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4.25 pistons super M

W

WFE270NWIA

Member
In the super M to 450 blocks, when you pull sleeves out to run 4.250 pistons what do you do about the counter bores in the top of block for the sleeves? Thanks.
 
WFE270NWIA I take a die grinder and chamfer the counter bores where the rings and pistons don't catch and slide in. You can do it two ways. Knock the edge off and put the ring compressor into the cylinder or completely grind it down and put the ring compressor on top of the block. Murphy sells a head gasket for a 4.515 bore. Lynn
 
So if Murphy's makes a special head gasket I assume a standard gasket won't work without rings in the counter bores?
 
You won't be able to run 4.250 pistons in a 264-281 block, the parent bore is too big. By the time it cleans up the bore is too big. You can do it using the m block. Leave the counterbores alone but chamfer. I modify an old sleeve to compress the rings. Can make it to fit in the counterbore, works slick.
 
Interesting, I bought a 264 short block with 4.25 pistons, but the block is cracked. So the stock block in my M has enough meat to bore to 4.25? I've heard that the 450 block has more meat than the 264. I have a 450 parts tractor. Could I bore that block enough to use a sleeve with the 4.25 pistons?
 
There are a lot of SM, 400, running the MW stroker kit 4.25 bore and 1/2 in stroke , makes 326 cu, around 75 hp. , you are right about the 264 and 281 blocks having more meat, don't use a m 247 block you will run into trouble. In my pulling tractor I have a 281 cu 450 block bored to 4,310 with a 1 3/4 stroke.
 
I measured the bore on a 281 block. It would be 4.255 at best by the time it honed clean. I would do like what was said. Bore a 264 or 281 block to 4.310 or 4.350.The old m&w 4.250 kit required boringand used sleeves. I put one years ago in a super m.
 
The 281 and the 264 in the 400 are the same block. The 264 in the Super M was lighter. I have notes on this but from memory I think the difference is the serial number on the Super M has R1 in it and the 400 has an R2 in it.
 
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