Kick Ass 61mm / 170cc Piston, Prototype

11494 Views 37 Replies 23 Participants Last post by WynstonWolf, May 10, 2016

Brian S

Discussion Starter · Nov 27, 2013

Happy Thanksgiving Everyone,
It's been a while since I have posted. Too many sites, and not enough time. I'll try to do better. The first Sheridan Racing Design / Kick Ass 61mm big bore pistons arrived at the shop. They turned out better than I could possibly have expected. So now it's R&D / dyno time. I have a couple of cylinders completed, so the testing will comtinue through December. I want to order the first piston/sleeve production parts by the end of December, so that there are customer piston kits for February. I attached a couple of promo pictures for you guys & gals to look at.
Brian
SRD/KARC

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Brian S

Discussion Starter · #5 · Nov 27, 2013

The compression ratio has been calculated at 10.3 / 1. The Grom connecting rod has a 13mm piston pin, not a 14mm pin, so I don't want too overboard on the compression. The negative dome may look large, but remember the displacement is growing by 36%. A flat top piston yields a 13/1 ratio, way too high for the gas we have now. this conversion will require 91/93 gas as it is.
Brian

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Brian S

Discussion Starter · #7 · Nov 27, 2013

Guys,
Because of all the machining:
First the cast in sleeve has to be bored out
Then a counter bore machined for the sleeve lip
The new sleeve heat shrunk in
Then the new sleeve bored & honed
New piston, rings, pin & steel head gasket
Plus the price of the Honda cylinder, $75.00, if you don't want to exchange your parts
I'm trying to keep it under $500.00.
I'm talking to a California CNC shop to machine the cylinders on a big CNC lathe to bring the cost down of getting the old sleeve out.
Brian

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Brian S

Discussion Starter · #13 · Nov 28, 2013

Pictures to Compare

Here are a couple of photo's of the Honda OEM piston, and the SRD Kick Ass piston. It's pretty easy to see the size difference. In the last note before this, the writter said that he wants a dead reliable kit. I agree. I have six 61mm pistons sitting in front of me, on the desk. I could easily sell four of them tomorrow, and I could pull back some of the money I have in this project. But that's just not the way I deal with engineering. Yesterday I had a phone call with the manufacturer, discussing the testing, piston fits, (0.0015" total clearance), cc'ing the dome, etc. These are high silicane pistons, so we can run a very close piston to wall clearance, how close ??? The Grom does not have a lot of finning for cooling, it relies on oil to cool as well. So there has to be a few miles put on the test bike, using close fitting pistons, and looser fit pistons. It has to sit running for at least 15 minutes, with no air movement, just to see what happens. The first two pistons will get shipped back to the manufacturer after they are run. It's a process...
Brian

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Brian S

Discussion Starter · #20 · Nov 29, 2013

Guys,
All good questions:
The piston is forged from a 13%/16% silicone aluminum. Old forged car pistons had only 2%/3% silicone.
I chose 61mm as a bore size, one to be larger than the competition, and two, because 61mm with the correct amount of cylinder wall thickness, is the maximum diameter that you can enlarge the engine without boring out the crankcase. So it will slide right onto the engine. Who would want to completely disassemble the engine, get the cases custom bored, and then reassemble the whole engine, not me.
I purchased a new left side crankcase, the one with the dowl pins, just so I could be sure everything would fit correctly.
Brian

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