mk3 crank knife edging, cast tidy up (2017)

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turboboy

turboboy

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Hi All
any info and pic's of crank tidy up's / knife edging , how to's
I'm not really after making it light.
Just to make it more slippery through the air and oil.

Cheers
 
Don’t think it’s a ‘done thing’ on Norton cranks is it?

What would you ‘knife edge’ ? The flywheel is a great hunk of metal, and the two side cheeks also. I just can’t see what / how you could ‘knife edge’.

Best you could do IMHO is to polish it, as there is a lot of rough cast finish.

It’s an intricate thing to polish though, so it will be a big job. And I would be prepared to place a sizeable bet that it won’t make the slightest noticeable or measurable difference !
 
Yes, a lot of work for little gain -unless you have perspex engines cases to admire your hardwork through :).
 
Reminds me of my old team mate, Cal Lewis, who had spent an inordinate amount of time polishing the stock crank and flywheel on his Thruxton look alike Commando road racer. That crank was a shiney piece of art.

At the time, Cal was recovering from a broken collar bone and was letting another team mate race it when the flywheel grenaded and destroyed the engine, frame and engine/trans cradle.

I will never forget the look of the deep dent the flywheel bob weight left in the track surface....nor the look on Cal’s Face when the bike came in on the crash truck.
 
mk3 crank knife edging, cast tidy up (2017)
I polished mine. I used to work as a metal polisher when i was younger and have my own small set up at home. I am the only one that will know the work that is inside and that's fine by me. The crank originally had a bit of surface rust from the bike sitting idle for many years and i started to just clean that off and got carried away as usual. A complete waste of time though. mk3 crank knife edging, cast tidy up (2017)
mk3 crank knife edging, cast tidy up (2017)
 
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Tinsy said:
mk3 crank knife edging, cast tidy up (2017)
I polished mine. I used to work as a metal polisher when i was younger and have my own small set up at home. I am the only one that will know the work that is inside and that's fine by me. The crank originally had a bit of surface rust from the bike sitting idle for many years and i started to just clean that off and got carried away as usual. A complete waste of time though. mk3 crank knife edging, cast tidy up (2017)
mk3 crank knife edging, cast tidy up (2017)
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Beautiful! I would like to suggest you get another crank to put in your bike and put this one on display.
It is also my understanding that polishing a crank has benefits other than cosmetic. I believe it removes the tiniest of cracks that may eventually get bigger and cause a failure. If I am mistaken about this please correct me.
 
Nice job, I had polished quite a few , as it was the fashion years ago and I used to work for a short while into ships propeller factory where they polish the props blades after foundry/machining , but never to that level .........!!! how long does it took you ?
 
olbbeezer said:
Beautiful! I would like to suggest you get another crank to put in your bike and put this one on display.
It is also my understanding that polishing a crank has benefits other than cosmetic. I believe it removes the tiniest of cracks that may eventually get bigger and cause a failure. If I am mistaken about this please correct me.
Click to expand...

You are correct.

It can't hurt but I don't think there's much to gain with the cast iron flywheel as it is one big notch (ferrite with graphite nodules). Cast iron crankshafts are polished but typically it is the journals that receive the polish in order to reduce the surface asperities in order to increase the bearing life.

Polishing a cast steel bob weight, though beneficial for endurance, is pretty much unnecessary. Sure you increase the durability but it's in an area where it is not needed.

Where polishing (and other surface treatments such as shot peening and rolling) makes sense is in known problematic areas where a particular crank may begin to fracture. For a Norton twin crank, these known areas include the filet radius of the rod and main journals and the oil feed holes. Some have asserted that the rough drilling of the inside of the rod journals (sludge trap) and where the drill bit flutes shouldered are a source of stress risers. My opinion is that as ugly as they may look, they are not critical, especially since they are on an internal surface.

As for the Commando cast iron flywheel, if you are going to use the bike in anger often or lighten the flywheel, change to a steel flywheel; to do otherwise is courting with disaster.
 
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Dances with Shrapnel said:
For a Norton twin crank, these known areas include the filet radius of the rod and main journals and the oil feed holes. Some have asserted that the rough drilling of the of the inside of the rod journals (sludge trap) and where the bit flutes shouldered are a source of stress risers. My opinion is that as ugly as they may look, they are not critical, especially since they are on an internal surface.
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I remember reading in some classic bike mag (pre-internet days so it must be true :) ) that the specs for the filets had a maximum radius but not a minimum. Therefor the people making the cranks would dress the grinding wheel to get the tightest radius possible to maximize the number of cranks between dressings. The first of the cranks made after dressing the wheels were more prone to breaking. So goes the story....................Sounds good to me.
 
I can recall at least two cranks which had inadequate filet radius (non factory cranks) and they failed..at the filet radius. I had taken a billet crank to a local crank grinder and found he did not want to dress the grinding wheel to my spec so I sent the crank back to the maker of the billet crank for proper service. At the time I speculated that the owner just did not want to consume the grinding wheel any more than he had to. Sounds like we have similar stories.
 
According to my notes it took 30 hours including polishing the new nuts and bolts. Another 6 for the Con Rods, End Caps and Bolts and a further 11 for the Rockers and Valve Springs. Just as well i am not doing it for a living, i would go broke very quickly. Too late to put it on display, it's in the bike! https://s5.postimg.org/n1lxfniqf/2017-09-06_150913.jpg
 
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The advantage of a knife edge crank has to do with reducing crankcase windage and the associated friction involved. But it's most effective at high RPM. I suspect a dyno would see absolutely no difference in a stock-RPM Norton engine.
 
In conventional wet-sump (automotive) engines, windage trays are the first upgrade, followed by crank scrapers, knife-edged flyweights, then the ultimate; dry sump oil systems! Since we're already at the pinnacle :p of lower-end oil control, I'd have to go along with Mexico Mike's assertion that there's precious little to be gained over what we already have, at least as far as oil/friction control are concerned. The prior statements about stress risers still holds true, however.

Nathan
 
In engines like ours, where most moving parts are fed by splash, I do wonder about the wisdom of oil scrapers... designed to prevent the oil from... well... splashing...
 
It's important to remember that any "splash" oiling is not from a crankshaft spinning into/through the oil contained in the sump (whether wet or dry sump). The crank should never "dip" into the oil. Crankcase windage - the mini tornado that the crank generates can actually pull oil up from a sump (just like a tornado can pull water up from the ocean, forming a waterspout). This forms an oil cloud around the crank and that's why, as Nathan noted, performance wet sump engines have had windage trays since...well...a LOONG TIME. A properly designed windage tray reduces the "pull" and actually "peels" any developing oil cloud away from the crank. Ideally, the oil level and the lowest point of the crankshaft rotation are as far from each other as is possible. Obviously, ground clearance is a big issue which is why most performance oriented wet-sump oil pans are wide/long at the bottom, so the sumps are large capacity but aren't too deep.

A very interesting study was performed by Mopar back in the late 60's. They found that a 426 Hemi motor running at 7500 RPM with a proper oil level but NO windage tray could actually suck 5 quarts of oil up into a cloud around the crank. A properly designed windage tray eliminated it. They had dyno results showing 20-30 HP loss due to friction in the oil cloud around the crank. NOTE that this example was with the oil at the correct level, well below the crank - IOW, the crank did not dip into the oil to create this cloud; it's just a function of the crank-generated windage. A knife-edge crank generates less than a standard crank.
 
turboboy said:
Hi All
any info and pic's of crank tidy up's / knife edging , how to's
I'm not really after making it light.
Just to make it more slippery through the air and oil.

Cheers
Click to expand...

You are right - a complete waste of time. But it's mighty pretty! :) Nice job!!!
 
Is the windage tray just a barrier and how does it come to be properly designed? Is it by cut and try? Mopar had a way to measure the amount of oil in the 'cloud' in a running engine, but not sure how that is done either. Or is that no big deal with a dry sump (thought race engines might be dry sump though). At any rate 20 - 30 hp even a large engine is not insignificant.
 
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