Bolt torque discussion

pittsburghracer said

I did some rod bolt torquing today and that is where I throw everything I think about bolts out the window. Now we go by the book. Here was my dilemma. I bought a used set of Crower Rods and assembly. No other marketing on the rods bolts other than Crower so I measured the bolts and that are around 1.800 long- 7/16. The specksheat says 65 pounds .004-.006 stretch with 20-50 oil. The next bolt down calls for 75 foot pounds .005-.007 stretch with their lube. I decide on aiming for a hair over .005 with 20-50 oil. 72 foot pounds is my number for this build.

Click to expand...

FWIW.... Brings up some points to consider..... Stretch is the best method to get the desired fastener tension BUT the accuracy of the measurements for fasteners of this size becomes the problem..... .005" +/-.001" is a +/- 20% accuracy, plus any errors from angling of the gauge off-axis. Not as consistent as you might think. Torquing has more accuracy/resolution in a good wrench and operator reading it, but then the friction variables come in to effect the results, despite better resolution on the equipment.

If you pick the stretch method, the torque really just becomes a check on whether things are getting way out of whack.