Kdx220 piston design explained

[kdxdazz]

Been meaning to put together a video on the kdx220 Vs kdx200 stock piston comparison, here it is

[SS109]

Excellent video covering the issues. Glad you finally see it wasn't just BS. I think your planned mods for the stock KDX220 piston are smart and hopefully will rectify most, if not all, of the problems with it. Please keep us posted on how it holds up.

Now, on to some of the things you asked about. The open port on the intake side of the piston, along with the bottom edge below it, control when and how much fuel can enter the crankcase ie: intake port timing. The "chambers" on the side of the piston help carry fuel to the transfer ports in the cylinder itself.

On the rings, yes, the one with the groove will carry more oil but has less surface area so I personally think it's a wash as to which will actually last longer. Of course, the extra oil it carries would be nice on the exhaust bridge, which is probably what Kawasaki was thinking, so I would lean toward maybe it's the slightly better option.

Forged vs cast. Cast works just fine IMO/IME, as long as you don't use it for too long depending on riding type. That's why you hear most people opt to change them at about 100 hours of use. Personally, I've run cast much longer than that without issue but I'm a fairly mellow off road rider and not an MX'er. Cast will never live as long as a forged just due to the metallurgy of the two. As you know, metal fatigues over time and at different rates depending on the material it's made from and how it's run. Cast pistons actually expand faster due to their less dense grain structure, yet expand less, hence why they don't require near as much warm up time, and can run tighter cold piston to cylinder clearances, vs their forged counterparts. The place I see some people get in trouble with forged is not having the proper sidewall clearance when cold to allow for expansion as the piston heats up. That said, forged pistons of today expand much less than the forged pistons from 30+ years ago because of improved metallurgy and closer manufacturing tolerances. Following the aftermarket piston manufacturer's recommendation for sidewall clearance on forged pistons, over what OEM says, is a must!

The only critique I have on your video is to turn your camera sideways, if your camera allows it, next time as it will make for a better view for the details you are trying to show. Otherwise, great vid!

[kdxdazz]

glad just 1 person likes my vid on a 20 year old mystery lol, i'll experiment with changing the camera to the side but might need a taller tripod, i'll post before and after photos of the deburring process

have the piston and cylinder in front of me now and still can't work out the chambers in the piston,i see they cross the path of the transfer ports but they are never open to the crankcase so how does fuel get into the chambers? do you have any articles or diagrams to show the workings of this?

actually as ive been looking i see the centre of the chambers line up exactly with the bridge between the transfer ports so now i'm more confused

[SS109]

Yeah, trying to actually see how the ports work and transfer fuel/air is tough! I was told that years ago by an old 2T mechanic but, you know, looking at it now I don't see how that would work on the KDX's cylinder. Looks like it's probably more likely there to help lubricate the piston/transfer port edge. I might have to make some inquiries to get to the bottom of this.

[kdxdazz]

My guess is lubrication too but I good example of how myths begin, we hear something and repeat it only to find out 10 years later it wasn't true

[SS109]

My guess is lubrication too but I good example of how myths begin, we hear something and repeat it only to find out 10 years later it wasn't true

So true.

[KDXGarage]

Thank you for the various videos on your channel. I watched several.

This is a very good one. I appreciate you showing the differences.