bikerbc

Just out of interest is it an AMA rule that a clevis needs to be secured in some way ? I always ( almost ) use a small piece of tubing . I also like using certain plastic clevis's because they wont back out or in on their own . there is enough friction on the threads to keep them from moving . I like the Du Bro Safety lock Kwik-Link ones too ,they don't need any fuel tube because they have that little clip .

JohnBuckner

My Feedback: (1)

Ken I can say for a fact that some pylon racing venues in the specific competition rules do spell out that all clevis except the throttle must either be of the mechanical locking type or must be secured with the fuel tube. Have been turned around many times from tech inspection when I missed one.

John

HighPlains

My Feedback: (1)

I'd bet it is the SMFF

jaka

Hi!
International pylon racing rules! Not AMA.

CafeenMan

Well, I just broke a nylon clevis for the first time ever. Actually I think it was styrene, not nylon. It was hooked to the throttle of a Norvel .061 and has been there untouched since the day I finished the final adjustments on the model. I was pulling the engine because it was so gummed up the throttle wouldn't move and the muffler had so much burnt oil on it you couldn't see metal anywhere on it.

Anyway, when I opened the clevis the arm snapped right off. I'm replacing it with another nylon clevis. Nothing wrong with them at all and I've never had one fail in use. I've opened some ones that had a lot of use and it was scary how much the pin was worn down. But that's my fault for not checking things often enough.

jester_s1

The DuBro nylon clevises are many times stronger than they need to be for .40-.60 size models. If you doubt that, hook one up to a servo arm and see how hard you can pull on it. After many years of UV exposure, the nylon will degrade and get brittle, so it's a good idea to pop them open from time to time to see if they are still flexible and give them a good yank to make sure the pin hasn't worn out. I've gone to using a little zip tie to secure mine though. I had this odd problem on my Kaos of the fuel tubing splitting nearly every time I went to the flying field so I put a zip tie on it out of frustration. It was still there after a year, so I'm a believer in the method now. So once I get a plane dialed in the way I want it, I put zip ties on all the nylon clevises and dab a drop of CA on so they won't slide back. Yes, I have to cut the zip tie off if I want to remove the clevis later, but this is on planes that are fully trimmed out and won't need anything adjusted for the foreseeable future.

CafeenMan

Probably some sharp mold flash was cutting your fuel line keeper.

jester_s1

Possibly. It didn't cut the zip tie though.

JohnBuckner

My Feedback: (1)

For some of us who choose to use nylon clevis on certain types in our fleet and safety it with fuel tube then if you have been using medium fuel tubing for the safety I recommend using large silicon. The medium size is a bit of overstretch the large which seems to work very well on most clevi'. This will tend to greatly enhance its durability requiring less maintence even with exposure to UV.

John

JollyPopper

My Feedback: (6)

The various kinds of clevises are kind of like the various glues we all use. The particular situation will dictate which to use. They each are good in their own way and in their own place but they both have down sides too. I was fooling with a metal clevis a few days ago that came already installed on a plane that I got from a very good builder, but once I spread the legs of the clevis to get it off the servo arm, it remained spread. It was made of some soft steel that had no spring in it. It simply stayed where I put it. I threw it away and replaced it with one that had some spring steel in it that closed on its own. I used a fuel tubing keeper on it anyway. And running an engine with a metal clevis threaded on a rod but not connected to a servo arm will produce a dance that would make Fred Astaire jealous. They have to be backed up with a nut. on the other hand, nylon clevises will get brittle and break after a time or the pin will wear out. You just have to check them from time to time no matter which you use.

bikerbc

I agree , There is no substitute for regular maintenance . I could not begin to count the amount of times I have caught things simply by looking my plane over before or after a flight . . Sometimes serious things that could cost you a plane like a servo screw missing on the elevator or servo a clevis ready to come apart ..