Rebuild Top end?

[AZdirtRiDeR]

Are there specs somewhere for how many hours before you rebuild Top end.

I just read through the other post, and though very well done, didn't see how often it was needed.

Thanks,

[Johnniespeed]

  I too was wondering about this. I was not able to get a straight answer from anyone. I didnt want to ruin my cylinder by waiting too long, and didnt want to tear down my first new virgin bike too early.  What most people said was " when you notice a lack of power" or  "when it kicks over too easy"  Some people also rely on compressin readings, I have seen way too many guys get tripped up over faulty compression testers. A compression tester will vary its reading, depending on the spring pressure of the lower schrader valve. (word to the wise)
  I tore my upper end apart after I had put two hundred gallons of fuel through it. What I found was a perfect cylinder, perfect piston, excessive oil film everywhere and the piston rings gooey and sticking in the piston grooves. I decided at that point that I didnt need that much oil, so I discontinued 32 to 1 and switched to 40 to 1, I may even switch to 50 to 1 next year. I washed the power valves,beaded the ring grooves, replaced the rings and went back to riding with no more worries.  The cylinder head was never removed from the cylinder and I still have the virgin head gasket intact.
    It is very easy to remove the cylinder and piston, the only point of concern is the adjustment of the kips lever. Elsewhere on this site is information on how to shim the valves from overclosing using a ball bearing, once you get that figured out and how to adjust the lever, this job is super simple.
  Hope this helps, John

[KXcam22]

I simply waited until I noticed that it was a bit easier to kick over before I did my top end.  Lasted 13 years at 60:1.  The cylinder and powervalve were in near perfect condition with no wear or carbon buildup.  Piston and rings were worn (as expected). Piston was almost reusable - except for a small crack.  Installed a wiseco, set the powervalve minimum travel (important) and I was back in business.  I never did bother to do a compression check since it with the 500 it is fairly evident when there is enough compression. Maybe I should have. Cam.

[demographic]

In Eric Gorrs book he says that if you do a compression test after a rebuild then (using the same compression tester) when that figure had dropped by 20% you should rebuild it.

[gowen]

Eric Gorr is coming back for business (wahoo). That was a big factor in selling my KX too.. No more rebuilds. Either way, I go by the compression factor too.

[c-152]

I put a new set of rings in my 92 kx500 last winter.  According to the previous owner, it had never been rebuilt.  Everything was in good shape and there was no need for a piston.  The only issue was the powervalve needed cleaned from years of running 32 - 1.  I decided that was proof enough to bump up to 40 - 1.  I plan on rebuilding it every year because I am going to race it.  That actually might be overkill but it is so cheap and easy to do, it is worth it.