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Old 06-27-2025, 08:43 PM   #6
Bored&Stroked
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Join Date: Jan 2011
Location: Central Ohio
Posts: 5,723
Default Re: 21A rods set up on a 4" Merc crank

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Also, if you can have the rods "shot peened" . . . that is a good process to stress-relieve and add some strength. You'll need to balance BOTH ends of the rods and make sure that you do NOT grind the strengthening rib off of the rod-cap.

You need to make a fixture for your lathe to cut the side-area of the rod caps to set the big-end weight. Ford NEVER ground the rib on the bottom and these rods do not have balance pads like modern rods.

Couple pics on my setup:

2015-02-02 21.34.39 copy.jpg

2015-02-02 21.34.42 copy.jpg

2015-02-10 13.16.06 copy.jpg

2015-02-07 19.33.56 copy.jpg

Here is what most shops will do . . . they grind the bottom cap rib! They don't know any better and weaken the cap:

CapGrindingExample.jpg

Video on bearing sizing:

https://www.youtube.com/watch?v=CyVLsPdbhS8
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