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    rotax 503 cooling question
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    I picked up an old sled with a great running rotax 503, its fan cooled (yes I know water cooled is better) *what should I do to increase cooling. *I was thinking that I should pull off the shroud although that directs the air flow from the fan across the heads...opinions???
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    Re: rotax 503 cooling question
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    Millenium Member nutz4sand's Avatar
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    If you do use that motor make a scoop that directs air towards the intake of the cooling fan and be sure to have a lot of room for the hot air to exit the motor.

    The biggest thing for a two stroke is RPM range. The air going through the motors crankcase and hitting the bottom of the piston and the motors insides cool it as much or more than the air past the fins. If you do not run the motor enough RPM's then it will build heat up inside. You can't/should not lug these motors much if at all. Gearing it deep enough to adjust for the weight of your buggy vs the sled it came out of helps to. Overgearing to high will burn em up. Gearing to low will just limit top speed.

    Is this motor still in a sled? If it is you might consider looking more for a liquid job. I have seen nice liquid cooled sleds for $200.00. *If its (The motor you have) in the sled and rideable you might sell it and find a liquid cooled wreck for a tiny more. Bill
    Now that NOBAMA has PROVEN he is the absolute WORST president in the history of history Jimmy Carter can thank him for stealing the dunce crown.

    Lets hope the next guy repeals NObama care along with the rest of the stupid crap this blight on our windshield has done.
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    Re: rotax 503 cooling question
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    Sled was about 580# and topped out at about 115mph, I predict my buggy will be about the same weight, maybe even slightly less (figures are without me in it or on the sled) *Im hoping to be running 60mph max....most runs wont ever get over 30mph. *I wanted a water cooled sled but even wrecks around me are going for $500+ if the motor is still good, I have only found 1 for under $300 and its not running. *Airflow around the engine shouldnt be too hard, Im building a panther and seems to be a pretty open design.
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    Re: rotax 503 cooling question
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    Millenium Member nutz4sand's Avatar
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    Keeping it light will help but do not make it so light that there is not enough metal in a crash to protect you. Just remember that you have rode sleds even with two people on them and pulling another behind on a plastic sled or saucer and it would still haul pretty good. Plus a lot of people overlook the fact that the sleds track takes *A LOT of power to spin it. (Yank the belt off and try to spin the clutch fast to move the track. Good bit of work. Once your buggies rear end is built spin it. MUCH freer! You will free a lot of power loosing the tracks drag factor.

    The sled motor should be nearly as fast in the buggy as the sled. Especially if the weights close. Get the gearing and the clutches right and you should enjoy much. Just don't compromise the exhaust. If you can fit the sleds pipes into the Desert Kart frame it will (usually) be easier to mod the frame a lil than mess with fancy pipe mods. Plus look to bigger tires if you hope to hook it up vs spinning all the time. Good Luck with it. Bill
    Now that NOBAMA has PROVEN he is the absolute WORST president in the history of history Jimmy Carter can thank him for stealing the dunce crown.

    Lets hope the next guy repeals NObama care along with the rest of the stupid crap this blight on our windshield has done.
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    Re: rotax 503 cooling question
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    I have 503 for my sled and I'm going to try a muffler from a ultralight, it will fit in the buggy better then a sled muffler.
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    Re: rotax 503 cooling question
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    Senior Member opsled's Avatar
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    Your 503 could be worth enough to buy you a nice liquid cooled engine with $ left over depending on the year and condition. They are very desirable in the ultralight world and can bring well over $1000 if in good CLEAN!! condition. What year and model sled did it come out of? Single or dual carbs? Points or CDI? These things make a difference on value as well.

    *Personally I think they are a slug and no 503 will ever make 90 mph in a sled let alone 115. If it were mine I would get it running (good) clean it up and ebay it. If you want a Rotax I would look for a 583 or 670. They are very tough engines that will haul some serious mail. Of all the different 2 strokes out there both liquid and fan the 503 is far from the top of my list but I buy every one I can if the price is right just to resell. Rotax is king in the UL world because they supply all the parts and assessories to fly them. The 503 is the most popular because of it's displacment and the fact that it is air cooled which fits UL applications nicely but there are many better options for your needs.

    * * * * * * * opsled
    I reserve the right to change my mind if someone can prove to me it needs replacing.

    Sarcasim is my weapon of choice.
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    Re: rotax 503 cooling question
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    the sled was an 85, dual carbs, not sure on the ignition (havent looked that far yet) *fires up on the first pull of the rope. *I like that exhaust idea, there is about no way the stock system will work (its huge!!!!) I think UL exhaust are only like $20 on ebay. * *Im stuck with a 500 class engine because I plan to race in a regional race that has CC limits... and just to answer the concern of dont built it too light and sacrifise safty, Im actually using 1"x.120 instead of the 1"x.095 the plans called for. *The steel yard screwed up the order and didnt charge me any extra.
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    Re: rotax 503 cooling question
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    BANNED renegadespec1's Avatar
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    Air cooled motor will work fine...
    opsled is right, and knows his sled motors altho the ultra light pipe/muffler will deliver a different power band than you will like in yuor buggy..
    Gearing will be huge and air ducts a must I used to take air off the roof and run it over the motor with no problems
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    Re: rotax 503 cooling question
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    Senior Member Akpilot's Avatar
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    Actcrazy,

    My first build 4+ years ago was a 503 Rotax and it turned out great, no comparison to the stock FL350 motor. *I have not had any issues with the cooling system, granted I live in Alaska, and the temp is 60-70 degrees when we ride. *I chose the Rotax motor because I did not know how much HP the stock Honda transmission could handle, also because easier to swap no radiator/hoses/fan ect.,

    The Fl503 is great on hard pack, probably 60+ MPH, it does need more HP in the sand IMO. *For a woods/trails machine it is great.

    If you use the motor, keep the shrouding around the motor it direct it around the fins. *I looked at opening up the shroud at the last part of the engine where it direct the air straight up, but chose to leave it there, maybe Skidoo wanted it there for better heat transfer. *I did however leave the jetting the same as the snowmobile, on the rich side for summer temps, as I too had reservations about the heat.

    I talked to a Snowmobile Mechanic about this same question and he felt it should be OK. *He said snowmobiles engines run on frozen lakes in the spring time, 40-50-60 degrees, with kids putting around-start and stop all day long. *The engines are completely enclosed with the hot air recirculating over and over, so the temps they can endure is pretty high. *Now can it run in 80-90 degrees with long up hill climbs or in sand - don't know.

    One thing that made me decide is the engine size, twin cylinder 2 smoke, is approximately the same size as a Liquid motor, thus if I burned it down the engine swap was not in vain, just bolt in and plumb for a liquid.

    Good luck
    Wayne
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    Re: rotax 503 cooling question
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    You did a good job installing that motor.
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