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Old 05 April 2010, 09:21   #1
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Mallory "half keystone" rings?

I think I've already answered this through a process of deduction, but I'll throw it into the pit for confirmation / discussion.......

When I got the new (Mallory) pistons for the Merc rebuild, the pistons have parallel slots for the rings, wheras the rings themselves are what I can only describe as "hybrid" - one face parallel, the other on a taper (keystone style). No "top" markings, so using conventional logic, will go in either way up.

But they're not symmetric, so presumably one side is favoured as the top. One was broken on reciept, and the replacement (again asymetric) had a dot. I'm not going to say on which face so as not to bias any opinions.

So, the question - Taper face towards the spark plug or the crank?
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Old 05 April 2010, 11:59   #2
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My guess would be tapered side toward the compression chamber. The pressure will be higher on that side, which will help push the ring against the cylinder wall.

Not that this is not based on *anything* other than reasoning (which may, of course, be subject to any number of fault inducing conditions, including, but not limited to: a poor understanding of mechanics, a serious lack of caffeine, residual alcohol, and a lack of sleep.


jky
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Old 05 April 2010, 12:00   #3
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Originally Posted by jyasaki View Post
My guess would be tapered side toward the compression chamber.
Ditto.
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Old 05 April 2010, 18:17   #4
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half keystone, taper to top.
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Old 06 April 2010, 03:54   #5
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Cheers Guys,

You have all confirmed my suspicions, and just for the record, the dot on the replacement ring is on the taper side, again, singing the same tune.


Right, time to start the rebuild.........
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