place that supplied them provide you with a torque spec for these? Factory spec might not be correct.

You could drill a hole in the heads and use lock wire :thinking:

I am at the same stage. My engine used lock tabs with the cap bolts and i intend to use the same.

Not a good idea. Strands that long would probably vibrate and eventually snap off and go wandering around in the sump.

You’re not going to use cotter pins in those conrod nuts, are you?