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ndibiase
Joined: 19 Oct 2008
Posts: 8
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 Posted: Wed Jan 28, 2009 3:06 pm Post subject: rotax 912 over-run experience |
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Someone as experience with over run 912 ULS engine and (bad) consequence ?
In fact after renting to a friend of mine my loved airplane (with a variable pitch propeller with stops too light loaded - so possible over run ) i experience a power loss.
Spinning by hand my prop seems that one cylinder has less compression than the other (I'll ask my local rotax representative do a compression check and i suspect something happened in valves seats or timing rods ).
But in my experience it is almost impossible to damage a rotax 912 with overrun. Rotax officials said me that they have seen 6800 rpm for tens of seconds with no damage...
I know that rotax says that over 6100 rpm for ......you must check all the engine but often reality is less tragic!
any stories or knowledge ?
thanks
Nicola di Biase
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K Dilks
Joined: 22 Sep 2008
Posts: 108
Location: UK
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| Posted: Thu Jan 29, 2009 4:00 am Post subject: Re: rotax 912 over-run experience |
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Its called over speed .
Above 6100 and with good oil pressure there is a good chance you have had valve to piston contact.
Compression check and lift all the cylinder heads. Inlet valves and pushrods are not cheap.
Why do you over speed? The limits are not there for you to pick and choose when you follow them!
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Thu Jan 29, 2009 6:42 am Post subject: Re: rotax 912 over-run experience |
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RPM over 5800 can cause valve float where the cylinder valve springs are
basically not strong enough to keep up with the high frequency. Then
you can get the valves smashed up and the piston deformed and lifters
crushed.
If you value your aircraft, why don't you believe the owner's manual for
the engine.
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Thu Jan 29, 2009 7:11 am Post subject: Re: rotax 912 over-run experience |
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Hi Nicola,
You most likely have damaged a valve seat, lifter or bent a rod. It needs to have the heads pulled to inspect the valve seats, lifters and pull the rods to look to see if they are straight. Don't just leave this and keep flying as you will incur further damage.
The Rotax is fairly indestructible when run under normal parameters.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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