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I've heard that the KDX OEM pistons have a tendency to throw the ring locating pin----that being the horizontal pin which prevents the ring from rotating around the piston. The result is total upper end failure including the cylinder. I'm told that the odds that this will happen sooner or later and has led a lot of knowledgeable owners to install Wiseco pistons --preventative maintenance!

I have two questions:

1. Is it a good idea for me to go ahead and install Wiseco pistons in my two 220's ('04 and '05 models) They still have the OEM and are running good.

2. If it is a good idea, then is it one size (69mm) Wiseco pistons fit all? or is it possible that the chrome lining of the cylinder from bike to bike differs enough that the 69mm piston may not fit properly? I ask because I know that the Yamaha 250 cc two strokes of yesteryear specified 4-5 different size pistons for replacement in a stock cylinder simply because there was that much difference in the thickness of the spray on lining in their cylinders from bike to bike.

I'd like to hear the 'real skinny' on this---and would think that some of the fellows on this forum could set me straight on the facts------? please comment.

Deseret Rider wrote:I
1. Is it a good idea for me to go ahead and install Wiseco pistons in my two 220's ('04 and '05 models) They still have the OEM and are running good.

Do you like playing with hand grenades?

Mr. Wibbens wrote:

Deseret Rider wrote:I
1. Is it a good idea for me to go ahead and install Wiseco pistons in my two 220's ('04 and '05 models) They still have the OEM and are running good.

Do you like playing with hand grenades?

Like Wibbly said. I've the skirts let go in my 200 but for a different reason than the 200 and it grenaded the whole motor, top and cases.

I have not heard about the ring locating pin but have heard about skirts letting go and it's not pretty.

I would change them out right away. I have not heard about different sizes for the standard bore so you should be just fine with the standard bore size with the oem cylinder. You'll have to check the cylinder wear, or even just post a pick of them here for some more knowledgable minds to see. Only remove the glazing on the cylinder with a scotchbrite pad. Don't hone it with anything, the electrofusion is fairly soft compared to nicasil or simmilar. Wiseco has rings for electrofusion and nicasil and it says so on the parts description so you can be sure.

The only reason for different sizes of piston on the kdx that i know of is for sleeved cylinders for rebores on them, You cannot bore an electrofusion and just slap an oversized in it.

SO post pics of your jugs

most commonly the skirt goes kaput and so does the motor.
There was some pics a while back from different users showing the cracked piston, not a myth.

just an example after a quick search
http://www.kdxrider.net/forums/viewtopi ... ton+damage

my 03 220 is still on its original piston, to date ive ridden approx 5000 miles on it without any hic ups (maybe i`ve just been lucky!) , she`s starting to rattle a little now so ive decided to strip & rebuild the top end & replace the OE piston with that from `wossoner` a quality german performance piston which comes as standard with a teflon coated skirt & mirror polished top. they also are available x3 sizes for a standard bore so you can get a much closer fit than you can with any other pistons on offer..maybe worth considering..yep i remember adding my thoughts to that thread regarding 220 pistons ... still been riding the bike for another 1000 miles..only just getting around to stripping the top end & like brittish bob my piston was in good shape also.

Wiseco pistons are the only choice to the 220, and only come in one size for stock bore. Pro-X (OEM) come in ABDCEF, but are of flawed design, and will explode at some point. The ABCDEF are not for bore changes from a boring machine, but to make up in VERY SLIGHT plating differences, or to compensate for plating wear. You can put a F piston in an A cylinder. The wiseco is like a F. Due to potential tighter clearance AND that it's forged just COMPLETELY warm the bike up before putting serious load on it.

I'm impressed with the quality of information that I'm getting here---exactly the kind of detail that I need to make an informed decision-----

Illl follow up here with results when I've completed my process----thanks for being so generous with your help. Great forum!

PS---between myself and my son and grandsons we have 5 KDX's (only one 200---the rest 220's ----and all running original pistons so we have a lot at stake on these questions.

it's kind of one of those thing where some will run the piss out of their stock piston a long time and not have any problem (those naysayer that don't believe there's a issue with the 220 piston ), while others will grenade after x miles...
would I replace it if it was mine? hell yeah, beats the hell out of breaking down in the middle of nowhere, having to push a 240 lb bike god know how many miles...the cost of the piston kit is worth it.

Right. Sure, some people are lucky. There have been enough low hour failures of the stock 220 piston for it to be obvious that there is an issue with it. Replace it with a forged unit, for your safety, wallet, and peace of mind.

All my KDX 220s were purchased used, and once the sellers started them to prove they ran, I brought them home and changed the pistons to Wisecos without running them at all. Its too great a gamble not to.

ktm950se

does this apply to the 220's only or the 200's also. i just bought a 2000 200 and would like to know before something blows apart.

94 Jimmy I've seen the 200 OEM pistons---and they appear to be the same cast piston as were found in my 220's. I can also report that I found one of my 220 pistons cracked ---with that crack running downward from the middle of the hole in the piston on the intake skirt---and thence all the way to the bottom of the skirt------It was only a matter of time before the skirt broke out on the piston side so I am very pleased that I followed these fellows good advise and changed to a forged Wiseco piston---I am certain that I'd have trashed the engine had I left the OEM piston in there. I've changed out both of my machines

I'd now be one to recommend that you at least check that 200 to see if it still has the original cast piston in there.

Again---thanks for the heads up to all the good guys that started me down this path.

The stock cast piston works fine for the 200, it's the 220 stock piston that has some defect.

Yep, 200's do NOT have this problem with the stock piston.

No more than it cost, I'd do a top end job with a Wiseco piston.

the guy i bought it from is the second owner and had only put rings in it a few years ago and no other motor work done. he has owned it since 2001. it has good compression and power so i will probably wait on the wiseco until later.

After installing the Wiseco in the 220's my compression readings were 135 on the one machine and 150 on the other. I expected more? I'm not positive of my guage either---the needle hangs up at 30# when it should go back to zero----so I don't know whether that has affected the high end reading or not? Then, the same guage shows 195 # when reading a newly installed Wiseco in a 200. Does that sound reasonable that the compression of a 200 is in that range---and the 220's are that much lower? Hmmmm?

I can also tell you that the ring gap in the first machine (the one with 135# of compression) was measured at .50 mm and the second machine had a .45 mm ring gap. The ring gap on the 200 was measured at .40 mm. All as measured at the top level in the cylinder which the rings would reach at TDC. It follows that the narrower the gap the tighter the piston would fit but this should not affect the compression reading substancially (I figure---maybe incorrectly?). because the ring gaps are offset and should create a positive seal regardless of cylinder ID. On the other hand the larger Cylinder ID should produce a higher compression reading ---NO?
All of that said---I'll be gentle in breaking in the new top ends---warming them up slowly and to operating temperature before I tax them much---and after a while, I'll take a second compression reading in them to see if there is any change. Oh---and one other 'fact' which probably has affected these readings is that I had sprayed a light lubricating oil in the cylinders on top of the new pistons before taking the readings---and with the first two the readings were taken hours after introducing the oil and with the 200 only minutes---the oil then would probably have bumped the 200 reading up. The above treatsie of probably useless information is reported more for my own edification than would be useful to anyone else----but I am curious about what the compression reading of a good tight KDX 220 and 200 should be??

I'm under the impression that the stock compression ratio of a 220 is less that of a comparable 200. Send the head to RB. Pronto. Send the carb too.

MadMax wrote:I'm under the impression that the stock compression ratio of a 220 is less that of a comparable 200. Send the head to RB. Pronto. Send the carb too.

I'm not following you? What's wrong with my heads and carbs? Why send them---and what will he do with them?