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Gasoline pouring onto the ground


opticsguy

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I went for a short flight today and landed.  During shutdown I noticed 3 GPM fuel flow at idle, and 2 GPM after engine shutdown.  After a minute of cleaning up the cockpit I got out and saw a stream of gasoline pouring onto the ground.  I quickly took off the cowl and gas was pouring from the pilot side carb bowl, a stream almost 1/8" wide.  I don't usually park with the fuel valve off, but I shut it and the fuel leak eventually stopped.  Did I mention it was dripping onto the exhaust manifold?

 

With some help from LEAP, it was determined that a press-fit guide for the floats had fallen out and left a hole in the carb bowl.  If this had happened away from an airport I would have been truly borked.  At a minimum I would have probably run out of fuel, but a fire is more likely.  You can see a drip of fuel below the boss in the pic.

 

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Too bad!

 

Should not the drip tray have caught the fuel and routed it away from the exhaust and onto the ground? That's kinda what it's there for!

 

Plus, the pins that guide the floats are just pressed into the float bowl. I've never heard of one coming adrift, but if they did, they would not leave a hole - so something else must be going on.

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Too bad!

 

Should not the drip tray have caught the fuel and routed it away from the exhaust and onto the ground? That's kinda what it's there for!

 

Plus, the pins that guide the floats are just pressed into the float bowl. I've never heard of one coming adrift, but if they did, they would not leave a hole - so something else must be going on.

 

They're press fit, but machined through.

 

 

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They would have to cut a notch or something to let the air out if it was a blind hole, since no air would escape in an interference fit. That's extra machining steps and sets up an area to crack.

 

It's EXTREMELY unusual for one of those to come out.

 

Also, many drip trays don't do a good job of catching fuel on the ground, but fine in flight. I don't like the ones we have installed in all of our CTs either.

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 I don't like the ones we have installed in all of our CTs either.

 

Just wanted to point out the ones installed on a SW are different than the LS. The LS was an improvement, but still not great. I guess that is an added bonus of the injected engine. No drip trays.

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I recently had this exact issue in my CTSW. It can't be that extremely rare. Roger helped with the proper repair procedure.

 

I also put a dab of epoxy in the open holes on the bottom of both carbs. If this happens again, the holes are sealed. If the seals leak, they should just seep and will be easier to catch, instead of dumping a gallon of gas onto my engine in minutes (again).

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This does happen from time to time, but as you said it is rare compared to the number of carbs out there on 50K engines. When that float guide pin comes out the floats can not control the fuel flow anymore and the carb floods and over flows. If you are running full throttle most all that fuel is being used until you throttle back and the excess flows out. The easiest fix is to use some Loctite 648 in the hole and on the pin. Either press it back in place or tap it back in place and let it sit for the night. It will be fine.

 

If you are away from home on another field and caught this I would just tap it back in place until you got home. It may stay forever if you tap it in firm enough. Applying the Loctite will make sure it stays. I have repaired 3-4 like this without any issues and they are still flying today.

 

p.s.

Even though having your fuel hit a hot exhaust isn't the best situation to be in it is unusual for it to start a fire on a Rotax. (but never say never) Some engines aren't so lucky. I see leaking carb bowls fairly frequently from bad gaskets.

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Does everyone know what a Service Difficulty Report is?

 

Available online here: http://av-info.faa.gov/sdrx/

 

It's a way for mechanics and owners to alert the FAA, and indirectly a manufacturer, of a mechanical problem that may be design related, material related, caused by improper maintenance, that sort of thing.

 

Has anyone filed an SDR on this issue? This failure mode could have such dire consequences that I would want to be sure the FAA and ROTAX were aware of the issue.

 

It may be rare, but we have about a half dozen reported here already, in a small subset of all ROTAX owners. So, even if rare, it's common enough to be of concern.

 

If you have not submitted an SDR on this, I would encourage you to do so.

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This does happen from time to time, but as you said it is rare compared to the number of carbs out there on 50K engines. When that float guide pin comes out the floats can not control the fuel flow anymore and the carb floods and over flows. If you are running full throttle most all that fuel is being used until you throttle back and the excess flows out. The easiest fix is to use some Loctite 680 in the hole and on the pin. Either press it back in place or tap it back in place and let it sit for the night. It will be fine.

 

 

 

Roger, you had me use Loctite 648.  Is the correct number 648 or 680, or will either work?  The 648 bottles says "retaining compound" which certainly sounds like the correct stuff.

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Hi Andy,

 

It was a misprint in my post. I fixed it. It is 648.

 

Anything that breaks or malfunctions on a Rotax ought to have a CISR (customer incident service report) done, but unfortunately this only happens maybe 10% of the time. How can you get people to file these reports when only 20%, which is up only 5% since LSA in the US, to file their new engine registration.

 

If mechanic's and owners are satisfied with 3 line annual logbook entries those same people aren't going to go out of their way to file another report.  

 

Good documentation is a taught and a DAILY practiced habit that bleeds over into other parts of our ownership.

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Service Difficulty Reports are a way for mechanics and owners to bring design deficiencies to the attention of the authorities, who can take corrective action if necessary, in the form of Service Bulletins and Airworthiness Directives.

 

Of course, another alternative is to just ignore a problem until an accident or a chain of accidents occur. I vote for SDR's.

 

It's hard to imagine a more terrible end than burning to death. Fuel pouring out of a float bowl onto an exhaust pipe (not all ROTAX-equipped aircraft have drip trays) sets the stage for such a tragedy. Plus, the coming adrift of the float guide could also cause a power loss as the now free float and pin rattle around in the bowl. That, by itself, could cause an accident leading to injury or death.

 

Can an SB or AD be annoying and/or expensive? Sure. But they serve a valuable purpose.

 

Incidentally, I refuse to get dragged down into a debate involving the demonization of the government in general or the FAA in particular. If that's where this thread goes, enjoy it without me.

 

 

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Keeping it inside the Rotax and Flight Design domain is a good thing....involving ANYTHING in a government database is not....

 

Disagree in this instance. There's a lot of ineptitude in government, but they don't have a bottom line interest in keeping flight safety issues quiet.

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Rotax is very good about addressing issues once they know about them and unlike the auto industry that has to have the NTSB after them to do anything Rotax takes the initiative to let people know and issue new parts. You may not like it when it included you, but they do go public right away for their customers. I would rather have a company that jumps in and doesn't only act when the government jump on them and forces their hand.

 

The key here is for everyone to file CSIR with Rotax or their is no way to track issues.

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I just replaced my left bowl and gasket and ran it up.  No leaks.  The pin was loose, but not out, of the hole, in the old bowl..  This has scared me so much that I will no longer take passengers or my wife up in my CT.  Luckily, I was just on a 20 minute flight to stir up the fluids, around KSUE in Sturgeon Bay.  Had I caught fire, I probably would have flown it to within 30 ft of the water and bailed out.

 

This is a serious issue and shouldn't be blown off by Rotax.

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In perspective:

 

It's extremely rare. No different than anything else that can go wrong with any engine and other things that can shut down an engine are far more common.

 

 

I suppose that depends on one's perspective.

 

We have 6 documented here in a fleet size that's only a tiny proportion of the worldwide fleet.

 

If we're dealing with, let's say, 100 CT's that we're familiar with, that's 6% of the total.

 

Problem here goes beyond shutting down the engine - its a failure that can pour gas into the engine compartment - no trivial matter.

 

Even the problem stated in the thread title - gas pouring out onto the ground, can also have dire consequences.

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I highly recommend that owner/operators epoxy the holes on the bottom of the float bowls. It's quick, easy, and should be an effective mitigation in the case of a pin coming loose. At the very least any leak will be more likely to seep instead of dumping fuel, giving you time to catch it on a preflight.

 

BTW I have 7-8 hours of time since my repairs and have not seen a molecule of fuel leaking since. I have a new float bowl for that side, but I'm reluctant to replace it when it seems to be doing well. I will probably keep an eye on it and keep the spare bowl at the ready for now.

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I noted Brett at LEAF epoxied a little ball pressed into the bottom of my carb the last time he overhauled them.  My 100 hr./yearly is next week.  I'm definitely going to epoxy the float pin holes on the bottoms of the float bowls. As Andy indicates, at the worst, there will be a slight weeping or slight wetness that will result which will be noticed.  For "plan B", I'm tempted to just pull the pins, loose or not, put a generous dab of loctite 648 in the hole and coat the bottom of the pins and tap them back in.

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I think plugging the holes with a little epoxy should be a required safety mod.  My pin worked out enough to leak but the not enough to affect float motion.  For those of you who do your own annuals, checking these pins every year is a must.  I could see how hundreds of hours of vibration could cause them to work loose.

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I think plugging the holes with a little epoxy should be a required safety mod.  My pin worked out enough to leak but the not enough to affect float motion.

 

Mine was the same, the engine ran and performed normally; I only noticed the issue on the ground after the flight.  I'm not even sure there is enough room above the pin for it to work out completely.

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What freaks me out is that I have to turn off the engine to shut the fuel valve,  meaning that that leak would continue for about 2 minutes (how long it took to stop on the ground).  If I could have shut the fuel off and ran the engine until it stopped, I possibly could have starved a fire.

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If you use the Loctite you'll be fine.

One last little tip of the day. You can heat the pin hole fairly HOT and then seat the pin with the Loctite in place. The reasoning is the hole will be expanded a tad and then the pin will seat a tad deeper and tighter.

 

p.s.

Make sure the pin and the hole has Loctite on and in them.

I doubt you will ever have another problem.

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