Commando Crankshaft Porn

After much contemplation concerning splitting the center balance weight and figuring the volumes and weights of metal to remove I decided to take the plunge. No turning back from this one.



It wouldn't do any good to check the weights during the cut as I would be removing all the metal from the counterbalance side first and then graduating into the rod side.
According to my figures I should end up pretty close to what I needed with a .560 wide cut. The smallest straight cut I could make was 1/2 inch wide so that is what I did. One 8 hour cut.



After weighing the rods and pistons I figured I needed a 1269 gram bob weight. It balanced out at 1270 grams.



Now just round of the corners a bit and I will send it to the heat treater next week.

The stock crank weighs 24 lbs.
My old crank weighed 27 lbs.
The new crank weighed in at 28 lbs. Jim

Heavier is better. Nice work Jim.

Hope you have a nice big radius in that cut in the center bob weight.

Care to give the final details of journal sizes, both rod and main.

Dances with Shrapnel said:

Heavier is better. Nice work Jim.

Hope you have a nice big radius in that cut in the center bob weight.

Care to give the final details of journal sizes, both rod and main.

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3/16 inch radius on the center cut.

I had originally planned to use a Honda rod journal at 1.888 but after ordering in a set of K1 Honda rods and looking them over I sent them back and ordered a set of 6 inch long, 2 inch journal rods for a small block Chevy from Molnar Tech. I was much happier with them and the 2 inch journal diameter will do a lot to help crank flex. Plus the recip weight was lower with the Molnar Chevy rods.

The main journals are 35mm so I can use a 307 on the drive side and a 207 on the timing side. I would use a 307 on both sides but the 307 on the timing side ends up uncomfortably close to the timing spindle hole. Jim

Just caught up on this thread after some time away. With regard to main bearing journal, the Norton rotaries have their eccentric shaft running on FAG bearings but the inner races are discarded with the rollers running direct on the journal. This gives a large diameter journal and while I know the rotaries don't have a massive throw like a conventional reciprocating engine, there are good few wankel Nortons about with in excess of 150,000 miles on them.
Splatt, you hanker after a Colchester Chipmaster. I did my apprenticeship on one and while it was a precision piece of kit, the variomatic gearbox was troublesome. This can be overcome by controlling speed with a tricked up single phase voltage supply instead of the normal 450v 3phase supply we use in UK

Running roller races directly on the journal would require higher RC hardness on the shafts than would be obtainable with a 4340 crankshaft. You would need 300m or similar. Jim

a cool vital detail in Rotary development ... as heat flow=power went up, bearings and cranks exploded.

Some of the detail developments are interesting to recall. For example, it was found that the forged steel rotor shaft journal diameters, which are casehardened, grew in diameter during the first few hours of use due to the high temperatures developed in these early engines. It was only after a cryogenic treatment was introduced into the production process that this problem was overcome.

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rest of the story
http://www.nortonownersclub.org/history/rotary

Awesome Jim. I wish I had 1/4 of your skills.
There are indeed some highly talented people about.
Here is something you and others might be interested in.
I know it's not Norton and I hope it's not getting too sidetracked for you but another guy with amazing talents. If it's a problem let me know and I will pull it.

http://www.britbike.com/forums/ubbthrea ... 979&page=1

Mark F said:

Awesome Jim. I wish I had 1/4 of your skills.
There are indeed some highly talented people about.
Here is something you and others might be interested in.
I know it's not Norton and I hope it's not getting too sidetracked for you but another guy with amazing talents. If it's a problem let me know and I will pull it.

http://www.britbike.com/forums/ubbthrea ... 979&page=1

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Pretty cool, I always like to see peoples innovation.

Now if I could just get Scottie's formula for transparent aluminum to make a set of cases I would have it made.

Ready for a trip up to the hear treater.

comnoz said:

Now if I could just get Scottie's formula for transparent aluminum to make a set of cases I would have it made.

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Wouldn't that be outta sight. :mrgreen:

http://www.mufon.com/FamousCases/Aurora ... 20File.pdf
Aluminum saucer material only becomes transparent when the helical plasma thrust/stabilizing ring is resonating opposite phasing of the local flux photon fields, duh, then can look out the craft like it wasn't even there. The ones i've been on are otherwise boring as no acceleration felt so not near the thrill of my tri-linked waddler.

Hobot, I am so happy I don't understand a word of that post, it would really worry me if I did

Some more progress, not as much as i have wished but the side of the crankcheek and mains are turned within 0,3mm
and oil holes are drilled as well.



I will go for 35mm mainshaft like Jim, with driving side staight and use a driving hub with inbuild cone (the best describtion i manage in english)
I get more freedom to put on whatever i wish and adjust the hub sideway, the other benefit i think is the more secure clamping force by the bigger diameter of the cone.
I happened to find 4 NUP 207 ECP/c3 bearings, maybe i can use it on the register side?
I take off that loose ring and just press the inner race on as in standard fitment. opinions?
The roller cage is plastic but you said it was ok, Jim. This is a picture of my modyfied boring bar:



To get between the crankcheek i milled the side down, then reinforced it with welded on bars, that made it stiff enough not to vibrate turning the crankcheeks.

Jim, if you read this, i talked to the technician at the heat treatment store about our discussion, he was still absolutely positive that i should nitrocarburate. The hard outer skin will be 0,02mm or 0,0008inch( must be that white layer you are talking about)
He also said that Volvo Diesel trucks use it on their cranks, and a lots of customers building racing engines.
I do mentioned the problem with flexing Norton cranks
He confirmed a lots of what you said but was still positive to Nitro caruration.

Sten

Sten,
Looks good, I think the bearing would work, you will probably want to use the ring for thrust loads.

I am going to go ahead with a plasma nitride treatment on my shaft. That way I can leave the weights soft so I can change the balance if needed.
My crank should be back from heat treat today. I had them temper the shaft at 1100 F. as required for the plasma nitride. That also leaves the shaft softer so it is easier to thread and cut the keyways. Jim

Sten, what is the od of the 35mm bearing?
I am getting a lot of flack from the Vincent machinist crowd for using 30 mm mainshafts on my Vincent crank (built by others, this is beyond my capability) Standard mainshafts are one inch, and the argument is that with the larger diameter bearings, the bearing speed in fpm is greater at any rpm, therefore failure is possible.
I am not concerned about this because 30x 72 is standard Norton Commando bearing size and they seem to handle 6500 or higher rpm just fine, at least the Superblends do.
Now reading about Sten's oversized Commando mainshaft at 35 mm, it occurs that the bearing OD high bearing FPM problem may be a theoretical problem only.

The problem of flexy mainshafts is real enough. When Vincent was working at getting the contract to build multiple Picador engines (aircraft drone) for the British Military in 1954, they started dyno testing with stock Black Shadow engines. The requirement was for sustained 70 hp for 12 hrs. The first engines tested quickly snapped their mainshafts when run at 5500
Rpm sustained, some in as little as twenty minutes running! To solve this they built a "Picador " crank with bigger mainshafts, that worked very well.

So in the tradoff between bigger mainshaft and bigger bearing/higher fpm, it seems the bigger mainshaft is the way to go.

Glen

The bearing with 35mm ID is the NJ207 with an OD of 72mm -same as stock. They have an RPM capability well over the Norton RPM range and slightly less load capacity than a stock "Superblend" but higher than a HD ball bearing.

The 307 bearing has a 35mm ID with an 80mm OD. It has much higher load capacity but you have to bore the case for them. Jim

There's also the NJ2207E but this requires machining 2mm off of each side of the inner and outter race.

Larger main journals are the way to go. Larger journals greatly increase the endurance of the crankshaft. Also approaching or achieving an overlap between the main journal and rod journal greatly increases durability. Not practical on a standard stroke Norton but pays dividends on shorter stroke Nortons.

Hi Glen, as Jim said, my 207 NUP and his 207 NJ bearing has the same 72mm OD diameter as standard
If you look at SKF or FAG catalogue the 207 bearing can take 11.000 rpm and the 306 with i`ts bigger OD can take 9.500 rpm, quite enough.
A bit off topic maybe, but that tecnichian i talked to even mentioned because of the very hard and wear resistant skin that you can use your 4340 steel or our equivalent 2541 for making camshaft, finish grind before nitro carburating and polish afterwards, making it tougher against flexing being so long and thin as has been talked about in this forum.
Enough said, i promise not to argue more about that heat treatment if you don`t want but it was interesting to get some input, Jim.
Hope i will get some more time to progress before Cristmas.

Sten

billet said:

Hi Glen, as Jim said, my 207 NUP and his 207 NJ bearing has the same 72mm OD diameter as standard
If you look at SKF or FAG catalogue the 207 bearing can take 11.000 rpm and the 306 with i`ts bigger OD can take 9.500 rpm, quite enough.
A bit off topic maybe, but that tecnichian i talked to even mentioned because of the very hard and wear resistant skin that you can use your 4340 steel or our equivalent 2541 for making camshaft, finish grind before nitro carburating and polish afterwards, making it tougher against flexing being so long and thin as has been talked about in this forum.
Enough said, i promise not to argue more about that heat treatment if you don`t want but it was interesting to get some input, Jim.
Hope i will get some more time to progress before Cristmas.

Sten

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I have made camshafts before. Worked great. Just never had a good way to cut the tach drive gears. Jim

Dances with Shrapnel said:

There's also the NJ2207E but this requires machining 2mm off of each side of the inner and outter race.

Larger main journals are the way to go. Larger journals greatly increase the endurance of the crankshaft. Also approaching or achieving an overlap between the main journal and rod journal greatly increases durability. Not practical on a standard stroke Norton but pays dividends on shorter stroke Nortons.

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Yes, the NJ 220 could be an option i considered at the drive side if it weren`t for the steel cage.
I think i will use NJ 306 at the drive side.
To increase the endurance of the crankshaft by bigger journals was exactly what i was looking for as you mentioned.

comnoz said:

I have made camshafts before. Worked great. Just never had a good way to cut the tach drive gears. Jim

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Wow! That`great!
Has actually thoght about it myself. How do you make them? I saw in another thread that you pressure feed it, how big is the hole?

Sten
Yes, it is off topic but i couldn`t resist asking