Several years ago I was doing an engine rebuild for an old customer when I encountered a situation I had never come up against before. We were aiming for a motor with some enhanced performance, and the customer had obtained a number of competition bits, including a new camshaft. The customer also chosen the machinist, a very capable and experienced feller well known for his work on high-dollar machinery of the Ferrari and Aston Martin variety. Unfortunately, unless you were spending tens of thousands of dollars at his shop it was a little hard to get the man’s attention long enough for him to complete a job in a timely fashion. After months of waiting we were finally able to take delivery on the cam, crank, pistons, and block, which was supposedly line-honed, bored, fitted with the new cam bearings, and ready for assembly. As I was closing the van door after loading all the stuff (and after paying the man) he made the comment, "Oh, by the way, that cam was a really nasty fit. Hmmm. Not a good sign".

Back at my shop I found out pretty soon that the machinist had been understating the case. The cam was not just "a really nasty fit," it was no fit at all. It absolutely would not go into the block. All the journals measured the same as those of the old cam. The front journal of the new cam fitted the front cam bearing perfectly. Same for the rears. The two inside bearings were the correct size for the middle two camshaft journals. And to cap it off, the original cam no longer fitted in the block. Obvious deduction: something screwy with the bearings. Of course the original cam bearings were not available for comparison, having long since been trashed by the machinist. At this juncture I would like to call your attention to the first point made in the Norman Nock’s Restoration Procedures - Do not throw any parts away!!! I generally follow that principle to the letter, but had never extended it to cam bearings. It pays not to make any exceptions.

Well, after some head-scratching and careful observation and research and discussion with other mechanics. I ultimately determined the problem was that one of the internal bores in the block, for one of the middle cam bearings, did not line up exactly with the other three. So, even though all the dimensions were correct, this slight off-centeredness—only 0 .002 to 0.003 —prevented the cam from ever fitting unless you put a u-joint in it somewhere. Hardly a practical solution. If you look in the factory manual in SECTION T SERVICE TOOLS you’ll see that in the factory they had Service Tool 18G123A, Camshaft Liner Reamer, with all its cutters and pilots, which line-bored the bearings in the block to give them their finished internal diameters in a nice, concentric alignment. This would work fine even if all the bores were not perfectly in line, especially if oversize cam bearings were available to give any offset cut a little more "meat" on the thicker side. I could not find any oversize cam bearings listed in any of my parts books or supplier catalogs, although I was told by one or two old-time suppliers that O/S had once been available but had been discontinued and NLS for sometime. The internal alignment disparity in my block was great enough to preclude line-boring standard cam bearings. The off-center cut in the errant bearing would have left an oblong hole, causing a significant gap between the journal and the bearing on one side, sort of like this (proportions greatly exaggerated):

The only reasonably straightforward answer to the problem was fitting oversize cam bearings and line boring them in place. If these bearings could not be bought then they must be created. I knew that machinists spoke of "re-pouring" or "babbitting" worn lathe bearings, and that some antique car rebuilders had to send used engine bearings out to be "built back up" because new spares were unavailable. I had never tried this before, but figured it was worth a shot, especially considering the relatively minor forces cam bearings are subjected to, compared to rod and crank bearings. But where? Hemmings Motor News to the rescue. The advertisers for this particular service were few, and I wound up going with Paul’s Rod & Bearing in Parkville, MO. The cost for this kind of work at the time, I believe, was $30+ per bearing, but it’s only necessary to do the two in the middle. You leave the front and rear bearings standard and they are the pickup points for the line-boring. I sent Paul the two middle cam bearings, and when they came back (promptly) they were each about a quarter inch thick. Paul does not scrimp when he builds up a bearing. Now I had my oversize bearings, so it was time to line-bore. For this I went to the legendary Bill at Coleman Bros. Speed Shop in beautiful downtown Elkridge, MD. Bill has been machining motors for many a year, and has pretty much seen everything. Tasks that would make an ordinary machinist cringe and slink towards an exit are routine for Bill. I left the block, cam, and bearings, and when I returned a couple weeks later the cam was in place, and a perfect fit.