kdx200 '87 piston in an '83 barrel.

[kdx Geoff]

There is nil stock world wide of a piston/rings suitable for the '83-'85 200.

Plenty of people looking but other than getting a piston made (l made a couple of calls, not keen on making a 2 stroke piston and one maker that would look at the job was talking $300 plus each for a batch of 20) I'm looking at if the later model air cooled piston will work with minimal mods and be as reliable as the correct piston.

A '83
B '87
C I75 This is here because its also 66mm and l think the rings will be suitable for the '83 piston. They wont fit the '87 piston as the ring grooves appear to taper inwards and so the ring won't fit into the grove like it does on the 175 and '83 200.
Its not suitable in the 200 as the small end is around 3mm closer to the crown.

The skirt window is centre and the ring pins are marked.





The exhaust side shows the lube holes for the bridges between the exhaust and power valve ports on the '87.




Piston weights and the ring pin locations which l checked twice. The left side pins are in line and on the right the '87 pin is further outboard than the '83 . The inlet port may be wider and explain that difference...
The extra weight looks to be more metal around the lube hole area.






Both 200 pistons are the same height, ring groves in the same locations (the different profile of the groves is visible here) and small end is in the same location.



If l fill in the lube holes in case they're uncovered by the exhaust port in the '83, check the reason for the different pin location is the inlet port width and so shouldn't be an issue with the inlet...but maybe the transfer is close.

Have l missed anything ?

[80-85 husky]

some nice work there....

[Lozza]

C I75 This is here because its also 66mm and l think the rings will be suitable for the '83 piston. They wont fit the '87 piston as the ring grooves appear to taper inwards and so the ring won't fit into the grove like it does on the 175 and '83 200.
Its not suitable in the 200 as the small end is around 3mm closer to the crown.

There is something you missed, a +5mm longer rod with the high pin piston 1mm spacer plate and 2 0.5mm gaskets.

With ring peg location centre of the port is OK toward the edges of the port window is no good(on end will stick out). Very few piston manufacturers will take on less than 20 pistons in Minimum Order Quantity(MOQ)

[GMC]

Went through this a year or 2 back with a forum member and pretty sure his outcome was the 86-88 pistons will fit the earlier 200's fine.
No need to fit early rings, just use the rings that suit the piston your using.
If any doubts about holes or ring end pins then just hold the piston in the barrel while they are off the engine, you can move the piston up and down with your fingers and you will be able to look into all the ports to see if anything is protruding where it shouldn't.

The only other thing to check is when the piston is fitted to the crank do the skirts miss the crank at BDC.
Pretty sure they will be fine

[tymes]

I know someone who has three, just in case they become hard to find.
I got a wosner off a guy in the states who did a run of them some time back.
Mrs kdx has had a rebuild  last year with the later 86 on siezco piston with a sleeved cylinder. One of the ring end gaps protrude into one of the ports, a very reputable engine guy here in nsw relieved the port a bit and it has been going well for about a half dozen vinduros so far. The engine that came out of her bike also had a later wisco in it with no problems to the end of its servicable life with a nikasil cylinder.
I found that the wisco and wosner pistons are both heavier than the original pistons and the motor vibrates much more than if you use the standard piston.
Mrs kdx used an aftermarket conrod kit with a slightly heavier crank pin and it didnt vibrate as much with the wisco piston.
The standard piston and standard crank pin run very smooth when used together. (Thankyou to KDX legend GeffFredett for his advice) "Balance factor"
You can still get rings for the original pistons, the later 92 or so genuine bottom ring is the same as the 83-4-5. You just have to buy two sets because the top ring is different.

[tymes]

13008-1116 is the part number of the later ring set that the bottom ring fits the 83-4-5.

[kdx Geoff]

No need to fit early rings, just use the rings that suit the piston your using.

I have an '83 piston with no rings, l think the 175 rings may fit as the ring location pegs look the same in both pistons.

I know someone who has three, just in case they become hard to find.

Under lock and key l hope 


Both pistons are at bdc, 58 mm down with the crown level with the transfers.



There's a big difference in the size of this port between barrels.
How much of an issue is this ?



The lube holes for the bridge on one side makes a brief appearance.


So the only real issue is how to resolve this ring end in this port at the bottom of the stroke.

Chamfer the edge of the port...fill the port in where the ring is exposed....or not worry about it ?

[Lozza]

Leave the bottom ring out with the high inlet port and fill the lube holes with JB Weld the lube holes. You could fill the top of the port but the juice isn't worth the squeeze

[GMC]

Had a new 86-88 Wossner piston in stock so I checked it out with an early barrel that I had



The stroke is supposed to be 58mm so I measured the top of the piston down to 59mm from the top of the barrel and the ring pins were not visible in the ports.

Its possible the ring pins vary between brands so;

[kdx Geoff]

Is that ring pin on the right in the top ring groove ?
The top ring doesn't come down into the port and it looks on that piston that the bottom ring isn't in the port either.