B

Bob Axsom

Well Known Member
I pulled the airbox off of the engine tonight to mount a platenut on the bypass door so I can selectively lock it down without going through the latest control cable mod. developed by Van's. In the process I disconnected the control cable. I was quite surprised that the pin had nearly worn through the front edge of the lever attached to the "flapper" plate. I loaded it up to make sure it didn't partially open when carb heat was not desired and that is probably the reason. However, I'm probably not the only one that did this and it might be a good idea to disconnect yours and look at it the next time you have the cowl off. The wear cannot be seen with the clevis pin and fork in place. I probably have less than 1/64" left before breakout after 223.3 flight hours.

Bob Axsom
 
Bob Axsom said:
I was quite surprised that the pin had nearly worn through the front edge of the lever attached to the "flapper" plate.
Click to expand...

Hi Bob,

I'm not sure I follow - are you saying that the stainless wire from the push-pull control has almost worn through the little steel arm that attaches to the door?
 
Configuration?

Perhaps mine is unique. I have and wire end that is cut off flat. To that is attached an end fitting that clamps down on the wire end like the end of a drill motor on a bit. A forked fitting is attached to the back of the end fitting and the control lever from the door extends into the open fork. A clevis pin extends through the holes in one side of the fork, the lever and then the other side of the fork attaching them together. When I pull on the carb heat knob the wire follows it backward pulling all of the items attached to it and the door swings down to block the normal induction air inlet path. The mechanism works perfectly but I never pull that knob except for an occassional test. The problem is the hole for the clevis pin in the lever attached to the door has elongated itself roughly double the original size and is about ready to pop out of the front end. Like I said, is probably due to the preload I put on the system to make sure the door stays full open. If you just have a bent wire in the hole and the carb heat contol wire has no preload on it, it may never be a problem. I am going to have to splice on a new arm end, reduce the preload and keep my eye on the interface.

Bob Axsom
 
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picture ?

Bob can you post a picture of that so I can see if
mine is going to have this issue in the future. ?

Danny..
 
I will do that but ...

I will try to remember to take a photograph today and post it tonight. It is not assembled because of other work I am doing but I will try to photograph the lever with the wear.

Bob Axsom
 
Carb heat lever wear fix

Bob,

I have a slightly different setup, but I found the same thing going on. My wire is also straight, and fastens to the lever with a AN3 bolt that I drilled a small hole in. This -3 bolt had almost chewed itself through the lever as well somewhere around the 200 hour mark. I found a piece of fiber reinforced silicone tubing (probably about 1/4" ID x 3/8 or 7/16 OD) and stuck it over the lever. Bacause of the sizes of the lever and tube, it was somewhat stretched until it was essentially flat. Prior to putting the tube on, I punched a hole through both sides of the tube which align with the hole in the lever. I may have put some lubricant in the hole, I don't remember. Anyway, the -3 bolt now rides in the punched hole in the tube, and likely doesn't touch the metal of the lever anymore. I probably had to play with the hole diameter until the -3 bolt could rotate freely in it during lever actuation.
 
Photos

Alex

I think our setups are very similar My "pin" may be an AN3 bolt too I believe and not a clevis pin as I had stated earlier. I'll check when I get back to the hangar. I will study your fix carefully and see if I can come up with a similar fix (identical perhaps). These photos were taken on January 25, 2001 when I hooked up the carb heat door lever.

Bob Axsom

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Going to change configuration

I've got a left over rod end bearing and I going to use that in the interface with the lever. That way I can eliminate direct relative movement and ise the existing hole with just a little cleanup. Since it will be locked down, I wont have to worry about wear on the hole walls.

Bob Axsom
 
The wear photo

I verified that the last "pin" I had in this hole was actually an AN3 bolt tha same as Alex. The original instalation in the 1-25-01 photos appears to be a clevis pin. The notch in the edge of the lever was cut by the body of the fork. I made up an a new interface from available material including an extra rod end bearing. It is a little heavy but should be reliable.

Bob Axsom

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newer carb heat arms are made of steel now

That must be why the newer carb heat arms are made of steel now. I think that my airbox kit was made in 2004.
 
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