Commando Engine Weight and Balance Information

I've posted these tables before, but this is my latest update, and there appears to be some current interest on this data in one of the threads.









Hope someone finds it of interest.

Ken

Thanks Ken. I'm thinking about my next project, putting JS long rods and light pistons in an Atlas.

Greg

Such a great batch of data here from someone who's done it all with our bikes.
I have an older copy in my files I refer to all the time.

Thanks, Ken

lcrken said:

I've posted these tables before, but this is my latest update, and there appears to be some current interest on this data in one of the threads.
Hope someone finds it of interest. Ken

Click to expand...

Ken, Thank you for this data posting. It would appear that you have invested a lot of time and money enjoying Norton race bikes.
Which of these builds would you recommend for a simple street touring Norton 750?
Specifically a rigid mount 750 - spending its day at 2000-5000 rpm.
Thanks for your time on this.

lcrken said:

I've posted these tables before, but this is my latest update, and there appears to be some current interest on this data in one of the threads.

Hope someone finds it of interest.

Ken

Click to expand...

That's a great collection of specs Ken. You can see that the balance factors are all over the place. Wild figures and lots of guess work here and its not based on science or any kind of measuring equipment. Lots of talk but who is actually making a reliable, verifiable test?

Here's a hint:

balance-factor-scratch-test-tool-t15134.html?hilit=BALANCE%20FACTOR%20SCRATCH%20TEST%20TOOL

p400 said:

lcrken said:

I've posted these tables before, but this is my latest update, and there appears to be some current interest on this data in one of the threads.
Hope someone finds it of interest. Ken

Click to expand...

Ken, Thank you for this data posting. It would appear that you have invested a lot of time and money enjoying Norton race bikes.
Which of these builds would you recommend for a simple street touring Norton 750?
Specifically a rigid mount 750 - spending its day at 2000-5000 rpm.
Thanks for your time on this.

Click to expand...

Boy, that's a really open ended question, but I'll give it a shot! For your application, I'd probably just stick close to stock with the engine. Most of the race style improvements give you more power above 5000 rpm. With the stock cam, which is actually pretty good, you probably want to stay at 9.5 compression ratio or less. The biggest bang for the buck you can get for the 2000-5000 rpm range is raising the compression ratio, but in most localities you are typically limited by the available gas to 9.5 max, and maybe 9.0 for safety with unknown gas quality. With a racier cam, you can get by with a bit higher compression ratio, but I don't think it would be worth it in your case. If you want to spend the money on head work, the sky is pretty much the limit. That's where most of the horespower gain is found in a Norton twin. Fitting 1/16" larger intake valves and doing a good multi-angle valve job will give you gains throughout the rpm range at a reasonable cost. If you want to send the head out for a serious port job, you can pick up a little more, but having it done right will be expensive. Stock pipes with the good pea shooters would be my choice of exhaust. For carbs, anything from stock (if not already worn out) to new Amals, Mikunis, Keihins, etc. would be fine. I wouldn't go larger than 34 mm (35 for Keihin FCRs) with dual carbs. For a stock engine 32 mm would work great.

The really important part is assembling the engine carefully. I would have the crankshaft and connecting rods crack tested, just to be safe. You can do that yourself with a dye penetrant kit. It's worth the effort to make sure the head and cylinder surfaces are flat, and I'd go with the stock flame-ring composition head gasket, and be sure to re-torque after initial running.

It's a subject you could write a book about, but that's all I can come up with off the top of my head. I'm doing basically the same thing right now on an 850 MK3 for my grandson, so we can have a pair of them for our rides. I'm keeping it pretty stock, except for a 920 cc conversion, and have yet to decide on carbs. I'll probably do the 1/16" larger intakes and bronze guides, nothing more serious. I'm probably going to stick with the stock cam. My aim is to keep it mild enough to putt around town, but still have enough grunt out of corners to be fun in the twisties.

Now that I've rambled on a lot, if all you were really asking was which balance factor to use, I don't have a stock answer. With a rigid mount it really does depend on what frame you are using and whether the engine is straight up like an Atlas or tilted forward like the Commando. It's pretty easy with the Commando, which isn't really all that sensitive to BF, but that's not the case with rigid mounting.

If vibration is an issue with your bike, you might look at the JS long rod/light piston setup. I bought one from Jim, but haven't used it yet, so I can't give you any input from personal experience. There's a fair amount of information in other threads on the forum from people who have tried them.

Ken

Thanks for the data; a gracious gift to us all.

lcrken said:

p400 said:

Ken, Thank you for this data posting. It would appear that you have invested a lot of time and money enjoying Norton race bikes. Which of these builds would you recommend for a simple street touring Norton 750? Specifically a rigid mount 750 - spending its day at 2000-5000 rpm.Thanks for your time on this.

Click to expand...

If vibration is an issue with your bike, you might look at the JS long rod/light piston setup. I bought one from Jim, but haven't used it yet, so I can't give you any input from personal experience. There's a fair amount of information in other threads on the forum from people who have tried them. Ken

Click to expand...

Thanks for your views on this, great information. Yes vibration is the issue and I am looking for pre Commando use of Jim Schmidt light/long components in ridged frame Norton, specifically vibration over 3500RPM.