Is cold torque the same as warm torque?

[oldtuckunder]

So there I am in the workshop this evening, and its a bit cold "like getting down toward freezing" and I'm torquing up main bearing caps as the block is going for a line bore check tomorrow.

 

And I get to thinking all this metal is getting down towards freezing and I'm torquing bolts up to a setting from the manual that was set/measured on a block that was at what? temperature.

 

Which got me thinking OK I assemble an engine in the cold of winter when all the metal is shivering and as hunched up as it can get, and I torque everything up to specified settings and then it gets warm, and then I run the engine and it gets hot.

 

What happend to those torque settings? What happens to Main and BE shells that are designed to compress a bit at those torque settings?

 

A question to ponder on a winter night

 

Alan

[Motorsport Mickey]

" and I'm torquing bolts up to a setting from the manual that was set/measured on a block that was at what? temperature."

 

I'm a trained toolroom engineer and I can assure you the thought has occurred to engineers probably about 120 years ago !

The block was machined at standard machine shop temperature of 68 deg F. ALL machining is done at that temperature so as to have a uniform expansion of material and tolerances and importantly interferences where the tolerances are sometimes measured in 1/10s of thousands of an inch (as per the bearing crush items you mention).

Because the engine is designed to be run at temperatures which can encompass frigid cold and tropical heat it's tolerances are designed to still be uniform because the whole assembly expands and contracts together, and it's various components run within the operating tolerances, if they don't...tough, you can only control the initial machining process. Importantly answering the second part of your question that's why it's important that all the components are at the same temperature, ie main bearing caps bolts and the block kept together.

 

Tomorrow you will be dropping your engine off into an environment which should be maintained at the same 68 deg F temperature and after a period of "acclimatisation" the blocks temperature should stabilise and it's tolerances return to the original machined settings, then the block will be checked and line bored.

 

I'm pleased you asked the question, it's a piece of knowledge imparted to my group of apprentice engineers within our first 10 days as we were taken around the machine shop by our trainer who had fun "batting" away many obtuse questions from young minds straight from school.

 

Mick Richards

Edited February 16, 2016 by Motorsport Mickey

[Alec Pringle]

Yes Mick, and I can recall as a young chap dropping an engine block into the machine shop in the middle of a Lancashire winter . . . . . and expecting it to be done in no time flat.

 

The foreman succinctly explained in unexpurgated terms just what I could do with my expectations and where I could stick them, then lumbered an apprentice with explaining in simple monosyllables to this tatty head that the block fresh out of my freezing garage, and transported in my Bedford van devoid of heater, would be wheeled into the waiting room to acclimatise and relax . . . . and they'd look at it in a couple or three days at best..

 

It's a long learning curve !

 

Cheers

 

Alec

[mike3md]

.....so, I need to speak to the head of the household about assembling the engine in the dining room (after leaving to acclimatise, of course)?

 

Could be tricky.........

 

Mike

[RogerH]

Hi Alan,

I believe your question was of torquing not machining.

 

Machining is done to fine tolerances (unless I'm doing it) and temperature can have a serious bearing.

Even the machining process can affect the dimension and hence cutting/cooling fluid is used in copious lumps.

 

However torquing is a much more coarse affair.

If you set a torque load at room temp - 20'C - or there abouts then at freezing, with the miniscule shrinkage of the parent metal,it will reduce the torque load a tiny fraction if at all measurable - but !!! don;t for get the bolt will shrink as well.

 

If you now run up to working temp then the parent metal will now expand so increase the torque load - but - the bolt has also expanded so negating any temp effect.

Assuming that the materials are fairly similar then expansion/contraction will compensate for all the joined bit - to a fair degree.

 

Don't Panic

 

Roger

[Motorsport Mickey]

"the engine in the dining room"

 

Only if you are machining it there ! ! ! normal rebuilding and assembly can quite confidently be carried out in a less well heated area, frigid garage for you my boy !

 

I thought we answered the question of torqueing above by stating

 

"Because the engine is designed to be run at temperatures which can encompass frigid cold and tropical heat it's tolerances are designed to still be uniform because the whole assembly expands and contracts together" which of course covers the torque tolerance as well. That's why I stated that ALL the components should be stored together at the same temperature, nevertheless as Roger clarifies the torque would be broadly unaffected by temperature variation.

 

Mick Richards

Edited February 16, 2016 by Motorsport Mickey

[oldtuckunder]

Thanks for the feedback guys! Guess I'd better pack a thermometer and do a QC check on the environment when I drop the block off. In these days of high energy costs.........................

 

Alan

[john.r.davies]

Thank you guys!

It's points like this that are lost by us amateur engineers.

Now we know and no excuses!

 

John

[mike3md]

Thanks chaps, although Valentines Day went well, I wasn't looking forward to suggesting an alternative use for the dining room.

 

Back to the garage!

 

Mike

[ianc]

If one is torquing an alloy head using steel bolts/studs, temperature can make a very small difference.

When I owned an Austin 7 Special with an alloy head, I would put the head into the refrigerator (the head on A7 is quite small!), get it cold, then fit it as rapidly as possible. The alloy would expand more than the studs, thereby increasing the torque a smidgen.

Ian Cornish

[Don H.]

If one is torquing an alloy head using steel bolts/studs, temperature can make a very small difference.

When I owned an Austin 7 Special with an alloy head, I would put the head into the refrigerator (the head on A7 is quite small!), get it cold, then fit it as rapidly as possible. The alloy would expand more than the studs, thereby increasing the torque a smidgen.

Ian Cornish

 

Why didn't you just torque the studs a little tighter at room temperature, Ian? What am I missing?

[ianc]

DonH - the A7's block is alloy and the studs very small (from memory, 5/16"), so, and especially with an uprated engine (as was mine), there is always the risk of pulling the stud out of the block when tightening the nut. Cooling the head allows one to apply a reasonable torque, which then is increased slightly by the expansion of the head. That is the theory, but whether it makes much difference, I cannot say.

Ian Cornish

[Peter Cobbold]

Ian, Aluminium expands about 22um per metre thickness per degree C.

http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html

So a three inch thick head ( = 0.075m ) warmed from -20 to + 20C will expand about 2.6 thou.

Not sure how much more of a turn on the head nuts that would equate to ...

Peter

[Malcolm Tatton]

Interesting comments on a site which was mentioned on here a while ago

 

http://theshopmag.com/features/how-properly-lubricate-classic-engines

 

Under the heading 'Engine Assembly Tips' they refer to Torque values for different lubes (oil and Moly). I thought Torques were generally dry?

[stillp]

The manufacturer will often specify if the torque settings are dry or lubricated, and if the latter, what with.

 

Pete

[Motorsport Mickey]

Err...no.

 

They are what the engine manufacturer specifies, did you miss this statement ?

 

"The component manufacturer (engine block, cylinder head, fastener maker, connecting rod maker, etc.) will usually specify a torque value for related fasteners based on the use of either engine oil or a moly lube. Pay attention to this. "

 

There is no mention of lube on TRs hence the fastenings are tightened up dry. However if you replace any of the fastenings using ARP for example they (ARP) will specify not only the torque but also the lubricant required on the thread (sometimes supplying it).

 

 

"Torque values will differ depending on the thread lube, since moly will reduce friction and will usually require less torque application as opposed to oil. For example, if a spec calls for 40 lbf./ft. with oil but 36 lbf./ft. for moly, follow the recommendation for the type of lube that you're using, otherwise, you'll end up under- or over-tightening."

 

Hence with TRs all fastenings need torqueing up dry otherwise you risk overtightening the bolt or stud because the use of lubricant reduces the friction between the threads and cause an increased clamping force, which is what it's all about.

 

Mick Richards

Edited February 19, 2016 by Motorsport Mickey

[stillp]

This looks a bit confusing. I was replying to Malcolm's "I thought Torques were generally dry?". Mick, I assume you were too?

 

Pete

[Motorsport Mickey]

See what you mean Pete, yes I was replying to Malcolm's enquiry, you're just quicker typing than myself.

 

Mick Richards

[oldtuckunder]

 

I'm a trained toolroom engineer and I can assure you the thought has occurred to engineers probably about 120 years ago !

The block was machined at standard machine shop temperature of 68 deg F. ALL machining is done at that temperature so as to have a uniform expansion of material and tolerances and importantly interferences where the tolerances are sometimes measured in 1/10s of thousands of an inch (as per the bearing crush items you mention).

 

Importantly answering the second part of your question that's why it's important that all the components are at the same temperature, ie main bearing caps bolts and the block kept together.

 

 

 

 

Only if you are machining it there ! ! ! normal rebuilding and assembly can quite confidently be carried out in a less well heated area, frigid garage for you my boy !

 

That's why I stated that ALL the components should be stored together at the same temperature,

 

There is no mention of lube on TRs hence the fastenings are tightened up dry.

 

Everything back from machining and balancing, so its a trial build this weekend to check clearances.

 

Re the 68 deg F, I think I found the only reference in the Triumph manual which hints at this, where it says the gudgeon pin into small end bushes should be a light hand push fit at 68 deg F.

 

Anyway may be a bit anal, but as everything (crank and block) were machined after about a week of resting at the machine shop, and I'd have guessed at somewhere around 68 deg F (from what it felt like to me) Then if I'm checking clearances it seems only appropriate to check them at around that temperature, but at the moment the temperature here is dropping to close to freezing at night. So yesterday I built myself a cardboard chamber and have been gently warming the block, crank, and caps (without trying to heat the whole workshop) hoping that by this evening everything should be nicelt warmed through and around the 68 deg F mark.

 

 

 

Cap Bolts are all squeeky clean after going through the cleaner, but I'm just hovering on the bone dry torquing. Not thinking of greasing or lubing, but absolute bone dry doesn't seem quite right. If I remember from my manufacturing days all the unplated black steel bolts when new were always covered with a tiny film of some very light oil to stop them going rusty, and I can't remember if they were always cleaned and bone dry.

 

Somebody just give me the courage to say "no they should be bone dry"

 

Alan

[RogerH]

Hi Alan,

what will make the bolts go rusty inside the engine!!

 

Roger

[Lebro]

There is no danger of Roger's block not being climatised to workshop temperature :P

 

Bob.

[RogerH]

...they probably have it out the back in the yard !!!!

 

Roger

[oldtuckunder]

what will make the bolts go rusty inside the engine!!

 

 

well I hope they won't! no its just the thought of torquing up a squeeky clean bolt in a squeeky clean cap into a squeeky clean block that makes me wince! everything screams at me "give it a tiny bit of help!"

 

Alan

[acaie]

 

well I hope they won't! no its just the thought of torquing up a squeeky clean bolt in a squeeky clean cap into a squeeky clean block that makes me wince! everything screams at me "give it a tiny bit of help!"

 

Alan

 

And if it's really clean giving a lot of friction, the bolt preload (the thing you're trying to achieve) will be reduced at the specified torque.

[oldtuckunder]

Well did the trial build this afternoon and assembled the main cap bolts dry as the factory intended, and to be honest they felt quit nice torquing up and then undoing afterwards. The rods have ARP's so used the lubricant on those. Trial build a great success every clearance came in smack bang on target, so now its do it all again for real.