Hard versus strong is easy to explain, but I'm not sure what physical
parameters denote it, certainly not grade 5, grade 8. A strong bolt can
stretch but won't break, a hard bolt won't stretch but when it reaches
yield it cracks rather than stretching. The ARP bolts seem to be both.
>From my limited metallurgy reading (mostly associated with knife making) I
think the "psi" number is strength, that is, they stick a sample in a
measuring tool that tries to pull it in two. Hardness is a different
number, which as I recall is measured by pressing a graduated diamond
point into the metal and seeing how deep it penetrates with a specific
force applied. Sometimes you see knives with little dimples where they did
that. There are a bunch of other tests, like Charpy V-notch that tests the
resistance to shear forces. And Brinell that measures another aspect of
hardness. But it all distills down to "buy some really good bolts", and
that basically means "pay ARP what they ask".
I probably should read a couple of the metals books in my library. It's
interesting stuff.
-----Original Message-----
From: Barr, Scott [mailto:sbarr@mccarty-law.com]
Sent: Thursday, March 28, 2002 11:17 AM
To: Bill Babcock
Subject: RE: flywheel bolts
Yes, I thought I'd switch to ARP bolts, anyway. I still don't know how to
evaluate whether a bolt is "hard" or "strong", but at least I'm more
comfortable that my flywheel bolts won't break... :-)
Thanks!
-----Original Message-----
From: Bill Babcock [mailto:BillB@bnj.com]
Sent: Thursday, March 28, 2002 1:17 PM
To: 'Barr, Scott'
Subject: RE: flywheel bolts
Once I switched to ARP bolts I haven't had any more bolt breaking or
stretching problems. I'm considering adding two more bolts as KAS
suggests, but one of my engines has a billet crank which is so hard it's
almost impossible to drill.
-----Original Message-----
From: Barr, Scott [mailto:sbarr@mccarty-law.com]
Sent: Thursday, March 28, 2002 5:00 AM
To: Bill Babcock
Subject: RE: flywheel bolts
Hi Bill. Have you ever gotten a good answer on just what is meant by
"hard"
in this context? If I were shopping for "hard" bolts, what would I look
for
-- what sort of rating system are we talking about? For example, I don't
think we're talking about the Grade 5, Grade 8 type system. And not the
AN
grades. Are we talking about the "PSI" grade that I've seen on ARP rod
bolt
packages? (e.i., 320,000 PSI)
Scott
-----Original Message-----
From: Bill Babcock [mailto:BillB@bnj.com]
Sent: Wednesday, March 20, 2002 1:07 PM
To: 'Mike Munson'; fot@autox.team.net; gatriumph@gatriumph.com; 6pack
list
Subject: RE: flywheel bolts
Yup. Breaking the bolts is a common topic. You need to get some good
bolts, not just strong but hard so they won't flex. Kas has posted
extensively on this issue. When the engine is running at any serious RPM
the crank flexes enough to make the flywheel wobble like a cheap yo-yo.
Lots of force is being applied to the bolts, and it's not all in shear.
I've taken out crank bolts that were seriously stretched, and broken more
than a few
-----Original Message-----
From: Mike Munson [mailto:fasttrs@mindspring.com]
Sent: Wednesday, March 20, 2002 10:51 AM
To: fot@autox.team.net; gatriumph@gatriumph.com; 6pack list
Subject: flywheel
Hi guys,
I pulled the transmission on my TR6 IT racecar Tuesday. The flywheel was
held
on by two bolts(barely), and the other two bolts were broken. The
crankshaft
looks like there is metal from the flywheel molecularly bonded to it! Has
anyone ever experienced this before or have an explanation for this
phenomenon? The PO must have run it a while with the flywheel loose.
Mike Munson
Atlanta
73-6 AC,Hardtop,4Wheel disc brakes
70-6 IT Racecar
80-8 wanting affection
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