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Doh! Top end rebuild...

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Posted by: duncanstives---------------------

Have ridden about 2000 miles in the 6 months I've had my KDX... Time for a rebuild... I was freaking because I was worried it was beat and damaging the cylinder coating so I took it apart last night. After getting it apartm I have a couple questions (this being the first time I have ever delved into the internal parts of the motor):

Cylinder looks good to me... No goughes or anything in the cylinder wall but how do I know if the coating is intact? I understand its got a nickle/silcone electroplated coating that can be scraped off if you let the top end go too long...

Second question is simpler: Like an idiot (hence the "Doh!") I broke the nut off the end of the rod that operates the KIPS system trying to get it off (don't have it here with my but I just read somewhere its reverse threaed which would explain my issues). Cheapest place to source another rod?

Finally: I understand the piston is usually replaced when doing the top end? If so why? Its one fo the more exspensive parts and I can't really see anything wrong with it... The cost is not a huge deal its just that I hate to spend if I don't have to...

Thanks.


Posted by: _JOE_---------------------

The piston skirt can crack from fatigue if left in too long. This usually happens when the skirt gets worn allowing the piston the rock in the bore. Replacing them before this happens is definitely more cost effective.


Posted by: duncanstives---------------------

So is there a way to detect this wear or is it just a PM kind of thing?


Posted by: _JOE_---------------------

Kind of. You can measure the skirt at the base. That will give you an idea of how worn it is but it can still fracture even if it's not terribly worn. I always just replace the piston when it's apart, it doesn't cost much at all when compared to a replate/bottom end rebuild.


Posted by: duncanstives---------------------

Quote:
Originally Posted by _JOE_
Kind of. You can measure the skirt at the base. That will give you an idea of how worn it is but it can still fracture even if it's not terribly worn. I always just replace the piston when it's apart, it doesn't cost much at all when compared to a replate/bottom end rebuild.


Fair enough. I will go ahead and replace it. It seems worn anyway.... Measures about 65.75-65.9mm at the shirt (depending on where I measure and how much pressure I apply to the caliper) and the bore itself measures 66-66.04

Anyone have any insights on how to know if the plating on my cylinder is OK and where to get that powervalve rod?


Posted by: duncanstives---------------------

Did some searching... Article from HERE suggests it should be about $20 but people HERE selling it for $60....

Any better deals?


Posted by: reepicheep---------------------

Parts keep going up... the bike makers aren't making much on bikes anymore, so they have to recover elsewhere. You could try service honda (a board sponsor). They have always had fair prices.

For the plating, the rule of thumb (ha ha) I have always heard was that if you can feel something in the cylinder with your fingernail, it needs re bored.

I think the factory plating actually goes pretty deep. When I was talking to Eric Gorr about replating my shot 200 cylinder, he recommended going to the 220 even if I didn't want more power, as removing more material helps ensure the original factory tungsten disposition coating won't interfere with his Nicisil coating.



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