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Author Topic: M90 Piston rings  (Read 238 times)

yozhek

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  • Location: Somerset, England
M90 Piston rings
« on: February 05, 2020, 05:41:57 pm »
Not sure if this will be of any help as the stock M90 O ring piston seal seems tough as old boots, but just for the heck of it i fitted a piston ring to mine, OS engines part number 25303400 fits the bore perfectly and there is plenty of room on the piston land to machine a 1mm groove for the ring between the crown and upper o ring groove. 
I was a bit skeptical if it would work well or not, but it is perfect, just as good compression as the O ring and no extra drag.
Kind regards
Ade
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Nick

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Re: M90 Piston rings
« Reply #1 on: February 05, 2020, 10:41:52 pm »
Thanks for the tip, have saved it for future reference. By the way, Welcome to the forum  :)
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Nick

yozhek

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Re: M90 Piston rings
« Reply #2 on: February 06, 2020, 04:14:57 am »
Thanks Nick :-)
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Belugawhaleman

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Re: M90 Piston rings
« Reply #3 on: February 06, 2020, 05:16:12 pm »
Interesting. Thanks for the tip :)
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PAUL
Civilization is the limitless multiplication of unnecessary necessities.

70Rcode

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Re: M90 Piston rings
« Reply #4 on: February 06, 2020, 11:15:44 pm »
Just wondering,...the RC model airplane OS engine blogs all make a big deal about maintaning a properly Crosshatched, honed, roughed up cylinder wall for propper metal piston ring breakin & compression seal ....i noticed my new M90 series engine has a very smooth, hard, rubber o-ring compatible cylinder wall finish. After M90 metal ring conbersion, will the new ring breakin & seal properly to the smooth bore ?
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yozhek

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Re: M90 Piston rings
« Reply #5 on: February 07, 2020, 03:42:32 am »
Hi 70RCode,
I was thinking there would be a problem bedding the ring in myself, but mine acheived very good compression after a 10 minute run.  I am not sure how a cast iron ring will work with the stainless bore but so far so good, no friction issues or black oil residue to indicate anything bad occuring.
The most important part is machining a groove in the piston that is smooth and flat sided parallel to the ring side so the ring can seal against the piston groove sides otherwise the seal will be poor.
Kind regards
Ade
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