Obscure Technical Tips in Restoration

//Obscure Technical Tips in Restoration

Obscure Technical Tips in Restoration

There are at least five places in the Stearman that utilize screws with thread types that are not often found in the assembly.  These are 1/4 inch, #8 filister slotted, drilled heads, and 36 threads per inch.

One place is the two screws that hold the collar on the end of the rudder pedal shaft. The screws thread into the plug that goes inside the shaft and retains the spring.

These screws are worn off on the top by shoes sliding across them, and are usually thrown away on disassembly. 

An 8-32 won’t fit unless someone has forced one in or rethreaded the plug sometime in the past.  Or, any new production is probably threaded for 8/32’s.

Also there is a clevis pin on top that holds the tow adjustment tab, not a bolt and nut.

None of the supply houses carry the filister 8/36, but after a long search a supply was located in a surplus house.  Dusters and Sprayers now has a limited supply if you ask for them.

The other location is the single screw  on the end of the elevator control tube just in front of the idler arm. (Yes, it will be safety wired)

The small triangular plate that bolts to the rudder pedal adjustment rack tube, also has an unusual assembly requirement according to the drawings. The rudder balance cable that routes through the large pulley around the front of the fuselage across the back of the firewall fastens to this plate.

Since the cable has to move outboard from the rudder rack to the outside of the pulley, it ends up pulling at an angle to the rack. Boeing addressed this problem by placing a washer between the plate and the tube on the front of the plate, and a washer on the outside of the plate on the back.  This cants the plate outward so that is it more in line with the pull of the balance cable.

As a reminder, don’t forget the safety bolt in the front hole of both front rudder racks.

Another place that the tension in the rudder cable pulls at an angle to it’s attach point is on the idler arm. The cable that comes from the rudder rack to the idler arm is pretty square to the arm. However, the cable that leads aft from the idler arm angles in since the fuselage narrows. 

The eyebolt swedge fitting that attaches to the idler arm is bent slightly (about 5 degrees) so that the body of the fitting is in line with the cable going back to the rudder. This prevents the cable from being kinked at an angle as it exits the swedge fitting.

The idler arm has been a weak point in the Stearman design. Heavy usage in the past can leave the arm with a crack at the point the tail wheel control cable attaches.  Inspect yours thoroughly to make sure it is sound before you install it.

However, if it does develop a crack later, or even breaks, the job of replacing it with the fabric cover on is formidable.

The drawing shows the bolt through the pivot at the bottom of the idler is to be positioned with the head outboard and the nut inboard, according to standard.

Unfortunately, this positioning means you can’t remove the bolt to the outside to replace the idler arm, with the cage and fabric in place.

This possible maintenance problem would seem to warrant installing the bolt in the other direction.


By |2016-11-13T09:33:38+00:00November 15th, 2002|Flying-Wire|Comments Off on Obscure Technical Tips in Restoration

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