Need a builder who talks flathead near springdale AR or somewhere close or who should I ship it to? I have a 39 mercury 239 block and I need a cylinder crack fixed and sleeved and bored to match other cylinders. bottom end****embled valve seats replaced. with a sleeved bore whats the biggest oversize it can be opened up to?
Will sleeving it eliminate the crack, or does the crack run out of the cylinder and into the deck? I don't think anyone can answer your question about the max oversize bore without knowing the current state and measurements of the remaining cylinder walls, is there core shift present, severe corrosion, etc. However, it is not unheard of to take 239's out to 3.375" bore (3/16" over stock). I would volunteer to help you, but the machine shop I had been using in Springfield closed last year and I haven't found a suitable replacement.
Crack from exhaust port to cylinder. I****ume the sleeve would be in new condition with no core shift. The reason I ask is that the cylinders are all bored to 60 over so if the cracked one can be sleeved can it be opened up to 60 or not?
I think most flatheads left the factory cracked in that area. Installing a cylinder sleeve and new hardened valve seat will go a long ways in correcting the problem. You will have to determine if the runs deep enough to connect the exhaust port with the water jacket, in which case, a bit of brazing or welding may be in order. If you are currently at 0.060" over bore, you have plenty of room to go bigger. You will be able to sleeve it to what ever final bore size you want, like I said, it was common to bore 239's out 0.188".
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