348 engine problems

july2849

Well Known Member
thanks for all the replies-went to Shop today, motor was torn down, here's what they found and I saw: block was excellent-they measured and scuffed bores they were fine-bearings all fine and re-usable-they did not look new but close. Crank was fine looked like it was just polished. The #7 piston was not the worst it was #2. Gouges worse than my friends 1st wife was capable of. Oil Pump looks good but will replace because of the piston shavings. Shop foreman said just the pistons and they would cover work and 1/2 cost. They thought it all happened right away because of a dry start from sitting a couple years.
Here's my other problem, block had a welded water jacket, nickel welded, got about 5 pin hole leaks at the juncture of weld and block- Don't want to use an additive just yet-does lock tight 290 work-jb weld or maybe flex seal-
 

Greg Reimer

Well Known Member
Sounds like they sized the bores too tight. Are they cast pistons, or forged? The reason I ask is that a cast piston runs with far less wall clearance than a forged piston requires, and that the engine's pistons began to drag on the cylinder walls probably before the engine achieved any where near full operating temperature. I've seen machine shops make that mistake before- when a forged piston expands .006-.008" in a cylinder when it was set up with .003-.004" wall clearance,this will happen. If this is the case, any replacement pistons, a new hone job with proper clearances, rings and bearings, and that should fix it. The fact that you say that the crank looks good indicates it's not a rod, bearing,crank,or main problem.
 

july2849

Well Known Member
I looked and looked for 427 Johns Marine Tec and finally found Marine Tex-but decided to go with Locktight 290-their Tech Report has a specific section on sealing Weld Porosity with 290 which I followed with block on the bench, requires warming the block. We'll see.
I believe that Greg hit the nail on the head. Forged Pistons, doing everything he's recommended already and replacing the oil pump to assure no piston shavings are stuck in the old pump. I'll post the old piston photos.
 
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