Conrod engine problem Brisbane -

CRACKED / BROKEN

The connecting rod ( con rod) is a very highly stressed component. The con rod is also precision ground to fine tolerances. It is possibly the most over looked engine component during a home or back yard engine rebuild. Con rods can break in service due to fatigue causing catastrophic damage to the block and associated components. Excessive load and high revs can stretch the con rod to a point where the rod breaks(usually half way down the rod) or a rod bolt breaks and comes apart at the big end usually severely damaging the crankshaft. The con rod transfers all the torque and horsepower developed by the engine from the piston to the crankshaft. The con-rod small end can house the piston or wrist pin in a small end bush(fully floating) or via press interference fit. The small end bush is press fit into the rod end and then requires precision machining to the correct clearance for the piston pin. The big end of the con rod houses the big end bearing and imparts bearing nip to the bearings by way of precision crush specifications. During the working life of a con-rod the small end bushes become worn and the big-end tunnel looses it's shape and is stretched out of round. The process to restore the big-end of the rod is referred to as "close and hone".   The process to "Close and Hone" the con-rod requires the rod cap faces to be precision ground, bolted and re- tensioned to specifications. This process now has the big end of the rod tunnel undersize so now it has to be machined and honed back to standard specifications. At UMR Engines we use a pin boring machine for the small- end bush and a Sunnen rod hone for the big-end restoration. With performance applications the rod bolts are always replaced with new bolts as they are prone to break if reused. Con rods are checked for alignment / straightness in a jig and can be realigned to restore slight bend. Badly bent rods have to be replaced with new rods. Disclaimer Agreement : Every care has been taken in writing this information and procedures, but no responsibility can be excepted for errors, omissions or misuse of this information and procedures. The information available on this site is for your instruction only and cannot be copied for sale, © copyright 2001 UMR Engines