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SKIDOO/ROTAX 503 & 550F BIG BORE's

503 FAN BIG BORE SLEEVE

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#1 RotaxFlyer

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Posted 01 March 2013 - 07:22 AM

I have a Skidoo/Rotax 503UL fan cooled engine.

 

 

Bore 2.84" / 72.0mm Stroke 2.40" / 61.0mm Displacement 30.31cu.in. / 496.7cm³

 

What is the Biggest Bore Sleeve I can put in one of these 503 cylinders?

 

Will 550F cylinders bolt onto a 503 Case?

 

Will a 550F Crank bolt into a 503 Case? I understand they have Bigger Bearing Rods.

 

What was the first year of the 550F?

 

Does anyone know, the 503 and 550F Cylinder, & Head Bolt Patterns?

 

I'm told, you can Sleeve a 550F cylinder, for 81mm Pistons, for a 629cc motor.

 

Thanks

Rich Gillen

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#2 coyotekiller

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Posted 01 March 2013 - 07:48 AM

2003 is when they came out with the 550. I don't have a clue what answers are to your other questions but would be curious to find out.

#3 rich1374670x

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Posted 01 March 2013 - 08:09 AM

isnt the 550 a reed engine where the 500 is a piston port?

#4 coyotekiller

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Posted 01 March 2013 - 09:08 AM

yup, good point.

#5 Carolla

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Posted 01 March 2013 - 05:42 PM

Cylinder reed though not case reed.



#6 DOO_TINT

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Posted 01 March 2013 - 05:59 PM

here is a flying fanner

Attached Images

  • MVC-047S.JPG
  • MVC-049S.JPG
  • MVC-051S.JPG

If somethings not broke,i will fix that!

#7 dtfly

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Posted 01 March 2013 - 10:01 PM

here is a flying fanner

Yup, put many hundreds of hours on in FRONT of a fanner... :) It's all good until it gets quiet!



#8 tommc56

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Posted 01 March 2013 - 11:16 PM

here is a flying fanner

 

 

I like the steel shrouds B)


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#9 RotaxFlyer

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Posted 02 March 2013 - 05:14 AM

I was told some of the early 550Fs had the provision 8 holes around PTO needed for gear drive. Only have photo's to look at, but the 503, and 550 case is very simular. Yes, the 550 Cylinders have reeds. Heads are bigger, but head bolt pattern looks the same. Newer 550Fs, don't have the boss's/holes, needed for the gear drive. With all the New Engine Coatings, Ceramic Crank Bearings, Bigger Bearing HD Rods, hopefully we will keep them from going silent for many hours to come. I have mainly 583, 617, 670, parts to play with, but I have a 503UL(50hp at 6500rpms) on my plane right not. A 629cc Big Dog, sounds nice. Since I need to keep RPMs to 6500 MAX for endurance, a better tuned pipe, and bigger bore is about all I can do. They recomend 92 Octane, but that's getting harder to find. I would really like to build it to live on 87 Octane, and make 75hp at 6500rpms. That's only for takeoff, 1-3 minutes, then you throtle back to about 75% power on average. Average rpm range is 4000 to 6250rpms, depending on how fast, or what MPG you want.

 

Rich

 

503 PRO8 FRONT VIEW.jpg


#10 RotaxFlyer

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Posted 05 March 2013 - 04:36 AM

I found out yesterday, LA Sleeve, still makes a Big Bore Sleeve for the 500/503(72mm) that takes it to 76mm, but Dave of LA Sleeve, didn't remeber what Piston they used. There Sleeves can be over bored 2mm. So with a Big Bore 76mm Sleeve, 76mm x 61mm you have a 550(553cc), with a 78mm x 61mm you have a 583.2cc engine. I would really like to use 550F RODs which have bigger Bearings. Then you could also use 550F (76mm) Pistons. A guy told me his 2004/5 550F with 34mm carbs dynoed 70hp at 68/6900rpms. He said, newer 550Fs have smaller 30mm carbs. He built the custom 81mm x 61mm out of the 550F to make a 629cc. He never got to dyno it.

 

Rich Gillen



#11 coyotekiller

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Posted 05 March 2013 - 05:20 AM

That is cool, if you doo this mod, make sure you post it.  How much for the sleeves?  Are you only going to do this on your Ultralight, or do you have a sled to modify?



#12 DOO_TINT

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Posted 05 March 2013 - 07:24 AM

the eng in my pics has some big Bing carbs,,not sure what size,,but im guessing 38mm,,its stored in the garage next to my house,,which i could measure the carb


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#13 RotaxFlyer

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Posted 06 March 2013 - 02:57 AM

LA Sleeves, 503(72mm) to 76mm Big Bore Sleeve, are around $115 each. If you upgrade your 503 Crank to 550F Big Bearing Rods, you could just use 550F(76MM) pistons. Still looking for a Piston to work with the stock 503 small bearing Rods. Blank 76mm Sleeves are MUCH cheaper. There is a guy who makes Porting Templates, but I haven't heard back from him yet.

 

I thought 503ULs used Bing 54, 36 mm carbs, or did you upgrade to 38mm bigger carbs?

 

I reread his letter to me. A guy who dynoed his 04 550F with 34mm carbs got 70hp at 69/7000rpms. Newer 550Fs come with only 30mm carbs, and I think I read, they make 58hp at 6800rpm. But I have read 58hp at 6500rpms also.

 

Actually, I just found a 94 Sled with a 500 Fan on Craigslist for $200 obo, I may eperiment with that 500 for a while. My 503UL on my plane was just rebuilt last fall, and only has 14hrs on it. Never thought then, to research some upgrades for the 503UL, I was looking at only 583, 617. 670, water cooled engines. I stll like the idea of the Big Dog, 629cc idea, (81mm x 61mm). Nice sleeper sled engine idea. :)

 

I can't believe a web site this big, and been around this long, and there is very little info on making any Custom Pipes, or Big Bores for these older 70/80/90s engines, or any Billet parts designed for these older engines. With 3D CAD programs cheap today. Alibre 3d is like $99, and they even have a CAM module. It's about $800, but free, if you know how, and where to look. I'm just learning this 3D stuff. I was working on 583/617/670 Billet Head idea with a CAD guy, but he has disappeared on me. So that Idea is on hold till I learn this better.

 

If we can get a stock 503 Port Map, or Trail Sport Port Map, you should be able to print it out, and tape/glue it onto a Blank Sleeve, and cut, or mill in, the ports yourself. This guy makes some, http://www.racelogic...hatissportport/ but his web site doesn't show any 503 or 550 Templates.

 

Rich



#14 ace_xp2

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Posted 06 March 2013 - 04:42 AM

Not very knowledgeable on porting, but the pics I have of a 503 vs. 550 look very similar apart from the boost port on the 550. How visible should the changes be? 

If they are otherwise the same, I wonder if copying that and adding some boyesen ports with a reed would build the same power if we can find a suitable piston?  I suppose you'd have to change to the newer pipe too. Maybe you'd get decent gains by just going to the 550 bore and adding the aaen pipe?



#15 RotaxFlyer

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Posted 06 March 2013 - 09:31 AM

Not very knowledgeable on porting, but the pics I have of a 503 vs. 550 look very similar apart from the boost port on the 550. How visible should the changes be? 

If they are otherwise the same, I wonder if copying that and adding some boyesen ports with a reed would build the same power if we can find a suitable piston?  I suppose you'd have to change to the newer pipe too. Maybe you'd get decent gains by just going to the 550 bore and adding the aaen pipe?

Actually I'm told the new 550F has real small ports, so an old 503/550 Hybrid, may make even more hp. With a stock Rotax 503UL Ultralight pipe, it makes 50hp at 6500rpms, with a R&D RD-1 Ultralight Pipe, the same 503UL motor made 62.3HP AT 6500RPMS, A 12HP gain. So if you can find a Good Pipe, and increase the CC to 550 +2mm, I would think 70+hp is possible at 6500rpms.

 

76mm x 61mm = 553cc

77mm x 61mm = 568cc

78mm x 61mm = 583cc

 

One Piston option would be to upgrade to 550F Big Bearing Rods, and just use 550F Pistons. Either the 503 Crank Pin Holes can be made bigger on the 503 Crank, or turn the 550F Crank Pins down on the ends to the 503 Crank Pin Size. That way, you get two upgrades, Bigger Rod Bearings & a Bigger Bore. I believe 503 Crank Pins are 30mm, and newer 550s are 31mm.

 

Rich







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