Replacing top end on KX85?

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Aug 2, 2001
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#1
I am hearing all these things about replacing the top end after 10/20 hours of riding. What you people mean by replacing the top end, could anyone explain this to me? How would I go about doing this on a KX85? Please help...
 
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Aug 2, 2001
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#2
Holy $#!T...

Are you telling me that you people spend $100 to replace the top end after 20 or so hours of riding? That would cost me like $1,000,000 a year. I ride everyday for about an hour, and usualy 4-5 on weekends... Man, when should I replace the top end on my KX85? ALso, do I need to replace it this often or what...
 
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Dec 10, 2000
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#3
Top-end replacement intervals can vary widely from rider to rider, depending on how hard you ride, how well you maintain your bike, engine size, etc. If you like to rev the snot out of your bike, the top-end will need replacing more frequently than a rider that rides more conservatively, if you neglect your air filter, don't run enough oil in your gas, etc...What I would reccomend is after you do your first rebuild and break it in, do a compression test, and write the result down. Repeat the test every few hours of riding, and once the engine has lost 10-15% of it's original reading, it is time for a top-end. In general, 20 hours is a long time on a piston in an 80 for someone that is racing and pushing the engine hard all the time, but someone that just casually trail-rides may get twice this or more. This is an area you don't want to push too long, because a piston failure from running it too long can become a very expensive repair job, costing several hundred dollars, instead of the 100 or so dollars replacing the top-end when it was due would have cost.
 
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Aug 21, 2001
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#4
If you do not plan on replacing your top end that frequently, you should do the most you can to keep your bike running good. If you clean your filter and change the oil in your bike frequently, this will help things last a little longer. I dont know how you are on bike maintence, but I would recomend trying to change your filter everyday after you ride ( or maybe every other day seeing as how you said you ride for only an hour). I would also recomend changing your oil 2-3 times a week. You could set up a schedule to change it after your weekend ride, sometime in the middle of the week, and then again before your weekend ride. It is very importand though that you at least change it 1 a week, and I mean at the very least. Another thing you can do to prolong changing a top end is to change the rings on the piston every 2 weeks, and then do the whole top end during the next two weeks. Or if you want ( im not sure if this one would be ok, maybe someone else can confirm this for me) you could do two ring changes before you actually did your top end. That would mean that you change the rings, than change them again 2 weeks later, and then 2 or 3 weeks later do the whole top end. Let my clarify that not everyone changes there topends all the time, so dont feel like an idiot if you dont. However, you do lose power, and it is a good idea to at least replace the top end a couple times a year. BTW evertime you change the rings, use new gaskets.
 
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#5
Originally posted by yamaracer747
I would also recomend changing your oil 2-3 times a week. You could set up a schedule to change it after your weekend ride, sometime in the middle of the week, and then again before your weekend ride. It is very importand though that you at least change it 1 a week, and I mean at the very least. Another thing you can do
What does changing the tranny oil in a two-stroke have to do with top-end wear? You should also only re-ring a piston once.