Chuck---Others have told you that these bearings are listed in the major
supplier catalogues, and were original equipment in the Mark III
Spitfire. So far as actually using these is more a matter of whether
you want the added expense and how much you plan to 'build' your engine.
It's my belief that KK advised them for engines to be used in
competition. This would mean high lift cams with serious valve springs.
The thought being that it's easier to replace these bearings when
inevitable wear occurs, than to throw the block away.
About 10 years ago I purchased a set of these from TRF. My plan was to
rebore the block for + .020 pistons and line bore for cam bearings. The
machine shop advised me later that their machine couldn't handle the
'long' block. I was not able to find a local shop that could, so
somewhat reluctantly I put the engine back together without them.
There's been no bad things happen because of this, but I use the stock
cam and valve springs. Unless you know the cam bore to be worn, or are
going with heavy springs, the engine won't know that there's no cam
bearings.
I also use the nut-on-bolt method to determine thread stretch. If it's
going to happen, it will be at the thread root or an area unprotected by
the tightening.
My block leaked oil after reassembly (from having it boiled and acid
dipped) in two places. The aluminum (threaded) plug under the fuel pump,
and the large plug (2"?) at the end of the cam. Replacing this with
several 'stock' plugs-on-a-stick didn't solve this, and ended up with
using a bolt that 'ran out of threads' before the head so I could
tighten it enough to stop the seepage. The plug behind the cam bore
couldn't be replaced until the engine was again removed. Grrrr. These
kinds of snafus can get you familiar with an engine in a hurry!
Dick T.
'73
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