Head + Rocker cover torques...

[Laverda Dave]

Tell me more Bryan about the 'spring balance' check. My SP torque wrenches are 3/8“ and 1/2“. The 3/8 range starts at 5lb but when I've set it to 8lb for a 6mm thread it stripped.
We had a torque wrench calibration station at work and I used to walk past it thinking I would bring my wrenches in from home to test them before I retired, of course I kept forgetting and now I've retired!

[Bryanj]

Clamp the square drive in the vice having set the torque wrench to any arbitrary setting, measure 1 foot from centre of square drive and affix a loop of strong twine or wire, attach one end of spring balance to loop and pull the other. Balance should read set number of lbs in lbs ft when wrench clicks. If it aint 1 foot long do 9 inches and spring shold be 9/12 of set reading when clicks.

OR if you are passing Gloucester call in and i will check it with my Snap On Torque Meter.

Remember most torque wrenches are only calibrated + or - 10%.

[ka-ja]

don't forget to "break" it a few times before testing, they can seize after prolonged storage

[Laverda Dave]

Thanks Bryan, I may take you up on the offer in May when we go to stay in a barn in Crasswell in Herefordshire 😊.
Thanks also Ka-ja.
I do always make a point of unwinding the wrenches after use to leave them on a zero setting as told in my school days leaving them 'set' weakens the spring and results in false readings. I don't know if true but I've always done it.

[Lobo]

Laverda... I’m away from my CB400 manual right now, but am pretty sure the max torque quoted for the 6mm bolts was 6 ftlbs. If you applied 8 then I guess the threads would strip?

[Laverda Dave]

Lobo, the Haynes Manual I have gives a generic torque figure for 6mm threads of 7-9lbs. I played safe and went to 8lb and a couple stripped (now helicoiled due to lack of any metal around the damaged thread). But going on what Nigel mentioned in his earlier post it could have been caused by me adding copperslip to the thread coupled with the wrench calibration being out and likely thread damage caused by previous P/O's.
Strangely the 6mm threads on the CB250RSA are also torque set at 8lb none have stripped! 

[K2-K6]

I've come back to this as it links into a question I was asked about the figures given for torque settings on manuals.

Question was "Why do the torque figures range over such a larger percentage difference given that some of the tolerancing is so very very fine and precise?" I couldn't answer this with credible logic.

Now,  if we apply it to these bolts only,  7 to 9lb per foot, has the top figure something in the order of 9 being 33% increase on the 7lb setting!

If you add in "marketer's" psychology of giving a price range,  the middle one being what you sell most of,  the lower figure to make the middle purchasers feel they've got something a little bit better for their informed choice,  and the highest cost,  is just pure additional margin for those foolish enough to shell out for it 

Comfortable we are in choosing the centre point,  and it just seems so logic doesn't it. So,  if you take the 8lb and work through possible errors/ potential for unquantified effects, you can get 8 + 10% torque wrench accuracy (depends which way it defaults) + 15% for grease/coppaslip change to torque measurements,  you can end up with 10.1lb measured torque.
Or for those making a decision that you should use the highest torque figure, something like 11.4lb 

It's easy to see why they are often stripped. Also why they gave us just screws on many of the covers on these engines so that generally people can't load too much torque onto them with just a screwdriver.

If you look at the joint on these cam covers,  they are metal to metal with no gasket to compress (once touching with the o-ring compressed) so have no yeald built into the torque interface.

If you had to specify it,  once the casting faces touch,  then you'd only need something like 2 to 3lb of torque to prevent the bolt backing out in use.  So a safety margin of double that, 6lb, would be a good set point to make sure they reliably exceeded a practical minimum during engine use.

Then if you set your torque wrench to 5lb,  lubricated the threads ONLY,  made sure the underside of the bolt head was clear of lubricant,  along with the casting face.  You should get a true torque of between 4.5lb (if torque wrench was 10%error in minus) to 6.3lb with all errors maximised to plus figures in above illustrations.

This would minimise potential of stripping them,  and make sure they don't  release in use.

[ka-ja]

After a lifetime using spanners etc. I still trust my hands and fingers on small items, never stripped one yet.Things like cyl. head and crank bolts are more critical.

[Bryanj]

+1 on that last one.

[Lobo]

Great food for thought Nigel, I’m a coward and by default always take the lower figure.

You mentioned lubricating the threads only - one turn of a 6mm thread would be approx 18mm, so (eg) a dozen turns would be getting on for 20cm worth of minimised thread friction? Would this not be very significant in terms of falsified torque readings?

Ka-ja / Bryan... you guys have the experience / skills of a lifetime fettling such things, us mere mortals can’t hope to accurately set torques using fingers!

[K2-K6]

As ka-ja and Bryanj point out,  long term experience can encompass many of the subtle elements that are not immediately apparent to someone new to these subjects.
In addition to that,  it's the reason why flat spanners and Allen keys etc have diminishing lengths as they go down in bolt size, to in effect limit the torque applied by the user and give some semblance of feel consistent with each size when tightening.

This is effectively subverted when using a socket set with one length handle for all bolt sizes,  especially if you are using 1/2 inch drive with 10mm socket.

Even when using an appropriate rate torque wrench it seems like you aren't really tightening them enough.

I've no problem in judging without a torque wrench for non critical bolts,  but have been involved with writing manuals in which a task has to be accomplished by users with very different skill levels. It's quite a challenge to convey the correct route to such a wide range of familiarity, and end up with the same final result.

There's an old description for this " those that can do and know they can are fine, those that know they can't do and seek assistance are fine, those that can't see that they can't do are where problems exist" 

This thread seems to be more "behind the scenes" discussion of how the spec is affecting the final method on these engines.

To answer your last torque question Simon,  it's useful to compare the cam cover bolts to the cylinder head studs to show the difference.  The head stud has flanged nut operating on washers to reduce the torque measured from straight surface friction.  This allows it, during tightening, to pull the stud into tension within its elasticity. The resistance in torque reading will mostly come from the thread pitch lengthening on the stud coming into conflict with the nut threads which are being compressed. 
The cam cover bolts are never going to be at that level (even those size steel bolts will easily take something in excess of 10 tons of tensile load,  they'd pull the alloy threads out of the casting long before that)  so they delete the washer with the resulting torque you measure being just from friction between the underside of the bolt flange and the alloy casting. The threads really aren't being measured in this application. 

It occurred to me that the numbers quoted in the manual are not really assembly accurate figures.  They appear to be a range that "includes" torque wrench typical error figures. I.e. aim point plus or minus 10%.
That's not the same as giving the mid range figure and accepting the error of torque would do the job.  It allows,  promotes? A situation in which you can start at the extremes of error and then add some more with a torque wrench. 

[ka-ja]

Always consider with small diameters, the lower the torque settings, the more inaccurate they become, unless you have a wrench with a very low range.

[K2-K6]

Something like this

 https://www.wiggle.co.uk/x-tools-essential-torque-wrench-set/

1/4 drive and from 2nm about 1.5lb-ft

[ka-ja]

Looks the part in a handy case, My smallest is 3/8 drive britool about 40 yrs old.

[Nurse Julie]

Looks the part in a handy case, My smallest is 3/8 drive britool about 40 yrs old.

Trig uses the old Britool torque wrenches including the little 3/8 drive.