McFarlane Throttle springs

by Sean Lillico in General Tech Discussion 8 years ago

I have a 912ULS with a McFarlane throttle cable and reduced tension McFarlane throttle springs (PN6822) installed. Two springs have broken within a few hours of each other, coincidently both on the right hand carb and both on the lower hook. Carbs are synced and no abnormal vibration evident. Has anyone else experienced failure of these McFarlane springs or have an idea what may be causing it.

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Re: McFarlane Throttle springs

by Kevin Machniak » 8 years ago

Kevin Machniak

6 167 40

I have had one fail , from bottom first to second coil area. They shipped replacements and were very interested in the details of the spring failure. They said they have had a few break on aircraft that had vibration issues. another possibility is if you use some tool that nicks the loops when installing.
I also noticed that when installing the new springs that the spring bottom does not clear the rotax drip trays by very much, I took some material out of this area with a dremmel to provide a little more clearance. A good carb sync and a dynamic propeller balance may be in order, I have done the first and will be doing the propeller in the very near future.

Thank you said by: Sean Lillico

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Re: McFarlane Throttle springs

by Roger Lee » 8 years ago

Roger Lee

126 5.14k 4.58k

I have been watching this on other forums. My guess is that McFarlane needs to change springs. The steel in their springs are too brittle to handle constant movement coupled with some vibration. I have seen others replace their own springs from places like Ace Hardware and they have had no issues. It would be worth a call to Mcfarlane and tell them so. My bet since they have had quite a few fail they may just change springs. Vans RV12 guys have had several.

It's just a phone call.

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

Thank you said by: Sean Lillico

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Re: McFarlane Throttle springs

by Sean Lillico » 8 years ago

Sean Lillico

1 2 0

Thank you Kevin and Roger. I've contacted Ben at McFarlane and sent him the pictures he requested.

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Re: McFarlane Throttle springs

by Sean Lillico » 8 years ago

Sean Lillico

1 2 0

Update: McFarlane are replacing the failed springs.

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Re: McFarlane Throttle springs

by Alan Arnold » 8 years ago

Alan Arnold

20 188 145

On the advice of my airframe manufacturer, Just Aircraft, I removed the springs and actually have a much better feel with the throttle.

Of course, as an experimental, I can do this with no regulatory issues.

Also, my throttle cable assembly is very robust and I have no slightest fear that it will break or disconnect in flight, unlike the carb retaining springs that came with the engine.

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McFarlane Throttle springs

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