Oct 14, 2023 Engine Update - Did the clearances for the main bearings today. Bit of a learning curve with using the plastigauge, but was going smoothly by the end. I had initially measured clearances with the original shims, which were all between .003" and .004". Decided that I would need to reduce the shim thickness to .0015" as I was going for the lower end of the .0005" to .003" range for my 1955 235. Initially was getting clearances averaging around .002 except for the interior rear bearing (thrust bearing), but more on that in a bit. The crank was spinning pretty easily with these clearances, so decided to try no shims. Pictures 1, 2 and 3 show the rear, inner front and front bearing in that order with no shims. Pretty much where I want them.
While I was working through the process, I noticed that when I torqued down the inner rear (thrust) bearing it locked the crank solid. Could not turn it by hand at all with the .0015" shim I had in there. So continued to try different shim combinations until I was at .002" on ether side. At this point I could turn the crank, but it was comfortably snug. I went back and measured clearances with the plastigauge again, first with out shims and then with the .002" shims on either side. Picture 4 is no shims and showing a .002" clearance and picture 5 is with one .002" shim on each side and showing a .003" clearance. I would have assumed that adding .002" shims to both sides would have increased my clearance more than it did. Would also assume that the .003" bearing clearance would see the crank turn easier than it did. However, I iteratively increased shim thickesses, sometimes by as little as .0005" with only that bearing torqued down, and I can't argue with the crank being locked, and then not locked. The side clearance of the thrust bearing is about .011", which is slightly high (I think, I only have the manual for a 1952 216), but shows that it wasn't binding.
Will be going to the engine forum on this one for thoughts.
