As a result, connecting rodreconditioning is a critical part of all diesel overhauls. Uponteardown, the old connecting rods are inspected, magnafluxed, checkedfor alignment, parting surfaces re-machined, and new rod bushingsinstalled and pin-fit. At the same time, the rod bolts are measured forstretch. This is all normal, day in, day out activity at any heavy duty engine facility.
Pin Bushing Failure
Pistonpin bushings can turn and spin in their housing bores. Engine failurequickly results. To prevent this we suggest that when new rod bushingsare installed in the reconditioned rod that they be expanded to contactand conform to the small end bore. To expand this bushing simply pressa hardened steel ball through the ID of the pin bushing.
Weadvise using a ball .005? larger than the ID and an old piston pinsmaller than the inside diameter of the bushing to push the oversizeball through. This broaching operation will enlarge the bushing OD tofollow the contour of the housing bore. This will lock it in andprevent spinning. If you heat the rod to install the new bushing, werecommend that you allow the rod to cool before pressing in the steelball. For Perkins 4236, 4248 and 6354 engines you can use a hardenedball 1.366" in diameter to broach these piston pin bushings.
Serrated Mating Surfaces
Oftenin connecting rod reconditioning the rods are disassembled and the rodcaps are cut on a cap grinder. Perkins rods present problems thoughbecause their rods have serrated surfaces where the cap mates to therod. They can not be ground on a cap grinder. Some people havesuggested hand filing these surfaces to recondition them. We feel thatthis is slow and inexact in a critical area. (Remember: diesels fire bycompression and rod heights or center-to-center distance is critical.)
–Tech Tip courtesy of Foley Marine & Industrial Engines
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