Rotax Compression Check
 

Don?t own a Rotax but curious.
Noticed a post calling out compressions of 82/85 etc. on a 100 hp Rotax. Question is are Rotax compression checks done at 85 psi? Most other aviation engines are 80 psi. Is there a specific reason for the he 85 psi?

The Rotax maintenance manual calls out 6 bar or 87 PSI. Since the gauge is easier to set for 85, that's what I use. At 450 hours, we have yet to see a detectable drop in pressure... all four are 85/85.

You need to read the Rotax manual before attempting. Also, you need the specific compression tester for Rotax. Not one for antique engines. The orifice size is different. A Rotax 9xx should loose little compression through out its life, if cared for correctly.

The orifice specified for the tester for a Rotax 912 is .040. That is the same diameter that is used for a Lycoming.

Correct. The aviation specific testers I looked at needed only the correct spark plug adapter.

And in case you're in the mood to save a little money... I looked at numerous similar compression testes intended for automotive use. All look and work the same, but the automotive testers are a fraction of the cost of course. Unfortunately not a single one of them has any detail about the orifice. When I asked, without exception they either simply didn't know or were unwilling to say what it was. I bought one from an aviation supplier.

We made our own by breaking apart a used spark plug and welding an air fitting onto it.

So did a friend of mine, My welding skills are insufficient.

no welding equipment here, but bought the 14mm adapter from ACS (12-01283), available from other vendors as well :)