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Top end time...why not just rings?

Joined
May 23, 2000
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#1
I've had my 1990 KDX 200 for many years now and it's been the best bike I've ever had. I know it must need a top end replacement, just because of the mileage I've put on it, even though it runs fantastic. I plan to buy the piston/rings set, but I'm just curious, why I can't just put a set of rings in it?
 
Joined
Mar 27, 2007
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#2
There's no reason that you can't just put rings in it, as long as the piston is still in good shape. I'm of the opinion though that once the top end is torn down, it's easier just to spend the extra bit of money and put a piston in it as well and do it all at once.
 
Joined
Aug 16, 2004
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#3
Over time the skirts of a piston take a real beating. Forged pistons will begin to collapse, cast pieces will fatige and eventually break. It's best to just replace them when the number of hours gets high, can save a lot on the long run.

We just had this discussion at work today. A buddy of mine had an older YZ250 that "Runs great with 4 years on the same top end, I ain't changing it" despite what we all told him. Skirt broke of, piston/rod jammed up, he ended up needing a crank, cylinder, and piston/rings. Proper maintanance would have been cheaper!
 

dirt bike dave

Sponsoring Member
Joined
May 3, 2000
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#4
When I had my '90 KDX, I would usually replace a piston every other ring change. Did the rings about every 1,000 miles. Worked fine for the 5+- years I owned it.
 
Joined
Oct 21, 2006
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#5
check the rings end gap! on new rings
check the cylinder coating if wore it might need re coated or steel sleeved
 
Joined
Feb 12, 2007
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#6
just did my top end,piston kit and had the cylinder replated runs great i have had mine for about 4 years and just decided to do the whole thing so there were no problems.i have i question for you, how does your bike run smoke wise mine seems to smoke a bit and was thinking about jetting do you know how your carb is set up mine is stock.ps i have the same,90' kdx and love it.
 
Joined
May 23, 2000
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#7
My carb has the stock jetting and it smokes a little bit. I run synthetic 2 stroke oil at a 40:1 ratio with a B8ES plug. I did some reading on jetting changes, my bike has a pro circuit pipe and a 12 tooth front sproket, and I just can't convince myself to change anything. This bike runs awesome, always starts on the first kick when warm, and gives me no problems.