Crank bolt torque for timing belt change (10v)

[SJ]

As Huw has done, I've been mulling over this topic for several days now.
2 + 2  dont add up to 4.

I think I have come up with the answer to the problem.

*****  Tool 2079 was designed to be used with a torque wrench of a specific
length. ******

Whats the specific length? Ahhh . . thats the mystery.

Let me elaborate on that statement.
The designer who developed Tool 2079 had a certain length torque wrench that
he was working with. The torque figure of 258 ft lbs was based on the
formula:
Final torque = torque wrench setting(torque wrench length + Tool 2079
length)/Torque wrench length

or FT = WT(A+B)/A    . . . . A=Torque wrench length . . . B= extension
length

And 258 ft lbs was the number cited later on in the manuals. The
relationship between the torque setting and the wrench length was
overlooked, and forgotten. All anyone remembered was tool 2079 and 258 ft
lbs of torque.

Take a good look at (A+B)/A
As A gets larger . . B becomes less of a factor . ..At a large enough number
(A+B)/A approaches 1.
Then FT = WT

Look what happens when the wrench is same length as the tool extension:
FT = WT(1+1)/1 = 2WT
As you can see, the Final Torque can vary from 516 ft lbs all the way to 258
ft lbs . .it all depends on the length of the torque wrench.

We have discussed this formula at length.
What has stirred the debate is that when you reduce the problem to its base
elements . . the numbers dont add up. And that is because we either held the
torque wrench length at some set value . . .or we varied the length. No
wonder the numbers never came out right.

But, if you plot the Final Bolt Torque as a function of wrench length, you
will find that the Final Bolt Torque will start at 516 ft lbs and quickly
drop and approach 258 ft lbs as the wrench length approaches infinity. The
most dramatic changes in Final Bolt Torque occur between wrench lengths of 1
foot to 4 feet.

Using a 1 foot torque wrench and a setting of 258 lbs, the Final Bolt Torque
will be 516 ft lbs.
A 2 foot wrench will give you 387 ft lbs
A 3 foot wrench will give you 344 ft lbs
A 4 foot wrench will give you 322 ft lbs.

Most would agree that torque wrenches capable of indicating 258 ft lbs will
be between 1 and 4 feet in length. My wrench measures 1.46 feet . . 250 ft
lbs is its highest reading. If you have a wrench that indicates 258 ft lbs
at the middle of its scale, the length would be around 2 feet. A wrench
indicating 258 ft lbs at the bottom of the scale would most likely be over 3
ft in length.

If I use Tool 2079 in conjunction with my torque wrench, the damper bolt
will be tightened to 430 ft lbs.
Ameer using a 3 foot wrench will get 344 ft lbs at the bolt.
Huw with his 4 foot monster wrench will get 322 ft lbs at the bolt.
And we will all have used a torque wrench setting of 258 ft lbs. Big
difference between 430 and 322.

Another way to view this is to reduce the forces to their basic elements >
lever and force

258 ft lbs = 4 ft X 64 lbs of force
Now add a foot(tool 2079) to the length of the lever, but the force remains
64 lbs
Torque at the end of tool 2079 = 5 ft X 64 ft = 320  (322 if you add more
decimal places to the base numbers).
This is the same torque value as predicted with the formula.

Try a 100 foot wrench.
258 ft lbs = 100 ft X 2.58 lbs
Add a foot to the end(tool 2079) to the length of the lever, but the force
remains 2.58 lbs.
Torque at the end of tool 2079 = 100 X 2.58 = 258 ft lbs
Again, same as the torque value predicted with the formula FT = WT(A+B)/A.
FT = 258(100 +1)/100 = 260 ft lbs  . . . we wont quible about the decimal
places.

As you can see, using tool 2079 and a torque wrench set to 258 ft lbs dont
mean diddly if you dont know what the torque wrench length was. Now you can
understand why I wanted to know the bolt torque value and not the torque on
tool 2079.

Everyone seems to agree that the torque at the bolt is in the vicinity of
340 ft lbs. Ok, that coincides with a wrench of 3.0 foot length. Sounds
reasonable. But it would sure be nice to get some confirmation on that
torque number.

In summary, to set the crank bolt to the correct torque using tool 2079, you
need to:
1  know the required torque at the bolt
2. know the length of YOUR torque wrench
3. know the length of tool 2079 (I'm assuming it is 12")
4. calculate the torque setting for YOUR wrench using the above formula.

This is a good site that shows how to make an extender using tools that you
already have. Nice pics also. Hell of a big extender . . . an inch-ounce
wrench would probably get you the 340 ft lbs at the bolt!
http://www.specialpatrolgroup.co.uk/spooky/torque/torque.html

Other interesting stuff.
http://www.geocities.com/motorcity/downs/3837/torqwren.html

http://www.madsci.org/posts/archives/dec2000/975805815.Eg.r.html

SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q