Commando Crankshaft Porn

RennieK said:

I was thinking it would be of interest if the posters could edit their posts giving the weights of the bare cranks at least but any other info like BF etc. also and whether they are designed for 750, 850 or ______.

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Interesting idea. I don't norrmally weigh the crankshafts. Once they are balanced for a particular application, I figure the total weight is what it is. But I'll weigh the ones I can in the next few days and post the weights. I'll include the BFs for the ones I have used. Maybe some other details too. They all work for both 750 and 850, as long as they are balanced accordingly. A couple are MK3 configuration, and I'll add that info.

Ken

I don't have any fancy aftermarket crankshafts. I only have my dammaged 73 850 crank. And my replacment 75 MK3 crankshaft. I have modified the 75 for width and the output shaft for length. I am going with lighter rods and pistons, of unknown manufacturer as of now. Looking into the many options, Forged Aluminum short skirt coated pistons for sure. Aluminum or steel rods, depends on price and weight. I will probably take some of the weight off of the crank. Taking ideas from everyone and mashing them together.

Here are some pictures of my cranks, first ones are the 1973






and my 1975 that I will use.

The crank was an ex Atlas ,and a friend of mine had copied more or less the "Maney" flywheel"on his milling machine,
that will be fitted in the Seeley frame alongside with Jim Schmidt pistons /rods , and the recent Santa Claus camshaft /camfollowers of the same origin (JS Motorsport)......it's a long, very long job !
The crank weighed 18 pounds , this morning.........but need to be re balanced , cause my best friend (living 300 miles from my home), do not remenber which BF we agreed !!!

marinatlas said:

this one is from Jean Noel Gindrat, a french tuner who made most of his stuff himself..........

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This is quite an interesting grind not to mention the alum rods but I'm curious to see the other side. Is it possible to post another photo showing the opposite side of the flywheel?

this one is from :http://www.britishclassicbikes.de/

and right now is looking very interesting , and if i was to make 'or better to say have to ask to my buddy to make one!!
I will go this way (somewhere , looking like one of ken's collection....)

marinatlas said:

this one is from :http://www.britishclassicbikes.de/

and right now is looking very interesting , and if i was to make 'or better to say have to ask to my buddy to make one!!
I will go this way (somewhere , looking like one of ken's collection....)

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I knew I'd seen this one before. WEAL Norton has posted this one last year. It's an interesting concept with the interchangeable weights.

It's amazing how many ways there are to aproach the Norton crankshaft issues. I really enjoy seeing this stuff.

A number of years ago I had an ex-Boeing engineer who specialized in titanium design draw up some ti Norton rods for me. He went bankrupt, I lost my investment, and the rods never got made, but I had some interesting discussions with him before the end. He gave me a titanium valve spring he had developed for some Harley drag racers, and showed me a titanium piston that had been tried in a NASCAR engine. It was an interesting design. He suggested I do a titanium crankshaft for a Norton. I didn't think much of the idea, for a variety of reasons, but it certainly could have been the lightest one around. Titanium doesn't make such a great bearing surface, but there are all sorts of exotic coatings now that solve that problem.

Ken

RennieK said:

I was thinking it would be of interest if the posters could edit their posts giving the weights of the bare cranks at least but any other info like BF etc. also and whether they are designed for 750, 850 or ______.

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OK I pulled out my scales and my notes and edited my post. Jim

Much better than winter oil thread! Ken reported Peel's crank at 21 lb so just a couple-3 less than factory and just a couple-3 more than lightest. Hope it Goodie Locks just right. Norton cranks are innately heavy compared to other lightened engine crankshafts, so sorta funny like the Model T guy telling me he upped CR, lightened crank increased cam lift and re-jetted carb to about double hp to 40 so was thumbing his nose as rest of the T- parade finally got to town a few minutes later.

What impressions are out there on 'heavy' vs light cranks on Commando type bikes?
Just rev-acceleration or sense of handling ease or resistance?

Ken just reported he's still breaking bits to finish plugs holes. ugh.

Something to keep in mind with similar rpm range as this example adjustable BF slugs. Machinist prono site, head thickness gauge of junk sale pliers and more.
http://ryanbrownracing.com/Bill_Jones_P ... llery.html

With engineering to those standards and a top speed thats already higher than a Jap four, then maybe an entry to Bonneville 2011 should be considered?

I think the best idea to to cut the flywheel as in the photos below, radius the PTO shaft to keep it from breaking and then nitride the cheeks/journals to strengthen and stiffen things up. 3/8 fasteners of course. If new stock cheeks are available at reasonable cost - this may be the cheapest setup and I doubt if there will be any problems when using lightweight pistons. See the radiused PTO shaft at bottom.

jseng1 said:

I See the radiused PTO shaft at bottom.

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With the radius pto shaft, are you undercutting the bearing face, and what size radius is being used,anyone ever had the radius rolled, or is that like trying to find rocking horse crap.

Soooo, how many of you have actually broken a standard crank on a road bike that didn't have some other cause for the breakage, like a run
bigend and broke after regrind.

I also noted that JIM C is starting to use heaver cranks, will that have all of the sheepole tearing their injuns down to get weight added, you have done a full circle it would seem JIM, have you found them nicer to ride or is it just where it ended up and thats where it will stay :?: :?:

splatt said:

Soooo, how many of you have actually broken a standard crank on a road bike that didn't have some other cause for the breakage, like a run
bigend and broke after regrind.

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I've never broken one in a street bike, but I've taken two different 750 street Commandos apart that had seriously cracked crankshafts, one at the usual spot at the mainshaft/cheek juncture, and one at the drive side rod journal. I'm pretty sure both would eventually have broken. On inspection, I found that the one with the cracked rod journal had the center hole in the forging seriously off-center, and I assume that had something to do with it cracking. The rod journal was standard size, and looked good otherwise. I don't know the history of the bikes. Both were bikes I bought for parts back in the '70s when I could get a complete basket case bike for $300. I bought them to get engine parts for the race bikes. I have seen one street Commando with a broken crank that pretty much destroyed the engine, but it was used pretty hard and regularly revved past redline. Still, I don't think it is a common occurence in a street Commando.

On the other hand, I have broken sevral standard crankshafts in race engines, both 750 and 920, but usually after a lot of race miles.

Ken

jseng1 said:

I think the best idea to to cut the flywheel as in the photos below,..... and I doubt if there will be any problems when using lightweight pistons.

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Hm, I tend to disagree with this one slightly: Except for Hartmut's (WEAL) crankshaft all the others more or less stick to the original concept of placing most of the counterweight's mass in the middle - even if some place heavy metal in the outer counterweights. I'm a big fan of the idea of getting as much of the balancing forces as close as possible to the main bearings. That would reduce the flywheel to exactly its original role more or less - and thus also reduce its tendency to bend the crankshaft. Heinz Kegler send me some info a few years ago that he actually did exactly this on his racing Nortons.

Combining outboard counterweights and lightweight pistons IMHO is probably the best way to reduce overall stresses on the crank train and crankcase.

Just my €0.02....

Tim

I broke the crank on a 20,000 mile 72 commando years ago. Drive end snapped but still got me home from work! It was Christmas eve, commando was my only transport and I was broke so I spent all day Christmas day under a fishing umbrella in the snow - removed engine,stripped and fitted new (secondhand 850) crank and was back at work boxing day . Same main bearings, bigend shells, bigend nuts and bolts and lots of locktight. Bike ran for another 16000 miles trouble free and then got written off. Rebuilt it but never touched engine until rings went 9000 miles later! Still got it but its been in big bits for several years now. One Day!!!

Tintin said:

Hm, I tend to disagree with this one slightly: Except for Hartmut's (WEAL) crankshaft all the others more or less stick to the original concept of placing most of the counterweight's mass in the middle - even if some place heavy metal in the outer counterweights. I'm a big fan of the idea of getting as much of the balancing forces as close as possible to the main bearings. That would reduce the flywheel to exactly its original role more or less - and thus also reduce its tendency to bend the crankshaft. Heinz Kegler send me some info a few years ago that he actually did exactly this on his racing Nortons.

Combining outboard counterweights and lightweight pistons IMHO is probably the best way to reduce overall stresses on the crank train and crankcase.

Just my €0.02....

Tim

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I tend to agree with that idea. One of the other things we tried in the '70s, in addition to the heavy metal slugs in the "outboard counterweights" (a much clearer terminology than my use of "cheeks") was welding plates to the inside of them. The only drawback was that you would have to grind the welds off to remove the plates if you wanted to re-grind the journals, then weld them back on and re-balance the crank. I only had to do that once. Usually the cranks cracked at the output shaft before the rod journals needed grinding. I like the idea of the bolted on weights a lot. I used the welded plates because that's how the flat track guys were doing it. Wish I had some pictures to post, but never took any.

Ken

splatt said:

Soooo, how many of you have actually broken a standard crank on a road bike that didn't have some other cause for the breakage, like a run
bigend and broke after regrind.

I also noted that JIM C is starting to use heaver cranks, will that have all of the sheepole tearing their injuns down to get weight added, you have done a full circle it would seem JIM, have you found them nicer to ride or is it just where it ended up and thats where it will stay :?: :?:

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Well here is my story. After blowing up the second lightened stock flywheel in my racebike many years ago I built the crank with the center main and made it as light as I could. I built the rest of the motor the same as it had been before the explosion. After that I found that I could no longer run with Larry Kirby and the the rider from Big D Cycle who had been the guys I had been swapping leads with for some time. I fought that for most of a season trying to figure out why. One day I was talking with Ken.C and he said a light crank isn't always better so I started doing some reasearch. Kirby was racing a shell 750 Yamaha and I asked him what he had for a crank. He said it was stock except for the steel bands around it for added weight. I also talked to a few other people who had a reputation for being fast. So I pulled my motor apart and welded on the two steel bars around the center two porkchops which added several pounds near the edge of the flywheel to get maximum effect. The very next time out I beat Larry. The next crank I built was even heavier and my track times improved even more. The bike actually felt slower with the heavy crank but the watch doesn't lie.
Maybe this is just me and my particular riding style I don't know but it worked for me and after talking to knowledgeable people I found I was not the only one who felt this way.
The only reason I like to add weight to my streetbike crank is the fact that it makes the motor vibrate less. I also have to think the reduced vibration has to help the life of the cases, bearings, ect.

What a great story myjota. True bikers are forged outa these situations. What were the symptoms you were getting and how was it you were able to limp home? and what were you doing revving that high anyway when there was snow on the ground? You must have been caught up in the Christmas rush.