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is setting the ring gap on an OEM piston essential??

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hey guys, i just rebuilt my 2009 250SX with an OEM piston kit and didn't set my end gap.

Will it work properly without setting it or do I need to pull the bike apart to set it to whatever its supposed to be? :smirk:

Thanks, Mike.

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Um I have never rebuilt a 2 stroke engine before, but have read my manuals from front to back a few time and read numerous how to's on it, and I would say yes you need to open her back up and set the ring gap properly. If it's too small, when the ring gets hot and starts to expand, the ring may overlap and break or get hung up on something cause massive damage to your piston, cylinder walls, bottom end and anything it may come into contact with. If the gap is too big, the ring may not seal properly, mess with engine compression and all the other gases and stuff moving around the engine while operating.

So YES get the gap right!!!

Ray.

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You already know the "right" answer.

However, I have never found any new ring to be too large (gap too small), EXCEPT on a freshly bored cylinder. A worn cylinder should be OK, as the rings are probably manufactured to new tolerance.

Then again, my experience is only based on about 12 different rebuilds.

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I've check the gap on all my 2 strokes bikes for probably 25 years or so, but have yet to ever need to adjust any of them, personally I would just ride it!!

Mike

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I've check the gap on all my 2 strokes bikes for probably 25 years or so, but have yet to ever need to adjust any of them, personally I would just ride it!!

Mike

I agree. With a KTM piston and rings you should be ok.

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Last set of rings I did on my 300 requires a bit of a grind to set the minimum gap. Fail to check and the possibility is there that you catch a ring on the power valve or a port. It is a simple check and fix and an expensively lame reason to loose an engine

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I did my '08 300 top end this winter with a Vertex Piston & Ring Kit (OEM). Had the cylinder replated and honed.

Out of the box...Ring end gap was exactly perfect...right in the middle of the tolerance range.

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I agree. With a KTM piston and rings you should be ok.

"Should" to me means "hopefully". It could turn out to be a pretty expensive hope.:smirk: Hope, see where that got us with Obama, haha.

Last set of rings I did on my 300 requires a bit of a grind to set the minimum gap. Fail to check and the possibility is there that you catch a ring on the power valve or a port. It is a simple check and fix and an expensively lame reason to loose an engine

Agreed!

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In 25 years, I've never had to adjust one. Imo It's not worth pulling it back apart.

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In 25 years, I've never had to adjust one. Imo It's not worth pulling it back apart.

+1

I'm w/ puffer on this one.

I think it should be fine. BUT!!!! It's your call. If you're losing sleep over it, then pull the cylinder, pop off a ring and check end gap in the bore.:smirk: It isn't tough to do...as you know...just time consuming.

-Jay

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Sometimes.....It's better to be safe than sorry. Who knows?

imagesCAJYK71U.jpg

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If you're a member of KTMTalk check this thread out. I'm not saying it was a ring gap issue but sure does look like a possible culprit. I'm no expert but my philosophy is better safe than sorry. I'm sure its an OCD thing, like me changing my tranny oil after damn near every ride.

http://ktmtalk.com/index.php?showtopic=422170&hl=inspect%20top%20end&st=0

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yeah just pin it. as long as you didnt line up the gaps you should be good.

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Is it even possible to line up the gaps?

My piston had pins that located the gaps.

I Didnt check ring gap. Just figured that the rings would be slightly tight on a new bore and mine was used. I would agree that they "should" be checked. But if you have ran it a bit then you are probably ok.

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Well I rode it without checking it, and it was fantastic! :lol::smirk::lol:

warmed it up completely, soft riding for a few minutes and then full throttle up hills in mid revs. There's more power and its not blown up :smirk:

quick question though :lol: there's this weird sound at high revs with low throttle that's always been there. its a weird scratching? sound. anyone had this before? Its not due to not setting the ring gap because its been there for years but i've barely ever been in high revs with not much throttle :lol: so it hasnt annoyed me untill now.

Mike. :prof: thanks for the replies guys :lol:

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"Should" to me means "hopefully". It could turn out to be a pretty expensive hope.:smirk: Hope, see where that got us with Obama, haha.

Agreed!

Ok! I'll rephrase that. :smirk: I've been rebuilding/racing dirt bikes for almost 40 years. I've ridden KTM's for the last twelve years. In that time I've never seen a stock KTM piston ring that had the end gap wrong on it.

Does that mean it can't happen? No. What's the chances of it happening? Very slim.

So, since the guy had the engine together, with those odds, I would not pull it back apart.

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Why bother posting since you were going to do it your way anyhow...:smirk:

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Why bother posting since you were going to do it your way anyhow...:smirk:

Because if everyone thought it'd blow up, then I would of taken it back apart :smirk:

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Well I rode it without checking it, and it was fantastic! :lol::smirk::lol:

warmed it up completely, soft riding for a few minutes and then full throttle up hills in mid revs. There's more power and its not blown up :smirk:

quick question though :lol: there's this weird sound at high revs with low throttle that's always been there. its a weird scratching? sound. anyone had this before? Its not due to not setting the ring gap because its been there for years but i've barely ever been in high revs with not much throttle :lol: so it hasnt annoyed me untill now.

Mike. :prof: thanks for the replies guys :lol:

I know you said "scratching" but could it be a pinging sound, like a lean pilot?

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I know you said "scratching" but could it be a pinging sound, like a lean pilot?

I'm at sea level, 20 degrees Celsius, 50:1 oil ratio and using a JD jet kit. The bike used to have a 42 pilot jet, but I put in the JD's recomendation of 38 just because it said to, but that's generic because even if it was 50 degrees at 8 000ft it still says to put in the 38 pilot jet.

I'll set the air screw. would this show if I need a bigger pilot jet because it would be almost fully open or almost fully seated?

however I don't think its a pinging sound and neither does dad.

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