Torquing through a spanner

[NDNDNDND]

I was trying to undo a tricky intake manifold bolt at the weekend so I could change the intake gaskets. However the shape of the intake meant getting a tool onto one of the bolts was almost impossible. Eventually I found a suitable, thin-walled box spanner that could just make contact with the bolt.

The problem comes with trying to find a way to correctly torque up the bolts when I remount the intake - I can't get a socket onto the bolt, so I can't simply torque up the bolt with my torque wrench. I could use the spanner and do it by guesswork, but I'm trying to cure an intake leak as it is, so I'd rather do it properly!

Is it possible to user the torque wrench on the end of the spanner? i.e. put one end of the spanner over the bolt, then use a hex socket in the other end and use my torque wrench to torque the bolt through the spanner? Would this be accurate or would the extra leverage of the spanner make the torque applied to the bolt incorrect?

Cheers for any words of wisdom and apologies for waffling!

[t400ble]

No your plan won't work. Sorry.

[Mud_]

Sounds like a DIY crow's foot.

[steveo3002]

if you make sure the gasket surfaces are perfectly clean then nip all the bolts up in a criss cross fashion you wont have any problems

[PositronicRay]

Surely if your torque wrench is on the end of a box spanner no extra leverage is generated? Or am I being thick.

[Blaster72]

If the handle of the torque wrench is kept at 90 degrees to the spanner then the reading will be accurate.

[NDNDNDND]

Thanks for the pointers guys, looks like it's not too clear cut. I guess I'll have to set up an experiment!

[voicey]

Did you use something like this?



If so then using a torque wrench on the other end will be fine. It's the same as using an extension on the wrench.

If you were to use a crows foot then you need to reduce the torque to take into account the extra length the crows foot gives you.

[DuraAce]

http://www.engineersedge.com/manufacturing_spec/to...

I'd just torque the rest up correctly and nip up the last one using your judgement personally! But it is possible to calculate....

[one eyed mick]

No problem at all all you are doing is using the box spanner as an extention and really manifold studs are [ in my experience 50+ years on the spanners ] not super torque critical ,head bolts ,big end ,main bearing bolts yes but not them

[NDNDNDND]

DuraAce said:

http://www.engineersedge.com/manufacturing_spec/to...

I'd just torque the rest up correctly and nip up the last one using your judgement personally! But it is possible to calculate....

Top work! That equation'll do the job nicely!

Yes, at a push I think I'd probably 'feel' the torque on another bolt with the same spanner and then pull the same amount on the awkward bolt. But it's good to know I've got a method for KNOWING I've got the right torque.

Cheers fellas!

[mickrick]

Blaster72 said:

If the handle of the torque wrench is kept at 90 degrees to the spanner then the reading will be accurate.

This.

[NDNDNDND]

Finally got round to getting those bolts torqued up last weekend. Process went very smoothly:



I used a Clarke torque wrench, a snap-on 9/16th box spanner (the only spanner with thin enough walls!), a 14mm drainage plug and a 19mm 1/2" drive socket. Quite a handful!

Calculation: (T x L) / (L + E) = Y
T= specified torque
L= length of wrench
E= length of spanner
Y= required torque

(40Nm x 0.4m) / (0.4m + 0.185mm) = 27.35

Wrench only went down to 28, not ideal as the torque wasn't in the mid-range of the wrench, but it went well. After manhandling the sockets for the four inaccessible bolts with the wrench set to 28Nm, I used the wrench directly at the other four bolts set at 40Nm. After completely torquing all the bolts down, I went back to one of the accessible bolts torqued directly with the wrench and checked the wrench + spanner method with the reduced torque. The bolt took slightly more torque (perhaps a 16th of a turn) before the wrench clicked, which proved the calculation got the torque pretty damn close to what it was supposed to be.

I'd call that success. Thanks for the help everyone - hopefully anyone who's in this position might find this thread and can benefit!

mickrick said:

Blaster72 said:

If the handle of the torque wrench is kept at 90 degrees to the spanner then the reading will be accurate.

This.

Oh, and this myth is properly dispelled. Always calculate your torque. Holding the wrench at 90 degrees will make no difference to holding it straight and will still result in a higher torque at the bolt.

[Blaster72]

NDNDNDND said:

Oh, and this myth is properly dispelled. Always calculate your torque. Holding the wrench at 90 degrees will make no difference to holding it straight and will still result in a higher torque at the bolt.

Glad you got what you needed but your last statement isn't correct.

You say holding the wrench at 90 degrees will make no difference, that isn't correct.

It's not a myth its a standard practice used for years.

Edited by Blaster72 on Tuesday 3rd November 15:33

[NDNDNDND]

In that case I consider myself thoroughly schooled!

Now I'm wondering how close my torques actually are, as the wrench clicked at different angles each time...

[Arbs]

FT

[tapkaJohnD]

Glad you're sorted!
There are other styles of torquing tool, other than the 'adjustable', which may be easier to use in a tight spot.
The beam type has much smaller head, you can get adjustables that come with a set of open-ended spanner tips.
Bike shops sell a style of beam wrench that works more like a torque screwdriver, but only for low, less than 10ft-lbs. Proper torque screwdrivers tend to read only inch-lbs!
John