engine revs but under load makes no power

Mr rat

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Mar 12, 2020
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I was wondering if anybody here could help as i now have no idea what is wrong with my engine
basically I broke the top compression ring and the engine ate it.
after opening the engine i found the ring had shattered and fragments of it smashed against the head. looking at the cylinder wall it seemed undamaged minus a small scratch running up the wall that I could barely feel with my fingers. the piston was far more scratched up but nothing sanding couldn't fix. after replacing the rings and reinstalling the cylinder and heat cycling the new rings the engine now has almost no power it barely goes faster than 11km/h and once it hits that speed it makes a fourstrokey noises and refuses to go any faster even when going down hill the engine screams and doesn't rev up. with the clutch out however the engine goes straight to red line and returns to idle nicely. I have a feeling this could be bad compression as the bike used to be almost impossible to cycle from a stand still with the clutch engaged. now i can leave the clutch engaged and cycle to the engine running making me think it could have really low compression. does anyone have any ideas what could be wrong with the bike?
 

Mr rat

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Mar 12, 2020
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I should also mention spark issues could also be the problem as the spark wire fell out of the cdi but has been screwed back in and no arking can be seen at night
 

allen standley

Well-Known Member
Oct 22, 2011
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Bangor, Maine
After removing the cyl. did you flush the engine case of fragments? You say "looking at the cylinder wall it seemed undamaged minus a small scratch running up the wall that I could barely feel with my fingers."
The tiniest of fragments left in the engine case will immediately or eventually regurgitate through the engine and destroy whatever new Top End parts you replace. Me thinks you gotta start over.

Once top end is removed the best way to flush is to completely break down the case int seperate halves. Without doing that pressure wash Flush at the car wash and hope you flush all the broken pieces out.
 

Mr rat

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Mar 12, 2020
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I did try to get all fragments out however there is a good chance a few shards were left behind. If I take the cylinder off and it has eaten more shards would the damage be obvious?
 

Mr rat

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Mar 12, 2020
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And if when I do open it there is damage deeper than the coating is there any way of saving that cylinder or does it just need a new one?
 

allen standley

Well-Known Member
Oct 22, 2011
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Bangor, Maine
Also, There is not a problem had with these motors which has not been discussed / fixed through the information you will gain by being a member of this here forum. Be ready to learn lots. Don't throw money at it til you know what you are doing. By the way Welcome!
My opinion-- for what it is worth, whenever you experience a catastrophic top end failure such as you have, always replace the cylinder. Top End Kits are very reasonable.
https://www.amazon.com/JRL-Cylinder...id=1584010967&sourceid=Mozilla-search&sr=8-10
Remember to flush that case out Well! Other problems can't be addressed til you get a new Top End.
 

Mr rat

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Mar 12, 2020
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Thanks I've been reading the articles here for a bit but I couldn't find anybody talking about this so decided I'd ask. I'll take a look once I've got home and see how things look internally. Thanks for your help
 

allen standley

Well-Known Member
Oct 22, 2011
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Bangor, Maine
Haha thanks
Yup, a side note---Know that there are 2 cylinder and piston types. It's important to replace with what is on the engine new. Pistons have a high wristpin hole and a low hole, Cylinders have a 30mm intake manifold and a 40. (stud spacing @ the intake)
 

Mr rat

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Mar 12, 2020
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Not only that but going deeper one of the rings is seazed its definitely ate a shard of ring :(