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Grinding & Honing, Balancing, and Pressing Pin
The constant loads imposed by the reciprocating mass of the small end of the rod and the piston eventually cause the big end of the rod to become elongated. Special machine operations can return the big end to a perfectly round circle that remains within manufacturer specifications.


Superior grinds and hones the big end of the rod to the high end of the manufacturer's spec. In this case, 2.4369"
 
With the proper honing mandrel in place, the rod and cap assemblies were run on this rod reconditioning machine.
     

This gauge verifies that the honed rod and cap assemblies meet the specification. All eight sets were processed on the rod reconditioning machine.
 
It was time to move on to the small end of the rod. First step was to verify the pin diameters.
     

From the micrometer to the rod reconditioning machine, the pin diameter figure is transferred.
 
Press fit pins should have a .0010 to .0015 interference fit with the rod. Each rod's small end is measured to determine the amount of honing necessary to create the required interference fit.
     

One of the eight rod's small end is honed accordingly.
 
A honing mandrel verifies the piston's pin bore is sized appropriately.
     

Once all eight rod and cap assemblies were off the reconditioning machine, it was on to balancing. Here, Augie finds the assembly with the lightest big end.
 
The lightest big end was 622 grams. The remaining seven assemblies were ground on the cap to reach the same weight.
     

The scale is tared with 622 grams on the deck. Now each rod assembly is measured to determine the lightest small end. The lightest small end in our case was 216 grams.
 
The remaining seven assemblies are ground on the small end to reach 216 grams.
     

Here's one finished rod assembly.
 
With the rod and cap assemblies ready for pistons, we needed to balance them as well. The lightest piston is found and a ball mill removes material on the underside of the remaining seven to create a matched set.
     

A rod heater expands each rod's pin bore.
 
The expansion allows the pin to be fitted. When the rod cools, the rod takes a bite onto the pin. The process was repeated for the remaining seven assemblies.
     

This twist fixture verifies the trueness of the rod and piston assemblies.
 
Twisted or bent rods will show themselves as gaps between the stationary and rotating machined surfaces of the fixture.
     

That's right, if a rod is bent or twisted, a little leverage and patience will bring the rod back to a true state. Better left to the experts!
   


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Posted by egahps, 12/22/07 08:33am:
Another alternative to opening up the pin bores on th pistons is to bush the rod with a 292 pin bushing which is .975 od and made for a .912 pin. this not onlly give you a full floated pin but does not compromise the strength of the pin boss.
Posted by snewton, 12/30/07 06:17am:
ESTIMATE OF COST
Posted by dwbachor, 12/31/07 09:47pm:
Good read, I did a set of 460 rods pretty much the same.
Posted by mvtofino, 03/03/08 02:57am:
Good information that got me thinking...my 351M was remanufactured last summer and I am happy with the result. But I didn't know enough at the time to check the shop's various procedures. Wish I had read this article prior to having carryied out the work on my engine!
Posted by job1bf, 08/20/08 07:50am:
i could not find any mention of the weight of the rods. Does anyone happen to know the weight of these factory rods?



 
 
Sources

Superior Machine
Augie Steinert

380 Freeport Blvd. #16
Sparks, Nevada 89431
(775) 358-4004

Probe Industries
www.probeindustries.com

Automotive Racing Products

www.arp-bolts.com



 


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