I recently did the top end of my wr200, with a replated barrel, piston kit, and small end bearing. After the first serious ride I noticed scoring in the barrel and on the piston but I am struggling to find a reason.
The is a groove in the piston directly on the centre of the exhaust port which starts at the bottom of the skirt and runs up the piston about 15mm, the are two marks on the barrel which coincide with the ring ends, minor scuffing elsewhere. The was a tiny section of exhaust valve which had broken away where the two halves meet.
The piston clearance is about 80 microns ( 3 thou ), ring gap and side clearance all good. The bike was carefully run in.
I noticed that the piston pin does not have any axial clearance from the pin clips, and when I stripped the bike I noticed that the pin clips had rotated about 90 degress from the position I installed them in. The OEM piston pin could slide between the pins about 1mm ( 40 thou ). Finally my question, is it possible that the piston pin expansion distorts the piston causing it to foul the bore. How much axial clearance should there be?
The is a groove in the piston directly on the centre of the exhaust port which starts at the bottom of the skirt and runs up the piston about 15mm, the are two marks on the barrel which coincide with the ring ends, minor scuffing elsewhere. The was a tiny section of exhaust valve which had broken away where the two halves meet.
The piston clearance is about 80 microns ( 3 thou ), ring gap and side clearance all good. The bike was carefully run in.
I noticed that the piston pin does not have any axial clearance from the pin clips, and when I stripped the bike I noticed that the pin clips had rotated about 90 degress from the position I installed them in. The OEM piston pin could slide between the pins about 1mm ( 40 thou ). Finally my question, is it possible that the piston pin expansion distorts the piston causing it to foul the bore. How much axial clearance should there be?
