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I'm not an expert but those grooves look severe. I wonder if the piston broke a ring or something. Is it the same on both pistons? Can these engines be machined and cylinder walls sleeved or do you just have to replace the cylinders?
 

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Depending on how deep the grooves are, cylinders could be repaired like at Millennium Technologies in US and Honda has + 0.25 pistons and rings available for CRF1000 at least, if necessary. Certainly cheaper than new crankcases but definitely not an inexpensive rebuild.
 

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Depending on how deep the grooves are, cylinders could be repaired like at Millennium Technologies in US and Honda has + 0.25 pistons and rings available for CRF1000 at least, if necessary. Certainly cheaper than new crankcases but definitely not an inexpensive rebuild.
I wonder how one rescues ceramic-treated cylinders after a boring job?
 

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Is this a CRF1000 or CRF1100? The cylinders are different designs. The CRF1000 has a steel liner bore and the CRF1100 is a hard coated bore similar to Nikasil. The cylinder scouring looks like a typical over heating situation where the piston outgrows the cylinder or a low oil partial seizure. If not under warranty and it is a CRF1000 it can easily be bored if oversize pistons are available. It looks like a .25 mm overbore will clean this up. I have a cylinder boring machine and have bored thousands of motorcycle cylinders over the last 40 years.
 
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