[ZekenSpider]

Bill;

Based on measurements I made today using the torsion bar TM recently sent me I think the 1 turn = 5 lb. force number is about right. The Torsion Bar adjustment bolt is a 3/4-10 thread which means 1 turn = 0.1" or 10 turns = 1".

Maybe (as you say) there are a number of different torsion bars used but I tested the one TM sent me for my 3326. I set up a test rig to apply a twisting force to one end of the TB and clamped the other end in a vice. (see attached photos)

I added water to the bucket to add weight to the end of the strut and then measured deflection of the strut as the weight increased. The strut arm length was 41.5 inches. I rotated the arm about 5 degrees using 8 lbs of weight. The resulting calculations gave me a torsion spring rate of about 70 in-lbs/degree.

This means that this torsion bar when fully twisted (90 degrees) would have spring back force on the top pin of the TM shell of 70x90/41.5 = 151.8 lbs. That is the force on one of the four struts attempting to lift the shell. The total lift force when lowered is then 4x151.8 = 607.2 lbs. This seems about right for the weight of a 3326 front shell. In the factory assembly video of a few years ago it showed about 14 men carrying the shell to put in place on the struts.

The TB adjusting bolt point of force in the cage under the TM has an approximate 2.5 inch moment arm which means the force on that bolt when the shell is fully down is 70x90/2.5 = 2,520 lbs. Adjusting that bolt one turn moves the TB angle about 2.29 degrees. That equates to 160.3 in-lbs of torque and translates to about 4 lbs at each strut.

John's information from the TM rep appears to be in the ballpark. If you wanted to compensate for a 65 lb awning added to the roof that would require 65/4=16.25 lbs per strut or about 16.25/5 (using John's number) = 3.25 turns at each torsion bar. It would appear the TB adjusting bolt can add or subtract about 40 or 50 lbs at each strut before it runs out of thread.

Hope I'm right. Comments are invited.

Jerry