Need help identifying this pully

12 posts in this topic

Posted

The right rudder peddle pully split in half. It’s not a standard pully and looks to be made out of a skate board wheel or something. I don’t have a set of Magnum plans so am unable to see what they used.  The dimensions: 1 1/4 OD, 1/2 wide and has a 1/4 bearing offset.  The  center hole is for an AN 5 (5/16) bolt. 

Pictures attached. 

 

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Posted

As thin as the area is around the failure point I don't think it would have survived if it would  have been machined out of steel. It needs more wall thickness. I'd be revamping it. My design considerations would include making it out of a material softer than the cable so it wears out before the cable. Give it plenty of wall thickness for the  material of choice. Include a cable retainer in the design to prevent it from jumping off track and binding. They seem to be pretty fond of those fiber compound pulleys in the aviation world. The material won't corrode because of a difference in metals like an aluminum pulley would. They are light and many come with a stainless steel cable retainer. I've got a lathe handy and plenty of plastics and aluminum so I might try making one if an off the shelf aviation grade pulley was not an option. Nylon holds up well under load too.

I'm sure someone will chime in with a part number for you and a vendor.

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Posted

Cloud, I would agree. The one on the other side was made the same but has a lot more material in the bottom of the groove. It is apparent this caused the failure. I also do care the the angle/side load on this bearing which may have caused pre-mature wear. I may order two new phenolic pulleys and make a mount off the planes structure. At lease this way the I can order a new one from A/S when it wears out. The problem right now is I can find a phenolic that will fit the application. They are all to big around. 

 

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Posted

You can machine phenolic material but it stinks like hell. I made thousands of inserts for Square D electrical boxes years ago. It cuts easy and leaves a nice finish. If you can't find any the right size you can always put a chunk in a lathe and turn it. I used a cnc machine but you could take an ordinary piece of tool steel designed to fit in a lathe holder and profile grind a 1/2 round shape on one end. Then just plunge cut it into the phenolic to get your cable groove. Before we had cnc's we custom ground many form tools for inside and outside profiles on screw machines.

I'm not sure if Sun & Fun has all the surplus aircraft parts vendors that the Oshkosh airshow has but if it does I'm sure someone on this list is going. Surplus phenolic pulleys are always available in the fly-mart at Oshkosh but that's a whole summer away.

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Posted (edited)

Wow, that must be a Magnum thing!  My old model C doesn't have these pulleys.  Just a couple of cable guides.

Edited by Turbo

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Posted

Why not take a standard aircraft cable pulley?? Just take the right size and you're good to go.

https://www.aircraftspruce.com/catalog/appages/phenolicpulleys.php?clickkey=9427

 

Its a cable pulley used to guide the cable. Get one close to size and make it work. A little smaller or larger, the turnbuckle will take up the slack or add some. Extend the mounting tabs if necessary and carry on.

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Posted

The right rudder peddle pully split in half. It’s not a standard pully and looks to be made out of a skate board wheel or something. I don’t have a set of Magnum plans so am unable to see what they used.  The dimensions: 1 1/4 OD, 1/2 wide and has a 1/4 bearing offset.  The  center hole is for an AN 5 (5/16) bolt. 

 

 

 

 

 

Something like this work Its 1 inch in diameter and 3/16 wide Model 4 kit foxes use these. 3/16 center hole.

0331191832.jpg

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Posted

Thank you for all of the replies. I wish it was as easy as calling up Spruce and ordering one the right size. The problem is all the Phenolic pullys they have are to big around. The way the build put this together makes it impossible to use any larger pully or get the mounting bolt out of the airframe. I could use a larger pully but it would require me to make a whole new mount for it. I was hoping to find something that would work without redoing the whole mount.  

Wypaul, I purchased something very similar to what you linked to from Amazon. It’s the same diameter, bolt and grove size of the one you posted. They will be here Tuesday. I’m crossing my fingers they work. My Zenith 701 uses a similar nylon pully with no bearing inside so I’m sure this will be adequate. 

Thanks again for all who replied. I can always count on young guys for great insite. 

:BC:

 

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