Ceramic Coated Piston

[jaguar]

I ride a 100cc two stroke Suzuki AX100 on the street here in super hot Paraguay. I know this isn't a "dirt bike" but the info I have to share is just as useful for dirt bikes. It's just easier to evaluate engine changes on the street because it is more of a controlled environment and the test parameters stay pretty much the same. Anyways I have a temperature gauge with the sensor at the base of the spark plug. When the temp exceeded 290 the power would fall off and it couldn't maintain/reach the normal highest speed. So I had a new piston ceramic coated by Swain Tech to see if the piston heat was slowing things down with the extra friction that accompanies heat. The piston/rings I was running in it were fairly new also. After installing the coated piston it lost most of its sensitivity to heat. But something totally unexpected happened on my second time out with it. After a high speed highway run I pulled off onto a really bad unpaved street and so was just putting along just above idle and the engine completely seized at around 100 feet down the street. I took it apart and found it had an intake skirt seizure. I run semi-synthetic oil at 30:1 and all the jetting was right on. So here is my thoughts on what happened: the coating prevents the piston top from absorbing as much heat but when the average combustion chamber temperature is reduced, as when reducing RPM dramatically, the coating also prevents the piston from cooling off as quickly as it would. So I increased the oil ratio and enrichened the idle mixture a bit. Since then the problem has not recurred.
So for any air cooled dirt bike I definitely recommend ceramic coating. I don't know if any power change would be noticed with a water cooled bike but it may help prolong piston life.

 

[jaguar]

It turned out that by accident I had an oil/fuel ratio about half of what it should of been. But still I don't think it would of seized without the ceramic coating.
The ceramic coated piston now takes longer to heat up but also takes longer to cool down. It still reaches the same maximum temperature because the top underside of the piston is still becoming black. (I know that means its slightly lean but that gives it the best power and my highway runs at top speed are no longer than a few minutes.) To solve that problem I've put a "channel" inside the pistons underside to route the incoming fuel charge up to the underside of the piston crown where most of its heat is. I've made it out of an aluminum beverage can and connected it to the piston skirt with a screw and nut. I'll post photos later. In a few days I'll try it out when I receive the new rings for my newest piston (oversize) which I've had coated with Swain Tech's thickest ceramic coating (50% more than before). The drawing above shows what I am talking about.

ps- This post started out in the mods/performance forum and was wrongly moved here to the frame cutting forum. I protest! If this isn't a mod-performance post then I don't know nothing.

 

[jaguar]

How much of the power loss at high temps is due to some of the intake charge being vaporized under the piston, expanding, and allowing less additional charge into the crank area?
The more the mixture is vaporized, the more retarded the ignition needs to be since a complete burn then happens faster.

 

[jaguar]

Here's the photos:

This shows aluminum from a beverage can held in place by one screw but it is also held in place by two edges it fits into (15mm lower) and its snug fit close to the crown.

See the aluminum sheet inside the piston?:

Probably Friday I'll be able to test it and then take it apart again to see how the aluminum flap is holding up.