Can you believe that 2 different pistons in block

merc20076

Petty Officer 2nd Class
Joined
Sep 9, 2009
Messages
156
Ok well I finally received my parts yesterday (piston rings and powerhead gaskets) to play in my first 4.5HP Evinrude that had compression problems. (I have a 4.5 Johnson also in good conditions)


Well when it's time to put in the news rings in, one set doesn't fit at all. The grooves are not the same size than the other one. Price for a piston is a 55-60$ + I have to get the connaecting rod in which does not seem easy to put in.

I guess now my project is no longer gonna work:mad: I think I'll keep the powerhead gaskets to replace some on my Johnson.
 

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garzilla

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Oct 24, 2010
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174
Re: Can you believe that 2 different pistons in block

Not sure about the boat pistons...but I had a snowmobile that had two totally different (sized) pistons in it....LOL

Put it back together, and rocked it the way it was for years...

P.O. must have gotten cheap and only replaced the one.

I'd have thought It'd shook itself apart like that, but it ran smooth as duck butter......
 

1946Zephyr

Vice Admiral
Joined
Oct 21, 2008
Messages
5,556
Re: Can you believe that 2 different pistons in block

Yea, I read a lot of posts here of guys boring only 1 cylinder in an outboard, which I think is odd. When I rebuild engines, I like everything to be uniform, so when the next nig nog has to go into it, he won't run into this issue.:cool:
 

pcrussell50

Petty Officer 1st Class
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Sep 21, 2008
Messages
296
Re: Can you believe that 2 different pistons in block

I read in the seloc manual that it is or was considered ok to run two different bore sizes because OMC already accounted for that by making the replacement overbore piston the same weight as the stock bore piston. Apparently, needing to replace a single piston is/was common enough that OMC made it so you would not have to do a complete overhaul to return the motor to satisfactory service.

if you're super anal, you might not be too happy with this, even though OMC is.

-Peter
 

samo_ott

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Joined
Jun 18, 2006
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Re: Can you believe that 2 different pistons in block

Huh.
 

F_R

Supreme Mariner
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Jul 7, 2006
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28,195
Re: Can you believe that 2 different pistons in block

I have rebuilt a bazillion motors with one or more oversize pistons, and it doesn't matter. However, the queston here was concerning the ring width. That in itself shouldn't matter if he can find the right rings for both pistons. But are the pistons otherwise the same? I see ports on one, but not the other.
 

merc20076

Petty Officer 2nd Class
Joined
Sep 9, 2009
Messages
156
Re: Can you believe that 2 different pistons in block

But are the pistons otherwise the same? I see ports on one, but not the other.

Not quite the same, you see their difference in the pic. And it's impossible to rebuilt like it was, one of the ring broke off (top piston on pic). I've checked on boats.net where I got the parts and there were 2 differents rings set.
 
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