Today I'm reminded that, sometimes, it's hard to get some fasteners to properly torque them down without some kind of adapter or lever. The problem is that when you add an adapter/lever to reach a hard to get to fastener you change the lever length of the torque wrench and thus change/increase the amount of torque that's being applied, sometimes by a lot. Fortunately there's math for that.
In the most simple application where we have to extend the total arm length we have to reduce the amount of torque applied the formula looks like this:
R = L * T / L + A
- R = The reduced torque
- L = The length of the torque wrench from the center of the head to the center of the grip.
- T = The initial torque required.
- A = The length of the adapter between the center of adapter heads.
In this case, I need to tighten a water neck bolt that's blocked by the water neck so I'm using a 10mm box end wrench as torque adapter:
- T = 93 in/lbs
- L = 240mm
- A = 120mm
When you boil this down you get the following:
- R = 240 * 93 / 240 + 120
- R = 22320 / 360
- R = 62 in/lbs
For a more torque adapter formulas, go here:
Side Note: The specified torque value for the thermostat housing/water neck on the 2.5L Ford Duratec is 89 in/lbs (7.1 lb/ft), I'm going with the higher generalized torque value of 91 in/lbs (7.6 lb/ft) because .5 lb/ft difference is effectively a rounding error.