source: http://www.oregonaircraftdesign.com/
Source file:http://www.oregonaircraftdesign.com/files/129360580.pdf

Quote from the pdf file

Something many people are unaware of is the fact that if a Rotax 912 or 914 is
overheated even once, the cylinder heads are destroyed. The excessive heat ruins the
metallurgy and they begin to leak. Also the valve guides can drift and the engine is
headed for a major failure.

I love two cycle engines, I have never had one fail that wasn't because of the dummy operating it. Keep your eyes open "trent palmer" cough for four cycle engines having more engine engine failures.

Yes. It must be true. It is on the internet. On my third lesson, the radiator on my 2000 hour 912s split. The Cht went off the clock and my instructor glided eight miles home. That engine needed a rebuild.
Three thousand training hours later.
I flew it last Sunday, eight year after the incident. It flies very nicely. 912s are tough and, apart from a few camshaft issues, since resolved on a handful of engines, are strong and trustworthy.
I do not accept this article which is complete rubbish

I rebuilt my A65 Continental after 4000hrs! Everything measured within tolerance except the rings. Bore wear was within spec so new rings and a hone did the job and I fitted new bearing shells . The only potential problem was slight wear between the oil pump gears and the case. I did a non-approved mod by opening out the case hole for the gears and inserted an oilite bush (they normally run in plain magnesium!). That engine is still running just fine.

I've been repairing Rotax 2T engines since 1989 and I've lost count of seized pistons/damaged bores/overheated piston pins etc. However, it still gives best bang for buck in a 'Max.

My own opinion is that I'd rather run an old A65/C90 than a 912 etc. Reason? Cost! The 40% or so extra fuel burn is completely offset by the purchase price of a 912 against keeping the old aerial tractor engine going. Call me a Luddite, I don't mind  

Good engines but at 170 pounds, quite a lump. Still plenty about though and not expensive by aircraft standards. Trouble is that a suitable airframe probably costs a fair bit. Maxes are in a different price range.     The 912 weighs  126. (A half 912 would be an interesting thing. Probably get it down to about 45 KG, 90 lb for 40 HP and burning 1 1/2 GPH (US).)

Quoted from tomshep

(A half 912 would be an interesting thing. Probably get it down to about 45 KG, 90 lb for 40 HP and burning 1 1/2 GPH (US).)

That is a very interesting idea..........

The downside would be price.................

Need to find a broken one. There is a big bore kit available I'm told so it will probably be cheaper than LJR to buy that. There is still the need for a water pump and radiator and an oil cooler but I think it would be cheaper and lighter to use a belt drive which would get the prop to around the same as a 447 max and the same rotation.

Hi
Having sold a rebuilt Global that I was going to use on my flat top Max, I eventually will face the "which engine to use" dilemma.  Many agree that the 447 was the engine most suited for many of the Max line.  I'm new to two cycle engines, and within the broad category of 447, there must be some sub sets or various options one has, for instance, dual or single ignition, which gear box has the best ratio, what prop has stood the test of time better than others, both in brand and pitch/length, and other variables as well.  When the day comes, I might just opt for the 447 but need to get educated on the subject before spending hard earned money.  I welcome any and all comments relative to this engine choice for my flat top Max, and, I would probably be interested in opting for electric start if it is an option that is available.  Thanks for all the help, keep up the good work and discussion.
Kim Brown
New Hampshire

Kim, you'll get a lot of views on here I'm sure. My view is based on having a 447 installed in my Minimax 1600R (it's called a 91 here in the UK). Mine has a 2.58:1 gearbox swinging a 60 x 42 wooden 2 blade prop. Peak revs static are 6100 and I cruise at 60kts at around 9 ltrs per hour. The engine is lowered with the gearbox swung through 180 degrees and so it's fan cooled and fully cowled. I have an electric start fitted (one I produce here in the UK   ).

Quoted from tomshep

Yes. It must be true. It is on the internet. On my third lesson, the radiator on my 2000 hour 912s split. The Cht went off the clock and my instructor glided eight miles home. That engine needed a rebuild.
Three thousand training hours later.
I flew it last Sunday, eight year after the incident. It flies very nicely. 912s are tough and, apart from a few camshaft issues, since resolved on a handful of engines, are strong and trustworthy.
I do not accept this article which is complete rubbish

No more chocalte butt holes for you.

Quoted from kfb

I welcome any and all comments relative to this engine choice for my flat top Max, and, I would probably be interested in opting for electric start if it is an option that is available.  Thanks for all the help, keep up the good work and discussion.
Kim Brown
New Hampshire

Here is a good choice: http://www.recpower.com/F-23%202%20cycle%2050hp.htm

F-23 2 cycle 50hp
The F-23 puts out 50hp at 6150 rpm and provides 42ft/lbs. of torque. This engine can handle any part 103 ultralight and most single seat experimentals. Opposed pistons cancel out each others internal inertia forces.  78lbs, including reduction unit, full exhaust, and electric start