Hard start 100 HP 912

by Kjetil Kristensen in 912 / 914 Technical Questions 13 years ago

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Re: Hard start 100 HP 912

by milo avram » 13 years ago

milo avram

2 20 0

Â¿ with engine idle over 1 500 rpm ?,

I'm following rotax advise from 1997, (when ever save and sensible),
accomplishing with an OPERATION IDLE around 2 500 to 2 750 rpm !!,

it does miracles, specially to the clutch,

cheers

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Re: Hard start 100 HP 912

by Richard Russ » 13 years ago

Richard Russ

6 29 0

Hello Milo, I don't have the information you are talking about regarding the 2500-2750 RPM but the operating perameters I received with my 2010 piperSport (with the 912 ULS engine) was to start and idle at 2000 RPM for one minute then increse the RPM to 2400. My low speed shut down idle speed is set at 1800 RPM. I do know mine is easy to start and runs great.

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Re: Hard start 100 HP 912

by milo avram » 13 years ago

milo avram

2 20 0

I'll be searching those bulletins for You , must have them,
Â¿ possibly it's technical,
but physically it's almost wrong to think about 2 400 rpm !!,
to understand physics, we need to think about 40 rps (second),

40 times intake 40 compressions 40 detonations 40 times exhausting,
!! in just 1 second !!, in idle !!,

and there we start talking about frequencies and harmonies, which
we may achieve with some few rpm's only,
(on a piston engine with hundreds of parts 'flying around in that metal box'),

engine vibration harmonies and propeller oscillations have to damp with each other, too,

that might be easy to write about, but not to achieve,

and if we manage to perform so, this does miracles, specially to the clutch,

cheers

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Re: Hard start 100 HP 912

by Roger Lee » 13 years ago

Roger Lee

125 5.11k 4.52k

On the first start of the day and or when cold start up and then idle is best at 2000 up to 2400 rpm. This is where it will run smoother than when at the lower idles of 1800 or lower on the first start of the day. The reason the low rpms beat on the engine/gearbox at low rpms is the compression ratio of the 912ULS at 10.5:1. This is also the reason for the use of 91 octane or more for fuel.
The 912 UL is only 9:1 so it can use 87 octane or more. The 9:1 compression is not so harsh as to make the engine
chug (chug= technical term ;) ) at low rpms like the 912ULS.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Hard start 100 HP 912

by milo avram » 13 years ago

milo avram

2 20 0

it's almost a tragedy to me, that thousands of engines never ever reached their TBO cause to that infamous
1 400 rpm operation idle approach !!!,

rotax engineers mentioned it in several occasions,
'field experience had shown ...',

it appears in several bulletins, but I just found this one for now,

rotax service instructions,
selection of motor oil and general operating tips for rotax engines type 912 and 914 (series)
SI-18-1997

section 3.4)

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Hard start 100 HP 912

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