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What can cause a piston ring to drift off the key? A friend of mine has an old kawi 350 triple, and he's running suzuki pistons, with the barrels bored out to match. Not sure what size the pistons are. His bike developed a "ticking" nose last night with only 80 something miles on the new top end. We found the the right piston had drifted off the key. We put it all back together again making sure everything was were it should be. When we kicked it over the nose was gone. But as soon as we started the bike it came back right away. Any thoughts???
 

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Maybe I'm missing something....I've put together a lot of engines...never used a "key".

The piston can't "drift" anywhere but up and down. Now the wrist pin might move back and forth and hit the cylinder walls if the wrist pin keepers are not installed correctly....or not installed at all.

JohnnyB
 

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Branson,

aircooled two strokes have pinned piston rings (perhaps the key he is referring to but I think he is talking about the land) to keep the gaps from lining up while the bike is running. Two stroked run such a loose tolerance (as compared to 4 strokes) that the initial break in is vital to engine life.

McB,

First which ring drifted? The first thing I thought of was the gap tolerances are out (if a ring has too much gap then as soon as you fire it it will want to fold on itself), the second I though is that the ring itself is out of spec and you need a new ring, Third I thought is that the ring land is damaged. Once the ring has "drifted" or otherwise bent then it is junk and you need a new ring - you can't use the old one.

What model suzuki is he using pistons from? T250? GT380?



Edited by - Geeto67 on Apr 24 2007 2:37:37 PM
 

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assuming you mean the piston ring is rotating in the groove? maybe the locating pin does not stick out far enough to keep the gap where it should be. if you replaced the rings only without replacing the pistons, and then honed the cylinders, you may wind up with enough clearance to spin a ring. if this is what you mean?

if at first you don't succeed, use a bigger hammer
 

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yeah, what geeto said.

if at first you don't succeed, use a bigger hammer
 

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if its bored too loose, you could have piston slap. if its a 4 stroke.

jc

aaron sent my wheel!
 

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Damn...someone post a picture of that shit.
Never seen such a thing.....course I've had about 1 two stroke apart in my whole life.
JohnnyB
 

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What, JB, A photo of the piston with the ring gap tit in the ring groove?

It surprised the poop out of me the first time I found out about it too. It was unbelievable. i finish putting the pistons on the rods, put the barrels on, bolted the heads on, and BANG. the engine is DONE. No gears, cams, chains, valves, . . . COOL.
 

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JB,
Two stroke pistons have an index pin in each ring land to keep the ring ends properly aligned. Without the pins the rings could rotate, thus allowing a ring end to snag a transfer port as the piston passed by. The index pin and ring end gap are positioned in the cylinder where the end gap's path is solid cylinder wall from top to bottom.

Cheers, Bret @ Glass from the Past

Edited by - bret on Apr 24 2007 10:10:04 PM
 

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if the pin is there in the piston, the ring will usually have a 'bevel' which slips under the pin...it is highly unlikly that the ring would rotate on the piston, really bad things happen when a ring finds a port edge..I have seen it, but in motors with really, really big ports (big single 2-strokes) and really, really worn rings, the rings expand (kind of buldge out) over the port and clip the top edge...very messy, very noisy, very expensive.

d.
 

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I have seen the pins worn off enough to let the rings rotate and it't not pretty.
The 4 strokers will carefully space the ring gaps at 120 degrees apart which doesn't really matter. I have put rings on so the gaps all line up and after running a few minutes they are all in different positions. If they didn't move 2 strokes wouldn't need locating pins.

FC
 

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I've always wondered if they move around on a 4 stroke. Seems like that would kind of negate the whole breakin proceedure where the ring is supposed to match itself to the hone pattern etc.

I've seen engine run with rings installed improperly where the end of the ring has worn a shiny spot on the wall....in one place, so it can't be moving too much.
JohnnyB
 

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I personally, would like to get the definitive word on whether or not 4 stroke rings move. I think they do.
 

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I hope not...I go to a lot of trouble to put the ring gaps in certain places. You'd think if they spent their time rotating around that it would wear out the ring grooves pretty quick. I know the 3 piece oil rings don't seem to move.
Iron rings rotating in an aluminum piston would you'd think wear out those grooves...or at least show signs on the groves that they've been rotating. I've seen small blow by carbon marks on pistons where the gaps are....so they have to sit in one place long enough to do that.
JohnnyB
 
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