I took some photos of Norton rods, two sets from 850 Commandos and one set out of a 1961 Manxman, all rods from 89mm stroke engines that are interchangeable.
It is common to hear people talk about how polishing is a no-no, as it removes the compressed surface that the forging process creates, well the factory does this for you anyway, and they often do a poor job of it. The early connecting rod has much less prep work done to it than was done on rods starting later in 1962.
If you look at the two sets of 850 Commando rods you can see some scary things though. It looks as though the factory first removed the forging parting line with an abrasive technique which went sideways, then they went back and hit it again going lengthways. The Problem is that in a LOT of the rods I have looked at they leave the sideways scratches and gouges in many places on the rod beam where it is a serious stress riser. On some rods you will see horizontal marks down in the radius before the big-end bolt, and in other cases you will find them right at the small radius blending into the rod eye, neither a very good place to have a crack starting. On the one set of dirtier rods you can see nicks the entire length of the rod on the corner of the beam before it wraps around to the rod side.
The cleaner set of rods is from a 850 E-start, one of which is a "D" rod. But if I ever saw a rod fail in a Commando with reasonable mileage on it, I would think first of the poor finish on these rod beams. They certainly need some careful finishing to remove these factory marks, and finishing up with competent shot-peening would not be a bad idea either. It looks like as long as you are a competent and smart mechanic, it would not be hard for you to improve the reliability of these rods with a bit of hand-work.
As they stand, the early rough-forged beam might be just as or more reliable than the later rod with their poorly done polish jobs.....
It is common to hear people talk about how polishing is a no-no, as it removes the compressed surface that the forging process creates, well the factory does this for you anyway, and they often do a poor job of it. The early connecting rod has much less prep work done to it than was done on rods starting later in 1962.
If you look at the two sets of 850 Commando rods you can see some scary things though. It looks as though the factory first removed the forging parting line with an abrasive technique which went sideways, then they went back and hit it again going lengthways. The Problem is that in a LOT of the rods I have looked at they leave the sideways scratches and gouges in many places on the rod beam where it is a serious stress riser. On some rods you will see horizontal marks down in the radius before the big-end bolt, and in other cases you will find them right at the small radius blending into the rod eye, neither a very good place to have a crack starting. On the one set of dirtier rods you can see nicks the entire length of the rod on the corner of the beam before it wraps around to the rod side.
The cleaner set of rods is from a 850 E-start, one of which is a "D" rod. But if I ever saw a rod fail in a Commando with reasonable mileage on it, I would think first of the poor finish on these rod beams. They certainly need some careful finishing to remove these factory marks, and finishing up with competent shot-peening would not be a bad idea either. It looks like as long as you are a competent and smart mechanic, it would not be hard for you to improve the reliability of these rods with a bit of hand-work.
As they stand, the early rough-forged beam might be just as or more reliable than the later rod with their poorly done polish jobs.....
