Bolts 101

[Ken in Oklahoma]

We never measured the torque on the clutch screws. None ever gave trouble of any kind. That would be a sample of hundreds of clutch removal and installations. We just knew how tight that they should be. I was in the /2, /5 and /6 service schools and never saw them torqued, or mentioned that they should be torqued. . .

I think you and I are in essentially the same camp, Duane, though our hands-on experience is vastly different. (You have a lot, me not so much.) I have developed a sense of how-tight-is-right so long ago that I don't remember actually doing it. But one memory stands out. I was tightening the bolts on a BSA Spitfire Scrambler primary chain case (aluminum to aluminum) when the 5/16 Whitworth bolt, I mean screw, suddenly felt cheesy. That one experience certainly caught my attention then and has stayed with me ever since.

I think by paying attention I soon developed the feel that I talk about now. The point I'm heading to is that though I didn't have the feel initially, but by paying attention and thinking about it I was able to develop one.

Over torquing has been on my mind the past couple days. I was watching a DIY house renovation show where I saw the subject, a young man, trying to replace a leaky valve on some 1/2" copper tubing. He was using a 12" Crescent wrench on the valve. Of course that looked strange to me since he wasn't using a second wrench to counteract the torque he was applying. Sure enough, as he applied a lot of force, the tubing twisted and he looked surprised and irritated about what had just happened.

Now that scene was probably staged, since the "theme" of the show seemed to be how much trouble can arise when you're trying to do a remodeling job. But notwithstanding that, I think the scene was representative of many people's experiences. I believe that with thought and some experience almost anybody can develop a good feel for how tight is tight enough.

Ken

[Garnet]

I don't want to start a tourque wrench thread but................ if you don't know how to use a "click" type wrench, then no mater how good it is, it will be WAY less acurate then a cheep "beam" type.

When using a click type you must position yourself so that the click happens when the pull of your arm is at right angles to the wrench. If it clicks when your arm is at either end of it's swing, you must lossen the fastner and re-tourque so that you pull is correct. It must also click when you are in mid swing of the wrench, not at the begening or end, as the acceleration of your arm will affect the resistance of the wrench.

Get out your cheep and cheesy beem wrench and practice on a bolt and nut in the vice. You can see plainly how the force shown changes with different movemnets of your arm.

Given the choice between a questionable beem type and a questionable click type, the beem type will allways be more consitant than the click type in ameture hands.

[dwire]

All interesting...
Duane is right, may common sense be your very best guide, lacking that, torque wrenches can be of value.
Fasteners are fun. I disagree with regard to the "best" sort of torque wrench being the beam type; while they work fine and reality speak is that with common sense, one should need worry little about just how perfectly they execute the procedure as well as how accurate the wrench is for your application. The best torque wrenches (certainly not the most convenient though) are the dial type and should be checked against a standard regularly.
I think we could guarantee only about 2% with a lot of those wrenches and 1% for the very best ones, like the image in its red case, even under controlled calibration. A force transducer/strain gauge setup is even better, but should never be needed on these old bikes...

Also, how does one tighten a torque wrench that is made in a circle? They look like a gate valve's handle with a dial meter in the center? Sorry, can't recall who made those and their proper name as I used them VERY infrequently and only for low torque compliance tests. Torquing fasteners with a torque wrench or any other instrument "PROPERLY" is much more likely to be far more difficult to learn than common sense and the feel method in my honest opinion.

EDIT :Those round shaped wrench indicators were called "Torque Watches" (Wow, surprised I remembered that... )

[dwire]

BTW, that fastener the OP posted, while I do not personally know if that is the correct fastener or not, one thing is clear, it has at least once been over-tightened beyond its yield point. You don't get that sort of elongation without someone really over-doing it. If you do the math on torque vs. clamp force for any given fastener/application/torque spec, you'll see what I mean. I would guess that's totally not the intended fastener (which 12 ft/lb. should not have done that to a cheap fastener) OR if it is, it was tightened to tremendous torque at one time (perhaps both...)

All I can think to say is anyone out there that ever has a tendency to over-tighten fasteners, just Google a bit and look into how you calculate clamp force for a fastener in a given application. While it can be complex, the crux of which is that at impressively low torque values, clamp force can get up in the range that is other-worldly and tremendous. There are a few things (Duane has a great list....) that are much of a concern to torque up to a certain spec and be so careful about it. Head bolts and the like are good examples, otherwise, most things, even on a motorcycle, one would be wise to error on the side of caution (low torque side) than to ever tighten too much. For liability reasons, many torque figures are truly elevated far beyond what they need be in reality. They calculate torque to yield (break the fastener/assembly) then find the bottom value where the interface fails from simply falling out or failing to do its clamping duties. Next, the only value of relevance in the computation for torque needed is its yield point. Calculate it, THEN AND ONLY THEN be certain that value is "X" many % above the low side (that being the fastener is so lose it fails to do its job...) and your figure is valid. Usually, the end spec is so far weighted toward the yield point (where you break the fastener with your wrench) than it ever approaches the low side, so keep this in mind when you get heavy handed and ham-fisted on a fastener...

Oh, and if you want to use your BMW to learn how to never again over-tighten a fastener, there's an easy training nut located under the front cover. Have a go at over-tightening the nut on the ignition advance. Cast Iron is a hard, brittle material that's not forgiving. When you are holding what's left of the end of the shaft under the advance unit, you'll likely never over-torque anything again... (BTW, I've never done such a thing, but have accidentally broken a similar shaft by an unexpected burst of torque coming out of a over 20 year old rechargeable drill... - How much faster was running that nut up with that driver than my hand? Several seconds - which led to several weeks to make the repair too...) Live and learn; and I already KNEW BETTER, just got caught by surprise!

[Major Softie]

(BTW, I've never done such a thing, but have accidentally broken a similar shaft by an unexpected burst of torque coming out of a over 20 year old rechargeable drill... - How much faster was running that nut up with that driver than my hand? Several seconds - which led to several weeks to make the repair too...) Live and learn; and I already KNEW BETTER, just got caught by surprise!

It's AMAZING how much work we can make for ourselves in the interest of just the tiniest bit of laziness.

[Deleted User 61]

I pulled one of these out of the trash bin in a computer room I was working several years ago - along with a Tektronic dual trace oscilloscope! IBM was "cleaning house"...

Now I am waiting for the same thing to happen at my current employ.

[dwire]

Nice Rob! Check that against a known standard, if it is in cal. or can be put back into spec, guard it with your life, for it will both serve you well and serves the wallet even better! (Many of those type of SnapOn's run anywhere from $1.5k to $4k and up.) The scope is a good find as well; good job.

@MAJOR

It's AMAZING how much work we can make for ourselves in the interest of just the tiniest bit of laziness.

Ah... I was young then. You are 100% correct. It was simple laziness. Hope I've learned that lesson by now; sadly I'll bet I'll get to post a few more assanine repetitions of such a basic lesson before I am through.

[Duane Ausherman]

I have no idea how many times I have explained this, but here goes again.

I would estimate that of the leaks, broken fasteners, parts fallen off and stripped out holes, 90% were due to being over tightened.

In most cases it is better/cheaper to err on the side of under torque.

We made a lot of money from over tightening and a little on parts that fell off.

It is your bike, do as you wish. The BMW isn't a Brit bike, relearn mechanical principles and save your BMW.

[bbelk]

According to the guy at Lonestar BMW, the bolt is a simple Stainless Steel bolt and it was used by BMW for only two years. Most airheads have shorter bolts.

I looked at two R65s motors at Airhead Salvage and both had this kind of bolt. The bolts are not supposed to be changed each time, but the wave washer is. I have ordered a set of both. Another week on the lift.

[templetommy]

Thanks for the heads up on the Honda Common Service Manual I looked it up and there are many downloads on the net
Templetommy