- Joined
- Oct 19, 2005
- Messages
- 18,978
I continue to hold the view that Rods are Norton's Strongest feature! This is not w/o some of my own and others evidence such at this example,which agrees with every report a good post mortum revealed something else let go first...
This is the connecting rod from a 1975 Norton 850 Commando. I had wandered into the service department during the party & joined a chat with one of Raber's expert mechanics, Lucky, who had just split the cases on this Norton. He had conducted some postmortem forensics to determine the cause. Here's what he came up with. The owner was probably over-revving the engine. First, it spun a rod bearing, probably from inadequate oiling. Once one bearing shell half slipped under the other, the rod beat itself up so badly that it bent. The bend then shortened the rod and changed its geometry. This allowed the bottom of the piston skirt to meet with the center flywheel on the fast-spinning crankshaft, which literally ground a relief in the bottom of the skirt. At the same time the bend in the rod put the rod in contact with the camshaft which ground a smooth pocket into the face of the rod itself.
What makes this so weird? Considering that the piston & connecting rod are both made of fairly soft aluminum, its amazing that it stayed together. I would have expected this engine to grenade on contact. Think about all those fast-moving parts flying around the hostile & tightly-packed environment of the crankcase. Things are so tight in there that, in ideal conditions, the camshaft just misses the rods by a few thousandths of an inch. And the pistons almost graze the crankshaft in normal conditions. This very slight change in shape of the rod caused all these parts to hit one another, weird enough in itself, but nothing shattered. Normally, engines explode into hundreds of tiny pieces of shrapnel when something like this happens. Lucky's explanation: The Brits have a long history of good metallurgy, dating back to Roman times, and they just knew how to build things right, and out of the right materials, so that even when met with catastrophe, they somehow hold together. Not always, of course...but this time, at least.
http://www.classic-british-motorcycles. ... 11-16.html
This is the connecting rod from a 1975 Norton 850 Commando. I had wandered into the service department during the party & joined a chat with one of Raber's expert mechanics, Lucky, who had just split the cases on this Norton. He had conducted some postmortem forensics to determine the cause. Here's what he came up with. The owner was probably over-revving the engine. First, it spun a rod bearing, probably from inadequate oiling. Once one bearing shell half slipped under the other, the rod beat itself up so badly that it bent. The bend then shortened the rod and changed its geometry. This allowed the bottom of the piston skirt to meet with the center flywheel on the fast-spinning crankshaft, which literally ground a relief in the bottom of the skirt. At the same time the bend in the rod put the rod in contact with the camshaft which ground a smooth pocket into the face of the rod itself.
What makes this so weird? Considering that the piston & connecting rod are both made of fairly soft aluminum, its amazing that it stayed together. I would have expected this engine to grenade on contact. Think about all those fast-moving parts flying around the hostile & tightly-packed environment of the crankcase. Things are so tight in there that, in ideal conditions, the camshaft just misses the rods by a few thousandths of an inch. And the pistons almost graze the crankshaft in normal conditions. This very slight change in shape of the rod caused all these parts to hit one another, weird enough in itself, but nothing shattered. Normally, engines explode into hundreds of tiny pieces of shrapnel when something like this happens. Lucky's explanation: The Brits have a long history of good metallurgy, dating back to Roman times, and they just knew how to build things right, and out of the right materials, so that even when met with catastrophe, they somehow hold together. Not always, of course...but this time, at least.
http://www.classic-british-motorcycles. ... 11-16.html
