From: hotrod@dixie.com (The Hotrod List)
Subject: rod side clearance
Date: Sun, 03 Jan 93 00:49:39 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.
To: hotrod@dixie.com
Reply-To: hotrod@dixie.com
Posted-Date: Saturday, Jan 02 19:49:35
X-Sequence: 3158
X-Gifs-To: met@sunset.cse.nau.edu
X-Gifs-From: ftp.nau.edu


 I came across something interesting the other day.

 With relatively minor modifications, the 6.0 inch Olds rods will work
in a small block Chevy.

 The conversion involves bushing the small end down to Chevrolet pin
size, then turning the Chevy crank .007 undersize, and running .030
undersize Olds bearings.  Unless you can find .040 bearings somewhere,
you're limited to one try with this setup.

 The only real problem is the slight difference in rod widths - the Olds
rods are about .010 narrower than the Chevy rods.  That's an increase of
.020 on the rod side clearance.

 Now, most of the references I have vary madly all over the place as far
was what the "correct" rod side clearance is.  I can't find any mention
in any official GM stuff I have, but Jenkins recommends .020.  Tearing
down a 262, a 307, and a 350 - none having been rebuilt - I found the GM
clearances to run between .006 and .009.  That indicates I'd be looking
at around .030 side clearance.  That looks a little wide to me.

 That leaves widening the rods.  The first thought was to braze some
material to the big ends, then face it off on the lathe.  The other was
to either peen the big ends (doubtful I'd get enough displacement to do
much) or build a ring-shaped die from tool steel and stamp a ring in the
side of the rod to displace metal, then face it off.

 Frankly, brazing the extra material on looks like the way to go so far,
unless anyone has any further ideas.

[Brings up a point of question I've had for quite some time.  What is 
the reason to worry about side clearance on the con rod big end
other than to make sure it is not too tight?  It is not intrinsicly
obvious to me and I've never been given a reason other than something
that invariably boils down to "that's the way we've always done it."
JGD]

 -------

 Now, some of you might be wondering exactly what I'm doing here, and
who don't I want to shell out $450 to $650 for a set of cheap aluminum
or steel 6.0 inch rods.  It's because of the 262, you see.  I can bore
it out .060 to take 305 standard bore pistons, which have a much higher
pin height.  Then I can use the six inch rods, and turn the lip around
the dish of the piston off on the lathe, and wind up with a flat top,
high pin piston.  Assembled, I'd have a flat top, 6.0 rod, 3.73 x 3.1
motor of 272 cubes, an interesting replacement for the 235 six in the
Bel Air.  The six has enough power (I know, it's time for my medication
again) but the gas mileage stinks.  The small V8 would certainly get
more than 14.5, particularly with an Offy Dual port and AFB or an old
Cross-Fire TBI setup (remember those small runners?)  Besides, once I
figured out all the parts would fit, how could I resist?

 Oh, yeah - to retrofit the late model hydraulic rollers, all you have
to do is fabricate three standoffs (like PC board standoffs) to hold the
late lifter retainer plate, then add a generic cam thrust bumper.  The
extra-deep lifter bores on the late blocks basically don't do anything -
the lifter never even comes to the top, much less past it.  Of course,
once I tracked down everything and figured it out, I found that Crane is
already making a retrofit kit.  <sigh>
                                                    

----------
Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
Newsgroups: alt.hotrod,wiz.hotrod