A physicist's look at rusted bolts

[PtMD989]

When my teacher told us to torque them till they snap then back them off a half a turn he was just kidding with us. He made sure we looked up the correct specs in the right service manual. Best teacher I ever had besides my dad.


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[Pavogrande]

I think the gm "stretch" bolt thing started with the 350 diesel trying to solve the head gasket problem --
Could not solve the design problem of too few head bolts --

[lylejb]

I recently learned about this. In the case of my 1987 GM 6.2L diesel, it was a technique called Torque to Yield, and is meant for one-time-use bolts. The head bolts on my motor are this type. I've been told that GM discontinued this practice, but I'm sure others still use it. The bolts cannot be reused, as they have been pushed past their yield point. Apparently, someone thought it was a good idea for a while. I haven't researched why though.
BDGR

Sorry to say they're using them more and more. Not just on head bolts either. Most vehicles built in the last 20 years have went to multi layer steel head gaskets, and that virtually guarantees the use of torque to yield bolts. Its all manufacturers now.

[Clark]

I have been buying old guns, chisels, and screwdrivers, just to clean off the rust and get them in working condition.
I know it it silly. I don't need any of this stuff, but I budget time to enjoy cleaning off rust.
My favorite is motor oil and toothbrush. Sometimes I use a bronze brush.

[beezapilot]

Torque specs are a continuing headache in the shop. If there are two friction points, the surface area of the threads and the bold head to boss area- the torque specs obviously change should there be any lubricant on either one. If the thread are oiled, or dry, or have loc-tight on them there are different lubrication qualities to all. So if a spark plug is to go in and the specification is dry, but the tech puts oil on the threads and torques to full spec- it is easy to over torque the plug and stretch the threads in an alloy head. Sometimes there are "angle torque" bolts, so you tighten the entire bolt circle to a certain spec., say 20nm- then add 90 degrees to that to remove the variance of any lube on the threads. On the BMW race bike you have one time use aluminum bolts going into a magnesium alloy engine case at 3nm, plus 45 degrees, the analogy is a bolt made of butter going into a case made of jello.

This is a cool website that covers lots of "common knowledge'

http://www.boltscience.com/pages/tighten.htm

[alamogunr]

Lots of good information on that site. I'm going to bookmark it. When I was working it became obvious that many new engineers had very little knowledge of good bolting practice and really didn't see the importance. Many time an engineer would specify a stainless bolt assuming it was stronger. Took awhile to convince them otherwise.

Although I was not a mechanical engineer, I sort of became a source of information on bolting practice. During that process I accumulated several publications. One that was sort of pirated was:

Good Bolting Practices, A Reference Manuel for Nuclear Power Plant Maintenance Personnel.

This particular manual only covered small bolts and threaded fasteners, defined as up to 1/2". It was published by the Electric Power Research Institute(EPRI). I had borrowed this manual from an engineer at the company's large power transformer plant. He allowed me to keep it for a couple of weeks and then requested it's return. The pirating took place when I copied it.

Another source of information on a wide range of fasteners was a manual by Mac Lean-Fogg Company. I got this from a sales representative. It covers many types of bolts, nuts, washers, etc. and their coatings, platings, etc.

The third information source is a little book: What Every Engineer Should Know About Threaded Fasteners by Alexander Blake.
This little (202 pages) book is full of information needed for specifying threaded fasteners.

Although I have little use for this information now, it is still interesting to me. The mis-information that abounds "out there" is amazing. This thread has been very interesting to me. Many of the things contained in the above posts confirms what is in the 3 publications. Corrosion is a subject that is not always understood or considered in the extreme.

[Parson]

Among my "other" hobbies is the restoration and preservation of antique engines ...the old big flywheel engine..."hit and miss" style. Most are from 70 to over 100 years and when "found" the majority have been rusted stuck in one way or another...Guys in that hobby have probably tried everything known to mankind to free rusted up bolts, nuts, shafts, stuck pistons, rings, bearings, etc...

We use heat, Kroil, PB blaster, WD-40, and my favorite..Coke (the drinking kind!) An old saying with the old engines and with our old car hobby is that "rust never sleeps". I have a beautiful model 36, 3" square butt Smith that is from the 60's...it's a real nice one except for some minor "flecking" on the frame in one spot...I've gently worked that spot to try and at least hold it as it is but if I'm not on it all the time...it will still show a little minor increase..."rust never sleeps".

I'm old enough with failing eyes, etc that I don't take chances with the better firearms I own...if they need work and I'm at all concerned about my ability or tools..they go to a local smith..

For grins, a couple of pics (before and after) of a 3 hp hit and miss I restored a few years back....nothing turned or moved on this one and it ended up being a terrific runner.

Attachment 194246

Attachment 194247

Thanks for that. My great grandfather had one on the thrashing machine. I think it was an international. I never knew him, he died young but when I took over the homestead in about 1967 there were a few old timers that remembered him and that engine. They all remembered the common remark "it fired once in the morning and once in the afternoon." Don't remember anybody calling it a "hit and miss", thanks again

[AZBronco]

Check out the u-tube vids on rust removal with a battery charger and washing soda . !!

[Multigunner]

I remember reading a news paper article from the early 19th century describing a new steam engine. They were very impressed that the piston and cylinder were machined to such a close tolerance that you couldn't slide a Penny coin in between them.
Of course this sort of arrangement would expand with heat so it had to be loose fitted when cold.

[Steven Dzupin]

Heat the Part and apply Beeswax ,let it wick in and give it a try.