Re: 5 cyl timing belt questions

[DeWitt Harrison <de@aztek-eng.com>]

On Fri, 19 Feb 1999 12:11:18 -0800 (PST), Orin Eman wrote:

>> > - Crankshaft bolt torque. I have the locking tool (2084) and the
>> > extension (2079), thanks for the generosity of Gurdev Sethi. I have read
>> > many times that the correct torque with the extension is 258 ft-lbs. I
>> > take that to mean that you should set your torque wrench for 258
>> > ft-lbs--but that doesn't make any sense to me. You have to consider the
>> > length of the torque wrench, right?
>> > 
>> The length of the torque wrench doesn't matter, what does matter is that the
>> shaft of the torque wrench remain in line with the tool.  Do you actually
>> have a 3/4" drive torque wrench?  I've always made do without one in the
>> past, but I recently picked one up from eBay for a really cheap price (got a
>> 3/4" drive ratchet there too).  
>
>I thought this horse was dead... for a normal torque wrench, Wallace's
>formula matched that in the instructions for my torque wrench.
>You must correct for the length of the wrench.
>
>For a torque multiplying wrench, all bets are off... I'll take a look
>at the physics of it when I get chance.

Not that big a deal, provided the wrench and extension are kept in a straight
line orientation. So, to put another bullet into the equine corpse:

  Let Tw = torque wrench setting/reading
        T = torque actually applied to bolt
        Lw = length of torque wrench (drive to point of force application or
                      approximately the center of the hand grip)
        Lx = length of extension

  Then T = Tw (Lx + Lw) / Lw      or        T = Tw[1 + (Lx/Lw)].

The use of the extension is less accurate since it depends on the
"effective" length of the combination, i.e. it depends on how you
hold the wrench. The wrench readout accurately measures the
torque around the wrench's driver but, unfortunately and as much
as we would like to believe otherwise, this torque is not related directly
to the torque at the business end of the extension. The two torques
are only related by the relative lengths of the moment arms.

DeWitt Harrison
Boulder, CO
88 5kcstq