Calculating Torque

[MikeH]

After pricing out quality torque wrenches capable of handling 200ft/lbs of torque I've come to the conclusion I don't need one that bad.

If my math is correct you can achieve 200ft/lbs of torque on a flywheel nut with a 100 pound girl standing on the end of a 2 foot breaker bar when the bar is parallel to the ground.

My daughter weighs 105 and I already own the breaker bar so that gives me a workable solution with a small margin of error.

Can anyone verify this math?

Theory
Torque is the cross product between a force and the distance of the force from a fulcrum (the central point about which the system turns). The cross product takes only the component of the force acting perpendicular to the distance. Using trigonometry the torque is defined as:

Torque = Force x Distance to fulcrum x sin (0)

the force will be perpendicular (90degress) to the distance. The sine of 90degrees is one, therefore the torque will be:

Torque = Force x Distance to fulcrum x sin (90degrees) or
Torque = Force x Distance to fulcrum x 1

In this example Torque is applied to a fulcrum, but since I'm acting "radially" on a nut I'm not sure this is the right formula.

[gokart]

That's correct. I used the same method to tighten my flywheel nut. Also works for rear brake drum nuts.

You don't have to find a 100 lb girl. Just calculate the distance from the socket needed with your weight:
Distance = Torque (divided by) force

[MikeH]

Well..... with my weight I need a fairly short bar. ;D Since my breaker is 2 foot long I have to go with the weight required to use that.

I had a nice 1/2 inch drive ratchet that was one foot long but broke that trying to get the nut off initially.

Since my daughter is almost exact and comes with the added benefit of being able to step up and balance on the bar, it's a perfect combination.

[dubfreak1]

I use the same torque on the flywheel and axle nuts: me + 8ft pipe and repeat over and over again

"you might have to take this off some day","you might have to take this off some day","you might have to take this off some day"..................

[gokart]

Unless you only weigh 25 lbs, that's a lot of torque.

[gokart]

Here’s an idea: For 200 ft-lbs, use an 8ft pipe, stand on a bathroom scale, push down on the pipe until the scale reads 25 lbs less than your actual weight.

[dubfreak1]

Well, those might be the right weight digits, but the decimal is off ;D. However I can't put all my weight into torquing the nut.

The point is that I get them nearly as tight as I can. This is probably over tightening according to the published specs, but I have had axles and flywheels come loose when stopping at the "correct" torque. I've heard the stories of broken flywheel gland nuts, but always wondered about the quality of the part. The dangers of too little torque due to friction or some other factor are greater to me than the fear of overtightening.

[MikeH]

Actually a good quality hanging scale like a fish scale connected to the end of the lever and the ceiling would work.

Simplest method though is just sit the right weight on the right length of lever.

An 8 foot pipe would allow you to generate massive amounts of torque 500+ easily just with arm muscle. That seems more likely to crack a nut or flywheel than sticking to the VW spec.

[vw1s]

Or....
Get a "torque meister" or "torque dude" or whatever you want to call it. It's been covered a few times in other threads. Multiplies torque by 9. So, 30 lbs at the wrench, is 270 at the flywheel. I can tighten gland nuts and axle nuts with a 3/8" ratchet! I can remove rusted axle nuts with no heat, no lube, and without removing the cotter pin...with a 3/8" ratchet!

[ghiastein]

Just be careful and don't go to tight. If using a stock VW original crank purchase a new original style gland nut and don't go over the torque listed in Bentley. The fancy high torque gland nuts should only be used with new fancy cranks that are able to take the extra torque load.

I stop at the recommended torque for everything and I have never had a flywheel come loose. Also I don't drag race or autocross.

When it comes to torque wrenches I have 2

A cheep Harbor Freight 1/2" that I use usually for wheel lug nuts. My wrench is not accurate but I am sure it makes all 4 or 5 lug nuts/bolts around the the same torque for each wheel.

My very precise one is a 3/8" craftsman dual beam
www.sears.com/shc/s/p_10153_12605_00944690000P?prdNo=2&blockNo=2&blockType=G2
Currently for $24.99

The 3/8" drive torque wrench is my most used tool when it comes to VW engine assembly. When I did research I found that the click type torque wrench routinely needs to be recalibrated and only the high dollar ones can be recalibrated. The twin beam is recalibrated by bending the straight rod back to "0" before use. Yes the dual beam can be harder to use but is gives me a better feel for how tight the bolt or nut is.

When it comes to the gland nut or rear axle nuts I borrow the calibrated snap-on 3/4" 4' long torque wrench from work. Sorry.

[MikeH]

Aug 1, 2011 16:39:16 GMT -5 ghiastein said:

When it comes to torque wrenches I have 2

My very precise one is a 3/8" craftsman dual beam
www.sears.com/shc/s/p_10153_12605_00944690000P?prdNo=2&blockNo=2&blockType=G2
Currently for $24.99

Had one of those in my garage for 15 years. Wouldn't fit in my tool cabinet. Never used it once. Got sick of it and threw it away... Then got a Ghia and have regretted it ever since. Also threw out a pickle bar for tie rod ends. Didn't know what it was.

Funny how owning a vintage car changes your perspective and education.

[teamafx]

I use a 4' pipe and a 1/2" breaker bar (Until it broke) I always go over on the spec. I also don't want it to come loose. I need to get a torque meister, the next time I see a used one I will get it.

[tarrich]

Sound like the discussion I had removing the rounded Jeep lugs nuts that lost their chromed shells. A hammer to seat the twist-on remover and working the breaker bar with the help of someone with greater mass than me got them loose.

[67type1]

I think Patrick is on the right track with the Torque Meister/Dude. I don't have one, but its on my Christmas list.

While we're on the topic of torque wrenches; I have an electronic torque indicator which is use to test & calibrate torque wrenches. So, if you'd like to check yours; stop by for the Tech Session (Sun., 8/7/11). Some torque wrenches have an adjustment, so if its off; we can get back within specs.

[81pumagtc]

I have got a Wright click type torque wrench for inch / pounds for precise measurement that is a fantastic tool for use with carbon-fiber bikes and VW oil sumps, and a good Craftsman beam type for many engine projects.

Well worth the money.

I generally try to stay with spec for engine work...they know better than I do what works, and what doesn't.

The Torque Meisters work great too. Haven't had to use one yet, but I need to replace my emergency brake cable, so one is calling me soon.

I get my Wright adjusted ever couple of years, and always back it off to zero when finished.


Dave