Torqueing Lubricated Head Bolts with a dry spec.

[ducked]

Time to put the head back on, which means deciding on head bolt lubrication and torque, a bit classic and fundamental.

CB20 manual says dry. CB23 manual doesnt say.

Torque specs are slightly different but 40 ftlbs is in the overlap

I have no manual for my CB22 engine but assume dry 40 could apply.

My problem is I've never installed any threaded compnent dry and am rather reluctant to start now with a high torque item.

Engineering Toolbox suggests reducing dry torque by 30-40% for SAE40 oil used as an assembly lube

https://www.engineeringtoolbox.com/t...ts-d_1693.html

Was going to do that, when I came across this suggestion for deriving a "torque and angle" spec from a dry torque which could then be applied to a lubed bolt.

" Take the dry bolt and torque to a 1/4-1/3 of its published dry torque spec. Then, mark the bolt and the part, and torque to its full value. Note how far it has turned. Now, with the lubed or Loc-Tited bolt, torque he same 1/4-1/3 torque you used earlier, then tighten to the same angle of rotation as when it was dry

.”http://www.thumpertalk.com/forums/to...greasing-a.../

Not sure the apparent assumption that the initial torqueing is unaffected by lubrication is valid, but if it is,subsequently you should get the right bolt tension with a lubed thread (though any initial “dry galling” damage is already done),

If doing this, aluslip might be more persistent and thus a better choice.

Tried it. Torqued in 4 X 10 ftlb increments dry (washed with carb cleaner) from finger tight, laying a ruler on the head to record starting angle.

I used a feeler guage set as a carpenters angle gauge (which I dont have here) and read off the angle with a geometry set protractor.

Fiddly and probably error prone. A possible systematic error is I had all the bolts initially finger tight but the outer ones loosen as the the inner bolts are tightened.

Should probably have started them from finger tight individually.

Initial Angle for the first 10 ftlb increament. in order of the tightening sequence was

180 130 160 135 200 180 100 225

Total Additional Angle for the last three increments. in order of the tightening sequence was

139 195 191 245 118 128 127 256

The next step would be slackening off, lubricating, torquing to 10 ftlbs, and tightening it to those angles, BUT variation doesn't give me a lot of confidence in the method (in my hands, at least)

[Stealthee]

If torque spec says dry, install dry. Period.

[ducked]

New sentence


Or not.


Replacing the head after packing the cylinders with rope to stop engine rotation (worked, but I still couldn't shift that crankshaft bolt, just bent my cheaters) I used the “torque translation” procedure when I put the head back on, recording the angles while dry torqueing in 10 ft-lb increments


Bit more convincing/consistent this time, though I knocked the box holding the bolts in sequence over, so they are randomised WRT the original order.


Plotted in Calc (which I’ve just started to use. Formats a bit screwed compared to Excel) one can see that Bolt 5 hardly changes angle between 10 and 20 ft lbs, i.e. its stuck. Maybe thats what galling looks like on this view. though I would have expected it at higher torque values.


forumosauploads-12829.kxcdn.com/original/3X/a/9/a9...g


According to the previous owner, this engine has had a head gasket failure, so the bolts have probably been re-used at least 4 times (though of course I don’t know if they were used “dry” by the pros and would doubt it.)



This may be enough to compromise the thin black oxide coating and allow galling.


If I have to do it again (which unfortunately seems likely) I’ll probably lubricate them and use the angles.


I may just start from finger tight and use the total angle, since I’m not sure of the rationale for starting at 1/4 torque.


It seems to assume the initial torqueing is not affected by lubrication, which seems unlikely


Question mark

[Stealthee]

Torque is affected by lubrication. Do not lube bolts that are supposed to be torqued dry.

Dry threads create more friction which causes the proper bolt stretch to achieve the proper torque value. A lubricated thread is going to take as much as 30% more stretch to achieve the same perceived torque value. That is enough to cause significant damage and can snap bolts.

[ducked]

Double post, see below

[ducked]

Originally Posted by Stealthee

Torque is affected by lubrication. Do not lube bolts that are supposed to be torqued dry.

Dry threads create more friction which causes the proper bolt stretch to achieve the proper torque value. A lubricated thread is going to take as much as 30% more stretch to achieve the same perceived torque value. That is enough to cause significant damage and can snap bolts.

This misses the point, and doesn't, in detail, make sense.


Friction does NOT "cause the proper bolt stretch" and the "proper torque value" is incidental to the objective, which is to achieve the proper bolt stretch, and hence the proper clamping force.


For a given thread pitch, bolt stretch will depend on degrees of rotation, and will be independent of friction, which will only influence how hard it is to turn. i.e. the applied torque.




However, a couple of other issues did occur to me with the ““Torque Translation”” method outlined above (as well as the fairly critical "where do you start?" issue already mentioned) though, of course only after I put aluslip on the threads.


In a situation where re-torqueing is likely to be required, say because the head gasket compresses further after a few hundred miles, if you use the angle to replace your torque spec, you can’t do it, since the angle wont change.


Only work-around I can think of is to record the final torque reached while setting the final angle, and then re torque to that.


Dunno how accurate that’s likely to be.


There isn’t really any rotational force applied to head bolts in service, so clamping force is whats important, and thread friction doesn’t matter much.


OTOH there definately IS rotational force applied to say…oh… just picked at random…a crank bolt, so I suppose reducing the thread friction there, even while applying the correct clamping force MIGHT be an issue.


Only if I can get the bloody thing off though

[Stealthee]

Friction absolutely plays a pivotal part in proper torque. Any half ass Google search shows that.

I repeat yet again, if torque spec says dry, install dry. Period.

[fredjacksonsan]

Lubrication reduces friction. Torque spec requires friction hance, when lubing something that is supposed to be dry torqued, you will overtighten.

As stated, dry is the way to go here. I've never seen a "lubricate then torque" specification.

[ducked]

Originally Posted by Stealthee

Friction absolutely plays a pivotal part in proper torque. Any half ass Google search shows that.

I repeat yet again, if torque spec says dry, install dry. Period.

New sentence.

Friction and torque are of course directly related, half-arsed Google search or no.

Friction and bolt tension are NOT directly related.

If a half-arsed Google search suggests they are, the half-arsed Google search is wrong. Might be using ChatGPT.

Torque (at least in the context of head bolts) does not matter. What matters is bolt tension.

Bolt tension is directly related to how much you turn the bolt.

[fredjacksonsan]

Originally Posted by ducked

...

Torque (at least in the context of head bolts) does not matter. What matters is bolt tension.

Bolt tension is directly related to how much you turn the bolt.

Correct! And with lubrication, the bolt will turn more than designed before reaching the torque specification; therefore the ultimate tension will be beyond what is specified.

Torque dry.

/thread

[ducked]

Originally Posted by fredjacksonsan

Lubrication reduces friction. Torque spec requires friction hance, when lubing something that is supposed to be dry torqued, you will overtighten.

As stated, dry is the way to go here. I've never seen a "lubricate then torque" specification.

Its not unknown to see "lightly oiled" recommended, and the Engineering Toolbox ref above gives recommended torque reductions for various lubricants.

https://www.engineeringtoolbox.com/t...ts-d_1693.html

Aftermarket head bolt manufacturers like ARP spec their own lubricants which I think tend to have molybdenum in them, so lubricated headbolts are hardly some weird heresy.

Here's a general article on it, with some quoted text.

https://www.enginebuildermag.com/200...re%20installed.

“As a rule, the threads and underside of the head on most standard automotive head bolts should be lubricated with motor oil before the bolts are installed.”

""Most service manuals recommend using straight 30W oil or 10W-30 multi-viscosity oil. Though 10W-30 is obviously a thinner oil than straight 30W oil, one gasket engineer we interviewed said the difference is negligible and has almost no measurable effect on bolt loading""

The "torque translation" method I'm using isn't very widely recommended, though, and could be regarded as a bit experimental, but if you cfan't get experimental with a 37 year old car with no market value, when can you?

[ducked]

Originally Posted by fredjacksonsan

Correct! And with lubrication, the bolt will turn more than designed before reaching the torque specification; therefore the ultimate tension will be beyond what is specified.

Torque dry.

/thread

I'm using the dry torque to determine the required bolt rotation.
Then I'm applying THE SAME bolt rotation to the lubricated threads

That's whu I'm calling it a "Torque Translation" technique. I don't reference torque for the final tightening.

This seems to bypass this repetitively expressed concern. Unless I'm missing something.

[fredjacksonsan]

Originally Posted by ducked

I'm using the dry torque to determine the required bolt rotation.
Then I'm applying THE SAME bolt rotation to the lubricated threads

That's whu I'm calling it a "Torque Translation" technique. I don't reference torque for the final tightening.

This seems to bypass this repetitively expressed concern. Unless I'm missing something.

It's your vehicle, do what you want! Best of luck, hope your eyeball of the rotation is as accurate as the torque wrench, and the applied lube doesn't allow the bolts to back out under vibration.

[ducked]

Thanks. Im using a cheapo beam type wrench so not very accurate or precise, but less likely to lose calibration than the clicky type.

Im not very concerned about head bolts vibrating around since only the threads were lubricated, not the washers or under the bolt heads.

This would be a concern with the very hard to remove crank bolt, which, unlike a head bolt, IS subjected to rotational forces. Might not do it with that

[Blue Bowtie]

This is one of the reasons many critical applications are defined in a one- or two-step initial torque plus degrees rotation instead of simply torque.