What Compression Tester to Get

"The orifice in this test unit and the gauges on it aren't suitable for Rotax. Toss the test unit. "

Alternatively fill the orifice with HD epoxy - using a 1mm drill bit make a 1mm hole.  The 3 mm specification is unlikly to be met, however as I keep emphasising this is a comparative test ie the more you do over time (each 100 hr service) the more relevant the information. This is the same principal used for testing/analysis of the crankcase oil.

Sure you can compare your individual test readings with a Rotax standard but this is always going to be subject to any variations delivered by technique & the test equipment.

Reducing the variables is key, testing by the same equipment is more important that equipment accuracy.😈

Sean

I think you misunderstand the purpose of the orifice requirements.  The readings as given in the Rotax manual are so you can compare your engine to factory callout standards.  Rotax did the verifications using standard aircraft specification leak down test equipment.  The main variable is they use metric and the aviation standards were outlined decades ago by industry.  For example the orifice in a standard aviation tester is .040 inch by .120 inch.  The metric call out is basically the same, 1 mm by 3 mm.  The use of 80 psi air pressure does not translate well into a nice European number, where they tend to use BAR pressure rather than psi, Rotax calls out 6 BAR which is much higher than the normal 80 psi used in other engines.  The significance of the orifice by diameter AND length is what controls the bleed.  Larger orifice or shorter length will change the bleed.   The significance of the call out in the manual is to use norms that other aviation maintenance providers have or can obtain.  The manual expressly states that standard practice for maintenance methods from AC 43-13B are acceptable.

While you are correct in that this is a comparative test for some reason you do not think it is worthwhile to use the tooling called out so your numbers will be "comparable" to the Rotax values.  I am a bit lost on the logic that you want to "reduce variables" but start with different equipment that would negate comparison to what is in the manual. 

Cheers