Opinions Please

Hello
New to this forum and a long time Norton rider.
I am looking for opinions to this question. Should connecting rods be replaced in an engine that was run without oil pressure to the point the engine froze?
Some background info on the situation.
I am repairing a Norton 850 that, while running lost oil pressure. Unfortunately for the engine, it was kept running until it froze.
In the subsequent tear down, all indications are that no oil was coming in and it scavenged all the oil out. The pistons had not stuck to the bores(in the tear down the cylinders pulled off) but did score the pistons quite badly.

One rod could barely moved when attempting to move the crank by hand with the cylinders removed. The other could not be moved at all.
Removing the rods reveled that the bearings had smeared themselves all over the crank.
The crank has been ground and it took 20 thousandths to clean it up.

So the question is, are the rods ok to use? I have had them xrayed and see no sign of damage in regards to cracking or fractures.
The small end fits the new wrist pin ok.
The big end on one side measures with in tolerance but towards the maximum allowed. The other side is out of tolerance by being smaller. I can't figure out how it got smaller,but it is.
So I was going to get them both bored and use them.
However now I am wondering if they should be replaced due to the heat they were exposed to when the old bearings were run without oil? There are no signs of overheating such as bluing or discoloring. Seems like the bearing shells took all the damage.
Obviously, replacement would end all questions. However they are not inexpensive and waste not want not. Hence the question.
Thanks in advance.

If the bearing shells did not turn in the rod- IE the tangs are still intact- then you should be OK with just reconditioning the rod big ends with new bolts and a rod hone. If there were signs of bluing on the cap or overheating I would get new ones. Jim

I concur with Jim--in my experience the stock rods are almost supernaturally robust and typically survive most serious engine failure modes. If you decide after all you need one or two I've got good used ones for a reasonable price--good luck with your project.



Tim Kraakevik
kraakevik@voyager.net
Three Commandos

The rods are next most over robust Commando item 2nd only to the Z-plates.
What will suffer most in seizure is the rod fasteners so must be brand new and seats trimmed so no swarf gets under in nip up. Might have them polished up then shot peened for extra peace of mind. Have yet to hear of Norton rod failing before some other component first that then takes em out. Crank will jump rope and pistons pull apart and valves float and clash before rods let go, unless surface is scored.

Hello and Thank you
I really appreciate the relies and the confirmation of what I have read about the Commando conrods. Here are the images from xraying the rods. This is the rod
and this is the big end,
Thought they were interesting to look at.
Further information. The rod bearings had not turned in the big ends. I could not find any evidence of heat damage to the rod or steel cap.
I am having a machine shop bore the big ends. A boring operation is done because honing cannot be done with accuracy due to having an aluminum rod and a steel cap. If a hone were used it would tend to hone more of the softer aluminum than the steel cap.
New 20 over bearings, new bolts and nuts and it will be all ready to go.
Thanks again

If you bore out the big ends you will need to get custom bearing-shells from some source or other, they only make standard oversize bearings to fit a re-ground big end crank pin. not a resized big end con-rod hole.

dave M is right, you'll have to get some kind of "custom" big end shells if you bore the big ends of the rods out. Why would you bore out the rod big ends anyway ???

Correct way of resizing a big end journal is to remove a small amount of material from the mating surface of the cap, and then bore to the stock size. But if its distorted any appreciable amount, then its a good idea to replace rods if they are still available.

Carbonfibre said:

Correct way of resizing a big end journal is to remove a small amount of material from the mating surface of the cap, and then bore to the stock size. But if its distorted any appreciable amount, then its a good idea to replace rods if they are still available.

Click to expand...

Seems to me that you have an over-the-top excuse to visit with Jim Schmidt...

RS