Torque settings - Lubricated or dry?

[JerryTR5]

I have just been doing some research on this 'ere forum to see if I could find a consensus on the procedure to re-torqe the head on a Sprint.
Won't bore you with the details but this has clearly been a hot topic over many years.

One item which I still need clarification on:
Are torque values given in the workshop manual for lubricated or dry threads?
One forum post asserted that "The torque figures quoted in the BL manual are for the threads oiled".
Can anyone confirm or refute this claim?

None of my Triumph or BL manuals specify thread lubrication which is odd given the difference in clamping force.
I have always assumed it is for dry assembly but most of my Triumphs are from the pre-BL era. Maybe there was a change in engineering practice over the years.
Jerry

[Mad Mart]

I don't know if the figures quoted are for dry or lubricated threads but as one would usually lubricate the thread before torqueing I assume the latter.

[Bumpa]

I have always believed that threads should be lubricated before torquing them down. The tightness of the bolt or nut is not the important thing. It is how much stretch, and therefore clamping force, have you applied. If the threads are dry and therefore may not be moving smoothly, you could end up achieving the correct torque reading without actually getting to the right clamping force.

[bazyerma]

Hi

I have always taken torque figures to be dry, as all lubricants have a different coefficient of friction (0.15 for the copper grease I use).

I have a slide rule I use to convert if its a really important torque, but if not I just use the figure supplied.

Regards

Barry

[shaunroche]

For the last four years I've used that sequence and figures on my race engine and I've never had a head gasket issue, and I drive it very hard!

[cleverusername]

Torque figures will be dry, Haynes generally gets their numbers from manufacturers workshop manuals and I very much doubt they bothered to oil/grease bolts in the factory. Why would they? They didn't care if the bolt seized up in 5 years time due to rust.

To be honest I wouldn't worry about it, roughly right is going to be good enough for something made in the 1970's.

[JerryTR5]

Thanks for all the comments.
I did read somewhere that lubricated or non-lubricated threads could make up to 40% difference in clamping force, but don't know if that was for ship building or watch making.
Cheers, Jerry

[cliftyhanger]

Thanks for all the comments.
I did read somewhere that lubricated or non-lubricated threads could make up to 40% difference in clamping force, but don't know if that was for ship building or watch making.
Cheers, Jerry

When I used some ARP BE bolts, they supplied a specific oil/lubricant. The specified torque was significantly lower than the figur esoecified for using 30W oil. So even different lubricants make a difference. Saying that, ARP suggested measuring fastner stretch as the preferred method for tightening

[shaunroche]

Dry bolt torques are approximately 30% higher if a bolt is lubricated with for instance SAE 30 oil - the torque compared to a dry bolt is reduced with approximately 40%, obviously due to the thread interface having the mating friction reduced by the lubricant.

It's possible that if torque specified for a dry or slightly oiled bolt torque is applied to a lubricated bolt - the bolt may overload and break which especially applies to older, less exotic fastener materials as used on our engines.

I say this with the knowledge that the head bolts on a Cummins cylinder head are torqued to yield of the bolt, plus 90°...let me tell you that is the most horrible feeling ever when the bolt stretches, it feels completely counter intuitive!

[sprint95m]

I don't know if the figures quoted are for dry or lubricated threads but as one would usually lubricate the thread before torqueing I assume the latter.

+1




Ian

[Rgf]

There is another side to this question,if you lubricate bolts whould the lubricant not travel up the studs on to gasket face and mating surfaces leaving some area's moist on a dry gasket application?