kdx200 now 240cc

[kdx Geoff]

Hi,

Having 3 200's in the shed that don't run, yesterday was the day l started sorting through them to end up with one running bike.

The engine with the best top end turns out to have around a 72.5mm bore instead of the standard 66mm, which means its been sleeved to 240cc. The number on the piston is 8286G and other than the transfers looking a bit wider, the porting seems fairly stock.



Aside from maybe sleeved barrels don't transfer heat as well as non sleeved barrels, what should l know about this mod, I've never seen one before.

Cheers

Geoff

[Nathan S]

Was a conversion available through Serco for the C/D models, using a Wiseco piston and an LA Sleeve sleeve. I've not heard of them being fitted to the A/B models, but the two motors are so similar that it makes sense that they exist for the A/B too.

I asked Serco a few years back about whether the kit was still available, and they dismissed the question off hand - I don't know what this means for the availability of replacement pistons.

Added a bit of torque, not a lot more. Have heard a couple of people describe is as a significant step backwards, but not from anyone who says that they spent the time setting it up properly.

[80-85 husky]

ol mate has a very smick kdx 200 86 that he cant vinduro . a mate with a bike shop traded it on a new kato in 05 or so and it was a rea l1 owner on the road job. pristine orig condit.

he has hit it with the $$ brush and found and installed a 240 kit, a hot pipe and muffler (DG I think) some port work and a kx 80 rear disk. it flies. I raced against it at a nat terrain and it matched the 400 up the hill easily

so they are still around, may not be serco tho. im sure his came from the states (could be NOS). I might ask him.

great find I rekon.

[MaxPower]

I would think that if the ports aren't touched there is a lot of power hiding in that cylinder. Adding 40cc is a good amount and the angles of the ports need to be changed to that bore size. Have you asked Ferdette Racing about your 240?  He is the person to ask anything kdx200


I would like to hear opinions about the steel sleeve myself. I have a 83 kx125 cylinder with a sleeve and would like to have that cylinder tweaked to get the most from it. But if the sleeve is a limiting factor it's not a good choice.

[kdx Geoff]

I would think that if the ports aren't touched there is a lot of power hiding in that cylinder. Adding 40cc is a good amount and the angles of the ports need to be changed to that bore size. Have you asked Ferdette Racing about your 240?  He is the person to ask anything kdx200

Thanks MaxPower. I've started looking for a piston and Serco cant help me. l didn't use a micrometre to measure the bore but according to the article l can take it out to 73mm.

Here is part of an ADB test from November '86 written by Terry Shulze.

[John Orchard]

So where is page 62?  ;-)

[kdx Geoff]

So where is page 62?  ;-)

Here's the page 62 part 

[Slakewell]

Is the pipe and muffler standard ? I cant see how on the 2T you get much real advantage till you tuned all the bits. So yes I agree with Nathan. 

[John Orchard]

It's not so critical when you just go bigger with the bore, port & pipe timing is related to stroke, everything still is still the same with a larger bore.

[LWC82PE]

Download some Wiseco catalogues and look at piston sizes. You might have to use the Wayback machine to find older catalogues going back to early 2000's and then have a look at some of the snowmobile/Jet ski pistons. I also suggest you contact Jeff Fredette. He will have the answers for you. Also RPM MFG in USA would also be of help. I know they sell 300cc big bore conversion kits for air cooled KDX250 and KX250 from early 80's which they have designed themselves and from memory they were using existing Wiseco pistons from something else to do it. 72mm sounds common. I am sure the kits used a piston from something else.

[80-85 husky]

great conversion for a sensational bike. check out my natural terrain clips from last year, race 2 has a mate on his 240 kitted kdx giving the 400 a run for its money.

https://www.youtube.com/watch?v=pB8ZyVgXwBY

[Ktm181]

Geoff,

I rode one way back when, also rode a stocker the same day, both were slow against my '85 Kx 250...go figure! BUT, the 200 versus the 240 - about the same top end, both had stock pipes and same Sydney made after market alloy muffler on them, the name escapes me, anyway, the thing I disliked about the 200 was the lack of torque (relatively speaking), the thing I liked about the 240 was it had a HEAP more torque and similar top end or a bit more than the 200, both were stock other than the muffler and big bore kit, I LIKED IT but liked my Kx a whole lot more even in the bush (go figure again !!) I reckon think Ktm250 versus Ktm300 in same year model and both stock...both make similar horsepower but the 300 makes a stack more torque AND A LOT MORE HEAT!

The 200 with the big bore done right...porting, bigger carb, bigger exhaust header etc would be similar to a HUSKY 240 of the day, nice power and get it all to the ground. The only suspect would have to be gearbox and big end/mains longevity???  125 bottom end aren't they?  Got to speak to Al Tomkins next week so will ask him what he remembers about them , I KNOW he loved the 200 STOCK though, especially the air cooled ones.

GO LOWNDSEY,
Kt.

[kdx Geoff]

GO LOWNDSEY,
Kt.

Very lucky to make the shootout tomorrow !   

Edit;

Really, good management rather than luck.

[kdx Geoff]

l pulled the motor out of this bike today and started the strip down, it was really rattly in the bottom end so l was thinking the 240 top end may be hard on the standard 200 bottom and I'd have to replace the big end..... then l got the side cover off.




The crank nut was off the crank and floating between the side cover and the end of the crank. Although the primary drive gear was still tight that would explain the noise and then l looked at the clutch  That nut had come off the shaft too and the basket was loose and floating around. The engine ran alright it was just really noisy especially at idle.

I'll refit those nuts and put it back together, l imagine it may be a bit quieter now.

[oldfart]

Very lucky indeed ... I would be inclined to replace both  lock tab washers as a precaution. As the one in pic appears to have lost its tab.