I have an old but rebuildable head that I believe is from a XK120SE but not sure. The head/engine number is F3997-8, casting number C6733 and it has 1 1/2" intake and 1 3/4" exhaust valves. Is this from a high performance XK120 engine?
Any idea of its value? It has the cams (but no cam bearing caps), missing two exhaust valves and it has the valve covers.
Thanks for your help.
F series engine numbers were found on late XK120’s. It produces a bit more power than the earlier heads. If it is missing the cam journal caps, I believe it is worth very little more than scrap. Finding the journal caps is not difficult, but the head and new caps would have to be line bored as a unit. It would be difficult to find a local shop that can line bore a cam bore that long. @Dick_Maury can probably shed more light on that.
That’s an XK120 number but if it was from an SE it would have an “S” suffix, as in F3997-8S.
The standard A-type head featured 1-3/4” inlet valves and 1-1/2” exhaust valves. The exhaust valves in an SE head are an eighth inch bigger, 1-5/8”.
i have heard this about cam bearing caps…yes they are numbered for exact placement…with corresponding number on the head…:.curious tho…in a line bore what would hold the caps in any one particular correct place…exact as to the cam journal size…as there is only one size cam bearing…no over/under. Since the factory line bore (if one was really done)…wouldn’t all have been the same all the time…why would not other caps actually fit…? Could other caps be installed,torqued…and see if the cam rotates as it would in a all original number caps situation?
Yes. Having a careful look at it is vital, but if the cam turns…
I once had to replace a missing main cap for an MGB engine build. Found it on ebay. My machinist said it was as close as he could have line-bored it. Just by chance it was perfectly aligned. I don’t think that’ll happen again.
Not saying it has never happened, but I have never been able to swap cam journal caps and been able to turn the cam. Line boring does not affect the journal size.There are hollow dowels that positively locate the caps relative to the head, but this is no guarantee that the bearing bores are located exactly the same as another head. The studs for the caps and cam covers run up through the hollow dowels.