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Bolt strength


George Rohrbach
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Replacing bolts on 20's and 30's cars, with modern bolts. I understand (I think I do), the markings on the modern bolts. But what sort of strengths were the old ones? I am trying to figure out just what to replaces them with.

For example: new stainless bolts can have a tensile strength of 85,000 psi, compared to grade 8 - 150,000 psi.

How can you figure out what old bolt needs to be replaced by what? Or is 85,000 psi, already more than the old metallurgy produced, so it makes no difference?

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Hi, George...

I am not an expert on bolts and there markings, however, I can offer the following.

In the foundry business, a casting (ductile in this case) at 85,000 p.s.i. is used for industrial castings that demand internal pressures upwards of 3,000 p.s.i. and are suitable. Compared to cast irons with 25, 30, 35000 p.s.i. on an average.

I would think a bolt with 85,000 p.s.i. would be more than enough for automotive use.

You did not mention where the bolts are utilized, so, I am assuming the engine block, manifolds, etc. Cannot imagine an 85,000 p.s.i. bolt failing in this atomosphere.

Possibly someone will chime in who may have more knowledge in the bolt area.

Regards, Peter J.

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Hi, George...

For Kingpins and Control Arms, as long as they are tightened correctly, I do not see a problem with replacements from a "GOOD" automotive parts supplier.

Now, sitting here, I am looking over an "Iron Casting Society" tech chart, which list every grade of malleable, ductile, and, cast iron to include recommended use, elongation, yield.

Do not know how far you want to investigate, however, if you e-mail me, I will send you a copy. It lists recommended uses for all of the above ferrous irons, to include white irons.

Also, if you would like, send me one of the "old" bolts for a "DESTRUCTIVE" test, and I could provide the grade & matrix, except for CE (Carbon Equivalent). For CE, we send the piece to an independent laboratory at a sizeable cost. Destructive means, it will be useless after the test.

Must interject a reminder to reading bolt designations from fairly recent headline news: Anyone recall the scam pulled on our Air Force some years ago, whereby, so called "ductile" bolts were contracted. The recipient of the contract sublet the order to Asian suppliers, did not tell the Air Force folks, the bolts sheared, were not to ductile specs at all, and, jail time ensued.

What I am pointing out is watch out where you buy such items. Ask where do the the National Automotive Chains buy metal products? You are no on your own so I do not get a "Legal Beagle" problem. Go to an "American" supplier!!

Get back to me, George.

Regards, Peter J.

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Peter,

I would like to take you up on your offer to "test" one of the bolts.

I will be at Hershey Wednesday through Saturday, spaces RNA 65-67. Perhaps we can hook up? I will also email you.

Bill,

Thanks for the website. It seems they have Stainless Steele bolts available with much high strengths than I have found elsewhere. I am sure I will order some stuff from them.

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Hi, George. Do not know if you are enroute to Hershey and cannot access this memo. See you at Hershey and read this when you return.

To the Forum, I will post the results of the test on George's bolt for your benefit. It dawned on me, after the above dialogue, to pass along follow up test results along.

I think it will be interesting to see what the metallurgy of the '20's & 30's bolt compares to today's. As for Industrial Castings, in my relative experience, the Silicon content was higher back then in grey iron.

George, that was Bill Stoneberg's tip to go for Grad 8 bolts and the website. I agree with him totally.

Regards, Peter J.

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When I replaced lower ball joints on my father's '62 Ford Galaxy, about 20 years ago, the factory joints were riveted to the control arms, and the replacement TRW joints included grade-8 hardened bolts in lieu of rivets.

That has always stuck in my mind, and ever since, unless I'm using junk from Home Depot to attach a license plate, I've always gone with graded hardware when replacing fasteners on chassis and engines.

Not sure about the "stainless vs. hardened" issue; just on gut instinct, I'd tend to favor the hardened stuff; besides are you really going to need the rust resistance of SS ?

I'm looking forward to Peter's report on the vintage hardware analysis...

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Hello, Frank. Hope all is well...

George Rohrbach and I spoke via cell phone at Hershey on Saturday.

Unfortunately, George had his hands full waiting for a tow vehicle, loading his goods, etc. He will send me one of the early bolts soon and the analysis will only take a matter of a few minutes.

Regards, Peter J.

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  • 1 month later...

George, having not heard from you since Hershey, should I consider your request to test and report on the metallurgy of your '20's bolt, a mute point.

Here of late, my non-gratis offer to answer casting questions, re-produce some castings, and, do metallurgical tests appears to be rejected.

Should anyone need help, or, answers you know how to get ahold of me.

Regards, Peter J.

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  • 3 weeks later...

Hi, George.

Just a note that I received the bolt today.

Will have the lab do their thing with the Spectrometer on Monday.

I'll get back...

Regards, Peter J. <img src="/ubbthreads/images/icons/wink.gif" alt="" />

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Hi, George (and other folks reading this.)

Just a quick update. Should have the analysis published here next week. As I told George, I bought a comparable bolt of recent manufacture so we can compare metallurgy.

Doing this in between my paid job. Want to put the report of Si, C, etc., into laymen's terms, too.

Going to torque George's sample to the max to see where it either snaps, or, doesn't snap. At least we'll have the highest rating.

Regards, Peter J.

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Peter and others:

They also reduced the size of the heads of bolts about the time they introduced "graded" bolts. (As we all see when we try to use a modern-sized bolt next to a 1920s original.) Will this have any effect on strength?

I await the test results.

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JB-ed...how are you?

Good point. The bolt we are using is "graded". I'm at home now. Will check difference in dimensions next week.

My curiosity is heat treated, or, quench & tempered traits/differences. I believe this would have more of an effect than, say, a mere .005, or, .008 dimensional difference in bolt head size. For "most" automotive torquing, it is done by brute strength, or, air wrenches on an assembly line. Basic comments most of you folks would be aware of, but, the torque we will use, I guarantee, none of us would ever see in auto restoration/repairs.

Who knows what we'll find. There is a possibility one, both, or, none will shear, but, at least we can make a comparison, and, the metallurgical chemistry report will be a reference to ascertain the reasons. May wind up with a yield & elongation contest vs. shearing of the head. Who knows? We'll find out, folks.

Regards, Peter J.

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Pedro, Re; the torque we will use....none of us will ever see... You've never met my Diesel Mechanic , Pedro. He'll use a torque wrench to the indicator "sound"/click and then keep pulling on it, while saying to hisself, "check, check, check!" We had to take an oil pan off a Detroit Diesel some years ago and drill the oil plug out. Never say never about mechanics. They can be as dumb as truckdrivers! tongue.gif Waiting to hear the results. I always thought stainless fasteners were not as strong as hardened steel ones. Wayne

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Hi, Bill. Good to hear from you.

As for Whitworth bolts, I really do not know. I am the original owner of my TR6, never had the engine out, or, had a need to get into the details of the bolt manufacturer. Have some books, of which, I will scan through to see if there is any references to Whitworth, years of utilizing said bolts.

If you are looking to sell the wrenches, I know a very good mechanic who works on Triumphs, MG's who possibly could use them.

Best regards, Peter J. <img src="/ubbthreads/images/icons/wink.gif" alt="" />

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Peter,

No, not interested in selling, You never know when I might find a Bugeye, E-type or an old BSA that I just have to have. If I do, I will need the wrenchs for sure. Same goes for the Uni-syn gauge that sits in the toolbox.

I was just wondering if Whitworth was still being made and used. They used to be a pain because they were only used in a few places. They were real coarse thread and didn't stand up to vibration.

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This is going to be a "long" one folks. I will start, with due respect, to George Rohrbach, who, made the initial post/query. In decending order, I post direct/simple opinions of "old" bolts vs. "modern" manufacture. Afterwards, the technical findings of the study, again, in decending order.

George:

--Go with Grade 8, or, other Tempered Bolts and Nuts for replacement on steering, tie rods, etc. applications. Your sample of a 1920-30's era bolt failed convincingly compared to Grade 8 and the jh Tempered Bolt. As Bill Stoneberg posted, Grade 8, or, other good Tempered Bolt.

--85,000 p.s.i. is normally for internal pressures for pressure vessels. Brinnell Hardness, or, a Rockwell Scale reading is the question: Again, replace with a high Grade/Tempered bolt.

--Bolt Head Dimensions:

(Did not use a Stainless bolt, as I personally would not use them for steering applications)

Tempered Bolt: .532

Grade-8 Bolt: .534

George's Bolt: .539

--Brinnell Hardness of the Tempered jh Bolt tested was first: 327.5-344.5

Brinnell Hardness of the Grade-8 Bolt tested was second: 293.5-310.5

Brinnell Hardness of the 1920-30's Bolt tested as third: 258.0-271.0

--Torqued Shear Points of the 3:

Tempered jh Bolt: Withstood 200 ft. lbs.

Grade-8 Bolt: Withstood 200 ft. lbs.

George's Bolt: Sheared at 147 ft. lbs.

(These bolts were all bolted down into tool steel with the heads flush to the surface.)

--JB-ed posted: "the Head Size was reduced about the same time bolts were "Graded" and would it have any affect on strenth?" in so many words:

Not in my opinion. The measurements of George's bolt head (.539)to the lowest measurement, the Tempered Bolt (.532) is miniscule, although, we are not creating a Space Shuttle here. We are looking at a difference of .007. The millage of the coatings could be just the difference.

--De Soto Frank posted: "...TRW joints included grade-8 hardened bolts in lieu of rivets". THAT ALONE SHOULD TELL YOU SOMETHING WHEN REPLACING BOLTS ON SUCH A SAFETY ITEM. The study I found sure backs it up, folks.

--Now, the chemistery findings:

(NOTE: Copper I found to be "Residual", meaning, it was present in either re-cycled metal, and, passed along to the bolt when it was produced.

Moly (Molybdenum, Mo) The Grade-8 Bolt appears to have been intentionally inoculated with Mo with a reading of .20. The Tempered Bolt had .02 and George's Bolt had .00, so, they read as residual. THIS BACKS UP BILL'S AND FRANK'S INPUT, THAT, ONE SHOULD USE A HIGH GRADE. 8 IN THEIR EXPERIENCES.

Here we go:

Grade 8/ Tempered/ George's Sample

Carbon © .39 .40 .35

Silicon (Si) .21 .23 .16 (Look out, folks!!)

Phospherous (P) .008 .012 .007 (Low)

Sulphur (S) .012 .011 .024 (Air Quality back then??)

Manganese (Mn) .73 .69 .64

Nickel (Ni) .02 .02 .01 (Low)

Chrome (Cr) .99 .10 .09

Copper (Cu) .01 .01 .05 (ALL 3 RESIDUAL)

Molybdenum (Mo) .20 Intential .02 Residual .00 (Non-existent)

Magnesium (Mg) .00 .00 .00

--Bottom line, go with Bill Stoneberg and Frank's advise...Grade-8 for replacement.

--This is one of those posts you hate to "hit send" in the sense that the "Legal Beagles" could rear their heads, however, the study was done on ISO Certified Spectrometers, and, Gauges, all of which, have been Certified within 4 days. IT WAS PERFORMED TO HELP STEER HOBBYIST'S IN THE RIGHT DIRECTION CONCERNING SAFETY ITEMS.

"Sorry that the line items are not in columns...been a long day."

Regards, Peter J.

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Peter - very good explanation and interesting test results. I agree with conclusions. After a review of this thread for comments about "dressing" the head of the bolt. If the car is going to be shown in AACA the judges will certainly take deductions for dress mark bolts on the '20s and '30s vehicles. However it is an easy process to file or grind the marks off the head. Use modern bolts and dress the heads!

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Peter,

Thank you very much for taking the considerable time to do this study!

It will certainly help me in making the decisions on what bolts to use where. Looking at the number of times, that this thread has been viewed (640 !), the need for this type of information has been on the minds of others also.

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Folks, you are all quite welcome. I found it interesting, too. Glad George Rohrbach initiated it.

Remember to make note of ronbarn's 12/19 post, too. Ron also posted this a couple of years ago, and, to use a good tempered bolt, but, forget to grind the modern-day bolt designations will/could cause heartburn point-wise at a judged National.

Regards, Peter J.

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Thanks also from me for the data.

I would like to return to the differences in dimensions between pre-war bolts and modern. I suspect your differences in measurements were in the bolt shank. This, of course is relevant to the type of test you performed, which I think is torquing the bolt until it breaks.

However there is another form of failure, pulling apart of a bolted joint lengthwise against the bolt head and the nut at the other end. Frequently this will be an impact load, not a steady load.

Before about 1948, bolt heads were considerably higher (called cap height in many tables)than modern. Much more than 0.007 inches, more like 1/16 inch and very noticeable when you use a modern bolt to attach a water jacket plate along with original ones (for example). Many old handbooks (Machinery, Dykes, etc) show these dimensions in tables that can be compared against modern. Also, the distance across the hex changed over the years, meaning that you use a different wrench for some very old bolts of the same thread diameter as modern. It's also the case that coarse thread bolts required a different wrench size than fine thread of the same diameter. I have some old wrenches that actually specify their usage on them.

All this to suggest that I once heard that the cap heights could be reduced post-1948 when they began to grade bolts, thereby aloowing designers to specify higher strength bolts only when the strength was needed, and overall reducing the cost of the bolts due to less material and less shipping weight of the smaller caps.

M'gawd, does this all make sense?

Don't judges also look for "cap height" as well as grade markings when judging early cars?

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Makes sense. The comments about why then went to shorter heads is news to me but sensible. There certainly is a difference. As for judging, almost every judge will catch the bolt markings, thus the comments about dressing the heads. More experienced judges will catch head height and thickness of nuts, as well as where to use square vs hex nuts. Fortunately some of the restoration supply shops have sources for the higher head fasteners.

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