Polished Perfection

How To Polish Connecting Rods At Home

Mike Petralia May 1, 1999 0 Comment(s)

Step By Step

A stock rod is pictured on the left and a polished one on the right. Notice how the polishing was carried up to, but not over, the pin end. This is important because the pad on top of the rod is used for balancing the rod and should be left untouched. If you grind on it, your rods are ruined.

You’re going to need a little bit more than a flat file and some sandpaper to polish the beams on a set of rods. The Deluxe Engine Porting Kit from Standard Abrasives contains all sorts of grinding bits and cartridge rolls. The Standard Abrasives products are made specifically to work metal surfaces, unlike many hardware store–type abrasive products that might be designed for wood or other surfaces.

This special-purpose grinding bench has a giant vacuum underneath that pulls down and away from your work all the material that is ground off. Note the proper position of the grinder in relation to the rod. Keep the grinder moving slowly and steadily up and down the length of the rod beam.

This photo shows another tool you can use if you don’t have a high-speed die grinder. Pay special attention not to grind across the beam when using a disk grinder. But if you keep the disk positioned as it is in the photo, it will work.

An up-close look at a stock small-block rod shows a big casting ridge and thousands of small bumps and ridges, which might be stress risers that later could develop into cracks.

In the May ’98 issue we ran a story on low-buck 4340 connecting rods for small-block Chevys. Often, stock rods are the only way to go. Polishing your stock rods is an inexpensive way to increase strength and durability, and you can do this at home with little more than a die grinder and an Engine Prep Kit (PN 260003) from Standard Abrasives Motorsports. Racers have been polishing connecting rods for years to improve a stock rod’s durability and to decrease weight. The benefit to polishing is that you remove the source of potential stress fractures.

All factory rods have ridges from the forging process that run the length of the beams. This is the weakest part of the rod and most likely the first place a crack will develop. You can remove that ridge with a high-speed die grinder and a 40-grit cartridge roll in just a few minutes. But if you don’t have a die grinder, you can still do a satisfactory job with a 120-grit sanding disk and an angle grinder; it will just take a little longer.

Before grinding on any set of rods, we’d recommend first having them Magnafluxed and inspected by a machine shop. These guys deal with these parts every day, and they know where to look for trouble spots that you might miss. This eliminates the hassle of wasting your time polishing a junk rod.

When removing material, be sure to grind inline with the long axis of the beam. Don’t grind across the beam, as this will leave microscopic grinding lines that could become starting points for fractures to develop. Also, don’t bear down too hard on the grinding tool; this will create too much heat and could damage the rod. After you’ve finished grinding, be sure and take the rods back to your machine shop for new rod bolts and big-end resizing. It’s also a good idea to have the rods shot-peened and balanced.

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