I pass along the following for whatever interest it may generate. A couple of
weekends ago at Road America, my new Spitfire motor blew up in a pretty
impre$$ive manner. My first thought was that a rod bolt on #2 had broken --
the #2 rod cap was seriously damaged and one of the bolt holes in the cap is
now D-shaped -- clearly, the ARP rod-bolt was not in its hole when that damage
occurred. But, these being ARP rod-bolts, I concluded that there must be some
other explanation -- that it had been starved of oil or something.
On disassembly, however, none of the other bearings show any real wear. My dad
(with 40-some years of experience in the engine building business) took a look
at the mess and concluded an ARP rod bolt broke. He showed the mess to a
Caterpillar Certified Failure Analysis Instructor, who concluded an ARP rod
bolt broke. See below for that discussion.
Anyone else have experience of ARP rod bolts failing?
Scott
-----Original Message-----
From: Jerry Barr [mailto:jerrybarr@charter.net]
Sent: Thursday, July 29, 2004 11:25 AM
To: Barr, Scott
I sat down with a Caterpillar Certified Failure Analysis Instructor (who now
teaches for Northeast Wisconsin Technical College). His thought is that the rod
bolt broke first then the catastrophic failure. The bolt shows signs of fatigue
fracture with small beach marks then brittle fracture when it separated and
fell out of the rod. The rod bolt showed no signs of over torque but does have
small amounts of fretting under the bolt head which leads him to believe it
started to break, loosened slightly, allowed the rod bearing to move, seize the
bearing, bolt broke off and fell out, cap ratcheted open, and all hell broke
loose. So the ultimate failure was a flaw in the bolt which allowed the bolt to
break. We should look at it under a microscope to prove that though.
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