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Crankshaft bolts ? #785155 09/23/19 1:48 am
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Rohan Online Content OP
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I bought a set of crankshaft bolts for a Model 7 crank,
no prizes for guessing who supplied them.

They seem quite well made - but don't appear to be hi-tensile ?
Should they be ??
Other than testing them to destruction, is there any way to confirm this ?


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Re: Crankshaft bolts ? [Re: Rohan] #785206 09/23/19 3:40 pm
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First off, I'm not a metallurgist, but I have a hardness tester (many machine shops will have this tool) and can tell how hard a bolt is.
That said, I don't think there's a way to tell how deep the hardening is or what the actual tensile strength is without destroying the bolt that I know of.
Even though I've fooled with these engines for many years, I don't recall ever replacing the crankshaft hardware while cleaning the sludge trap or seeing any break or come loose.
Are you possibly fixing something that isn't broke, or did I miss something.
I know con rod bolts and nuts are a different story.
Good Luck
Sam

Re: Crankshaft bolts ? [Re: Rohan] #785263 09/24/19 12:39 am
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Fair comments.
A crank came to me with no bolts, and I also have one with the nuts so
centrepunched-offset that I'd doubt they will come off cleanly - or at all.

The lack of them never breaking or even loosening is either very good bolt quality,
or they are not very stressed, or.... ?
Its oft quoted that the Norton crank flexing can be responsible for losing oil pressure,
so the stronger the bolts the less likely this would be ?
The ironhead oem headbolts are very good quality, and seemingly very high tensile ??

The local eng training mob have a calibrated jig, might see if I have any strays that could be destructed.
It might be worth it knowing that any new replacements are up to the job.

Re: Crankshaft bolts ? [Re: Rohan] #785283 09/24/19 3:08 am
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koan58 Offline
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Hardness is not the same thing as tensile strength.
To check tensile strength, measure stretch for applied torque. Easier said than done.
So much trust in suppliers, is it justified? How can we ever know?

Re: Crankshaft bolts ? [Re: koan58] #785293 09/24/19 6:10 am
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Originally Posted by koan58
How can we ever know?


In a past life I did some engineering 101 courses, including testing of various steels and metals and their properties.
The rig that did tensile testing ultimate yield simply pulled a bolt apart, and recorded how many TONS of
force it took to do it. (or part thereof for small diam bolts)

I've probably got enough crankshaft bolts about I can have tested an original and a newey and a generic grade 8, so we will see how they compare.
Mild steel is about 40 tons per sq inch, and I believe that aircraft and ARP's best steels are nearer 120-140 tons/sq in (?) these days, although
you wouldn't meet that quality every day, and the grade 8 should be at least 60-70 tons ?

The modern specs are all in MPa, will have to get up to speed on those...


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