When to do top end?

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#1
I have a 1992 KDX200 and the top end is sounding noisey. (compared to a Gas Gas trials bike) It has 2800 miles and so I was thinking it may need a new piston. However, I checked the compression and it is 180 PSI. (It was 180 PSI when it had only 180 miles too). Is a good compression reading enough to prove that the top end is good?
 

Hucker

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#2
From reading other posts, sometimes carbon can form on the top of the piston and therefore give you a higher compression reading than what is actual fact. Seeing that there is 2800 miles on it, I don't think a top-end would hurt :)

Hope this helps....
 

Thumper-meister

#3
I suggest you do a compression test. If you can't get it to read over 100 in around 4 kicks, you are due for a new top end
 

Hucker

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#4
Originally posted by Thumper-meister
I suggest you do a compression test. If you can't get it to read over 100 in around 4 kicks, you are due for a new top end
In his original question, he says its up around 180psi.
 
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#5
A compression test on a 2 stroke will tell you squat. Well that’s not totally true but close enough.

My guess is you are well due for rings at least & the powervalves will be gummed up & need disassembly for cleaning. Don’t be surprised if the gears on the top (LHS esp) have stripped.

Dig in there & have a look, it’s real easy so go for it. Do a search on powervalves & pistons & you will find all you need to know. Just remember anything you find wrong is a possibility for improvement.