Bolts, torque, and grease

[Nick1911]

When doing auto repair, do you use any lubricant on the threads of fasteners during reassembly?

I've heard a LOT of different information on this.  Notably:

"You should always use grease or motor oil on bolts, so they will come out without trouble next time."
"Anything other then dry will affect the clamping force at a given torque, and lead to over tightening."
"Only lubricate fasteners on the suspension/undercarriage"
"Clean bolts with wire wheel, the use grease before reinstalling."
"Clean bolts with wire wheel, then install dry."

Personally, I clean them up with a wire wheel if corrosion is present, and almost always install dry to the spec'd torque.  I was just wondering if there is an official stance on this.  It does seem that lubricant on the threads will lead to over tightening.

Thoughts?

[cassandra and sara's daddy]

anti seize on lug nuts

[charby]

Only if the manual says to. When I changed the from passenger side hub out on my Jimmy the boot said to cover the threads on the axle with grease before putting on the nut.

[Headless Thompson Gunner]

Anti-seize on metals that require it.

I have a bike frame that's useless because the dolt who installed the bottom bracket didn't use antiseize.  The bottom bracket is now welded to the aluminum frame and cannot be replaced. 

[Rudy Kohn]

Most of the repairs I do are of fairly easy things--stuff where I don't really care what the exact torque is, just that the bolt stays put.  That usually means cranking down on it so that it's significantly more than "hand tight."  The exact number of foot-pounds is not known to me, and probably varies significantly (most closely depending on the size of the wrench I use).

That said, I usually throw a little anti-seize on bolts before I reinstall them.  I haven't had any problems show up from doing this, and it has resulted in significantly sped up future repair work in a few cases.

If I was rebuilding an engine or doing something requiring more precision like that, I'd have to think about it more carefully, but my general MO is to put on a little anti-seize.  I never use motor oil, and infrequently use other greases on bolts.

I don't put anti-seize on lugnuts, though.  I'll usually clean them off and reinstall those dry.

[Boomhauer]

I don't put anti-seize on lugnuts, though.  I'll usually clean them off and reinstall those dry

My main issue with Lugnuts is tire shop technicians that crank 'em on with an airwrench, or jam them on like they are on a NASCAR pit crew. Those idiots will either crossthread the lugnuts or tighten them so much you will break a stud trying to get the nut off.

Lugnuts should be hand torqued to specifications. I've never had a problem with "dry" lugnuts if torqued properly...

[charby]

My main issue with Lugnuts is tire shop technicians that crank 'em on with an airwrench, or jam them on like they are on a NASCAR pit crew. Those idiots will either crossthread the lugnuts or tighten them so much you will break a stud trying to get the nut off.

Lugnuts should be hand torqued to specifications. I've never had a problem with "dry" lugnuts if torqued properly...

me too.. I always grab my torque wrench to check the torque on my lug nuts when I need to remove/replace the wheels.

[Brad Johnson]

Anti-seize on anything where you have two dissimilar metals in contact (like iron plugs or accessory mounting bolts in aluminum heads). A light coating of oil for most anything else.

Anything exposed directly exposed to the elements and could always benefit from a coating of something.  I don't know that I'd use heavy grease unless specifically called for, as the sheer volume of lube could screw up torque readings and result in loose or over-tightened fasteners.  A tiny bit of anti-seize shouldn't hurt, or even a light brushing with some ATF (which is a darn good long-term corrosion inhibitor).

Like Nick, I clean all fasteners before reinstalling.

As for the lugnuts at the tire store (the human kind) the atrocities I've seen them inflict on some poor unsuspecting slob's vehicle are absolutely appalling.

Brad

[cfabe]

I happened to work in the fastening industry for a few years...

Any sort of lubricant on the threads or washer face of a bolt will affect the clamp load delivered at a certain torque. Only about 10% of the torque you put in to a dry joint actually generates clamp load, the rest just overcomes friction. So when you cut that friction, you can end up with way more clamp load than you want (or the bolt is designed for). OEM fasteners on cars are usually designed with a particular coating or pre-applied lubricant to try to get consistency in assembly between vehicles. We would see problems with broken bolts in assembly plants when they got too much lubricant on the bolts (oil pooled in the bottom of the bin, for example). Generally, if a torque spec reads only the torque with no additional instructions, it means to assemble it dry. In all my years of DIY mechanic work, the only place I've ever seen a lubricant called out was when using high performance (ARP) fasteners for engine assembly. And in that case I actually used a bolt stretch gauge rather than a set torque to get exactly the deformation they called for. There are a variety of other fastening strategies out there used in OEM assembly that provide better clamp load control (angle control, torque-to-yield fasteners, torque+angle) but you don't generally run into those in mechanic/repair work.

I do use anti-seize on lug nuts, and tighten to the normal specs. I've had lugs I know I tightened properly break off after less than two years of northeast Ohio corrosion, and the anti-seize helps with that. I have also experienced over tightened lug nuts and stretched studs from tire shops, and have witnessed tire shop employees using torque wrenches improperly. Always torque them yourself with a good torque wrench.

[280plus]

if it has threads on it, I lube it. I haven't used anti seize in a while, it's kind of messy. I have a little plastic bottle throwaway oiler that comes with 20w non detergent oils for oiling electric moters. I also use wd40 if that's what I happen to find first. Today I couldn't find anything on the truck (cause I cleaned it) so I used the guy's 3 in one he had on the shelf right there. 

I've used grease. Something, anything so when it's time for it to come apart, it will. I'll admit to tightening everything to feel but I've been tightening stuff for a while now. Unless I'm putting an engine or a compressor together.  Then I use a torque wrench. I have one around here somewhere, I can find it, might take me a while. 

Haven't done any lugnuts in a while but I think I'm coming due. I've always lubed them.

[French G.]

And in that case I actually used a bolt stretch gauge rather than a set torque to get exactly the deformation they called for.

Agreed.

If the torque matters, pick a lube like moly, get the proper bolt stretch. If doing many of the same bolt you can derive a torque from the process of getting that stretch, check the stretch at that torque and move on torquing to whatever foot-lbs. value gave you that stretch. If you are building a race motor how about check the stretch on every one. If you prefer to torque in Newton-meters please move to Quebec and buy a beret.

Now, general passenger car stuff it really doesn't matter in most cases unless the bolt falls out or you strip the threads. A generic torque value based on bolt size, pitch, and material tightening into will suffice.

If it doesn't need Loctite then it needs anti-seize. Anti-seize on the taper of any bearing surface like a tapered allen screw or a lugnut will aid in the fastener coming back off again. If you really don't want it to fall off safety wire it or use a deformed tab washer or something.

Back to torques that matter, lube on the bearing surface of the bolt and washer is just as critical as on the threads, as is lube types. Like I said before, any critical torque I'm around uses moly in an oil carrier. Torques that specify dry torque are pissing in the wind as far as I'm concerned. If an engineer thinks lube will make too much clamping force then they should have specified a lower, with lube torque. The friction of a dry torque is too variable to mean anything. Bolt stretch is what loads the ramps of the thread against each other and holds the bolt in, torque lost in friction really leaves you not knowing what actual load you have on the fastener. If an engineer really cared they would tell you what lube, what bolt stretch. Anything less is an arbitrary number.

In the end common sense must prevail. If you can't develop a good feel for what you are tightening I am sure your local mechanic can and would love the business. That flared fitting seals on the flare, not by your monkey humping it with an 18" wrench. Go ahead and torque away on that sparkplug in an aluminum cylinder head. See what it gets you. In 15 years of airplane fixing(5 of that QA), 20+ car fixing, and a lifetime spent working on fast race cars since age 5 I have seen way too many cases of too tight than too loose. When I was 7 I was snapping off 3/8" grade 8 bolts tightening them because I didn't want a bolt to fall out of Daddy's race car. 

[zahc]

if it has threads on it, I lube it

Yep. It's from my bicycle (not to mention boat) days. Then again I almost never use a torque wrench unless it's something like a cylinder head or something. As already mentioned the proper torque varies greatly so unless it's an assembly line, new parts and known lubrication scenario, I don't see much point in following manufacture's torque spec. I watched a guy strip the cases on his motorcycle because he was trying to properly torque the nuts. Even with his rather nice torque wrench, he just kept turning way past the point I would have called "snug" because his wrench hadn't clicked yet.

[Jim147]

The ARP lube is some great stuff. It includes a teflon sealant for bolts into water. You can pick it up at most speed shops.
I used a lot of the stuff building drag and circle track motors back in my pre extra holes in body days.
If you don't have that on hand I use a 50/50 mix of WD-40 and ATF.
I keep it in a spray bottle. I mainly use it for keeping fresh honed cylinders from rusting.

Don't use more than a very lite oil on the bolt threads in blind holes. Remember liquid does not compress.

I have always torqued my lugnuts. Clean threads no anti-seize.

[280plus]

The friction of a dry torque is too variable to mean anything.

Well said, I may use that as my sig line. 

J/K