From: David Johnson <emory!wrs.com!johnson>
X-Source: The Hotrod Mailing list
Date: Feb 1993
Subject: Re: con rod reconditioning

>  If an engine is run for a long time under detonation, it'll eventually
> pound the big ends out of round.  If it has been run without oil
> pressure the bearing shells may spin.  If either happens, the rebuilder
> takes a little metal off the cap, then rebores the rod round.

I got my Roundel just the other day...  seems the new BMW hi-po motor
has the cap located by a deliberate fracture, now that's intense!

First it's disposable lighters, now con-rods.  What's the world coming to? :-)

[This technique is actually very old and works real well.  McCulloch has
done this since at least the 60s on their chain saw and kart engines.
In their case, they run needle bearings directly on the hardened rod.
They bore the hole and then fracture the rod at a built in defect.
The rather large grains in the metal makes the cap align perfectly.  JGD]

DAVE (johnson@wrs.com) Internet Z-Club member #51

From: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
X-Source: The Hotrod Mailing list
Date: Feb 1993
Subject: Re: con rod reconditioning

-> Imagine a con-rod that is one peice (ie, the would-be cap is part of
-> the rod, and cannot be removed { kinda hard to put on the crank too
-> :-)  }).

 Now imagine a Yamaha TZ700 four, with the crank built up out of lots of
little pieces pressed together over one-piece rods, then painstakingly
aligned and straightened.  Expensive too.  For real kicks, try one of
the old Bugatti straight-eights, all ball and roller bearing, pressed
together crank.


-> Now take the rod and break it where the would-be cap and rod would
-> normally be bolted together.

 This is where I'm still left pretty much in the dark.  A rod brittle
enough to break ain't worth much in a motor - you can usually bend even
cast rods clear in half without breaking them.  Are they dipping the
rods in liquid nitrogen or something?

[The chainsaw con rod is forged and can also be bent.  The grain structure on
the fracture suggests the rod is highly hardened for fracture and then
annealed later.  I'd anticipate the sintered metal rods to be brittle
but I don't know, having never seen one.  JGD]


-> assembly-line hangovers :-)  }), you now have a surface that yields
-> perfect alignment of the cap wrt the rod.  It also has the added

 Similar to the way most aluminum rods have sawtooth mating surfaces
instead of smooth like steel rods.