tell me about driveshaft bolts

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i'm a bit confused about correctly torquing up airhead driveshaft bolts...:confused:

there's a bmw crowsfoot type tool 33.1.620 that enables a torque wrench to be applied to the awkward to get at bolt heads. this is either it, or it looks like it:

5602.jpg


i can easily knock something up like that, but what i need to know is, the distance between centres of the 3/8 drive and the 10mm 12 pt.
looks like 1 1/4" or 45 mm in the pic to me. can anyone who's got one confirm?

secondly, having looked at several bits of reference material, i am still unsure of the torque setting. is it:

1) a true 40Nm applied to the bolt head, ie. 40Nm minus a correction factor to allow for the tool extension?
this is what the snowbum site seems to imply.

or

2) 40Nm being the figure applied to the drive end of the factory tool?
what haynes and probably bmw suggest.

or

3) a decent bit of welly, gauged manually, applied to the bolt head via my trusty snap~on 10mm combination wrench?
what it will actually get if i don't get an answer here :D
 
Number 3 is the airhead recommendation...tighten ( use new stretch bolts obviously, a massive £0.80p each I believe ) the bastards up with a ring spanner until very tight.:weights

Never failed me in 25 years of doing them:)
 
cheers kenny :)


minutes after my first posting, i found this on the HU site which answers all by questions, although further reading on other sites blurs the whether to reduce the torque figure for the adaptor question :rolleyes:

while i have done them up by hand in the past, it's nice to have the correct tool to hand. i'll fire up the mig in the morning.
 
I've always used the "FT" torque setting .

= Fecking tight.
 
If you need to use the adaptor, use it at 90 degrees to your torque wrench. No need to apply a conversion formula then!
 
omen said:
If you need to use the adaptor, use it at 90 degrees to your torque wrench. No need to apply a conversion formula then!
Click to expand...

good idea, but the jury's still out on whether the adaptor is counted in the factory figures. some say yes, some no :confused:
 
If you take a look at the formula the length of the torque-key is involved. It’s not possible to calculate a torque which is valid for different wrenches.
 
AliBaba said:
If you take a look at the formula the length of the torque-key is involved. It’s not possible to calculate a torque which is valid for different wrenches.
Click to expand...

but the bmw figure would be for the bmw tool which they know the length of.

on a slightly different point - why is the length of the torque wrench taken into account in the conversion tool?

surely the torque delivered at the drive of the torque wrench is set. doesn't matter how long the handle is or where you pull it, at the end or the middle.
 
Bleedin' 'eck - just had a peek in here and it's making my head hurt :confused:

I'm back off to the 1200 section to talk about what style of indicators are used on the 2010 bikes :rob

Hope you get it sorted Cookie :comfort

Andres
 
cookie said:
surely, if you apply x foot pounds of torque to the drive of any given torque wrench, that is an absolute figure.
Click to expand...
Yes!

cookie said:
adding an extension would only make a difference from the drive to the new wrench, wouldn't it? you can pull it at the end of the handle or in the middle, the length has no bearing on the torque applied to the drive???
Click to expand...
The length (and handposition) has a large effect on the torque.
Let’s say you have a long adapter (1m) and a short torque-wrench adjusted to 40Nm, this will give you massive torque. Maybe 200-300Nm. This is because you don’t measure the torque where the bolt is.

Maximum torque is at the middle. If you bend a stick it will break in the middle, if you move your hand it will break in the “new” middle. The longer it is the easier it will break.


But we do have tolerances….
 
AliBaba said:
The length (and handposition) has a large effect on the torque.
Let’s say you have a long adapter (1m) and a short torque-wrench adjusted to 40Nm, this will give you massive torque. Maybe 200-300Nm. This is because you don’t measure the torque where the bolt is.

Maximum torque is at the middle. If you bend a stick it will break in the middle, if you move your hand it will break in the “new” middle. The longer it is the easier it will break.


But we do have tolerances….
Click to expand...

i'm trying to get my head round this, but failing.

if i set my torque wrench to 20Nm, it doesn't matter where i hold it, i still get 20Nm at the bolt head as the the wrench reaches it's preset.
if i hold it nearer the bolt head, i just need to pull harder. how does this affect the formula for the extension?

i need to have another look at that page.
 
AliBaba said:
The length (and handposition) has a large effect on the torque.
Let’s say you have a long adapter (1m) and a short torque-wrench adjusted to 40Nm, this will give you massive torque. Maybe 200-300Nm. This is because you don’t measure the torque where the bolt is.

Maximum torque is at the middle. If you bend a stick it will break in the middle, if you move your hand it will break in the “new” middle. The longer it is the easier it will break.


But we do have tolerances….
Click to expand...

i'm trying to get my head round this, but failing.

if i set my torque wrench to 20Nm, it doesn't matter where i hold it, i still get 20Nm at the bolt head as the the wrench reaches it's preset.
if i hold it nearer the bolt head, i just need to pull harder. how does this affect the formula for the extension?

i need to have another look at that page.


edit: done that, and re-read your explanation and it's nearly making sense to me, er, i think.

my head hurts.
 
i'd be very surprised if the torque figure included the bmw tool.

Take it back to the design stage and the engineer calcs what he needs for the bolt to work.

The tool is an afterthought for the mechanic - not the factory.

My advice - reef it up with some loctite on it.

plus or minus 10 nm wont make any difference - they just want it tight -

not,i suspect anything to do with bolt elongation to impart a spring effect across the joint,thereby negating the need for a locking device.

PS use the old ones with loctite. Unless they've been overtorqued past their yield point, they'll return to their original properties.
 
i spent some time thinking about it while watching Spooks, and i think i understand how it works now :)

i also think, from historic evidence, it is safe to assume the haynes manual has got it wrong, and that the given figure is without the tool being employed.

i will probably just wang it up by hand with a combi spanner as i have done in the past.
the subject is more of theoretical interest to me really.

it is a bit odd that the answer to such a common task is so elusive, don't you think?
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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