2016 Ktm 150sx

pigpen203
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pigpen203
Has anyone heard of the ring hitting the powervalve or am i just that unlucky? The top end only had 6 hours before this happened, it scarred the cylinder pretty bad but luckily the part of the ring that broke went into the pipe. Is there something i should check when i finally get it back together or was it just a rare thing?
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Rockinar
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Rockinar 3/10/2017 1:54am
3/10/2017 1:54am Edited Date/Time 3/10/2017 2:02am
You say "the top end only had 6 hours". So you did a top end on it recently before this happened?

I don't think it hit the power valve. I bet your ring end gap was not set correctly or not at all. It needs to be set correctly AND filed evenly. If not, it does not have any relief when compressed, or it will have uneven relief (buy a ring end file), and it will drag on the cylinder wall and catch on the exhaust port..........SNAP. Also make sure the ring is not in upside down. There's a top and a bottom to the ring. Also there a notch on the piston where the ring ends go. The ring MUST be on there. This is to prevent the ring from rotating while on the piston and letting the end of the ring from catching on the exhaust port.


I'm betting one of these was the cause, not from it mysteriously catching the valve.


Get a new cylinder and new piston, correctly set your ring end gap with a ring end file to the correct specs in your service manual. make sure the ring is not in upside down, and end gaps are in the notch. It should run like a well oiled top.

Good luck.





HenryA
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HenryA 3/10/2017 2:28am
3/10/2017 2:28am Edited Date/Time 3/10/2017 2:29am
What kind of piston/ring did you run?
pigpen203
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pigpen203 3/10/2017 11:40am
3/10/2017 11:40am
Rockinar wrote:
You say "the top end only had 6 hours". So you did a top end on it recently before this happened? I don't think it hit...
You say "the top end only had 6 hours". So you did a top end on it recently before this happened?

I don't think it hit the power valve. I bet your ring end gap was not set correctly or not at all. It needs to be set correctly AND filed evenly. If not, it does not have any relief when compressed, or it will have uneven relief (buy a ring end file), and it will drag on the cylinder wall and catch on the exhaust port..........SNAP. Also make sure the ring is not in upside down. There's a top and a bottom to the ring. Also there a notch on the piston where the ring ends go. The ring MUST be on there. This is to prevent the ring from rotating while on the piston and letting the end of the ring from catching on the exhaust port.


I'm betting one of these was the cause, not from it mysteriously catching the valve.


Get a new cylinder and new piston, correctly set your ring end gap with a ring end file to the correct specs in your service manual. make sure the ring is not in upside down, and end gaps are in the notch. It should run like a well oiled top.

Good luck.





yes it had a new top end. I made sure the rings were in correctly but i did not know i had to check the ring gap. I will be doing that next time.
pigpen203
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pigpen203 3/10/2017 11:41am
3/10/2017 11:41am
HenryA wrote:
What kind of piston/ring did you run?
I run the vertex piston and rings. (dual ring piston)

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miketherider 3/14/2017 11:06am
3/14/2017 11:06am
I've heard cases where vertex ring gaps are not correct based on OEM specs. Always check twice.
Rockinar
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Rockinar 3/14/2017 11:47am
3/14/2017 11:47am
pigpen203 wrote:
yes it had a new top end. I made sure the rings were in correctly but i did not know i had to check the ring...
yes it had a new top end. I made sure the rings were in correctly but i did not know i had to check the ring gap. I will be doing that next time.
Setting ring end gap is important. It allows some relief on the rings when thing heat up and expand. If they don't have any relief, they will drag on the cylinder, break or even cause a seizure. This is even more important on new bikes that will have tighter tolerances.

pigpen203
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pigpen203 3/14/2017 5:49pm
3/14/2017 5:49pm
Thank you guys for all the help I will definitely be checking the ring gap now. It was a expensive lesson but at least now I know!
Rockinar
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Rockinar 3/14/2017 6:00pm
3/14/2017 6:00pm Edited Date/Time 3/14/2017 6:01pm
pigpen203 wrote:
Thank you guys for all the help I will definitely be checking the ring gap now. It was a expensive lesson but at least now I...
Thank you guys for all the help I will definitely be checking the ring gap now. It was a expensive lesson but at least now I know!

Another good video about 2 stroke piston rings. You have to make sure the ring ends are on the pins on the back pins. It prevents the rings from rotating on the piston and catching on the ports. You don't have this with 4 strokes. 4 stroke rings can float around.


https://www.youtube.com/watch?v=xyedUaK4hmI


2 strokes are really basic, but there's a couple critical steps.

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