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Yamaha RX-1 Snowmobile Engine Conversion

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Marc W

Well-Known Member
Joined
Mar 31, 2017
Messages
1,232
Location
Colorado
I first saw or heard of the Yamaha sled engines being converted for aircraft at the Copperstate Flyin last year. Teal Jenkins, the man behind Skytrax, had an Apex engine with a gearbox of his own design on it displayed. The sign said 160 HP at 165 lbs. I was smitten!

Recently a RX-1 engine, Skytrax adapter and Rotax "C" gearbox came up for sale. The seller started with a high price and I passed on it, as did everyone else. Weeks passed and the price dropped. A couple more weeks passed and I made a low offer and accepted a counteroffer. It was to good a price to pass up so I bought it. Here it is sitting in front of the airplane as I figure out the engine mount and where to hang accessories. Pictured is the "C" box, flywheel, Hardy disc and the Skytrax adapter.
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This is a picture of a RX-1 engine in a sled. The RX-1 is carbureted and you can see the tops of the four carbs. The other necessary parts are the thermostat housing, which is the aluminum domed object at the near end of the cylinder head. The radiator header tank is left and a little above the thermostat housing. The engine has a dry sump so you need the oil tank which is below the carbs in the picture with all the hoses going to it. The carbs are electrically heated and also heated by coolant.
upload_2020-1-30_16-1-49.png

The RX-1 was built 2003 to 2005 and was rated at 140 HP at 10,200 RPM. It was replaced by the fuel injected Apex from 2006 to 2008. The Apex gained 10 HP or so over the RX-1. They are basically the same engine. They both have COP electronic ignition. They also have 1.19:1 internal gear reduction with a rubber damper in the countershaft.

There are other companies that make adapters to run the Rotax gearboxes on the RX-1. I have the Skytrax adapter. There are quite a few of these engines on PPC's, autogyros and the like. There are a few on airplanes. You can run a low inertia prop with the rubber Hardy disc. People running heavier props can use the RK400 clutch. The RX-1 prop turns left.

Teal Jenkins makes a gearbox that bolts directly to the Apex engine. His gearbox uses three gears and so it raises the thrust line a little and it makes a little shorter engine. Since it uses three gears the prop will rotate to the right.

So there it is, my next project!
 

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