LA Light Six engine setting torques

[JT7196]

Well what you seem to be telling me, is that after being in and out of the Motor Trade for neigh on 60 yrs, I and all of my Mechanic mates have been doing it wrong!
I always assumed the the Torque applied to the Head Nuts etc was the clamping load, have never been told to take into account that if the Threads may have Oil on them , then the applied Torque should be reduced !!!
Am I wrong ????
I too Torqued down my Cylinder Head Nut down to 40 Lbs/ft , always will and will continue to do so !
Cheers Al

[Culbu]

I would tend to agree with Al...

[lilykill]

Yeah you really have to watch with lubricated threads, a chart like this explains it the best.

As the friction reduces it takes less torque to produce the same preload in the bolts. As an example from the chart, torqing down with dry threads with a coefficient of friction of 0.14 takes 15.2 Nm (11.2 Ft/lbs) and gives a preload of 8 Kn ( 815 kg). If the threads were lubricated at the 0.08 end, it would only take 10.2 Nm (7.5 Ft/lbs) to give a preload of 8.7 KN (887 kg).

[JT7196]

Hi , so basically what your saying is ,that you are tightening up Head Nuts/ Bolts by pure guesswork ,if there is there is the slightest amount of any Lubricant on the Threads according to your theory , so how are you going to be able to asses how much Torque that should be applied to each one ??
All the charts / Graphs in the world aren’t going to help solve that one!

Taking it a stage further, take the “ K” series engines for instance, the Head Bolts , go right down into the “Oily” Sump area, those are tightened down by “Degrees” not by Torque, so how do the rules you have supplied apply to these engines ????

Cheers Al

[lilykill]

Hi , so basically what your saying is ,that you tighten up Head Nuts/ Bolts by pure guesswork ,if there is there is the slightest amount of any Lubricant on the Threads.
Not the way I work , but each to their own I suppose !!

Cheers Al

Its more of the case that if give a bolt/stud wire brush and a wipe with a rag to dry it before tighening your more likely to be within the preload that it was designed for but if its got a heavy coating of oil/copper grease then you'll be appling more preload to the bolts for the same torque and pushing closer to the ultimate tensile strength/failure limit of the material.

In terms of the K series application, you would use torque angle with the torque wrench.

[Dobbinridesagain]

Taking it a stage further, take the “ K” series engines for instance, the Head Bolts , go right down into the “Oily” Sump area, those are tightened down by “Degrees” not by Torque, so how do the rules you have supplied apply to these engines ????

Tightening by degrees removes the friction component, because it moves the fastener a known distance along the wedge - a thread is of course a form of wedge - and thus stretches it by a known amount.
So when degreeing, oiled or not makes no odds. This is perhaps why degreeing is applied nowadays to some critical fasteners and those which will customarily be oiled.

When I owned a Silver Shadow I had all the service manuals as pdf, but subsequently I deleted them.
Do however remember the notations about oiled and dry torques, and I must confess that after 46 years of tinkering with cars, that was the first time I knew that oil, or not, mattered.

Which is not to say that one cannot usually get away with ignoring the issue, but I think it's as well to have it in the back of one's mind.

Here is another reference for those interested. https://www.engineeringtoolbox.com/torq ... _1693.html
As you can see, the minimum torque reduction is 30%.

Ivor

[Culbu]

I will no more dare tighten any bolts, oiled or not !!

[frenchy]

Just as a matter of interest, is the vehicle in question a six light or a light six.
There is a difference in the original engines fitted. One being four cylinder the other a six cylinder.
The six light has either the 1203 or the 1444cc . the light six has the 1378cc Cheers Frenchy

[Culbu]

I didn't know that there was a difference between "Light Six" and "Six Light".

My car has a 6-cylinder engine, so it's a light six or six light one... ?

[frenchy]

The six light refers to the no. of side windows on the LA ten saloon . The light six was a different model and it refered to the No. of cylinders.
It also had a fixed head. Frenchy