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beauford(at)tampabay.rr.c
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 Posted: Fri Feb 23, 2007 7:03 am Post subject: Rotax engine - Number of hours on engine before ove rhaul |
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Brother Olendorf...
Carbon encrusted 447's have a special place in my life.... I still awaken
abruptly in the middle of the night, drenched in a cold sweat, having
dreampt of a glacier-like flow of the stuff oozing up from under my Simmons
to silently overtake and smother me and my VISA card in our sleep...
Short version... I have a 447... it ran fine for 88 hours...clean as a
whistle... than it began to produce carbon... slowly at first, then with
increasing speed... There ensued an endless cycle of decarbonings,
fiddling with carbueration, etc... which ultimately ended in ring seizure
from the excess carbon and a number of out-of-wallet experiences over at
Castle Lockwood with new pistons installed...
The goons wearing the black hoods and a light coat of oil over there
eventually diagnosed the problem which brought me to ruin... it was the
gradual deterioration of the rubber seat at the base of the choke (or
enrichment circuit for you purists out there) piston in the Bing 54. Over
time this condition permitted the flow of increasing amounts of raw gas onto
the Rotax...much as if the choke were gradually being applied, more with
each passing hour. The result was carbon... cubic yards of carbon....
And the insidious part of this is that the choke piston appears to be fully
seated while this process is taking place. The only way to detect it is to
remove the part and carefully examine the rubber seal installed up under the
base of the piston to see if it has shrunk up and is no longer capable of
sealing the choke metering seat.
Midway in the process, my piston crowns had developed carbon which precisely
matches what your photo shows... Heinrich, the Chief Rotaxman at the
Castle, assured me that there was absolutely no reason for a normal 447 to
make that much carbon on the pistons if the fuels were being mixed to 50:1
specification and the Pennzoil air cooled was being used.
I would suggest that you take the time to check the condition of your choke
piston before pursuing other, more arcane theories about where the carbon is
originating....
Worth what ye paid fer it....
Beauford of Brandon
FF #076
(still waiting for the stinking BRS...)
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olendorf
Joined: 06 Jul 2006
Posts: 140
Location: Schenectady, NY USA
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| Posted: Fri Feb 23, 2007 7:30 am Post subject: Re: Rotax engine - Number of hours on engine before ove rhau |
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Now that's some good info beauford, brother, or maybe even dad 
Maybe I have the same condition. I did recently have the plunger out while changing the grommet and it looked ok at that point but I wasn't inspecting it, per say.
Maybe I'm just running too rich. I actually try to run it as lean as a can. At 5800 rpm I shoot for 1150 egt. You never really know with these things. I check the plugs every 20 hours and they seem fine.
I'll just keep an eye on it. I wasn't actually worried about it. I just wanted folks to see what things could look like after 150 hours. In my opinion at 150 hours the heads should at least be pulled off to look. This isn't that hard to do. Leave the intake and exhaust manifolds on, pull the heads off, admire your clean pistons, flip the head gaskets over and torque the heads down.
It usually boils down to people not wanting to do anything then looking for lots of reassurance that it will be ok to ignore.
Like with cars, it really burns my britches when people have a Check Engine light come on in their cars. They ALWAYS ask "how do I turn that light off?" That light is on to tell you something is WRONG and they don't want to fix it they just want the damn light off. ARRRRRG.
I wonder if these same people get serious anal bleeding and think OH MY GOD, how am I going to get these stains out?
Ha, I crack myself up. Oh well you picked a bad day to prompt me to respond. 
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_________________
Scott Olendorf
Original Firestar, Rotax 447, Powerfin prop
Schenectady, NY
http://sites.google.com/site/kolbfirestar/ |
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