The new breed of four-strokes have much shorter service intervals than the old XR style bikes we are used to. Despite the service interval recommendations in the manual a lot of folks who are racing these bikes are choosing to ignore them.
Under the heading a picture is worth a thousand words here's a graphic example of what tends to happen when you run the stock valve components too long. These pics are from a KXF 250 that I worked on yesterday.
If the springs and valves would have been changed more in line with the service intervals this wouldn't have happened. As a result the head is destroyed beyond repair, the barrel is junk, and the rod was bent and a bunch of other pieces are now scrap. Take specific note of the exploded tappet/bucket in the cam side view. Luckily the rider didn't get hurt when it let go. The interesting part is, with all this carnage the cam journal without an oil groove that people are worried about is in perfect condition.
The moral of the story is, if you are racing a 250F invest in an hour meter and pay attention to the service intervals.
Click the links below for the full size hi-res versions of the pictures
KXF Head & Piston
KXF Head close up
KXF Head broken bucket
KXF broken valve
Under the heading a picture is worth a thousand words here's a graphic example of what tends to happen when you run the stock valve components too long. These pics are from a KXF 250 that I worked on yesterday.
If the springs and valves would have been changed more in line with the service intervals this wouldn't have happened. As a result the head is destroyed beyond repair, the barrel is junk, and the rod was bent and a bunch of other pieces are now scrap. Take specific note of the exploded tappet/bucket in the cam side view. Luckily the rider didn't get hurt when it let go. The interesting part is, with all this carnage the cam journal without an oil groove that people are worried about is in perfect condition.
The moral of the story is, if you are racing a 250F invest in an hour meter and pay attention to the service intervals.
Click the links below for the full size hi-res versions of the pictures
KXF Head & Piston
KXF Head close up
KXF Head broken bucket
KXF broken valve
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