Freddo Frog
Recruit
- Joined
- Jun 1, 2013
- Messages
- 2
I have been rebuilding my 1985 Yamaha 140AETO, which is a European / Asian spcific model that is similar to the 130hp US motor of the same age.
When I came to replace the piston rings on the first cylinder, I removed the old rings and deliberately broke one to fashion a scraper to clean the cabon deposits from the piston grooves.
The new ring set had one ring marked with a red strip, which on close inspection turned out to be a keystone (tapered) ring. I would expect that this would fit the top groove (closest to the spark plug) and the parallel ring should fit the bottom groove.
However, when I came to fit the bottom ring, it seemed far too tight for the groove, even after some light cleaning with a jeweller's file. The ring would only go about 1/3 of the way to the bottom of the groove.
I closely looked at the old rings and discovered that both top and bottom rings were in fact tapered, and found the same on a second piston that I removed.
The outer thickness of the new and old rings are identical, and the tapered new ring fits the piston nicely.
It appears that either this is an intentional subtle design difference between the Euro/Asian engine and the US model, or that the engine was previously rebuilt by someone who didn't pay careful attention (I have owned the engine since 1994).
Can anyone comment on this?
The lower groove seemed very very tight even after quite some work scraping with the old ring and jeweller's file, could it be possible that an initially parallel groove had deformed over the last 20 years to such an extent that a parallel ring would no longer fit?
Would Yamaha have any reason to make such a minor design adjustment between the US and non-US models?
Was there a design change after 1985 to move to one parallel and one tapered ring?
When I came to replace the piston rings on the first cylinder, I removed the old rings and deliberately broke one to fashion a scraper to clean the cabon deposits from the piston grooves.
The new ring set had one ring marked with a red strip, which on close inspection turned out to be a keystone (tapered) ring. I would expect that this would fit the top groove (closest to the spark plug) and the parallel ring should fit the bottom groove.
However, when I came to fit the bottom ring, it seemed far too tight for the groove, even after some light cleaning with a jeweller's file. The ring would only go about 1/3 of the way to the bottom of the groove.
I closely looked at the old rings and discovered that both top and bottom rings were in fact tapered, and found the same on a second piston that I removed.
The outer thickness of the new and old rings are identical, and the tapered new ring fits the piston nicely.
It appears that either this is an intentional subtle design difference between the Euro/Asian engine and the US model, or that the engine was previously rebuilt by someone who didn't pay careful attention (I have owned the engine since 1994).
Can anyone comment on this?
The lower groove seemed very very tight even after quite some work scraping with the old ring and jeweller's file, could it be possible that an initially parallel groove had deformed over the last 20 years to such an extent that a parallel ring would no longer fit?
Would Yamaha have any reason to make such a minor design adjustment between the US and non-US models?
Was there a design change after 1985 to move to one parallel and one tapered ring?