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wdaniell(at)etb.net.co
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 Posted: Tue May 22, 2012 4:44 am Post subject: for interest - float bowl gaskets |
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For the record an interesting thing happened to me with my zenith which has
an aftermarket turbo fitted.
Above 11k full power caused vibration - I thought this was just a normal
"fault" of the aftermarket turbo. Take off from 8500 etc all normal.
However the problem got worse and manifested itself at lower altitudes.
We put on a vernier to manually adjust waste-gate and the problem showed up
at higher MP - over 34". Otherwise the engine ran normally. It felt like
fuel starvation.
New carb vacuum chamber diaphragms, carb balance, full fuel system check,
fuel pressure - no change. All readings completely normal except for the
vibration and minor power loss at higher altitudes and power settings.
Just out of interest we changed the carb float bowl gaskets which had been
changed recently using rotax original parts. We put in after market softer
cork gaskets because that's what we had. This cured the problem completely.
The conclusion was that the float bowls had been dropped or the mating faces
had been damaged in some very minor way allowing air to get into the system
but only at higher differential pressure - higher power settings and higher
altitude. There was no evidence of fuel leak. The softer aftermarket
gasket compensated for the minor flaws in the mating surfaces of the float
bowls.
We spent two days and maybe USD500 solving a problem which was turned out to
be a 5c gasket.
Will
Bogota
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budyerly(at)msn.com
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| Posted: Tue May 22, 2012 4:12 pm Post subject: for interest - float bowl gaskets |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> William and all Rotax / Jabiru owners:
At Custom Flight we are having the same problem with the new carb kits. Jim Glover had his plane in for major repairs and upgrades. The engine sat a while (six months) and we refurbished the carbs with new everything for Jim since the carbs had 300 hours on them. We have done this numerous times without distress or difficult tuning. The engine at altitude began missing. At low boost below 27 inches or low manifold pressures under boost, the engine ran great, but when the boost came up to 34 inches, going through 6000 ft., the engine went out of tune. We couldn't fix it so we had Jim fly down to Lockwood to have them have a go at it. They couldn't fix it either after new carb bowls, complete teardown and rebuild again. In desperation, Lockwood put two new carbs on the engine, tuned it up and it is back to normal at great cost and time for the mechanics and owner.
Now suddenly we are having a rash of 914 turbo leaks around the floats. N419PL and 12AY have had leaks as have Bob, William and others. A turbocharged engine must have proper seals on the bowls and compensator for sure to operate properly. Take this as some hard learned advice::
First, do not overtorque the float bowls to seal a leak on the 914, as the bowls bend and distort and they are $140 each.
Second, Bing has recommended cork gaskets for the float bowl for all the 912/912S engines with the bail clips. This is not sold as part of the tune-up kit (normally sold for about $50 with all the O-rings and paper gaskets for two carbs). You have to ask for the cork gaskets specifically. A Bing Tech at the factory told us that we should be using the cork on all the bail clip Bing carbs. Jabiru included. On the 914 they still recommend the paper gasket. We are not in agreement with Bing on the 914.
We are surprised that it seems that the paper gaskets are just not holding up in the 914, especially if it sits a while. So we are putting in cork gaskets now as a matter of course on the 914s to see how that works. Of course the cork gaskets cost twice as much, but between Kerry at Lockwood, Ed and I we are looking at the cork to solve this issue long term for leaky bowls.....
Regards,
Bud Yerly
Europa Tech Support.
[quote] ---
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klinefelter.kevin(at)gmai
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| Posted: Tue May 22, 2012 4:47 pm Post subject: for interest - float bowl gaskets |
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At the Rotax classes I've attended at Rotech in Canada, Rob and Mike have been recommending the cork gaskets for years now.
Kevin
On May 22, 2012, at 5:11 PM, "Bud Yerly" <budyerly(at)msn.com (budyerly(at)msn.com)> wrote:
[quote] <?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> William and all Rotax / Jabiru owners:
At Custom Flight we are having the same problem with the new carb kits. Jim Glover had his plane in for major repairs and upgrades. The engine sat a while (six months) and we refurbished the carbs with new everything for Jim since the carbs had 300 hours on them. We have done this numerous times without distress or difficult tuning. The engine at altitude began missing. At low boost below 27 inches or low manifold pressures under boost, the engine ran great, but when the boost came up to 34 inches, going through 6000 ft., the engine went out of tune. We couldn't fix it so we had Jim fly down to Lockwood to have them have a go at it. They couldn't fix it either after new carb bowls, complete teardown and rebuild again. In desperation, Lockwood put two new carbs on the engine, tuned it up and it is back to normal at great cost and time for the mechanics and owner.
Now suddenly we are having a rash of 914 turbo leaks around the floats. N419PL and 12AY have had leaks as have Bob, William and others. A turbocharged engine must have proper seals on the bowls and compensator for sure to operate properly. Take this as some hard learned advice::
First, do not overtorque the float bowls to seal a leak on the 914, as the bowls bend and distort and they are $140 each.
Second, Bing has recommended cork gaskets for the float bowl for all the 912/912S engines with the bail clips. This is not sold as part of the tune-up kit (normally sold for about $50 with all the O-rings and paper gaskets for two carbs). You have to ask for the cork gaskets specifically. A Bing Tech at the factory told us that we should be using the cork on all the bail clip Bing carbs. Jabiru included. On the 914 they still recommend the paper gasket. We are not in agreement with Bing on the 914.
We are surprised that it seems that the paper gaskets are just not holding up in the 914, especially if it sits a while. So we are putting in cork gaskets now as a matter of course on the 914s to see how that works. Of course the cork gaskets cost twice as much, but between Kerry at Lockwood, Ed and I we are looking at the cork to solve this issue long term for leaky bowls.....
Regards,
Bud Yerly
Europa Tech Support.
[quote] ---
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Wed May 23, 2012 8:52 am Post subject: Re: for interest - float bowl gaskets |
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Unless something has changed, the binder in traditional cork
gaskets will dissolved when exposed to ethanol in gasoline.
Trade one problem for another!
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craigb(at)onthenet.com.au
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| Posted: Wed May 23, 2012 12:12 pm Post subject: for interest - float bowl gaskets |
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Here it is illegal to use fuel containing alcohol in aircraft
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Remi Guerner
Joined: 14 Dec 2010
Posts: 284
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| Posted: Thu May 24, 2012 1:35 am Post subject: Re: for interest - float bowl gaskets |
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Its a pitty Bing / Rotax still use paper or cork gaskets were Viton would eliminate this issue, especially on the 914 were there is a significant differential pressure between the inside of the carb bowl and ambient.
Another thing is when you remove the carb bowls without removing the carbs from the engine, it can be difficult to put them back on without pinching the gasket. Use a mirror to make sure the gasket is positioned in its groove all around before tightening the bowl.
Remi
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