KX Riders

Maintenance & Technical => KX250 / KX125 => Topic started by: mustangfury on September 27, 2007, 10:58:02 AM

Title: How often rebuild?
Post by: mustangfury on September 27, 2007, 10:58:02 AM

I have a 93 kx 125.  Approx. how often do you usually have to rebuild the top end?

Title: Re: How often rebuild?
Post by: gowen on September 28, 2007, 01:40:53 AM

I usally shot for about every 20-30 hours with my 125s.

Title: Re: How often rebuild?
Post by: alan on September 28, 2007, 01:41:27 AM

I have always gone by compression to decide when to rebuild the top end. When it gets to between 75 to 80% it's time! :-D

Title: Re: How often rebuild?
Post by: hughes on September 28, 2007, 03:40:34 AM

Quote from: gowen on September 28, 2007, 01:40:53 AM

I usally shot for about every 20-30 hours with my 125s.

I agree that 20-30 hrs would be cool for the average person. If I was racing this 125 at a high level I would shorten that down to 10-20 hrs. 125 have alot of stress on them due to the fact they need to stay a high engine rpm to produce the power that is needed.

Title: Re: How often rebuild?
Post by: mustangfury on September 28, 2007, 04:02:39 AM

Thanks for the advice.  The last time I rebuilt it was due to lack of compression.  I think i might try going with that.

Thanks again.

Title: Re: How often rebuild?
Post by: gowen on September 28, 2007, 04:43:13 AM

You can measure by compression, but I try to veer away from that because I've seen 2 cases of pistons collapsing in the 125s due to excessive wear (30 hours) on the piston. He had great compression, rings were good, just the piston was warn out from over heating, over revved and just the normal things you usally do with a 125.

I'm pretty hard on my engines and I've never owned a stock 125 long before they hit the grinding block (144cc) and usally take about 5 hours back depending on how hard I run them during the season. Inspect it often if you are going to keep the piston there for awhile, it will develop hairline cracks around the wrist pin and so forth and you will never know by compression, it will nuke the motor (and I mean everything) if the piston comes to pieces.

Title: Re: How often rebuild?
Post by: hughes on September 28, 2007, 04:45:55 AM

Good advise. Inspection is key.

Title: Re: How often rebuild?
Post by: mustangfury on September 28, 2007, 03:07:25 PM

I usually inspect the piston, cylinder, etc. about every 5-10 hours.  I measure the Cylinder wear, check for scoring, check the ring end gap, the piston wear, the piston cylinder clearance, and the piston diameter.  If everything looks good, I just put the thing back together.  I was just wondering if there was an approximate time that things lasted before they need to be replaced, so I'm not inspecting or replacing things, that need to be, more or less than needed.

Thanks.