Crow's Feet.. LeVeRaGe???

James Scott · #1 06-25-2013, 01:49 PM

Does anyone know the actual engineering physics behind calculating how much torque would change (decrease) to equal the value for a given nut/bolt.. if I use a Crow's Foot on a nut .. rather than a direct access socket?

In other words.. If I can't get good straight access to torque a nut (like motor mount nut) at a fairly tight torque value (61 ft-lbs).. and I use a Crow's Foot socket-wrench to develop straight access (to avoid slipping/stripping nut) .. How much decrease (%) approximately should I apply to the normal torque (61 ft-lbs).. to compensate for the approximate 1" lever the Crow's Foot gives to the nut?

I would guess-ta-mate around 50 ft-lbs ??? Whaddayathink?

Thanks, Jim

dannmarr · #2 06-25-2013, 02:29 PM

Practice on another bolt on your workbench. Torque the bolt with a straight socket, then torque with the crows foot untill it matches the torque value.

svxcess · #3 06-25-2013, 02:35 PM

If you are able to torque the nut with the crow's foot at a 90 degree angle to the head of the torque wrench, you should not have to correct.

.

dannmarr · #4 06-25-2013, 02:56 PM

Because the center of rotation is different, there will be a small difference in torque value. There is a formula for this, do a search on the internet.

Blacky · #5 06-25-2013, 03:36 PM

I sent an email to my brother, retired Technical Director of GM Motorsports. He knows every formula known to mankind.
It appears to be quite simple if this info from The Net is correct.
desired torque x torque wrench length over
torque wrench length + crowfoot length = torque wrench setting to obtain desired torque

There is also this calculator:http://www.cncexpo.com/TorqueAdapter.aspx

James Scott · #6 06-25-2013, 04:35 PM

Thanks..
That seems to make sense.. .

61 x 18 = 58 for motor mount nut
18 + 1

P.S. Obviously not critical here.. I just dint wanna twist off the mount stud.. or strip .. so I could buy another $180 MOUNT!

Blacky · #7 06-25-2013, 07:18 PM

Confirmed by my genius brother by email. And yes if the crows foot is at 90 degrees the effective length of the handle is unchanged and so the torque setting.

EdWindows · #8 06-25-2013, 09:01 PM

Quote:

Originally Posted by James Scott

P.S. Obviously not critical here.. I just dint wanna twist off the mount stud.. or strip .. so I could buy another $180 MOUNT!

Should've bought a Group N STI or regular Impreza mount.
Only requires slight bolt hole modification and is 1/3 cheaper than stock.