The B.B. in the title represents that this is from the archive of the late Bill Bently, who ran a flathead Q&A informational site before he passed away. All threads from this source will be titled using the B.B. identifier on this site. We’re archiving some of the threads, so that his work is not lost or forgotten and so they will continue to educate flathead enthusiasts for years to come.
CYLINDER WALL THICKNESS: Ed Iskendarian in answer to a direct question in1953, stated “…… 0.060″ wall thickness is the absolute minimum for hopped up engines.” He went onto say “….. anything less usually results in the cylinder walls waving and flexing under heavy use and will cause the engine to come apart.” Today, most flathead engine builders say 0.100″ is the absolute minimum for normally aspirated street engines.I have no knowledge of maximum safe boring on blown engines. Be aware rust on the water side of the cylinders will eat away some of the cylinder wall which makes for thinner cylinders walls.BORING: I strongly recommend sonic testing when planning on boring in excess of 3-5/16″ to verify the absence of core shifts and thin spots caused by rust.This will also help determine the block’s safe boring limits. Sonic testing should be done after the block has had as much rust as possible scraped and removed from the water jackets. The rust scales and build up of rust on the water passages may hinder accurate sonic measuring. The cost of machining and prepping a block for a full-house flathead is too expensive and time consuming to chance using a questionable block. By the time it’s been hot tanked, acid dipped, magnafluxed, sonic tested, studs removed, bored, valve seats replaced and ground, cylinders honed, crankshaft mains line bored, block ported and polished,relief ground, block resurfaced, and cam bearings replaced, it’s just not worth taking a chance on a questionable block. Most of the things that are mentioned above are lost if the block fails after build…. and that is BIG BUCKS AND A LOT OF TIME!
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