View Full Version : 503 cooling - advice & opinions

27-Mar-13, 11:13 AM
The old lump is on the bench ready to turn it into a twin bing flying thing. The question I have is - while I have it apart, should I junk the forced air cooling in favour of free air cooling? It will free up a few more horses but is it reliable, are there any free air cooling ducts etc?

I'd like to read your thoughts


27-Mar-13, 12:50 PM
Hi Glen

If it is on a gearbox leave it on , or it will overheat



28-Mar-13, 11:07 AM
Hi Glen,

I'm with Lee, mainly as he knows these engines inside out and from personal experience.... I ran free cooled with a gearbox a few years back and seized the engine two if not three times in a season.... Rotax pistons ain't cheap!!!!!!



Fred Wilson
28-Mar-13, 11:18 AM
if your a new driver going into novices then I would suggest you keep the cooling as is for the time being.

Nick Drew
28-Mar-13, 01:23 PM

If you take the cooling off it will go fast but it will also go bang. It's a balancing act to get it to work without frying the pistons/barrels. I wouldn't do it without some sort of telemetry. EGT's and revs as minimum. I have run mine free air cooled with a belt drive. It is quick but not without its problems. I have seized a few pistons in the last two years of running it that way so I would say that its not a very reliable way to run the engine.

I've never run free air cooled with a gearbox but I would think Lee is right not to. With a belt drive you have so much more freedom with engine placement to gain optimum airflow round the top end.

Even with all the gauges and best design in the world you will still want it to go faster and end up pushing it into breaking point anyway ;)

Fred has a valid point. There is nothing to gain running free air cooled if you are doing a season of novices. Novices is all about getting races under your belt. The last thing you need is to be rebuilding engines and not going round!

On the other hand, you might run it free air cooled, with a gearbox, get the set up right and leave everyone standing!

Unfortunately the ultimate choice is yours. Just be prepared for much sucking through teeth and head shaking when you turn up with a naked one ;)


5-Apr-13, 12:19 PM
Looks like I will be keeping it forced air cooled. Thanks for the feedback guys.