searched and didn't really find anything relating to this, and my flathead rebuild book doesnt mention this... started putting together a flathead (51 merc engine) and as i was plasti gauging it, the thrust bearing clearance seemed very tight, like it's too tight... should i block sand the thrust bearing surface?
I am sure others will add to your question. But, I haven't used plastigage for over thirty years. I doubt that plastigage is very accurate compared to micrometers and dial indicators. These are, in my opinion, the best way to judge clearances and crankshaft end play. Somewhere in one of those manuals there is a number for end float.
Thrust bearing clearance is usually checked by measuring crank movement with a dial indicator. I'm not sure how you could use plastic gauge. The normal spec is .004"-.007".
I use a piece of fine emory cloth or wetsand paper on a piece of marble. Before you do any sanding I would "set" the bearing first. A few good raps on each end of the crank will make sure the thrust is tight to the block and main cap . (use a piece of 2x4 or something similar to protect the crank of course). I can't comment on flatties as I am building my first now, but too tight thrust clearance will take out a SB Ford quick.
According to the book "Ford Flathead V-8 Builder's Handbook 1932-1953" by Frank Oddo, "The correct end play is built into the thrust bearing. From .002" to .006" is acceptable. That's the good news. The bad news is that you have to remove the crank to install the upper half of the oil-seal retainer in the cylinder block."
"Built In" ? That sounds like a large leap of faith. There are manufacturing tolerances in the crank, block and the thrust bearing.
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