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There is no search function in the ask a member forum, but if you are a member (not sure if “offline” means a member or not), then you can go to the “active member forum” bar when you hover over “members only” on the top of the screen. There is a search bar there, but not under the plain “ask a member” forum page, which can also be accessed via the members only forum page. I could not find the piston ring set you speak of, but all of those motors are a similar size to my knowledge, and possibly have the same bore. Don’t bother replacing the piston rings unless they are bad enough that the motor cannot function. If you do replace them, this forum may be helpful. I also linked piston rings from a site that is named “oldmercs”, which I assume is owned or operated by one of the members here, and probably has enough knowledge about these things in addition to the fact that the part numbers match up.
https://www.aomci.org/forums/topic/mercury-ke4-piston-ring/
https://jetes-wgurh.volusion.store/product_p/39-21665.htm
"Outboards seem to multiply exponentially..........I find that for every finished project, there are two more waiting to be completed."
1 user thanked author for this post.
Otto gas engine works. Order rings by size. https://www.enginads.com/otto/
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.
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Piston ring part # 39-21665 application…All 1941 thru
Mark 7 modes with 2 inch bore
(1940 models use 2 wide rings)
Some later Merc use same rings,
If seller says ther rings will work, ask if he will take them
back if they do not,
With new rings you need to check end gap with ring in the cylinder it is to be used in,
Rule of thumb is 0.004 per inch of cylinder bore… better too loose than too tight.
If you order rings from OTTO
Gas Engine you have to measure
piston for ring size.
Cast iron rings will flex a bit and break if flexed to far. Been there done that.
Good LuckClamp ring between 2 thin boards in vise with just ends
exposed when using file to limit flexing/breakage,
Check end gap of ring at several points in cylinder bore to check wear. You can
calculate amount of wear using
difference between unworn bottom of cylinder by comparing end gaps and
math formulae for circumfrance
of circle. My exjperience has
been cylinders wear is least
at top and bottom and most in
area in between,
Cylinders often have a glaze
A light hone may help new rings
If cylinder bore is pitted as often happens when piston rings rusted stuck, find a
better cylinder. Do the same
for badly worn cylinder.
It is best to remove rings before removing a piston and
installing rings after piston
is installed on rod to avoid
crushing anti rotating pins
or breaking a ring,
Been there and done that also1 user thanked author for this post.
Green thumbs, like usual is right on! Also if you order rings from Otto make sure they have the relief cut that makes room for the locating pins in the piston ring groves.
dale
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I’ll second that Louis has the correct facts (Green Thumbs). Dave Bernard is also very experienced too. We are good friends & he taught me how to build a Mercury. Welcome to our club & Please when you get the new rings save the broken ones & use the factory end to clean the piston ring groove. Lightly drag in the groove to clean any carbon, it’s a perfect fit!
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