Torque conversion table...

[jwadle]

This is sorta a continuation of my other thread (bent ear on U-Joint)... The marina did a great job, and only charged me $47.50.. Well worth it.. So here is my next question.. Now I think I am a pretty smart guy (LOL), but I just can not make sense out of the torque conversion table for torquing down the retainer ring.. So I measured my torque wrench and according to the chart, I set it at 111 ftlbs to get 200 ftlbs on the ring... Seems simple, but I can not for the life of me figure out why a shorter wrench would have a lower number.. For example, at the other end of the scale if you have a 36 inch wrench you set it at 150.. I would think the chart would be opposite.. Since its longer you would need less force to get it to 200... So I would think that a 36 inch would be set to 111, and by comparison the 15 inch should be set to 150.. I know it has got to be right (and I did set it to 111, and everything seems right), but I just can not figure out why.. I figured I would ask here, since I know one of you would have a simple answer that even I could understand.. LOL..

 

[alldodge]

As a non-engineer type

Torque is (to my pea brain) the twisting force applied.

Everyone can understand that if you take a short wrench on a bolt it takes a lot of force to put much torque on it, If you add a long bar to it, it takes less force on the end of the bar to get the same bolt to break loose. The force applied to the long bar is also being absorbed in the long bar. The twisting is being applied to the wrench and to the bolt and is divided

So to apply 200 ft lb to the retainer which is 6 to 8 inches away. Using a shorter bar requires more force to achieve the same results but there is less of the force absorbed by the shorter bar

Formula is

Tw = Td*A / A + B

Tw - Torque wrench is set to
Td - Desired torque
A - length of wrench
B - length of torque wrench

I did some calculations and it works out.

Maybe a mechanical engineer will way in with more

 

[scoflaw]

I assume that the manufacturer of the torque wrench have already done the math on the length of the tool. So if your wrench says 200 lbs's, you grab the end of your tool and crank it down to 200 lbs.... done.

 

[alldodge]

Yes and No

Yes, if your tightening something that places the head of the torque wrench over the center of what is being torqured. Like placing a socket over a bolt/nut or a large enough socket to go over the end of the prop shaft.

No, if your using a crow foot, wrench or the tool used to tighten the retainer nut

 

[jwadle]

Thanks guys.. I can now sleep at night.. It was the comment about the socket over the bolt comment above that did it for me.. Makes sense, since the spanner wrench has a much larger diameter.

 

[achris]

It's to do with the ratio between the retainer wrench and the torque wrench.