912 Big Bore

[Av8r3400]

Fellow Kitfoxers, I moved the above posts to their own thread because this is going to have some good information that we will want to find again later.

Mr. Bill, Can you please give us some more details of what you are doing so that we can all learn more about this option for more power?

[mr bill]

I bought a late 2006 Rotax 912ULS engine with 36 hours TT. It had a prop strike with the previous owner, with one blade broken on a wooden prop, so I thought there was not much risk. The engine was installed and firewall forward was done. Recently I heard about big bore kits and after some brief research, bought one from Hal Stockman in Elko Nevada (recommended by Lowell Fitt) that increases the engine displacement to 1884 CC. He estimates horsepower increase to 104 and will be doing dynamometer testing in a few weeks. After pulling the old jugs, I found deposits from 100LL on the pistons, cylinder heads and exhaust valves. I bought the low compression version (9.7 to 1) so I can use auto regular. Then I thought that as long as the jugs are off, (an old story) I'll install the new flywheel, for easier starting and the oil pump conversion to increase the TBO to 2000 hours. Then I took the gearbox to Leading Edge Airfoil for a teardown and inspection and they found the propeller shaft flange was bent from the prop strike, so a complete rebuild was done. They also overhauled both carburetors. The engine is back on the plane and the cylinders , gearbox and oil pump are installed. Two steps forward and one step back. Now I know what the engine is. First start is still several months away.

[avidflyer]

Mr. Bill, you say that the prop shaft was bent from the prop strike. Did you ever put a dial indicator on the prop shaft before it went to LEAF? I guess I'm wondering if it could dial straight on the prop shaft hub, but still be no good. Thanks , Jim Chuk

[mr bill]

First they used a dial indicator on the propeller shaft in the case and then again in a v block after disassembly. The shaft was not bent, just the propeller flange. They replace clutch parts, which is required after a prop strike. They also went thru the cylinder heads completely. They cleaned up very nicely. Inside of the crankcase was beautiful, as expected with 36 hours TT. In my earlier post I said 1884 CC, should have read 1484 CC.

[Av8r3400]

You said the motor is a 912 UL S ? The 100 or 80 hp variant?

If you are starting with the 100 hp motor, that seems like a lot of work for an additional 4 hp...

[mr bill]

Yup, but I will be able to burn auto regular. They added 132CC to the engine, so I think the dyno testing will show more power than they are claiming.

[Av8r3400]

Bill - do they have a website somewhere showing details? Are these kits available for the 80 hp motors?