If it has no compression it might only need a valve grind.. I'd take it apart and confirm what is worn, and whether the crank is good enough to take a new piston and rings(if they are needed).
1993 Polaris trail boss 350
I have a 1993 Polaris trail boss 350 with no compression. I’m not sure if I should leave it stock bore or bore it over. If so how much and what position and rings should I get
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I appreciate the help. What would I need to look for to ensure the crank is good enough to take a new piston?If it has no compression it might only need a valve grind.. I'd take it apart and confirm what is worn, and whether the crank is good enough to take a new piston and rings(if they are needed).
Yeah.. that's the tricky part..haha.. You need some experience with them really.
You grip the conrod tightly and try pushing and pulling it feeling for play, and that's best done by having one finger spanning the gap between rod and crank feeling for any movement between them, and you push the rod against the crank and roll it forwards and back feeling for any roughness and you rock it from side to side checking for play. All of that has to be done at the point on the crank pin where the wear takes place, and that place is where the rod would be pushing when the crank has rotated about twenty degrees after top dead center.
The one simple test is rocking the rod from side to side. If it moves about four mills it's probably still ok, but if it rocks so the piston pin moves six mills it is too worn.. Estimates based on assume length of conrod and bearing sizes etc.. If the rod only rocks two or three mills.. and has no rough feeling anywhere when you are pushing hard and rolling it back and forwards, it's probably ok. Sometimes the rods get hot and the piston pin gets loose.. that's rare and less of a problem.
If you have zero compression though, it's not likely to be caused by the piston.. (just saying)..
You grip the conrod tightly and try pushing and pulling it feeling for play, and that's best done by having one finger spanning the gap between rod and crank feeling for any movement between them, and you push the rod against the crank and roll it forwards and back feeling for any roughness and you rock it from side to side checking for play. All of that has to be done at the point on the crank pin where the wear takes place, and that place is where the rod would be pushing when the crank has rotated about twenty degrees after top dead center.
The one simple test is rocking the rod from side to side. If it moves about four mills it's probably still ok, but if it rocks so the piston pin moves six mills it is too worn.. Estimates based on assume length of conrod and bearing sizes etc.. If the rod only rocks two or three mills.. and has no rough feeling anywhere when you are pushing hard and rolling it back and forwards, it's probably ok. Sometimes the rods get hot and the piston pin gets loose.. that's rare and less of a problem.
If you have zero compression though, it's not likely to be caused by the piston.. (just saying)..
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