The human torque wrench?

[VaSteve]

I have been doing a lot of work on my broken car and have been doing a lot of looking up torque values in the book. I have found that occassionally, I will tighten up the bolt by hand and when hitting it with the torque wrench, I'm not far off. Other times (usually the smaller bolts) I'm way off.

Since I have been huffing too much brake cleaner in the garage, I have been thinking theory.

For those of you that have been at it a long time, or especially those that do this professionally, how accurate are you as a "human torque wrench"? Do you ever not go back and check because you're that good?

[jorian]

As soon as I hear that click in my elbow I know I've gone far enough...

[chrisp]

I find that if I am using the same length wrench on the same bolt I can be pretty consistent. In a previous life I used to torque bicycle bolts pretty regularly and could nail a 35 ft/lb crankarm bolt pretty consistently.

Today I find that I will normally bring a lug nut up to 85-90 ft lbs before I confirm with the wrench that I am right wehere I want to be by hand.

[buster73]

After some years of wrenching you certainly get a feeling for the typical torque range. For non-critical bolts I usually don't use a torque wrench anymore. However I always use a torque wrench for all critical bolts (engine, tranny, CV's, brakes, suspension, wheel nuts, seal/gasket areas). My experience is that small fasteners tend to be over-torqued while larger sizes remain under-torqued if no torque wrench is used. Not worth the risk.

[bigchillcar]

As soon as I hear that click in my elbow I know I've gone far enough...

lol..jorian.

[David]

From the Machinery's Handbook

Method Accuracy
By feel +-35%
Torque Wrench +-25%
Turn-of-nut +-15%
Preload indication washer +-10%
Bolt elongation +- 3-5%
Strain gages +-1%

I go by feel a lot more than I probably should.

[yelcab1]

Only on non-critical stuff do I use a human torque wrench. For all important stuff (brakes, suspensions, engine, tranny etc) a calibrated torque wrench is the way to go

[oldE]

A friend of mine is 'that good'. He is a mechanic.
Years ago, he did a water pump and timing belt change on my 924S. I had a good drive home and then freaked out while reading the warning in the manual to the effect, "If the timing belt is replaced, under no circumstances should the car be operated until timing belt tension can be verified with Porsche part #blah blah..."
I called the nearest dealer and talked over the situation. They suggested if it hadn't slipped or slapped, it might be close enough to allow me to drive it in to their shop to check the tension.
When they put the guage on it, it turned out my friend had nailed the specification, just by 'feel'!. I was impressed.
Les

[Don Plumley]

My rear axle nuts required 300ft-pounds. I weigh about 150, so I stood on a cheater bar out 2 feet from the axle nut. 300 foot-pounds. Is that what you mean by human torque wrench?

[VaSteve]

Les,
I spend a lot of time on the 944 side of the site...that's what I have been fixing. There is a whole science/black majic around just twisting the belts to get the right tension.

David,
What the hell is "turn of nut"?

[tdatk]

Steve,
Funny thing bout the 944/928's is that as soon as you service the timing belt the water pump siezes up and really torques your nuts.......

Tim

[Bob's Flat-Six]

Just like with most skills in life, some guy's just have better mechanical ability.

A natural sense for how stuff works and how tight it needs to be.

[911pcars]

Probably not accurate to recheck unless you have comparable specs for bolt stretch. Torque is measured while the fastener is rotating, not after. Break-away torque is higher than the true torque applied.

Sherwood

[bbh03]

Originally posted by 911pcars
Probably not accurate to recheck unless you have comparable specs for bolt stretch. Torque is measured while the fastener is rotating, not after. Break-away torque is higher than the true torque applied.

Sherwood

True. If you torque by hand and stop and then switch to a troque wrench, the amount of torque to move the fastener further will be higher than the same torque wrench would have clicked at it it had been used in the first place. Thta is why you should always keep the torque wrench moving in a smooth motion when approching your value.

[TimT]

What the hell is "turn of nut"

"Turn of Nut" is a methed for tensioning bolts that is recognized by AASHTO, AISC, and other standard writing orgs. its more commonly used for large structural fasteners..

typically a nut is snugged by hand with a standard spud wrench ( usually taken to be 150 ft/lbs), then the nut is turned "X" amount more, depending on the thickness of the parts being bolted.

This method is used on some automotive fastners also, ie some BMW head bolts...they actually have you torques the bolt to a value, then rotate the nut 90 deg more.

[bbh03]

As do stock rod bolts in the 911.

[yelcab1]

and head studs on the 911.