Cracked Carby Socket

[Bluey]

I discovered just how important it is to very carefully check the Carby sockets before flight today. A crack had developed in one of the sockets and quickly developed into a larger crack. Not sure how long the crack has existed for. I noticed a slight roughness in the engine which I assumed was some icing. Given the low air temps today it seemed plausible. Also, a discoloured appearance to the top of the cylinder around the plugs was another clue. This was probably caused by fuel leaking out of the socket mixing with dirt and lubricant sprayed on the nuts and bolts after each flight. This made it harder to pick up what was really going on. The scariest part is that a friend picked this up as they had seen the same before and recognised the signs. It didn't take much effort to fold the Carby upwards to completely destroy the socket. An inflight failure was not far away!

 

Apparently, it's normal for the cracking to start at the bottom making it much harder to detect a crack beginning to develop. The trike is nearly 4 years old and has 679 hrs.

 

An inflight failure would have resulted in severe vibration leading to a forced engine shutdown and emergency landing. Failure to shut the engine down could result in the engine breaking clear of the trike.

 

Happy flying.

 

Bluey

 

 

[Bluey]

Attached is an image of the socket after we destroyed it by lifting the carby.

 

 

 

[alf jessup]

Bluey,

 

Yep they do break every now and then, doesn't take much when you lift the carby while it is attached to the rubber.

 

Seen it before a few times and people don't seem to bother looking too much at them during preflights.

 

You will now keep a good watch on them.

 

Alf

 

 

[Bluey]

Thanks Alf, any idea how quickly the cracks progress once they start? I know that once they reach a critical size as I think I was getting close today, it will just let go suddenly? Quite scary when I think about it. But you're right, I will be checking them religiously from now on. Also, any idea if there is a time before replacement. My understanding is that they are a five year item. Having said that though, I do lots of hours.

 

Bluey.

 

 

[alf jessup]

Bluey,

 

From memory I think it is 500 hrs, same as the carby diaphragms and needles & jets.

 

UV is the biggest killer on any rubber on a trike.

 

Alf

 

 

[Bluey]

Ok, thanks Alf.

 

Bluey.

 

 

[alf jessup]

$80 each is cheaper than putting down in a crappy paddock breaking something after the engine decides it wants to try and vibrate out of the airframe running on 2 cylinders

 

 

[Guest Maj Millard]

I had a set go in under ten hours from a service where I know I checked them. 222 hrs on them from memory. This problem has been highlighted for a few years now, and a close eye needs to be kept on them, and the 5 years rubber replacement observed...........Maj.....

 

 

[Bluey]

Are they still as big a problem today as they were in the past? I know quite a few operators with significant hours on their machines who haven't had any issues and are still on original sockets.

 

Bluey

 

 

[Bluey]

Has anyone heard of any in flight failures?

 

 

[Guest Crezzi]

Rotax issued a service bulletin about this years ago at the time they introduced a new style of carb socket.

 

The new style includes a spacer on the clamp to prevent over-tightening which was widely suspected to be one of the causes of cracking.

 

Has anyone heard of any in flight failures?

Yes - can't recall the pilots comments but the outcome was a forced landing with no injury or damage

Cheers

 

John

 

 

[metalman]

Just replaced mine, 190hours, although the engine sat around for a while, I noticed it a bit of rough running and thought it was a balance issue with the prop ,replacing the sockets fixed it.

 

Matty

 

 

[Bluey]

I had similar symptoms.

 

 

[facthunter]

I reckon they have always been something you should check all the time. Them and the exhaust pipes and springs. Nev

 

 

[Bluey]

Springs can fail without warning even at low hours. The good thing is the ones I've lost have happened on the ground with the trike in the hangar. The airborne exhaust must not be disassembled unless you have the short tube with the extra ball joint. They will crack if you work on them and then reassemble them.

 

 

[Guest Maj Millard]

Include a look at carb sockets in your preflight inspection, along with exhaust springs. Rotax suggested that the mounting and support of the carbs themselves, was a factor in carb socket failures. The support springs are not there to just look pretty, make sure they are tight and are in fact supporting. Figure on removing carb sockets for a close inspection every 50 or 100 hourly service, and replacing them every 5 years or 250 hrs. Failures seem to occur between 200-250 hours in my experience..........Maj...

 

 

[Bluey]

Just had a report from a friend who recently had a similar experience with his engine at 670hrs.

 

 

[Guest Maj Millard]

Yes that's not a bad run, really got a lot to do with how carbs are mounted I think. There were two rubber compounds used soft and not so soft !....The set I had let go we're the softer compound. Currently have a harder set fitted and so far so good. I'll have a good look at them next 50 though.....Maj....

 

 

[Jabiru7252]

What model Jabiru was it?

 

 

[Bluey]

Not a Jab in site here. We're talking trikes and Rotax 912.

 

Bluey.

 

 

[Jabiru7252]

Not a Jab in site here. We're talking trikes and Rotax 912.Bluey.

That should upset the jab bashers!

 

 

[Ultralights]

How are the carbs mounted? the 912's in a savannah have a aluminium airbox, which is mounted to the engine, and both carbs, so in effect, the carby are supported from both ends, and move with the engine, i have noticed a lot of carbs just have a single air filter at the intake side, and the carby weight, vibrations and movement are all through the socket. these setups seam to have the most socket cracking failures. i have a spare set of sockets i bought at 300 hrs, ready to change if i saw any signs of cracking, now at nearly 1000 hrs, still no signs of cracks, but they will be changed shortly as the 5 year limit approaches.

 

how much of a contributing factor in the cracking is caused by their setup and mounting?

 

 

[Guest Maj Millard]

How are the carbs mounted? the 912's in a savannah have a aluminium airbox, which is mounted to the engine, and both carbs, so in effect, the carby are supported from both ends, and move with the engine, i have noticed a lot of carbs just have a single air filter at the intake side, and the carby weight, vibrations and movement are all through the socket. these setups seam to have the most socket cracking failures. i have a spare set of sockets i bought at 300 hrs, ready to change if i saw any signs of cracking, now at nearly 1000 hrs, still no signs of cracks, but they will be changed shortly as the 5 year limit approaches.how much of a contributing factor in the cracking is caused by their setup and mounting?

Hi Rob, I believe set-up is a big factor, and so do Rotax as they have mentioned this in a past Service Bulletin. They also mention the need to have the supporting spring (carb to manifold) at the correct tension to act as a support also. The Lightwing set-up has the filters mounted remotely on an alt air/ carb heat box and the carb is connected to that with a length of scat tubing. I have still experienced cracked carb- mounts with this set up in the past and it is item 1 on my list for checking when the cowl is off...................Cheers Maj...