Torquing bolts without a torque wrench

[WingAdmin]

Our bikes have many, many bolts, each of which has a specific torque (or tightness) that they are supposed to be tightened to. The reason for this? Bolts actually stretch - believe it or not. When tightening something down, if the fasteners we used were so hard, so strong, that they did not stretch at all, you would turn the fastener until the head contacted the thing being fastened, and it would simply stop turning - it would not hold fast. The slightest vibration would loosen it off. For things like cylinder heads, which require tremendous pressure to seal the gasket in place, this wouldn't work at all.

Instead, engineers specify bolts made of a specific alloy, with known elastic properties. When tightening the bolt, the head contacts the thing being tightened, and you can then twist it a bit more. In doing so, the bolt stretches, and it is this stretching - and elasticity of the steel - that holds things tightly together.

However, if you turn the bolt too tight, it will actually exceed its elasticity limits, and the bolt will snap. Or, when the bolt is being screwed into something soft, like aluminum, it will actually tear the threads out of the aluminum and spin free - this fastener is then "stripped." Not tight enough, and the pressure exerted will not be sufficient to keep the bolt from vibrating loose.

As a result, virtually every bolt and fastener on our bikes has a specific torque value, expressed in ft-lbs (foot-pounds). Special wrenches called torque wrenches are used to make sure bolts are tightened to the correct torque.

Many people don't have a torque wrench. As well, there are quite a few fasteners on our bikes that are difficult or even impossible to reach with a torque wrench. For instance, the inner final drive nut on the GL1100 is almost impossible to access with a torque wrench. So how can you torque these correctly?

It's easier than you think. There's other ways of measuring torque than just using a torque wrench.

How I do it: I use a 12-inch long wrench, and a luggage scale from Harbor Freight:



The final drive nuts need to be torqued to 29 ft-lb. So I put the wrench on the nut, and on the other end of the wrench, I hook the scale. Lift the scale until it shows 29 lbs...and you're done:



You must make sure you are applying force at a right angle, so you aren't pulling the end of the wrench inward or outward:

Makeshift Torque Wrench

If your wrench isn't exactly 12 inches, you can get around that as well. Use the formula:

X = (12 / Y) * Z

Where Y is the length of your wrench in inches, Z is the torque the fastener requires (in ft-lb), X will be the number of pounds to have show on the scale fastened to the end of the wrench. Let's say you needed to tighten your 29 ft-lb nut with a wrench that is only 8 inches long:

X = (12 / 8) * 29
X = (1.5) * 29
X = 43.5

So you would hook your scale to the end of your 8 inch wrench, lift until you see 43.5 lbs show, and at that point, your fastener is tightened to 29 ft-lb.

[CMReynolds1]

WingAdmin gives a great breakdown on the need for torque wrenches and how to make a temporary one. My only add on to this is that we buy multi thousand dollar bikes, buy parts and even spend sums restoring older ones. Why not spend another $100 or less and add a torque wrench to your tool kit? I have three, 2 mechanical and now one digital. Here is a link to the digital I bought. It is very nice. But even mechanical ones with a 3/8" drive can be found for about $50.
Just wanted to address the elephant in the room, so to speak. Thanks!

http://www.bikebandit.com/manuals-tools ... que-wrench

[FM-USA]

Quite true! The need for torque wrenches is ALMOST an absolute must.
Steel bolts in aluminum is a disaster in the making. Over torquing by 10% combined with heat/cool cycles will in time damage the aluminum threads.
You can get a set of 3 Torque Wrenches for $50.00. That's 1/4" - 3/8" and 1/2" drives.
Unless you're very astute in "The Feel" of torquing by hand, don't use the 3/8" wrench for small nuts & bolts requiring the 1/4" drive.

Set of torque wrenches here...
http://www.ebay.com/itm/Set-of-3-1-4-3- ... 1511162052

[NVSB4]

Quite true! The need for torque wrenches is ALMOST an absolute must.
Steel bolts in aluminum is a disaster in the making. Over torquing by 10% combined with heat/cool cycles will in time damage the aluminum threads.
You can get a set of 3 Torque Wrenches for $50.00. That's 1/4" - 3/8" and 1/2" drives.
Unless you're very astute in "The Feel" of torquing by hand, don't use the 3/8" wrench for small nuts & bolts requiring the 1/4" drive.

Set of torque wrenches here...
http://www.ebay.com/itm/Set-of-3-1-4-3- ... 1511162052

I looked at these and they are the same that Harbor Freight carries. The shipper is also in Thousand Oaks where HF is based.
Every once and a while they put them on sale for about $10 each. I check each one against a known good one, and I haven't had a bit of problem with mine.