Replacing missing cam caps

[rjaxe]

I have seen a number of heads for sale which have some or all their cam caps missing. What would be involved in replacing them? I guess it means facing off the joint surfaces on the head and caps assuming one can obtain them, and line boring the assembly. In other words a similar exercise to replacing the main bearing caps. If anyone had experience of this operation I would be interested in their comments.

[512BB]

Yes Richard, likewise.

My understanding is similar to yours, in that, if you buy a head with no cam caps, you would obviously have to find some!!!!!!!! not difficult, THEN have it line bored. Would you then have to find some standard bearings but with oversize outer shells?

I had a phone call last winter out of the blue, from a guy who needed some such bearings, after it had been discovered that his head had been line bored but standard size cam bearings had been fitted. I was his last hope for finding such bearings, but alas could not help. He had tried EVERYWHERE, and as he admitted, if I did not have any, his head was US.

So the SO CALLED Jim Clarke head that recently sold on ebay for 1600 quid, that came only with new cam caps, is as far as I can see, a very expensive paper weight, as the correct bearings are unobtainable. Unless anyone knows any different.

Leslie

[andyelan]

Hi There

As far as I'm aware, oversize OD cam bearing shells don't exist.

The idea Leslie, as Richard says, is to first skim the head and cam caps slightly and then it should be possible to line bore out to the original dimensions. Boring such a small diameter over such a long distance would make it an job requiring a good deal of skill from the machine shop but as they would have been made like this originally there's no reason to suppose it couldn't be re-done.

Regards
Andy

[bcmc33]

Richard,

Burton sell cam caps - perhaps a call to their technical guys may shed some light on this issue.
I just looked at their website and they only show standard shells - unlike the main bearing shells that are made to suit line boring.
A call to a good auto machinist may help to establish if undersize caps can be machined without affecting the rest of the head.

Don't forget to let us know the end result.

[reb53]

"The idea Leslie, as Richard says, is to first skim the head and cam caps slightly ".

Wouldn't this have the effect of lowering the cams and thereby playing hell with tappet clearances necessitating really thin shims ? Not a lot of room to play with here and I would guess you'd not want to start skimming the tops of valve stems to find clearance.

Ralph.

[rgh0]

I have had to do this.

The process is to just skim a small amount of the cam caps but not the head and then line bore the cam tunnels taking the absolute minimum off the head and most of the material off the cam cap. The cam tunnels should still be in line in the head side so very little, only a few thousandths of an inch, needs to come off this side so the resultant change in cam postion in the head is not a problem and well within the normal variation you see in heads.

Most good machine shops should understand this approach
regards
Rohan

[rjaxe]

Update: Talked to Burton who confirmed that they supply a lot of cam caps but they do not supply oversize bearings. A bit vague on the machining detail as this is done for them by an outside agency but they confirmed that the head is not faced as Rohan has said. I expressed my concern about aligning the head acurately enough to do this without touching the half bores but the Burton man claimed a good machine shop should be able to do this work with no problem. I have not approached a machine shop yet as my project has now fallen flat on its face having established that someone had removed at least 0.2" off the thickness of the prospective cylinder head so I will not be buying it.