Just gotta throw this in here for the sheer joy of education, along with a little entertainment, I have a friend that was in the dump truck business for years. He owned quite a few of those trucks with the 427 tall deck engines, bust most of his stuff was GMC Brigadier with Detroit diesels. Well for whatever reason he had to put an input shaft in the transmission of one of the gasoline trucks. Next thing you know, the engine locks up. He runs to the Chevy dealership in Winchester and gets a short block, throws it all back together, and it locks up, he calls the Chevy place, they apologize and tell him to come get another short block, and they will throw in the gaskets and whatever, so he does it again, and this one locks up. He calls the Chevy place again and the parts guy has a little light go off in his head, he jumps to work and figures out that it's the wrong input shaft! Little too long, causing the thrust bearing to lock up! They gave him a new input shaft, new long block, and when he asked what they were gonna do with those short blocks, they gave em to him. He ordered new main bearings for them, and put them under the bench
this confuses me, the piston in the earlier picture when the engine was still together clearly is stamped std on top. How can a std bore engine be too tight? were some of the pistons changed with new ones that might have bee made too big?
Fresh Flathead yes a little too fresh to be having this issue and you need to know it's assembly history and drill that guy so you know what he may have missed . Engine needs disassembling and start FRESH again with an individual parts inspection gosh could be as simple as mismatched piston assemblies it's a common some mistake . Hope your crank is still good and no burn marks so also ring gap and well just start over again and seizing the engine multiple times puts strain on those beautiful 7" connecting rods . Take it to the machine shop is my professional answer and start like its a seized engine which of course it is. . I don't wish you good luck on this I wish you take it to a qualified machine shop . If you wanna do it on your own and you get frustrated enough I'll buy the mess from you for $250 . Gosh
Bummer. I raced karts for years and used straight hydrochloric acid to removed aluminum from cylinder bores. I didn't stick many of 'em but it happened more than once. Works cleaner (looked it up) main ingredient is acid, so I learned something new today. Thanks SS. Looks like you have a cobbled together POS someone called a fresh rebuild. Cobbling is not rebuilding. I hope I'm wrong but the cylinder scoring looks like overbore time. Just a guess. Let us know what your FH specialist says.
F = FLATHEAD R = REBUILT E = ENGINE S = SEIZED H = HOSTILITY ! That really sucks, that the engine wasn't, assembled properly, but then again, there were some major unknown's about it right from the beginning. Caviet Emptor, ( Buyer beware )
I don’t know about getting aluminum remnants of the pistons out of the bores, but would a brush hone clean them up enough to check taper? Like @Moriarity mentioned why would a standard bore piston seize up? Could be a home done job with sleeves and not sized, I dunno?
Thanks all after talking to my builder the pistons are .60 over but have std on them. So going to pull the motor and see about getting it oversized.
That sucks! But doesn’t the machinist have mikes to measure pistons and bores? Don’t go back to whoever built that engine. If those pistons are .060 over they should not even be able to go in the bore let alone move once the got em in!
Ive had a motor too tight on ring gap seize when warmed up. I agree these two things are your culprit and things that need addressing. Edit, saw the photos... Down right amazing someone put that together and sent it out the door like that.
I don’t understand how std or even .060 over can be so close to the head gasket . Does you flathed guy know this is a 255 merc ? .060 wont fit in a std bore but .006 might , if you had enough taper , this is what would happen . IF , IF and more
If the pistons are stamped STD and mic out as .060" over then I'm stumped. Crazy. And no, there's no way in creation even .020" pistons would fit in even the most worn out standard bore. No chance. Eight nine thousandths and they are flopping around in the bore.
That block looks pretty good with the exception of the bores. At least it looks real clean from here.
Just a tad off-topic but.....has anyone ever found a substitute for those big old oil can sized pistons with the long skirts? I wonder.......if a substitute was found and, the engine re-balanced because of the lighter pistons, if the flattie would be bit more high reving?! (ain't that what hot rodding is all about?) jus wonder'in....... 6sally6
Classic four corner seizure...lack of piston clearance most likely in this case.....It can also be caused by detonation from too much timing or lean fuel mixture or overheating... A bike photo but it applies here...One of my vintage racers, detonation caused four corner seizure at high rpm....Looks like the flattie piston...I saved the cylinder with a honeing but gained a bit more clearance..
Didn't they use to knurl pistons to tighten up the clearance? There are a lot of marks on the piston of to the sides.
Well the engines our and at the builder to be gone thru and punched out. Thanks all for the thoughts and comments.
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