Lubricated piston skirts

Not being able to leave well enough alone. I've done some research and added some piston skirt lubrication features to the pistons. The oil control ring has oil return holes that direct oil back to the inside of the piston on the down stroke. I've added a blind hole in the middle (see arrow) so oil can collect in the recess to be re-administered to the cylinder wall on the upstroke (instead of being directed to the inside of the piston). Some of that oil will remain there where its needed most to lubricate the skirt on the load bearing thrust side during the power stroke.



At the bottom of the skirt there is a generous chamfer so the oil will ramp between the skirt and the cylinder wall - especially important for the downward power stroke.



That little blind hole might not seem like much but just one drop of oil applied where its needed every stroke can make a difference. We'll see how well these lubrication features work after the miles pile up. In the mean time - the test pistons have topped 30,000 miles now and show a leak down of less than 1%. And this is without the added oiling feature described above.

Some people chamfer the piston skirt the opposite way, to scrape oil off the cylinder wall.

Triton Thrasher said:

Some people chamfer the piston skirt the opposite way, to scrape oil off the cylinder wall.

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That's right.

And I used to do that when racing, It's a trick I learned from C.R. Axtell. He used to do it to his Goldstars with Sammy Tanner riding. But today's pistons have a cam grind, side relief and a skirt tang that already reduces friction to a minimum. Coincidentally, just when I was going to ask JE Pistons to add a champher at the bottom of the tang, they started doing it completely on their own. They beat me to it. But the blind hole is a new idea as far as I know. Now days everyone wants their components to last forever. Hence the added lubrication.

The added lube is concentrated along a narrow vertical strip where most of the load occurs.

Note that the stock aluminum rods have an oil squirt hole that was intended to lubricate the cylinder walls back when they were having scuffing problems with an earlier piston design. Since then they managed to fix the piston. But the squirt hole remained.

I noticed that the Honda Fireblade has Teflon coated pistons and I wonder how much tolerance you would have to leave for that coating ?

acotrel said:

I noticed that the Honda Fireblade has Teflon coated pistons and I wonder how much tolerance you would have to leave for that coating ?

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If the coating is applied by the OEM piston manufacturer, you just follow their instructions! But actually, I believe (and only believe, I'm not saying its fact) it makes no difference as the coating thickness is virtually unmeasurable.

However, if you have It applied by another company after purchasing the pistons, thats a different matter, and caution should be taken discussing the exact thickness with the applier and considering this in your measurements. Usually, a reputable company will tell your precisely what to allow.

JE has a nice discussion of their coatings here

http://www.jepistons.com/PDFs/TechCorne ... atures.pdf

Some coatings are designed to wear in, and require no additional clearance, but the harder coatings generally require allowance for the additional thickness. Interesting stuff.

Ken

Thanks for the link, Ken.

Jim's top end parts are on my wish list.

xbacksideslider said:

Thanks for the link, Ken.

Jim's top end parts are on my wish list.

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