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Old 01-30-2008, 09:43 PM
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Default Piston ring stuck to the piston! WHY?

Just picked up a ktm sx 125 02, it was a pro action race bike, 1 hour on a new top end and the guy couldnt get it started after it cut out on him, got a four stroke sat in the garge for over a year... now i have it

Took the head off to find the powervalve seized, so lubed it up got it working.

Next i found why it wouldnt start and was lacking compression! The ring was stuck in the groove of the piston! I cant seem to get it out! But the piston still looks perfect, it as if were the ring splits has wedged together..

I will need a new ring.. so i think i will just snap it then see how the piston is!

Hopefully i just need a new ring.

Just wondering why this would happend.. bad ring ends? Or ran in too hot and kinda fryed together?

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Old 01-30-2008, 11:05 PM
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Default Re: Piston ring stuck to the piston! WHY?

Maybe it got real hot or something.
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  #3  
Old 01-31-2008, 06:06 AM
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Default Re: Piston ring stuck to the piston! WHY?

By the sounds of it, you better be gettin' a new piston too.
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Old 02-01-2008, 09:15 PM
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Default Re: Piston ring stuck to the piston! WHY?

Quote:
Originally Posted by AJ_YFZ View Post
By the sounds of it, you better be gettin' a new piston too.

Definately get yerself' a new piston. A new ring likley won't fit into the groove anyway.
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Old 02-01-2008, 09:35 PM
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Default Re: Piston ring stuck to the piston! WHY?

Quote:
Originally Posted by jrsturn View Post
Definately get yerself' a new piston. A new ring likley won't fit into the groove anyway.
Yeah orderd a full top end kit!
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Old 02-01-2008, 10:04 PM
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Default Re: Piston ring stuck to the piston! WHY?

If the ring gap is under gap spec thermo expansion causes the 2 ends to be smashed together. The expansion further and expands out on the cylinder cause more pressure and heat in essence welding the two ends together.
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Old 02-02-2008, 02:10 PM
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Default Re: Piston ring stuck to the piston! WHY?

did u check the ring gap?
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Old 02-06-2008, 07:32 AM
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Default Re: Piston ring stuck to the piston! WHY?

If it got THAT hot as to fuse the rings ends together, there would be other indicators of heat and friction on the top of the piston and the cylinder walls. That could be true and we just have not seen the pics.

I think something else is up.

Otherwise, I agree with everyone else.
Disassemble completely, put a complete new top end in it and start over. Make sure to check the ring end gap and adjust if it is out of spec.

Since this was a race bike, it's very important that you find out what mods where made to the engine.

Was the bore changed? If so, to what and
Was the compression changed? If it has been bumped up a bit, you better be feeding it race fuel.

Good luck.

Ian
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Old 02-06-2008, 07:43 AM
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Default Re: Piston ring stuck to the piston! WHY?

Not heat but heat, pressure and friction. No I guess it was from the Super glue..
No you wouldn't necessarily see it in the head or piston but you should see the scarring in the cylinder.
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Old 02-06-2008, 07:57 AM
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Default Re: Piston ring stuck to the piston! WHY?

Quote:
Originally Posted by dhighlan View Post
..... heat, pressure and friction..... you should see the scarring in the cylinder.
Agreed. I don't think I've ever seen a fused ring without some evidence in the plating. Just me,

I was thinking about combustion chamber evidence because he also said that the power valves were locked up.

Ian
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Old 02-06-2008, 08:03 AM
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Default Re: Piston ring stuck to the piston! WHY?

All I am saying is the expansion without adequate gap will cause the ends to wedge together. He was wondering what was going on here, the only way the 2 could be together is insufficient gap.
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Old 02-06-2008, 08:25 AM
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Default Re: Piston ring stuck to the piston! WHY?

The ring is made of fairly hard stuff, I doubt if the metal fused. If the ring end gap was non-existent then it's likely that fuel oil mix has seeped between the ring ends then carbonised due to the heat, this would cause them to be literally cemented together by the hard carbon.

Either way, check that the ring end gap is in spec when you install your new top end...
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Old 02-06-2008, 08:32 AM
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Default Re: Piston ring stuck to the piston! WHY?

Hi guys,

well the bikes been bored to a 58mm, had to specially order a top end kit, not bad for $125 ... weisco aswel!

The crank has 27 or at least i think its 27 i will check again later!

And the thing is freshly re-built!

I will get pics of the tope end and piston today and show you what i mean. the ring gap isnt welded, its just stuck in the groove somehow. like its expanded in there? Its wierd!
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Old 02-06-2008, 08:38 AM
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Default Re: Piston ring stuck to the piston! WHY?

Quote:
Originally Posted by Rocky_mx View Post
Hi guys,

well the bikes been bored to a 58mm, had to specially order a top end kit, not bad for $125 ... weisco aswel!

The crank has 27 or at least i think its 27 i will check again later!

And the thing is freshly re-built!

I will get pics of the tope end and piston today and show you what i mean. the ring gap isnt welded, its just stuck in the groove somehow. like its expanded in there? Its wierd!
Again, it's probably just baked in there with carbon, either that or the heat has distorted the alluminium groove to an extent...
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  #15  
Old 02-06-2008, 09:02 AM
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Default Re: Piston ring stuck to the piston! WHY?

Quote:
Originally Posted by dhighlan View Post
All I am saying is the expansion without adequate gap will cause the ends to wedge together. He was wondering what was going on here, the only way the 2 could be together is insufficient gap.
Again, agreed.

It's tough to convey tonality in text I guess.

I missed where he mentioned the ends of the ring.

In reading his words literally, I read "stuck in the groove". I was thinking about the stuck power valves and looking for correlating reasons why the ring would be stuck in the groove and went in a direction carbon/foreign matter fusing the ring to itself and the ring land etc.

Truth is, I guess we need more info. Was the ring able to float in the ring land but could not be removed because the ends were fused together? Or.. Was the ring "stuck" in the ring land. 2 different things.

We need pics and info to help him diagnose the problem.

End gap is a likely cause...Agreed. And, it could be other things as well.

Ian
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