1985 KDX Piston Substitutions

Discussion specific to the various air-cooled KDX models sold in the USA
linny
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1985 KDX Piston Substitutions

Post by linny »

Hello KDX rider, it has been WAAAAAY too long!

I have a 1984 KDX 200 that is plated and in excellent shape.....

And I also have a 1985 KDX 200 roller that is complete minus a muffler

The roller is going to become a race bike for the local hare scrambles around here, except for.....

The piston kits are not in existence anymore

Some solutions that I have seen is to either bore it to a 220 and use that piston, or use a 1997 kdx 200 piston as I have heard rumor that they fit

I can find all the other main parts like bearings, seals, gasket sets etc on Ebay for relatively cheap so I am wondering what solutions you guys have to this!
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1985 KDX Piston Substitutions

Post by linny »

Something else just occured to me as well.....

Buy a 1986 cylinder with the powervalve and use a 1986 piston?
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Re: 1985 KDX Piston Substitutions

Post by linny »

https://www.thumpertalk.com/forums/topi ... t-13581951

Sorry it's not the 1997. It's the 1995 piston
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

If that guy said it was just as easy as buying a Wiseco (which is for 1986 - 2006, by the way), then cut the extra 3 mm off it, I would look into that. That is me in the thread (KDXGarage) by the way.

I don't think bolting on a 1986 cylinder would be the way to go. It would still have the old crankshaft in it.
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Re: 1985 KDX Piston Substitutions

Post by linny »

I'm going to give the 1995 piston a try

I'm calling B.S. that it needs the bottom ground off. The OP said he didn't have to modify anything

We'll see what happens

I need a race bike!
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

Do you realize that the height of the piston is going to be the same between the Wiseco and the various OEM 1986 - 2006 pistons??

I am calling the opposite of BS on him cutting 3 mm off the bottom. He said it would hit the crankshaft. :naughty: :blink:

Off to search to see if my memory serves me well...

I STILL GOT THIS!!

:bravo: :boogie: :cool:

about 12 posts down
http://www.kdxrider.net/forums/viewtopi ... on#p137444

Here are some measurements on the OEM piston:

http://www.kdxrider.net/forums/viewtopi ... on#p129890

Can someone measure a new OEM or Wiseco KDX200 piston height for me PLEASE? :please: :prayer:
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

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Re: 1985 KDX Piston Substitutions

Post by KDX Geoff »

Jason wrote:http://www.kdxrider.net/forums/viewtopi ... 19&t=18379

CHECK THE RING PIN PLACEMENT!!!
I've been told one of the ring ends get exposed to the inlet port.
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

It was from the thread in which you posted all the ring ends and pistons, KDX Geoff. :prayer:
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1985 KDX Piston Substitutions

Post by linny »

So what I gathered from that thread...

The ring ends are different but will still work?

You have to clock the rings away from the ports so it doesn't detonate and catch on it???

I'm still not seeing where 3mm had to be taken off
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

The guy said he had a large chamfer in that area. You can't turn the rings. The pin IS where the pin is. I would be scared to run it like that.
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Re: 1985 KDX Piston Substitutions

Post by Dave B »

I raced quads in the early 90's (feeling old now), I would send my motors out for porting etc.. One of the many things they did was rework Yamaha YZ pistons to fit my Suzuki. They would pull the ring pins, drill and reinstall new pins in the proper location for the Suzuki's cylinder. A possible option to making them work.
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1985 KDX Piston Substitutions

Post by linny »

I've clocked rings at 120 degrees before on big bore four strokes, so I don't see why offsetting the rings would affect the performance. The ring shouldn't move much. I'm going to try that before I chamfer the intake port and screw the jug up.
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

Dave B wrote:I raced quads in the early 90's (feeling old now), I would send my motors out for porting etc.. One of the many things they did was rework Yamaha YZ pistons to fit my Suzuki. They would pull the ring pins, drill and reinstall new pins in the proper location for the Suzuki's cylinder. A possible option to making them work.
I was wondering if that was a possibility.

I would love to have the dough to get Wiseco to make a run of 12, but then everyone would want it for $80 like a normal one. :butthead: :butthead: :butthead:
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Re: 1985 KDX Piston Substitutions

Post by Dave B »

If believe the YZ pistons were a bit taller wrist pin to top of piston. An aluminum spacer plate cut in the same shape as the base gasket was installed below the cylinder to compensate. A lot of cool work to coax a few more ponies!
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Re: 1985 KDX Piston Substitutions

Post by Dave B »

Now that I think about it they didn't pull the ring pins they ground them down and then installed new ones. Don't want to see someone destroying a piston on my account!!
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1985 KDX Piston Substitutions

Post by linny »

The Honda motor I built was an XL 600R from 1985

There were no ring pins in the groove which allowed me to clock them 60 degrees apart

I bet there may be a 1995 piston with no ring pins being forced to index at the 6 and 12 o clock positions

Anyone who has one please chime in
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Re: 1985 KDX Piston Substitutions

Post by KDXGarage »

There are no ports for a ring end to catch on a four stroke, correct?

Apples

Oranges
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1985 KDX Piston Substitutions

Post by linny »

The XL did have a port in the barrel for their first attempt at a ghetto version of emissions control that had a filter to cycle exhaust gases through it. I think if one were able to rotate the rings 60 degrees to the left or right it might work.

I do some machining and a bigger chamfer can still catch the ring end if it pokes out as the ring end might travel down the chamfer and get caught. The chamfer doesn't really negate any risk imho.

Another thought.

How about another connecting rod with a longer stroke?
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1985 KDX Piston Substitutions

Post by linny »

Another thought

A KDX 175 piston has a 66mm bore but stroked shorter

I can find those all day long
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