Should I install my new piston? what do you think

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lizardfungus200
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Should I install my new piston? what do you think

Post by lizardfungus200 » 11:20 am Jun 14 2019

Skip to the bottom for my question

So, my 2000 kdx200 motor was all taken apart for investigation because it was burning transmission fluid. Before assuming it was a crank seal, I conducted a bunch of tests to find out where it was coming from, since I once owned a mint condition 02 RM125 that burned tranny fluid, a problem that was never cured no matter how many times I changed the crank seal or split the cases and changed gaskets. Crank bearings were good, the bike was always well taken care of. One of the tests was using a piece of 1/4" acrylic to seal off where the cylinder would go, and filling the crankcase with various fluids at different levels, while hooking a vacuum pump up to the acrylic, so I could see if there were any bubbles coming up. This yeilded no results, however one day I filled the crankcase up with blue devil transmission stop leak and took note of the level. I checked it the next day and the level had gone down significantly, about halfway down the crank seal, and some of the blue devil was pooled right around and on the crank seal. I filled it back up, came back the next day and the level had not changed, and there was none around the crank seal. I plan on running the bike and seeing how it goes

The stock piston had rock hard compression, but the top is completely covered in carbon, you can see a pic of it in my other post. The previous owner gave me a wiseco piston kit with the bike. Should I install the new one or stick with the old one till the rings wear out?

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Re: Should I install my new piston? what do you think

Post by SS109 » 12:13 pm Jun 14 2019

If you end up with any fluid outside the crank seals then they are toast. Even if it's just barely noticeable the seal is in need of replacement. Sadly, it's a split the cases type of repair.
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Re: Should I install my new piston? what do you think

Post by KDXGarage » 01:07 pm Jun 14 2019

Are you certain it is the correct piston kit?

Why would you NOT change it if the current one is coated in carbon on top?
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doakley
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Re: Should I install my new piston? what do you think

Post by doakley » 02:31 pm Jun 14 2019

I would definitely install the new with new rings, etc. and hold on to the old parts as spares. You can probably clean the carbon off the piston top BTW, but if I already had my top end apart, I wouldn't leave a new piston in its box.

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Re: Should I install my new piston? what do you think

Post by bufftester » 09:06 pm Jun 14 2019

If it was burning transmission oil, the ONLY place it can be pulling it is through the RH crank seal. A leakdown test would confirm it prior to tearing the motor down. Change the piston and rings since you have them. Hopefully you didn't pour the sealer in with your clutch pack, if so you may want to recheck it since transmission sealer works by swelling seals (and possibly clutch fibers). You may get by, but the real fix is new seals.

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Re: Should I install my new piston? what do you think

Post by lizardfungus200 » 03:48 pm Jun 16 2019

thanks for the advice guys. I put it back together with the new piston. It definitely runs a little better and can idle a lot lower, but isn't really snappy off idle, like mx 2 strokes. I am going to lay the bike on its side and let a pool of blue devil sit on the outer side of the crank seal for a few days, or weeks, since my wrist is broke and can't ride, and see if that fixes it. If not, please recommend your favorite puller! I originally confirmed the transmission oil with UV dye, with several tests to rule out coolant, and the vacuum test I did was not adequate enough because I could only pull a little more than half an atm due to a bad vacuum pump or leak or something. Please recommend a good puller anyway because I want to rewind the stator

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Re: Should I install my new piston? what do you think

Post by Vossman » 03:52 pm Jun 16 2019

The motion pro puller works well. Where you located? If your local to CO (slim chance) you can use mine.
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Re: Should I install my new piston? what do you think

Post by kdxsully » 05:41 pm Jun 16 2019

For pulling the flywheel? I just use the loaner one when I need it from the auto parts store.
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Re: Should I install my new piston? what do you think

Post by KDXGarage » 07:58 pm Jun 16 2019

Dennis Stubblefield Sales makes a good one. DSS, look on eBay

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