Rotax 505 / 503 part interchangeability

Hi Paul

Rotax engines used in aviation do not list Rods or pins.  They do sell the small rod end bearing and the bearings on the ends of the crank but not for the crankshaft centres.  They don't want the crankshaft pushed apart and "rebuilt" as it may lose the interference fit required.  It is more of  liability issue.  

Pistons, cylinders, and a lot of the other bits are fine but some special parts used in the 505 are now impossible to get.  These would include the heads, they had decompressors on them in a number of the versions.  The Bosch Polar Fire ignition is impossible to find and there are Service Bulletins to upgrade that to newer versions of ignition.  The exhausts and intakes would be very hard to get.  Best to try to find a motor glider group to exchange information on these old engines as they have been out of production for some 40 plus years. 

If you need the old parts manuals check with Rotax-owner, they have all the old ones as historical documents. 

Cheers

Historical docs direct link: https://www.rotax-owner.com/en/support-topmenu/engine-manuals#2-stroke-historical-documents

Many thanks - that's interesting and useful background. I think the answer is to look after my existing engine and use it as little as possible. I can't self-launch from my regular airfield anyway due to planning constraints in a national park.

If things do go wrong do you know whether the mounting flanges and crankshaft taper are the same for the 503? I know this engine was never certified but it was used in various 'permit' aircraft in the UK where I'm based, and there is a mechanism for using non-certified equivalents when original parts are no longer supported and available.

Thanks again, Paul

Hi Paul

The crankcase bolt pattern is exactly the same across all of the 503 type line (501, 503 and 505)

i am pretty sure that the 505 was certified to JAR part 22, Day VFR for motor-gliders.  The major difference from the 501 to 505 was the ignition.  501 was a Bosch points system.  The 505 was a Bosch dual "Polar Fire" CDI system.  The Polar Fire has not been supported for a very long time. 

Cheers

That's good to know. I'm just contingency planning at the moment but that does sound like a line of enquiry worth pursuing with the British Gliding Association. Paperwork and approvals always take longer than the job itself, so it's good to be ahead of the game.

Thanks again.