8/12/2009
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Diesel Rod Reconditioning
One key operation in rebuilding an engine is to recondition the connecting
rods. Because diesel engines ignite by compression, the connecting rod
dimensions are very important. As a result, connecting rod
reconditioning is a critical part of all diesel overhauls. Upon
teardown, the old connecting rods are inspected, magnafluxed, checked
for alignment, parting surfaces re-machined, and new rod bushings
installed and pin-fit. At the same time, the rod bolts are measured for
stretch. This is all normal, day in, day out activity at any heavy duty engine facility.
Pin Bushing Failure
Piston
pin bushings can turn and spin in their housing bores. Engine failure
quickly results. To prevent this we suggest that when new rod bushings
are installed in the reconditioned rod that they be expanded to contact
and conform to the small end bore. To expand this bushing simply press
a hardened steel ball through the ID of the pin bushing.
We
advise using a ball .005" larger than the ID and an old piston pin
smaller than the inside diameter of the bushing to push the oversize
ball through. This broaching operation will enlarge the bushing OD to
follow the contour of the housing bore. This will lock it in and
prevent spinning. If you heat the rod to install the new bushing, we
recommend that you allow the rod to cool before pressing in the steel
ball. For Perkins 4236, 4248 and 6354 engines you can use a hardened
ball 1.366" in diameter to broach these piston pin bushings.
Serrated Mating Surfaces
Often
in connecting rod reconditioning the rods are disassembled and the rod
caps are cut on a cap grinder. Perkins rods present problems though
because their rods have serrated surfaces where the cap mates to the
rod. They can not be ground on a cap grinder. Some people have
suggested hand filing these surfaces to recondition them. We feel that
this is slow and inexact in a critical area. (Remember: diesels fire by
compression and rod heights or center-to-center distance is critical.)
Tech Tip by Foley Marine & Industrial Engines