Anybody a Rotax 503 Guru of Sort!

[WillySteve]

Welp, bad as I hate to admit it I've been Hornswaggled into helping a friend with his Ultralight and I know some of you have dealt with this engine as I've seen many posts referring to 2 stroke SnowSled engines.
What I have here is a '90 model Rotax 503 2-cyl, 2-stroke Fan Cooled engine made in Austria. This engine was mainly used on a ton of Sci Doo Sleds but found it's way into the ultralights back in the 90's before it became obsolete!
Teardown inspection looks like 1 of the 2 Bing carbs stopped up and fried 1 of the 2 cyls. as the other looks immaculate.

If you've had dealings with this engine and in the know, MY Question is:
Are the Pistons and Cyls the same on aircheen and sled as long as they're Fan Cooled Engines? They appear to be but no one will positively verify in the sled biz, (which is about the only place to carry parts),.....guess they're afraid of a liability?

ANYBODY???

[Tomanytoys]

I’m not a Doo guy but I’ve got a couple friends that have close ties with both Bombardier & Rotax GmbH.
I’ll see what I can find out.
I’ve rebuilt a handful of 503’s over the years.
I assume the cylinder you have is regular steel sleeve?

[WillySteve]

I've hit some of the scored places with 600 grit and it didn't seem to scratch the clean part of the bore much at all so it's for sure hard but this engine definitely has an iron sleeve pressed in the alum cyl....so my guess is iron, unless the Ausies do things different and plate over an iron cyl which I think would offset the gain!

If it helps any, the #'s are Bombadier Mod# 4068877; 72mm Bore/61mm Stroke AND embossed on the main block is 6812200. ALSO stamped on the Exhaust Port on each cyl is the # 6823 641

[Tomanytoys]

Got word that the parts for the sled version 503 are not interchangeable with the aviation 503.
Apparently your best source for aviation 503 parts will be the internet.
Best of luck.

[Capt.Insane-o]

That's a lot of liability you are taking in your hands.

[WillySteve]

That's a lot of liability you are taking in your hands.

That's why I hold a Federal Aviation A&P license......and yes, even though it's an experimental I will have to sign it off!!

[H2OPERF]

That's why I hold a Federal Aviation A&P license......and yes, even though it's an experimental I will have to sign it off!!

Liability is the reason most A&P mechanics will not work on experimentals, that engine has no TSO so it never had any testing or had to meet any federal regulations it might as well have came off a lawnmower.. Anyone can and may have worked on it previously and that's where the problem lies, an A&P is only required for the 12 month condition inspection....Check with wiseco they make rotax pistons. Dave

[WillySteve]

Thanks Dave,
This one's log states everything done to it from inception. As stated, I was hornswaggled by a good friend or I wouldn't mess wit it to begin with!!
Sometimes being somebody's friend gets in yer way of doing what you'd much rather be doing!
I'll document a compression check and bore scope on it before it's in the air, just to cover my tracks!