Author Topic: Rebuild Top end?  (Read 2515 times)

0 Members and 1 Guest are viewing this topic.

AZdirtRiDeR

  • Guest
Rebuild Top end?
« on: November 22, 2006, 02:34:10 PM »
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,

Offline Johnniespeed

  • Hero Member
  • *****
  • Posts: 575
  • The Thrill of Speed overcomes the fear of Death.
Re: Rebuild Top end?
« Reply #1 on: November 23, 2006, 01:51:02 AM »
  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
Spring is here and the Mighty 500 wants to ride.
 2004 KX500 E16
 Michigan has the best groomed and mapped trail system, check out the Cycle Conservation Club of Michigan trail maps.

Offline KXcam22

  • Hero Member
  • *****
  • Posts: 1,677
Re: Rebuild Top end?
« Reply #2 on: November 23, 2006, 08:55:09 AM »
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.

Offline demographic

  • Hero Member
  • *****
  • Posts: 825
Re: Rebuild Top end?
« Reply #3 on: November 23, 2006, 10:01:22 AM »
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.


Offline gowen

  • Resident Newbie
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 1,350
  • www.KXRiders.com
Re: Rebuild Top end?
« Reply #4 on: November 27, 2006, 01:31:57 AM »
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.

Offline c-152

  • Full Member
  • ***
  • Posts: 106
Re: Rebuild Top end?
« Reply #5 on: November 27, 2006, 11:58:06 PM »
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.
?There are only three sports: mountain climbing, bull fighting, and motor racing. All the rest are merely games.?
? Ernest Hemingway

"I want to leave this world the same way I came into it: Screaming and covered in blood."