slogging through piston selection

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dingerjunkie
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slogging through piston selection

Post by dingerjunkie »

Hello All...I've been out of the 2-stroke top-end game for 25 years, and I'm hoping those who have kept in practice can give a bit of insight and honest opinion. This is all about the murky "art" of piston selection. If this is all covered well in other threads, then please excuse the "derp" moment and I'll follow whatever links you provide.

First...plusses, minuses and recommendations on various brands. Weisco forged vs. Weisco pro-lite vs. Vertex vs. Wossner vs. ART Pro-X. Some cast, some forged, some with ceramic treatments on the skirts.

Back in the day there were complaints of different tolerance requirements between cast-vs-forged pistons due to different expansion characteristics under heat cycling. What is the story today, and what advantages would I really expect to see fro ceramic-treated pistons when available? I know that people who have stuck to one brand will naturally say "it's the best." However, for those who have moved around a bit, what is the breakdown of what to expect comparatively from the various brands and options?

The second may be a model-specific question. In this case, we're talking about a '92 KDX250...effectively a '90 KX250 motor. Iron-sleeve cylinder? chrome plated? Nikasil? I'm assuming a plated bore, since I'm seeing "A-B-C" piston options rather than the standard "stock/10-over/15-over" that I'm used to seeing with iron sleeving. With plated bores, the wear would/should be extremely minimal, so how does one identify if it is time for an "A," "B" or "C" slug?

Thanks for putting up with the ignorance of an old-timer.
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Re: slogging through piston selection

Post by Tedh98 »

I will give you my preference on your first question - Wiseco Forged.

I like the piece of mind that it won't break into pieces like a cast piston could. With proper warm up (I let it idle while I put my gear on, make sure the radiators are warm/hot and slowly ride out of the parking area) I have never had any issues. It physically hurts me when I watch someone unload their bike, start it up and then hold the throttle wide open for 10 seconds.

You need to have the bore measured to see what size piston is appropriate. If you don't have the proper tool for that, a machine or engine shop should be able to do it.
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slogging through piston selection

Post by dingerjunkie »

Thanks for the opinion on the forged pistons. I can see where you're coming from. I'm still coming back up to speed here. IIRC, measure tolerances, cold, for forged-vs-cast pistons was different as well, yes? Have manufacturing tolerances/allowances changed in this matter?

Yup...I figured I'd need a mic for bore measurement, as well as a caliper set for pistons (both new and as they wear). I was just thinking that the range of wear to check for would be incredibly miniscule since we're talking about a layer of plating and not the wear one would see in a cast iron liner...easy to get wrong?
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Re: slogging through piston selection

Post by KDXGarage »

The 1992 KDX250 came with Kawasaki's Electrofusion coating (plated). After 23 years, it is probably a good idea to inspect it. Langcourt, Millenium and others replate, as well as are able to sell you a Wiseco piston kit (or perhaps other) to match well to their dimensions on the plating.

If you are talking about changing the piston, then the first thing that needs inspection is the cylinder.
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Re: slogging through piston selection

Post by Julien D »

The cast vs. forged debate runs on, and will likely do so forever. The old issues of additional clearance requirements for forged pistons no longer holds water. I don't believe there are really any downsides to forged, aside from cost. Barring issues that some bikes have with stock pistons (KDX220 for instance) a cast piston will work just fine for most casual riders.
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slogging through piston selection

Post by SS109 »

I agree with JulienD about the debate goes on and that modern forged pistons don't require the larger clearances anymore. My Wiseco forged runs very tight clearance per Wiseco's recommendation.
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slogging through piston selection

Post by adam728 »

I'll jump on board the forged train as well. If nothing else, they are much more tolerant of neglect. Run too many hours and a cast piston can drop a skirt without warning. Run forged too many hours and it will start to barrel shape the skirts and talk to you (rattle/knock). Same goes for starting off with clearances a little on the large side, forged is much more tolerant.

If you are great at doing regularly scheduled top ends (say 50 hours or something), and make sure piston-to-bore clearance is perfect each time, then it's back to the forged vs cast debate.
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slogging through piston selection

Post by dingerjunkie »

Thanks, gents. Looks like I have some decision-making to do on related parts now.

I'm going to go with a forged piston, for sure, and I'm likely going to put out the scratch to cover re-plating and fitting the piston to the bore as part of the deal. Has anyone here played around with ceramic treatments (thermal barriers, thermal dispersants, etc...) on pistons? I'm no a factory boy, but I'm all about maximizing reliability and minimizing wear if possible.

Now time to filter through the rest of the mystery. Much appreciated.
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Re: slogging through piston selection

Post by Tedh98 »

Justn my opinion, but on a KDX money would be better spent elsewhere than on coatings like that.

If you want to minimize wear, just run more oil in your premix(jet for it)
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slogging through piston selection

Post by adam728 »

I would only bother with coatings for something running on the ragged edge, or nearly irreplaceable. So things like a 125 shifter kart, dune bike, etc, or a vintage bike for which parts cannot be easily found.
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Re: slogging through piston selection

Post by newbbewb »

wiseco for the win. it's what, $30 more than pro-x?

...generally speaking, if you ride a lot, then plan on changing rings every year, and piston/rings every other
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Re: slogging through piston selection

Post by adam728 »

newbbewb wrote:wiseco for the win. it's what, $30 more than pro-x?

...generally speaking, if you ride a lot, then plan on changing rings every year, and piston/rings every other

Very generally.

An hour meter is the best. "A lot" for one guy might be 50 hours a year, for another it might be 200 hours.
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Re: slogging through piston selection

Post by KDXGarage »

oemcycle.com is cheap on Wiseco pistons. I have bought a couple there.
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slogging through piston selection

Post by SS109 »

dingerjunkie wrote:Has anyone here played around with ceramic treatments (thermal barriers, thermal dispersants, etc...) on pistons? I'm no a factory boy, but I'm all about maximizing reliability and minimizing wear if possible.
I had my Wiseco piston anti-friction and thermal barrier coated through Jet-Hot. Yeah, it may be overkill but I also like to minimize wear and maximize performance. I don't plan on having to replace that piston for a very long time. Don't let anyone talk you out of it. I have no regrets for spending the extra coin on it.
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Re: slogging through piston selection

Post by ohgood »

SS109 wrote:
dingerjunkie wrote:Has anyone here played around with ceramic treatments (thermal barriers, thermal dispersants, etc...) on pistons? I'm no a factory boy, but I'm all about maximizing reliability and minimizing wear if possible.
I had my Wiseco piston anti-friction and thermal barrier coated through Jet-Hot. Yeah, it may be overkill but I also like to minimize wear and maximize performance. I don't plan on having to replace that piston for a very long time. Don't let anyone talk you out of it. I have no regrets for spending the extra coin on it.

Explain the process please
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slogging through piston selection

Post by dingerjunkie »

Yes...very interested in the process, pricing and such related to JetHot. I was looking at shops working with Tech-Line, so this would be useful for comparison. Thermal barrier only with the anti-friction skirt? Dispersant on underside? What combination of treatments did you have done?

BTW...watched your "first-start" clip on YouTube with the treated piston. Lots of work done there. Very inspiring given what I have in front of me.
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slogging through piston selection

Post by SS109 »

IIRC, it was right at $65 to have both done. They applied their thermal barrier coating to the head of the piston only. This keeps more heat in the combustion chamber which should mean more power and a better overall burning of the fuel. It also helps keep the piston itself cooler. The anti-friction coating was applied to the skirt of the piston. It sure felt a lot slicker than aluminum! :mrgreen:

BTW, here is a pic.

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