Cam bearing replacement


(Roger King) #1

Now I’ve removed the cams I can see that some of the cam shell bearings are showing a little copper. I shall therefore be replacing these. I presume the set method is clean up properly, install new shell bearings, assemble bearing caps correctly and to torque to obtain the correct crush, then line-ream all four?
The cams don’t appear badly worn on either journals or lobes.
Thanks
Roger


(Robin O'Connor) #2

I would just replace and re-fit the cams, possibly plasti guage but you don’t line ream big ends or mains do you?


(Roger King) #3

No… but I always ream cam bearings! Granted, none of those have been fully split bearings, retained by caps.
Plastigage would work, my bore mic is too big to measure the cam bearings. What would likely clearance be - 0.0005"? Or just check for consistency?


(Robin O'Connor) #4

I’ll leave the clearance to somebody else as I am away from my manuals until tomorrow.


(Paul Wigton) #5

In the couple hundred XK engines I have built, I never reamed the bearings: that is much more for for press-in style bearings, not split shell.

Valves/tappets out, fit new bearings, use engine oil, and install cams. If they turn firmly, by hand, with no major stiction, yer golden.


(Roger King) #6

Thanks Paul, good enough for me.


(Rob Reilly) #7

If the original number matched bearing caps are lost or damaged you possibly would check the bores with the new caps in place without the shells.
You might want to measure the journals just for a record, but we don’t often hear of them being worn.
Are you doing all this without a Service Manual? DId we mention the Mark VII / XK120 Service Manual covers most of what you need on XK140, and there was an XK140 supplement covering a few things like the steering and wiring differences from XK120?


(Lee140FHC) #8

Do use plasti-gauge(on bottom shell halves) to check installed and torqued down journal clearances…might be shocked by excessive clearances, as I was during my rebuild. The clearance spec is pretty tight…1 to 2 thou.


(Mike Spoelker) #9

The most likely thing you will find to be worn beyond usability will be lash adjusting shims. Very common to find them worn.


(Nick 53 XK120 OTS) #10

the cam bearing shells press, then pop out with a little pressure from the side edge, careful not to score the surface,use wood or plastic, the cam bearing shells come in a set, just enuf, no spare, about $709or so USD,(I would have TWO sets on hand, it is easy to damage a shell on insert) the shells press in, and I have found on some of the manufacturer sets press in harder than others.,.near impossible to find Vandevell, but the others are OK, once mostly in and flush, ready for the caps that will torque down, no need to ream at all,in fact do not, the entire set up was in line reamed at the factory,done,there is only one cam bearing set size, no over, under,so if you made it larger at all you are cooked, Caps of course must be original, and note the small numbers on inner edges that match numbers on head lip, re install must be exactly the same, Cap nuts tighten down slowly across all evenly, to 11ft lb (per Coventry West) min, max 14 ftl lb,but use inch lb wrench 175in lb max is the 14., Do NOT over torque,one click and STOP, Put followers back in same place, Micrometer everything, follower thicknesses, the shims that come out, mic the new ones too even if marked, (shims, once mic in center can be turned over for reuse if dimpled in which case mic the outer edges for the true thickness dimension). It ALWAYS takes more than one process to have the clearances correct, Just the way it is, Since it is mechanical do make them exact to the thousandth, It can be done, should be done, may as well be done exact, I am sending to you a handy chart for shim selection,
Nick


(Nick 53 XK120 OTS) #11

Anyone that wants an email copy of my several files of XK120 Cams, cam clearance adjustment procedure,send a pvt message with your email to me and I will send em. It is an edited collection of the best practices posts and info I have found, much from these archives from trusted sources, and includes the PSalt excellent archive on Valve Adjustment, Saves a lot of archive hunt time.,
Happy to send,just a few clicks,
Nick


(Roger King) #12

Thanks chaps, I do have a factory manual on the way.
All caps are matching and correct, so I’ll assemble with Plastigage and see what I get. Interesting to expect 1-2 thou on small diameter bearings like these. I build 289 HiPos with 0.0015” for mains and 0.001” for big end clearances. If the machine work is up to snuff, the motor can run full synthetic right off the bat.


(Nick 53 XK120 OTS) #13

BTW it is important, perhaps essential, to have the set of Factory Technical Service Bulletins that deal with the XK120 140 150, about 200 or so pages for the full set,but many of them are for Mark 7 or other early cars, so fewer if only the XK SBs, ,but many specs were changed thru the years, and the SBs tell you what, when, what parts, what parts have to match with what new parts and specs, Some of that is essential in a rebuild, as well as fantastic night table reading, note pad at the ready,
Nick


(Rob Reilly) #14

And did we mention the Spare Parts Catalogue that shows when each old part was superseded by a new part?
Then there’s the Owners Handbook which tells you where to put in the gas and what the loud pedal is for.


(Paul Wigton) #15

I always wondered…:stuck_out_tongue_winking_eye:


(David Langley) #16

Can I suggest that you read the manual BEFORE you do the job? I would find it frustrating reading about all the things I did wrong or didn’t do at all AFTER I’ve put it back together again! One tip, replace the cam bearings before you bother even checking the valve clearances. In my experience it can easily make at least 1-2 thou difference if you measure with worn bearings. The tension from the timing chain tends to cause the bottom shells on the front 1 or 2 cam bearings to be worn the most.


(Roger King) #17

Of course. I should point out that I’m not actually doing this job now, this all started because it seemed sensible to remove the head whilst the engine was still in the car due to advantages of weight etc. As it happens, the head came off very easily. I’m just interested in discovering what condition everything is in before I get back on to the doors and return to the bodywork. Reassembly of this engine is a long way down the line. Technically it’s second in the engine queue in my workshop (there’s a 5MB 2.25 petrol Land Rover block currently sitting on the engine stand), but as the LR’s current encumbent seems to be behaving better than expected the Jag lump may jump the queue.
And yup, the hint of copper is on the lower halves of the front two shells as you suggest.


(Nick 53 XK120 OTS) #18

My laborious task but interesting, I am putting note tabs in the Manual, wherever a supercede part, or Service Bulletin applies, The SB index helps. In my own files, whenever I see a pertinent forum post or other info, I copy it to a file document by topic, ie cams, distributor, brakes etc, These are quite voluminous now, I would make the entire files available to any interested, on a USB flash drive, or on a singe topic by email download, The set of SBs is not scanned (by me),so far is only a paper book, Nick