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How long between rebuilds

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How long do you guys wait before you do a top end bike is 01 kx 125 do alot of beach riding and some racing also what should compression be at

Edited by Logan_Young

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at about 150psi, it's due a topend or at least rings. You can usually get away with 1 extra set of rings for every new topend. Make sure you order the extra set of rings at the same time so yo don't forget exactly what piston you have in there. The crank is a hit or miss. Some will last 5 topends, some will last one. Just be sure to check rod tolerances every time you do a topend. But I've seen brand new cranks go out in less than 10hrs (wiseco).

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How do I check the rod tolerences kind of new to the whole race bike thing. I know my way around a wrench just not the bike. Im going to swap out the pistons and get a extra set of rings with it and next year do the crank and pistons.

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first things first, get a manual. you can get PDF manuals all over ebay. It will show you where and how to measure rod end play. If you're not sure how much time is on the crank, replace it anyway. That way YOU know. Also hit up the FAQ section then remember the search key is your best friend around here. We'll help anyway we can but repetitive questions warrant the famous...USE THE SEARCH KEY.

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Thats exactly what I was thinking when it hit me that i made 3 posts in 2 days but kind of new so ill start using it

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The life of the motor is about the riding style of the operator. Can only speak from personal experience here, but a top end on my KX250 lasts me at least one season and sometimes two. I’m the putt, putt trail rider everyone is yelling at to get out the way. The power valve on the KX never opens. The only reason I opened up the cases after 5 years was because the main seals went. At that time the crank was in specs but I installed a new one anyway. Even the main bearings were still smooth. In contrast, my brother who is a much more skillful rider than me, changes his bikes top end annually and sometimes twice a year. He generally rebuilds the crank every other year. He rides on the pipe, screams down the trail and is half asleep waiting for me by the time I catch up. He runs much higher RPM’s through the engine than I do.

If you have purchased a used bike, and have any doubts about the motor, rebuild and monitor from there.

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dont have any doubts...now. my cousin who I bought it from was doubtful about the motor so she rebuilt it top to bottom before I bought it last summer so I will be doing what I plan doing the top end this year and complete overall next year too bad all my bearings in the linkage is shot and my spokes too :bonk: But I ride that thing hard it runs good but something was bothering me is it normal for me to be able to start it by pushing on the starter by hand :smirk:

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But I ride that thing hard it runs good but something was bothering me is it normal for me to be able to start it by pushing on the starter by hand :smirk:

If you are a well muscled person with bulked up arms , well, yes. For the rest of us bean poles, no. Do you think the compression is low?

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define well muscled LOL :smirk: But it feels like it should have more resistance than what it does. When I tear it apart I will find out what my compression is like.

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Starting by hand??? Are you talking about pushing or using your hand on the kickstart? 125's are always easy to push start but using your hand...a good compression motor will hurt like hell.

Here's a vid of my sons 125 with 65psi. The topend had it.

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Wow twice a year that is alot and SAPPERS thats nuts mine isn't that easy to start but If the compression is low will it not idle? I would be tearing it apart and finding out myself but its in my garage behind my quads and snowmobiles :smirk:

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Wow twice a year that is alot

Not really. If we race hard during a year, every other weekend plus practicing everyday, I'll do a topend or rings in his 125 every 2 to 3 weeks or so. His summer days riding from 8am to 10 pm everyday. Burning up 10-15 gal. gas @ 6.50/gal everyday. This doesn't even include if he rides the 250 too.

So feel lucky doing it twce a year.

If it doesn't idle, turn it up. :smirk:

Edited by SAPPERS

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I was going to say twice a year is the absolute minimum. If you were putting around on trails that's one thing. But sand and track has those 125's screaming.

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I was going to say twice a year is the absolute minimum. If you were putting around on trails that's one thing. But sand and track has those 125's screaming.

Yea they really do scream in the sand and on the track what is it doing for RPMs on average on the track?

If it doesn't idle, turn it up. :smirk:

Idled fine when I first bought it idled like a dream actually.

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On the 125's the small idle screw should have a jam nut to lock it. Most are lost within minutes. So that might be why it lowers itself.

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