Upgraded Conrods?

worntorn said:

There is an in between but it sounds like you have never experienced it. Maintaining a speed of 50 or 60 mph on a twisty mountain road is a lot of fun and, if done for a few hours, can take you to an entirely new place.
Glen

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My Norton is set up for handling, lightness and lots of torque, so much fun up in the tight twisties and high speed straights before the next tight twisties, seems Al has never experience those conditions and if he has was a very long time ago since he hasn't ridden on the road since he was 29 years old and only riding around raceways that allow him to race and even then very rare in his own words, Al you are a lot of talk but really you haven't experienced a well set up Norton on the road, you don't need to be up in the 6k+ RPMs rev line to enjoy a good set up handling Norton and so much more fun being allowed to take the bike out at anytime you wish and even better riding with mates you have grown up with as in my 52+ years of riding in the bush as well on the roads, getting out on our monthly rides together, finding new roads and mountain twisties to explore is what real motorcycling is about.
Some in our group like to push it but there are some who just like to cruise at their own pace, if we turn off the road we are on we wait for the others to catch up before getting back into it, and we have never had any failures of con rods or any other failures doing what we enjoy best, no need to push our motors to extreme limits to enjoy our ride times, no need for close ratio gear boxes where we ride, my stock 4 speed box does everything I need to do when out riding, my motor has most of its original internals with a few mods here and there, it has survived my youth of abuse/canning the sh it out of my motor/gearbox, I no need to push it too far, I have nothing to prove, I am happy to take it up to the ton every so often sometimes a bit more, but in the right places of course, getting my crank balance factor right on my motor has saved my motor for long life, can still ride it hard without over doing it and most conrod failures are from bearing, big end failures and punching holes through the crank cases when they do fail.
A lot of racers on here also ride on the road, they enjoy the lifestyle of motorcycling instead of watching it on YouTube.

Ashley

Norton pistons do not usually have high crowns to get more compression, so they are probably lighter than many. At high revs piston inertia is proportional to the weight of the piston. My crank is rebalanced to about 72%. At 7,300 RPM, it feels as though it could easily reach 8000 RPM without a problem. I just stop it from going there. I once modified BSA 350 Gold Star pistons by reshaping the edges of the crowns, to fit into a Triumph 650 motor with a squish band - the motor developed wings. The pistons were much lighter. Commando motors are much better. I doubted my 850 motor, however I now believe the design must be very correct. My motor has had almost nothing done to it, and it is fast enough to do the job.

velo54 said:

When i assembled my basket case '72 750 the standard conrods had been stretched at the big end, was oval by at least a couple of thou. Had to file the cap ends to get them back to close to round. Bit rough but it worked well. Bearing clearance is good. Apparently previous owner was not a gentle rider! Numbers don't match so he probably destroyed the original combat engine. When assembling the engine i was not aware of the radius mod on the crank, and my pistons look like swiss cheese thanks to JS example. Consequently i only rev it to 5500 max. Point being standard rods are not the strongest on the planet and need to be checked for stretch. One day i hope to redo engine with JS parts, modify the crank, nikasil barrel, etc. Only then would i be confident of revving it to its redline. Graham

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ALL connecting rods should be checked for ovality during overhaul. 5 minute job.

acotrel said:

Norton pistons do not usually have high crowns to get more compression, so they are probably lighter than many. At high revs piston inertia is proportional to the weight of the piston. My crank is rebalanced to about 72%. At 7,300 RPM, it feels as though it could easily reach 8000 RPM without a problem. I just stop it from going there. I once modified BSA 350 Gold Star pistons by reshaping the edges of the crowns, to fit into a Triumph 650 motor with a squish band - the motor developed wings. The pistons were much lighter. Commando motors are much better. I doubted my 850 motor, however I now believe the design must be very correct. My motor has had almost nothing done to it, and it is fast enough to do the job.

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But you still haven't experienced a well set up road going Norton, and how do you know your crank is balanced at 72% when all you done was plug up a hole, guessing is not a fact.

ashman said:

My Norton is set up for handling, lightness and lots of torque, so much fun up in the tight twisties and high speed straights before the next tight twisties, seems Al has never experience those conditions and if he has was a very long time ago since he hasn't ridden on the road since he was 29 years old and only riding around raceways that allow him to race and even then very rare in his own words, Al you are a lot of talk but really you haven't experienced a well set up Norton on the road, you don't need to be up in the 6k+ RPMs rev line to enjoy a good set up handling Norton and so much more fun being allowed to take the bike out at anytime you wish and even better riding with mates you have grown up with as in my 52+ years of riding in the bush as well on the roads, getting out on our monthly rides together, finding new roads and mountain twisties to explore is what real motorcycling is about.
Some in our group like to push it but there are some who just like to cruise at their own pace, if we turn off the road we are on we wait for the others to catch up before getting back into it, and we have never had any failures of con rods or any other failures doing what we enjoy best, no need to push our motors to extreme limits to enjoy our ride times, no need for close ratio gear boxes where we ride, my stock 4 speed box does everything I need to do when out riding, my motor has most of its original internals with a few mods here and there, it has survived my youth of abuse/canning the sh it out of my motor/gearbox, I no need to push it too far, I have nothing to prove, I am happy to take it up to the ton every so often sometimes a bit more, but in the right places of course.
A lot of racers on here also ride on the road, they enjoy the lifestyle of motorcycling instead of watching it on YouTube.

Ashley

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I have a friend who bought a Hyabusa because he wanted to know what 170 BHP was like. There was a group of A grade road racers who used to ride around the Black Spur east of Melbourne, and he is also an A grade rider. He could keep up with the group with his speed between the corners. I would never do that idiocy. The corners are blind, and cops sit among the trees with speed cameras. If you have never crashed a motorcycle at 100MPH, you do not know what you are doing. On a race track at 100 MPH, a crash is relatively safe.

ashman said:

But you still haven't experienced a well set up road going Norton, and how do you know your crank is balanced at 72% when all you done was plug up a hole, guessing is not a fact.

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I made a rig with two straight edges - grabbed one end in a vise, and supported the other end and used a level. I had an electronic balance and weighed the pistons and gudgeon pins, and balanced the crank by adding weights to the conrods. When I plugged the hole in the counterweight, the calculation came out at 72 %. I was aiming for about 78 %. I was about to drill the other side of the cast iron flywheel, thought about what I was doing and stopped. Norton drilled the crank to reduce the balance factor for the Commando. In whatever motor the crank originated, its balance factor must have been good for high revs before they drilled the hole.
If the balance factor of a 360 degree vertical twin is not high, the motor will never be good enough to race.

When I do things, I do not guess - I work on the basis of experience, and not even hearsay. If you read Phil Irving's book 'tuning for speed' - it is a starting point. This technology is 1950s stuff. Balance factor is important, but jetting is critical. I do not know what taper is standard on the carburetor needles on a Commando, but Mikuni needles fit. I do not trust Amal in that area. British motorcycles have been slow forever. One of the biggest fights I have ever had with my youngest brother was about needles and needle jets. He wins almost every race he ever enters.

acotrel said:

When I do things, I do not guess - I work on the basis of experience, and not even hearsay. If you read Phil Irving's book 'tuning for speed' - it is a starting point. This technology is 1950s stuff. Balance factor is important, but jetting is critical. I do not know what taper is standard on the carburetor needles on a Commando, but Mikuni needles fit. I do not trust Amal in that area. British motorcycles have been slow forever. One of the biggest fights I have ever had with my youngest brother was about needles and needle jets. He wins almost every race he ever enters.

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Gasoline or methanol?

Concours, or any one with a lot of experience with commandos, what percentage of standard commando rods would go in the bin due to ovality, when you do up an engine? Thanks, Graham.

velo54 said:

Concours, or any one with a lot of experience with commandos, what percentage of standard commando rods would go in the bin due to ovality, when you do up an engine? Thanks, Graham.

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0% for me. The only rods I ever didn't use:

1) One set where the bolts and bottom were so rusted that I couldn't get them apart.
2) One set where the pins were frozen in the small end - couldn't get them apart so I don't know what the issue was. The bottom end had sat outside for a long time with no cylinders.

Yes, all I've used have been carefully checked.

velo54 said:

Concours, or any one with a lot of experience with commandos, what percentage of standard commando rods would go in the bin due to ovality, when you do up an engine? Thanks, Graham.

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I have no idea.
The ones I've done have been 100% acceptable.
The steel rod cap helps.
All the out of round I've seen has been on car engines.

Thanks Greg and Concours. I must be the odd one out. Both my rods should have gone in the bin. But, as previously mentioned the previous owner [now deceased] had no idea that norton commandos have feelings, just like us. Graham

velo54 said:

Thanks Greg and Concours. I must be the odd one out. Both my rods should have gone in the bin. But, as previously mentioned the previous owner [now deceased] had no idea that norton commandos have feelings, just like us. Graham

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It's not that nothing ever goes wrong: https://www.accessnorton.com/NortonCommando/1972-750-interstate-resurrection.40645/post-695670 It's just that each of us has seen different things. He's had way more than his share of weird things!

The Combat I'm building right now has given me fits with a few things that were clearly original manufacturing errors and some replacement parts that also had manufacturing errors.

Has anybody come across "D Rods"?