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89 15hp Johnson Piston rebuild question

R

realjoe2000

Member
"Whats the concensus in using

"Whats the concensus in using Sierra pistons rather than OMC or Wiseco pistons in my 15hp Johnson? There cheaper, but Ive never used Sierra pistons. So I dont know there track record. I broke a ring and my machine shop will do the cyl and head work if needed. So I am looking at the quality of these pistons for the rebuild. Thanks for the help."
 
"In general You may use almost

"In general You may use almost most of the after market pistons, providing all pistons in the unit are from same manufacturer! In other words: If You are only changing one, stay with OMC/BRP."
 
I would NEVER use only one pis

I would NEVER use only one piston. I want it to be a quality rebuild. Just wasnt too sure on the aftermarket quality of Sierra or another one Ive seen is GLM. OMC pistons for these small outboards have just gotten way out of line from BRP. There at around $100 each now. Thanks for your help.
 
In that case I would have gone

In that case I would have gone up one 'size' (.020).
Don't forget new wrist pins and bearings at the same time. (comes in a package from some manufacturer)
 
"Even if my machine shop says

"Even if my machine shop says the cylinders are ok to clean up and didnt need boring, would you suggest going .20 over anyway? I value your opinion very much, Thanks for the help."
 
"One thing is what they 'l

"One thing is what they 'look' like, another is what they measure up to. The minimum is a 'de-glazing', but if the bores are already close to max in tolerances, re-size! From new that engine is known for its rattling piston noise, and being a '15' You get the HP only at the top of the RPM range.
Due to age restriction back in Norway (max 10HP below 16), we normally sold what was called 10XP/GT which in fact was the 15 with 9.9 carbs, or a reduction plate between carb and intake. It did not take long before they were all 15, and mostly run by youngsters on 10FT small dinghies easily doing 20 knots ++! They would run like that for years, until the kid got above age and got a bigger engine. Then Pa put it on his 15-16 ft fishing boat and few weeks later - pistons gone! The 9.9 the other way around.
Let the shop do a careful measurement of the cyl's, if close to the min allowed bore (top - mid -bottom), de-glaze and std pistons., if on the upper limit -re size."
 
"If a cylinder can be "cle

"If a cylinder can be "cleaned up" without exceeding the standard bore specifications, why would one want to bore it oversize? Running, say a four cylinder engine, with an assortment of standard and oversize pistons will not affect the running balance of the engine."
 
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