HOME and how to join Forum Open Area General Scott topics Small end bushes Re: Roller burnishing

#6083
Roger Moss
Participant

First, roller burnishing is a method of compacting a ductile material and if you want a compacted polished type finish, then it is a viable process.
I have noticed that some late Scott rods were made with a little end bush made from copper bronze. This material is quite soft and ductile and the gudgeon pin soon compacts the surface of the bush to a polished finish.
Now there is no hiding place for the oil and the result is that heat is generated from metal to metal contact with insufficient oil.
Years ago there was a mith that if you rebored an engine, you could also hone it to a mirror finish. This was proved wrong decades ago and much of the4 long life of current engine bores is because the bore is textured to hold oil. I use a course “Flexhone” to produce an oil retaining texture on the walls of the bore. The same principle applies to the little end bush.
There could be a great debate about what grade of bronze to use. I use aluminium bronze which is quite tough, but I semi finish it, then put in oil grooves to help spread the oil round the bush, then use a medium grit hone to take out the last thou and ensure correct fit to pin. Remember, if you make it too close a fit, you will again deny oil a good access and you will have overheating and accelerated wear.
I was involved with the design and manufacture of a very accurate transfer machine for Ford some years ago with my colleage John Underhill. That utilised roller burnishing very sucessfully. The technique does however need a good lubricant for production reliability