New member with a KDX 220 piston question

[TugSpeedman]

I'm a new member here and just purchased a 97 KDX220, Ive pulled the top end off to clean the KIPS valves and looking at the scoring on my piston decided I need to replace it. Its got a B stamped on the top. Measuring the bore shows in the X and Y top to bottom, my measurememts are 68.97 and 68.91 and the piston measures 68.72 directly above the wrist pin and 68.83 below the wrist pin. This seems smaller in diameter than Woosners pistons or anything else for this bike. Its an SK piston.I've never heard of those.

[Molly's 70]

What is your piston/cylinder clearance? Standard is between 0.079-0.089mm.

[KDXGarage]

Welcome to kdxrider.net.

I think SK is the company that made it to Kawasaki's specifications. That is the stock piston. Read up on some shatter failures from the stock piston. I think most are going to suggest you replace it. I would.

Look up kdxdazz info in the OEM piston, his comparison

EDIT ADD ON: Here's a Yahoo Japan piston picture:

[kdxdazz]

Did you check the bore and piston with a dial gauge and micrometer ?

[billie_morini]

tug,
the piston you photographed is a Kawasaki OEM piston. It is identified by the "SK" contained within doubled maple leavers and waffle patterns here and there on the piston surface.

The Kawasaki OEM piston is manufactured by casting. Many, not all, forum members experienced or know someone that experienced failure with these pistons. The failure, when it occurs, is shown to be catastrophic (e.g., "grenade"). This is why many forum members immediately replace them forged pistons manufactured by Wossner or Wiseco pistons. My personal preference is Wossner. For what it's worth, here's a forum post about the OEM piston identification: viewtopic.php?f=86&t=24789&p=213441&hilit=Ames#p213441

Your measurements are curious because the largest bore size and piston size, respectively, are 69.02 and 68.96 mm. So, like kdxazz inquired above, what did you use to make these measurements?

You may find it convenient and obtain a robust top end to have the cylinder recoated by a specialty vendor like Millennium Technologies in Plymouth, WI (https://millennium-technologies.com/). That's what I did and customer service by Jeff Meyer was superb. I've attached an order made with them in 2021 so you can see what I had them do and what it cost. They inspected and plated the cylinder, using a coating formula that is superior to the original Kawasaki formula. The power valve service is a cleaning service. This saved me some time. Also to save time and assure assembly could begin immediately following order completion, I had them gap the piston rings using the Wossner piston they were providing. This, too, saved me a little bit of time. (Time was a precious commodity in my life due to my job that involved providing Mission Critical services to the DoD on a worldwide basis. Thankfully, I am now retired!)

[Molly's 70]

Mellennium Is who I had my spare cylinder refinished by. Very happy. I would recommend them.

[TugSpeedman]

I have used Millenium Technologies in the past. They do good work. I used a bore gauge and a Mitutoyo caliper to get these measurements. I checked every thing 2x and am going to check again tomorrow. The bore sizes seem strange to me too. Smaller on the bottom than the top is not the norm. The B on the piston has got me wondering since Kawasaki doesnt offer oversize pistons and i wondered if this is an aftermarket piston in an oversize. My plan is to use a Woosner piston.

[kdxdazz]

Your piston looks to be in excellent shape, very nice clear photos by the way, the piston measurement I think has to be taken at the widest point
Bore gauge and micrometer is accurate so sounds like your piston measurements are correct but maybe not taken at the widest point
If shipping wasn't so expensive in the US I would ask to pay for shipping for your piston as I avoid forged pistons for the same reasons manufacturers don't use forged pistons
Seems to be nobody is reporting failures from SK pistons
I put an OEM cast piston in mine and like you say choosing a b or c is not an option

[Chuck78]

I'm a new member here and just purchased a 97 KDX220, Ive pulled the top end off to clean the KIPS valves and looking at the scoring on my piston decided I need to replace it. Its got a B stamped on the top. Measuring the bore shows in the X and Y top to bottom, my measurememts are 68.97 and 68.91 and the piston measures 68.72 directly above the wrist pin and 68.83 below the wrist pin. This seems smaller in diameter than Woosners pistons or anything else for this bike. Its an SK piston.I've never heard of those.

I'm not saying your measurements are incorrect, but I'd get a second opinion via a shop or via other measuring devices. I've noted that 2 of my 3 calipers are out of spec for critical precision measuring, and the Mitutoyo needs sent back to the manufacturer for rebuild and professionally certified calibration. The CenTech Harbor Freight version just needs replacement...

[TugSpeedman]

I think Im going to take the cylinder to a machine shop that has a dial bore gauge to get the accurate measurement. Im holding off buying the piston until I know if the bore is straight, or needs to be redone by Millenium Tech or Powerseal USA. If that the case Im buying the piston and sending it to them with the cylinder

[Chuck78]

I think SK is the company that made it to Kawasaki's specifications. That is the stock piston. Read up on some shatter failures from the stock piston. I think most are going to suggest you replace it. I would.

Look up kdxdazz info in the OEM piston, his comparison

the piston you photographed is a Kawasaki OEM piston. It is identified by the "SK" contained within doubled maple leavers and waffle patterns here and there on the piston surface.

The Kawasaki OEM piston...Many, not all, forum members experienced or know someone that experienced failure with these pistons. The failure, when it occurs, is shown to be catastrophic (e.g., "grenade"). This is why many forum members immediately replace them forged pistons manufactured by Wossner or Wiseco pistons. My personal preference is Wossner. For what it's worth, here's a forum post about the OEM piston identification: viewtopic.php?f=86&t=24789&p=213441&hilit=Ames#p213441

ART Pistons are the company who manufactured I'm guessing 85% +/- of the OEM 220 pistons "for Kawasaki." These are the notorious exploding pistons that wreck 220 cylinders and sometimes crankcases. Nearly all which failed are noted to be made by ART, with "ART" cast into the underside and with a very poor skirt design. ART mostly is only proficient at making 4-stroke pistons.
SK Pistons are the sole manufacturer of the 1986-2006 OEM KDX200 pistons, which are of excellent design, as well as a small percentage of the OEM 220 pistons, which seem to be the only high-hours survivors left in 220's these days if still original. The SK 220 pistons have significantly better skirt designs (thicknesses and chamfering and stress relieving etc) same as the OEM 200 pistons, and are not an issue other than when worn out.

SK Pistons are the ones who I'll describe as "the company that made it to Kawasaki's specifications" as you said KDXGarage. SK made it to proper 2-stroke skirt design requirements same as all OEM 200 pistons which they also made. ART cut corners and butchered the engineering/design of their version of the 220 2-stroke piston skirts.
My buddy's '99 Honda CR250R I did a top end on also had an ART piston in it, and guess where I found most of the missing portions of the piston skirt? Inside the expansion chamber! Same popr thin skirt design and poor edge deburring/chamfering as the OEM ART 220 pistons.

@ kdxdazz has outlined the differences between the two 220 OEM pistons, although using the common 200 SK piston as comparison I believe, as the SK 220 pistons are a small and scarce percentage of the total OEM 220 pistons ever produced. He actually ordered a new 220 piston a year or so ago and received one of the garbage ART pistons. It's unclear what years used the OEM 220 SK Pistons, but I'm guessing less than 10% of total production.
This 220 SK vs ART piston sourcing / design comparison is just something thats really only recently been noted, primarily by kdxdazz Daryl and myself. It's not really terribly useful info now, as the OEM SK 220 pistons appear to be out of circulation, and Kawasaki reverted back to selling the ticking time bomb ART 220 pistons sadly, so Wossner in the correct 69.00mm A, 69.01mm B, or 69.02mm C-sized piston is the clear choice. One should only run a Wiseco (only available in 69.00mm A-size or 70.00 overbores) or Vintco (rebadged Wossner but only available as A-size) if the cylinder measures to A-size spec or if one needs the 70.00mm overbore "225 kit" (223.2cc +1.00mm oversized bore).

[Chuck78]

I have used Millenium Technologies in the past. They do good work. I used a bore gauge and a Mitutoyo caliper to get these measurements. I checked every thing 2x and am going to check again tomorrow. The bore sizes seem strange to me too. Smaller on the bottom than the top is not the norm. The B on the piston has got me wondering since Kawasaki doesnt offer oversize pistons and i wondered if this is an aftermarket piston in an oversize. My plan is to use a Woosner piston.

There is a lot of talk recently about the quality of Millennium's plating. It seems they've again had some changes in the composition, and a lot of people are having problems and complaints about them, including shops which have had identical model cylinders done in bulk by Millennium, PowerSeal, & others (US Chrome etc), stating that the plating was proven to be the issue as compared to PowerSeal...
I was very pleased with the quality of PowerSeal USA's plating work, but after learning more about 2-stroke porting and having other professionas critique my PowerSeal repaired & replated cylinder, as well as seeing poorly machined cylinder repair jobs from PowerSeal from others, it became clear that Millennium does a much better job on inspecting and critiquing the cylinders. PowerSeal will just replate a cylinder even if the factory ports are uneven / crooked and or with improper chamfering. Millennium will contact you and advise they'd recommend porting cleanup work prior to replating. But now we're hearing significant quality control feedback from professionals and amateurs about issues with the plating composition and quality of the Millennium Nikasil. Millennium blames the piston ring quality every time. So of you use Millennium, specify that you have them supply a Wossner or Vintco A-sized piston only.
Another KDX owner had a cylinder done by Millennium recently and they sent it out finish honed to a C-size spec, and the owner was livid, and Millennium refused to do anything to make this better...

I've come to realize, in light of all this, that it's best to send the cylinder out to Ted Boyko of Boyko Racing, or Tom Morgan Racing, and have them do a basic porting cleanup, correct the chamfers and port openings etc, gasket match the transfer ports, and THEN have them send it out to PowerSeal USA for replating... Then you will have Millennium quality inspecting and cleanup/repair work (or better), with PowerSeal quality replating.
Ken O'Connor Racing is another good alternate.
It seems as if Freddette is winding down towards retirement these days but is still the go-to for KYB suspension work, KDX bottom end complete engine rebuilds, & parts. I personally would prefer a former OEM manufacturer race team engineer like Ted Boyko or Tom Morgan (EDIT - apparently Tom was formerly employed at Millennium and uses them for his plating?), or Mitch Payton (Pro Circuit) to do my porting work hands down. Those guys are the absolute elites.

Also, PowerSeal USA sends out their KDX cylinders missing the proprietary coolant pipe thread plug that it was sent in with, as I found out the hard way, and sends the cylinders out with a beadblasted head gasket surface that I would describe as total garbage for sealing a coated MLS head gasket, vs an acceptable surface plate 800 grit lapped finish or OEM milled surface finish.
Millennium does not screw this up.


Guys in the 2-stroke tuning or 2-stroke Research and Development group where James aka JZ05220R & I were cued in to these Millennium plating issues vs PowerSeal's plating durability and/or surface finish, had also mentioned that Millennium blames the piston rings for the odd plating wear vertical streaking in the bores. A few guys clearly blamed the poor finishing of modern piston rings, and said they really must be polished with a Scotch Brite pad on the sealing surface and edges to remove micro burrs from the manufacturing process. Also, the diamond hone surface finish left on the fresh plating job has a lot to do with how well the piston rings are broken in to mate perfectly with the bore.
Another guy said he laps/polishes the port edge chamfers on the freshly plated cylinders before install.
Another advised that meticulous cleaning of a freshly plated cylinder is critical, and an ultrasonic cleaner is the best method, + extensive flushing afterwards.


So this doesn't give us a clearcut answer, but Millennium clearly is better at the inspection, repair, & technical details, but may in fact have an inferior plating formula, application process, and/or finish honing vs PowerSeal's.

[billie_morini]

🫨

[Chuck78]

My "friend" just got word from Millennium that they will warranty his new plating job based solely on photos and description of the streaking and abnormal wear on the plating job in just a few short hours of riding time... that's good to know, so I'll take that as they will be working on improving the deficiencies that have crept into their plating process in recent times which have caused a lot of bad feedback from the professional engine builders.

[Chuck78]

I have used Millenium Technologies in the past. They do good work. I used a bore gauge and a Mitutoyo caliper to get these measurements. I checked every thing 2x and am going to check again tomorrow. The bore sizes seem strange to me too. Smaller on the bottom than the top is not the norm. The B on the piston has got me wondering since Kawasaki doesnt offer oversize pistons and i wondered if this is an aftermarket piston in an oversize. My plan is to use a Woosner piston.

There is a lot of talk recently about the quality of Millennium's plating. It seems they've again had some changes in the composition, and a lot of people are having problems and complaints about them, including shops which have had identical model cylinders done in bulk by Millennium, PowerSeal, & others (US Chrome etc), stating that the plating was proven to be the issue as compared to PowerSeal...
I was very pleased with the quality of PowerSeal USA's plating work, but after learning more about 2-stroke porting and having other professionas critique my PowerSeal repaired & replated cylinder, as well as seeing poorly machined cylinder repair jobs from PowerSeal from others, it became clear that Millennium does a much better job on inspecting, critiquing, and repairing the cylinders. PowerSeal will just replate a cylinder even if the factory ports are uneven / crooked and or with improper chamfering. Millennium will contact you and advise they'd recommend porting cleanup work prior to replating. But now we're hearing significant quality control feedback from professionals and amateurs about issues with the plating composition and quality of the Millennium Nikasil. Millennium blames the piston ring quality every time. So of you use Millennium, specify that you have them supply a Wossner or Vintco A-sized piston only.
Another KDX owner had a cylinder done by Millennium recently and they sent it out finish honed to a C-size spec, and the owner was livid, and Millennium refused to do anything to make this better...

I've come to realize, in light of all this, that it's best to send the cylinder out to Ted Boyko of Boyko Racing, or Tom Morgan Racing, and have them do a basic porting cleanup, correct the chamfers and port openings etc, gasket match the transfer ports, and THEN have them send it out to PowerSeal USA for replating... Then you will have Millennium quality inspecting and cleanup/repair work (or better), with PowerSeal quality replating.
Ken O'Connor Racing is another good alternate.
It seems as if Freddette is winding down towards retirement these days but is still the go-to for KYB suspension work, KDX bottom end complete engine rebuilds, & parts. I personally would prefer a former OEM manufacturer race team engineer like Ted Boyko or Tom Morgan (EDIT - apparently Tom was formerly employed at Millennium and uses them for his plating?), or Mitch Payton (Pro Circuit) to do my porting work hands down. Those guys are the absolute elites.

Also, PowerSeal USA sends out their KDX cylinders missing the proprietary coolant pipe thread plug that it was sent in with, as I found out the hard way, and sends the cylinders out with a beadblasted head gasket surface that I would describe as total garbage for sealing a coated MLS head gasket, vs an acceptable surface plate 800 grit lapped finish or OEM milled surface finish.
Millennium does not screw this up.


Guys in the 2-stroke tuning or 2-stroke Research and Development group where James aka JZ05220R & I were cued in to these Millennium plating issues vs PowerSeal's plating durability and/or surface finish, had also mentioned that Millennium blames the piston rings for the odd plating wear vertical streaking in the bores. A few guys clearly blamed the poor finishing of modern piston rings, and said they really must be polished with a Scotch Brite pad on the sealing surface and edges to remove micro burrs from the manufacturing process. Also, the diamond hone surface finish left on the fresh plating job has a lot to do with how well the piston rings are broken in to mate perfectly with the bore.
Another guy said he laps/polishes the port edge chamfers on the freshly plated cylinders before install.
Another advised that meticulous cleaning of a freshly plated cylinder is critical, and an ultrasonic cleaner is the best method, + extensive flushing afterwards.


So this doesn't give us a clearcut answer, but Millennium clearly is better at the inspection, repair, & technical details, but may in fact have an inferior plating formula, application process, and/or finish honing vs PowerSeal's.

[TugSpeedman]

I ordered the Woosner standard size piston. When it gets in, Ill measure the clearance, If its off, I'll send the cylinder and piston to who ever I decide on and be sure to remove the plug from the bottom of the cylinder.

[TugSpeedman]

Got the Wossner piston in. It felt good in the bore except for the very bottom where it measured small. I think the bore was not cylindrical and the piston was so loose in the bore that it ran but I could'nt replace the piston without running into the issues I did.The walls of the cylinder were very clean, No scoring, still had cross hatch. I sent it off to PowersealUSA this morning. MT has really upped their prices since the last cyl I sent them, thats why I went with PS.

[billie_morini]

This weekend I went to the Bagger Racing League (BRL) racing Rounds 5 & 6 at Willow Springs International Raceway. It was possible to hang out with designers, fabricators, engine builders, engineers, and racers that have remained in road racing following my departure 20 years ago.

One very successful engineer / engine builder / race bike prepped / fabricator and I talked about cast and forged pistons. This is the condensed version this experienced business owner said to me:

"Stock pistons are generally cast capable of enduring the environments originally intended by the OEM when designing such a part. In a lot of cases, the part is 'over engineered' to be as reliable as possible for a road-going vehicle that has a warranty. This is to the advantage of the engine builder up, but only up to a point. For example, two of the riders I supported had their bone-stock 2005 GSX-R1000s crack the cast pistons right across the crowns. This was due to Suzuki pushing for maximum performance from a stock part. Under normal street applications, these pistons would probably last the life of the rest of the bike. However, under racing conditions, where the piston is subjected to the maximum designed environment (or over)100% of the time...and the occasional hard downshift...the material fatigued and caused an engine failure.

For this reason, most race engine builders prefer to run a forged piston. Forging is a form of metal reshaping using a die in the rough shape you want and, under extreme pressure (hundreds of tons) forcing the material to take on a new shape. This forms a much tighter grain structure and pattern that ends with a much stronger part for the same given volume of material. In many cases, a forged racing piston can be made lighter at the same time as stronger because of its higher density. Also, forging alloys are usually of much higher quality materials, adding better durability there as well."

Two-stroke engines, in my experience except vintage trials bikes like I competed with, subject pistons to more extremes than four-stroke engines. I began using forged pistons in my own super-pumped, water-cooled, road racing twin after destroying many cast pistons. I never melted, cracked, or blew up another piston following this change.

If I ran a KDX 200 or 220 hard, then I'd definitely install a forged piston. I don't run my KDX 220 very hard, but am unwilling to gamble with a cast piston. This is why the OEM cast was replaced with a (Wossner) forged piston quickly after obtaining my KDX.

[TugSpeedman]

I agree. Cast is cost effective for manufacturers, but start raising the compression and adding horsepower and forged is the way to go. Im building this to be a reliable bike to do some enduros with when i relocate to the east coast. At 69, Im not going to be stretching throttle cables.

[billie_morini]

...At 69, Im not going to be stretching throttle cables.

Like dat! Tug, I'm 65. I say this, "I'm not trying to win trophies or break bones."