Engine builder's, cam bearing surface ???

From Mike at musclemotors
The real reason on why “my cam won’t turn”

For as long as I can remember, Mopar’s have been known for poor fitting camshafts. I even remember seeing a price sheet in the mid 80’s from a machine shop in Detroit that serviced the Big 3 specifying an additional charge for installing Mopar cam bearings. It even became standard procedure at Muscle Motors to test fit a cam before washing the block for final assembly. The standard solution has always been, “just carve on the bearings to make it fit”. While this mindset works it always bothered me. If it happens to you when you get your block back from your local* machine shop and want to put it together, you do what you need to do.

My problem solving nature never accepted the “just carve on them” solution (cure the problem, not the symptom!). I mean they make rod and main bearings within a few ten thousandths, why aren’t the cam bearings just as consistent (PS, they do make cam bearings just as consistent). So in a moment of clarity, I thought, if the bearings are being made correctly maybe I should check the block. I then started measuring the actual bearing bores in the block. This specification, by the way, is in every bearing book in every machine shop on the planet. What I discovered made everything I had struggled with for years make sense. Of the first 10 bocks I measured, not one of them was within spec on ANY bearing bore! Most were ½ to 1 thousands tight!!! To this day I have yet to measure a stock block that doesn’t need at least 2 or 3 housings opened up. The worst example was about 5 years ago when I measured a factory block that the #2 cam bearing was .003 tight!!!

Now the main reason most machine shops don’t measure this dimension is that even if they found something wrong, most shops don’t have the proper equipment to properly hone the cam bearing bores in the block! Due to stock blocks ALWAYS having some level of cam bearing fitment issues, our standard procedure at Muscle Motors is to hone ALL stock block cam bearing bores. This ensures if you get just a machined block or a short block from Muscle Motors, your cam will fit every time with no problem.

If you are having a block machined (at a shop of your choice) PLEASE insist that the shop measures (and corrects) the cam bearing bores BEFORE they install the cam bearings. This will save you time, effort, stress and the need to “carve on them to make ‘em fit……………….

Mike @ MM