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1996 90hp V4 Johnson OK to replace single piston

S

seadub

New member
"I recently broke a piston rin

"I recently broke a piston ring and spun a connecting rod bearing on one piston. I read in the service manual and was told by a machinist that it is ok to simply replace the ruined piston with an oversized one and leave the others alone. I planned to replace two pistons because one other is "marginal." Recently, I was told by another machinist that I should really "punch out" that is, replace all 4 rather than only the 2 pistons. Replacing 4 rather than 2 pistons is obviously much more expensive so I'd appreciate any suggestions on whether its the smart thing to do. Thanks for the advice!"
 
"it is accepted practice,to re

"it is accepted practice,to repl only the damaged one,or more...Personally,I dont do this,if i overhaul it,it gets overhauled."
 
"Thanks for the advice jwbmari

"Thanks for the advice jwbmarine. You implied that you would replace all the pistons if you were faced with my rebuild. What other components, besides gaskets/seals and connecting rod bolts, would you routinely replace even if they looked fine? Thanks!"
 
"gaskets, seals and bearings d

"gaskets, seals and bearings depending on how they look make sure you give the block a through cleaning colling passages and exhaust passages"
 
"The practice varies from mech

"The practice varies from mechanic to mechanic pertaining to piston replacement. Personally, I examined all of the undamaged pistons, cleaned them thoroughly, and if no defects were found, reused them, installing new piston rings of course.

Bearings..... If they were perfect, NOT chipped, worn, or discolored, I reused them also. Anything to hold the price down for customer satisfaction BUT cutting no corners that might degrade the quality of the overhaul.

Bottom line..... any part with the slightest imperfection was discarded, otherwise it was consider reusable."
 
[b]I recently broke a piston r

I recently broke a piston ring and spun a connecting rod bearing on one piston.
Is that the lower rod bearing or the wrist pin bearing?
I planned to replace two pistons because one other is "marginal."
So you have one trashed cylinder and one marginal?
I think I would determine what caused the damage before rebuilding. What is to prevent it from happening again?
 
"Thanks to all for great advic

"Thanks to all for great advice! I'm proceeding with this rebuild following Joe's approach and will let you know how things go.

Allan, I wish I knew the cause. I presume it was either excessive heat or inadequate lubrication that caused the problem, but I haven't dug down far enough into those components to get any better idea of the source of the problem. (nothing obvious when the engine was last running) During the course of the rebuild, I plan to replace, at least, the water pump impeller, since I haven't done that ever (I'm sorry to say). I will also rebuild the carbs and hopefully find something plugging up one of the jets in at least the carb for the damaged cylinder (#3). Any other suggestions for where to look would be greatly appreciated! BTW, I have been told by one person that, during his rebuilds on this engine type, he routinely drills out the carb jets by about 0.002" and retards the timing by 2 degrees. I'm presuming this is done so the engine doesn't run as lean. Any comments on whether I should be doing this on my rebuild?"
 
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