"Richard Lamb" wrote in message
nk.net...
Bret Ludwig wrote:

The Rotax two cycle snowmobile style engines sold for ultralight use
were upgraded versions and have fallen out of favor due to seizures,
even with liquid cooled versions.

First, calling a Rotax 582 a "snowmobile engine" is misleading. They were
(and are) sold specifically as aircraft engines, they put out around 65 HP,
and they had several upgrades internal to them (better wrist pin bearings
was one). The new price was around $5000. The snowmobile version of the same
engine (the 583) had around 90 hp, showing how much Rotax gave up in an
attempt to upgrade reliability..

The reason there was (is) such a reliability problem has to do with
carburetion. Several things that you'd never expect were common failure
modes. I remember the following:

The engine would shake so badly it'd foam the fuel in the float bowl - not
enough fuel getting to the engine caused a lean mixture, lean mixture causes
overheating, overheating causes the pistons to expand until they're bigger
than the bore. Pistons would seize. If you succeeded in landing, you'd find
the (now cool) engine would start and run fine. Get a pair of clean shorts,
then go back up?!??

This could happen other ways as well. The common thread was the thing goes
lean and seizes. Right in the operators manual, it says that the thing may
stop without warning. I had it drilled into me by my (now dead) flight
instructor that you "never fly over anything you can't land on."

The new snowmobile engines don't do that. Fuel injection is not subject to
such things - and if it does see the temp headed for trouble, it'll throttle
back - not die completely. My new Polaris Fusion 900 snowmobile (
http://www.polarisindustries.com/en-...nce/900Fusion/ )
has an engine that weighs less than a Rotax 582, puts out 150 hp, and is
fuel injected by a mature reliable design. It will also do 135 mph on
Harding lake from now 'till the spring thaw!

The only thing stopping me from ripping it out of the snowmobile and
mounting it on my kitfox clone is money, and a strong paternal feeling for
the snowbound F-16 fighter it's in now ;^}