Cam bearing caps

I’m getting into assembling the head on my 140 now, and would appreciate advice on the cam bearing caps.
I numbered everything on storage to ensure the same ones go back in their original position, but failed to note their orientation. Are the four caps mounted with the embossed part number in the same orientation - readable from the front of the engine, or the back? When fitting shell bearings, I usually position them so that the locating tangs are facing each other in their beds/caps. I don’t think this is possible with the cam bearing caps - does this matter?
Thanks all

Both the cam caps and a spot directly adjacent on the gasket rail were all stamped after the caps were on the head. You can verify the orientation most easily by fitting either the front or back caps, which are distinctive and noting the orientation of the stamp marks.

1 Like

Thanks Mike, got it.

1 Like

These are stamped "J 01, J 02, etc.

I concur, numbers on cap and head should match and be together and on the top, closest to the valley where plugs are. They should all have the same lettering and numbered 1 thru 8.

Thanks chaps, found the markings. I had assumed the caps were positioned with the embossed part numbers facing forwards, but they’re not - the opposite. I couldn’t see the markings as they were on the underside. Nothing tightened down so no harm done - mine are stamped RM1-8.

CERTAIN that cam bearing caps are properly placed and oriented EXACTLY as they were, then begin to hand tighten the bearing cap nuts, going to each one, a little at a time.
IMPORTANT *******Bearing cap re-install instructions , cautions.******Avoid undue pressure at any one point on the cam. flat at a time across all, noting there will be some valve to tappet pressure on down facing lobes to overcome, and lobes may try to turn the cam while tightening, be sure to keep cam alignment while slowly screwing cam cap nuts lightly down, do not torque until all are firm by hand and a light hand wrench, then torque evenly nut to nut a flat or two at a time til final 132-144 inch lb. (12 ft lb but use inch) per Dick Maury.(175 inch lb factory spec) is reached do not exceed) Use an inch lb torque wrench not a ft lb that at low torque may not be sensitive enough. When the torque wrench clicks once that is it. STOP. I will say all this again: Reinstall: in a similar manner as releasing them, but get the pressure lobe down with its cap firm but not final tight, and the ones next to it also, watch carefully for the pressure lobe cap: do not allow it to cock or tilt…then tighten all slowly, VERY slowly…a half turn to a turn at a time across all, evenly, to snug, then go round again evenly across all, and still a little at a time, and finish torque to 132-144 INCH lb. Use an inch lb wrench, , For final torque down, the cam must be aligned with the cam alignment tool,
Nick

Hello All - On the subject of XK140 Camshaft bearing caps I cannot seem to find their Ref. Number in the Parts Catelogue Plate F. Am I missing something?

I cannot find any with the head (in bits) that came with the car so I do not know how to source any without the correct Part number.

Any thoughts? regards Geoffrey

Geoffrey,

I’m not an expert in this area but the caps for the Camshaft Bearings were not available as a separate item.
They were machined during the assembly process and then stamped by the operator with the position number and his initials, in order to be sure that the correct cap was used on the correct position.
I’m not sure how to get these other than asking other XK owners whether they have a spare head or even spare camshaft bearing caps.
I imagine that it will be difficult (impossible?) to get a perfect alignment of all bearings if the caps have been replaced, and “line boring” may be required (if possible at all) but again I’m no expert in this matter.

Bob K.

Hi Bob - Thanks so much for your prompt reply. I realise now from what you have said that there would be no need to stock spares as the holders themselves do not wear only their shells. I am glad but concerned now that an ‘invisible’ aspect of the Head restoration has been raised. I will have to consider the next move carefully as anyone with an original head containing them is unlikely to separate the two if selling.

Thanks for this vital bit of information and all the best for 2024. Geoffrey

Over the decades several XK engine heads will have been scrapped for all sorts of reasons. You just need to find someone who thought to remove the caps and keep them. A very quick internet search throws this up, without even trying:

It shouldn’t be hard to find a set. Of course, these will need line boring, but any decent-sized engine rebuilding machine shop should be able to do this. Mill a bit off the underside, to close them up to undersize, then line-bore.

If you keep that head, you will need an align bore, after acquiring some used caps

Its a little bit complicated, as I found out many years ago myself, as it would seem the cam tunnels must have been align bored in the factory with caps on

The reason I say this with some confidence is that the align bore on that particular head was not parallel with the head surface,(weirdly), its a long story, but you would possibly need more than a full set

I recommend very careful measure

I do probably have some caps

interestingly late 4.2 litre motors they didn’t bother to number the cam bearing caps?

Hello Roger - Tony - Terry Thanks for the input. Just the first question, Why are the numbers C.2171 and/either/ or C.2172? Is the end one different on each cam?

Second question. Do the cam bearing holders have shells? If so and if they are line bored a second time will the shells still fit?

I am in UK if spare shells can be sold Tony. They do seem to be source able here nonetheless.

Any guidance much appreciated. Thanks - Geoffrey

the most interesting thing about this advert it is Steve Barratt the person who started SNG Barratt even in retirement he still needs to sell jag bits!

the ends one are different to provide seals for cam covers etc

Hi Geoffrey - yes, the cams run in shell bearings. If replacement caps are fitted to a head, they would need some material removing from the fitting surface to close up the bearing hole, then a fresh line bore through the lot to align them to each other. Then new shell bearings should be fitted. These would be original size and everything would be assembled exactly the same as the originals. There is only one size for the shell bearings. As Terry says, the two rear end caps are different from the others.

In the past, I could never find anyone who could align bore a Jag head.

2 Likes

Hello Chaps, Paul, Roger , Terry
Thanks for wisdom - yes I get it now - the cam holders are just castings through which a hole is drilled in common alignment with all the others for the same cam. The holder can be re-bored if there is enough material present where the new hole is required. As you say Roger the reduction of the existing hole diameter by taking material off the flat fitting surfaces can place new material in the right position to be bored.
Wow - this will need a careful briefing to the Machine shop as it cannot be an every day task.
Ok will mull it over. Ken Jenkins of JEC has kindly offered to trial/ loose fit a selection of cam holders at his place to see if we get lucky. I still have to find/ source the correct cams first.

Thanks all - Geoffrey

Hello Paul - Just as a reference, was your search in the UK? I am getting the impression that the skill set for line boring may be long gone although I have not looked thoroughly yet. Perhaps the racing fraternity might know as they get up to all sorts of tricks although that is usually an expensive place.
Thanks Geoffrey