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  #1  
Old 07-17-2019, 07:55 AM
Ted RV8 Ted RV8 is offline
 
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Default 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?
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  #2  
Old 07-17-2019, 08:35 AM
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DaleB DaleB is offline
 
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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.
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  #3  
Old 07-18-2019, 01:33 PM
N456TS N456TS is offline
 
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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.
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Old 07-18-2019, 02:03 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by N456TS View Post
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.
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  #5  
Old 07-18-2019, 02:17 PM
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DaleB DaleB is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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.
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Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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  #6  
Old 07-18-2019, 02:46 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
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The aviation specific testers I looked at needed only the correct spark plug adapter.
We made our own by breaking apart a used spark plug and welding an air fitting onto it.
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  #7  
Old 07-18-2019, 03:19 PM
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DaleB DaleB is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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.
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Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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  #8  
Old 07-19-2019, 02:19 AM
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DeeCee 57 DeeCee 57 is offline
 
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no welding equipment here, but bought the 14mm adapter from ACS (12-01283), available from other vendors as well
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