I just dismantled my 99A Mercury block for machining. What came out were 3-5/16 'STD' pistons. Stock bore is 3-3/16 as opposed to the Ford 3-1/16. My question, did the Merc blocks have thicker cylinder walls? Could I take this to 3-3/8 without the same problems a Ford block of the same era would have?
That sure is a purdy picture. If it's a 99 block it should go to 3-3/8 easy. But, is there any rust problem on the inside of the block?
3-3/8 if the water jackets are pristene. My 99 block won't safely go to 3 5/16 because of the deeply pitted water jackets.
It's rusty in the jacket, nothing more then what I've usually seen. But, I've never taken a block to 3-3/8 either. The picture is just after I dis***embled it. The engine has sat for many decades in here in So. Cal. Anyway, the next stop is the machine shop for a thorough Magnafluxing. No deadly cracks as far as the eye can see, so I have to keep my fingers crossed. I'd really love to run this Merc. OK, maybe not 3-3/8, so does somebody make a 3-5/16 .030 over flathead piston?
Try Egge. They make a nice 3-ring piston for flat motors that starts at 0.125" OS and a couple of sizes beyond. Ol Ron on the Ford Barn swears by them. Most folks only go as far as is necessary above 5/16" OS due to corrosion questions. A machine shop or non-destructive testing facility can use ultra-sonic equipment to tell how thick the walls are. You might check into that for piece of mind. Kerby
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