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Engine bearing technicals with direct bearing on this subject;
http://engineparts.com/publications/CL77-3-402.pdf
http://engineparts.com/publications/CL77-3-402.pdf
Commando Crankshaft Porn
- Thread starter lcrken
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Extensive educational reading on crankshaft phenomena
http://www.epi-eng.com/piston_engine_te ... issues.htm
http://www.epi-eng.com/piston_engine_te ... issues.htm
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Good stuff on the crankshaft fatigue test.
I have read in one place where the Nitriding increases durability by 25% but according to this graph it is closer to 70% if you take the best case. Maybe the 25% was referencing in comparison to heat treated or it could be that crankshafts are often designed with some use of the sloped part of the curves.
Also note worthy is that when the curves go flat, the endurance is at infinity or can cycle there indefinitely as long as the component is not cycled above the stress thresholds shown on "Y" axis of the chart. My understanding is that steel is the only material that exhibits this behaviour. That is exactly why you want to avoid aluminum rods like the plague if you need durability. :lol:
I have read in one place where the Nitriding increases durability by 25% but according to this graph it is closer to 70% if you take the best case. Maybe the 25% was referencing in comparison to heat treated or it could be that crankshafts are often designed with some use of the sloped part of the curves.
Also note worthy is that when the curves go flat, the endurance is at infinity or can cycle there indefinitely as long as the component is not cycled above the stress thresholds shown on "Y" axis of the chart. My understanding is that steel is the only material that exhibits this behaviour. That is exactly why you want to avoid aluminum rods like the plague if you need durability. :lol:
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Thanks for interpreting the graphic, over me head other than which came out on top. As to your Al rod comment, now ya just being contrary for fun, as applies only if scrimping on Al mass for sake of wining edge like racers are won't to do. Same as fast wearing race tires vs long enduring heavy touring tires, replace as needed ahead of time, but generally impractical for street use unless like me its worth while extra security to make it to pavement and cost effective with less crash risk. Enjoying rehashing images left on Mr. Becker's special cases and 3rd bearing crank.
I can see advantage of stiff center flywheel, same was as beams and cranes beef up their middle area more than the ends to resist flex and bending. Photo's of failed cranks would add to this subjects scope about now.
I can see advantage of stiff center flywheel, same was as beams and cranes beef up their middle area more than the ends to resist flex and bending. Photo's of failed cranks would add to this subjects scope about now.
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hobot said:
No I am not!
John Clease hobot said:
Was not my point but ok
hobot said:
See what I can dig up from the bin for the offerings to the gods of speed when I get back.
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Looks like a Dave Nourish NRE Weslake twin crank. Note the flywheel mass in the center
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pouchy750 said:
For the first few builds we used cut down Steve Maney aluminum barrels with the BSA lifters and bronze carrier. Examples of these can be found on Jim Schmidtt's web site. Once we destroyed that barrel Herb Becker made an aluminum barrel out of billet and he adapted a Dunstall style of lifter (similar to the BSA style but a bit beefier). These rode in bores in the aluminum of the barrel (no bronze bushing).
I don't have any pictures handy of the gear drive. Cam rotation was the same as stock. A pair of adjustable intermediate idlers were installed (upper & lower) where the cam chain slack adjuster was located and a Norton intermediate timing gear was adpated to the cam shaft. The idlers were made from two Norton crankshaft pinions. We started with bronze bushings (bad idea) and ended up with roller type bearings. This was a Herb Becker work of engineering, machining and art.
The motor has a nice whirring sound to it, not too loud but enought to let you know something is a bit different about the engine.
Glad to share.
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Heres one for you Hobot! This was the journal what put me out of action several years ago at Phillip Island, this crank was running a lightened steel flywheel at 11.5 : 1 comp ratio on methanol. I campained the commando for five years probably about twenty meetings over the years, before i made the move to metho It would regularly see 8000 rpm's. That last meeting I shut her down as I was experiencing some enhanced vibration and bad engine noise, we found the crack with some flaw finder spray as it was not quite as dramatic as it looks in the pic till I applied some force with the shop press.
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Ah heck, life and cranks are of un-predicable life time, so visitors can just scroll past our cartoon side trip. No one really understands what Ms Peel's 3 links provides in handling trills, but its enough G's to flash me back to LSD trips, more intense than Psilocybin at a rock concert! I've no misunderstanding I risk life, limb and bike on every ride and planning on a ride that's more intensely effective than any balloon tire Hi CoG crankshaft bike can deliver in rushes. Google any search term + images for pages of related photo's. Try Emma Peel for instance : )
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Back to our regular programming:
Below are a few pictures of the crankshaft I had built for the 750 Norton Seeley ultra short stroke. From recollection, the stroke is 72.5mm. Main bearing journal diameters were made to 35mm as opposed to the stock 30mm and a little black magic allowed me to fit the main roller bearings within the standard bearing/case envelope. I specified an increased main journal filet radius.
The product was nitrided.
I doubt this will ever break as the material is superior to stock and rod and main journals are getting close to overlapping, making it very compact and durable. This crankshaft has been raced since 2005.
I could have/should have had the rod journals bored out larger and fitted with high pressure alloy plugs as a weight saving; maybe next time.
Below are a few pictures of the crankshaft I had built for the 750 Norton Seeley ultra short stroke. From recollection, the stroke is 72.5mm. Main bearing journal diameters were made to 35mm as opposed to the stock 30mm and a little black magic allowed me to fit the main roller bearings within the standard bearing/case envelope. I specified an increased main journal filet radius.
The product was nitrided.
I doubt this will ever break as the material is superior to stock and rod and main journals are getting close to overlapping, making it very compact and durable. This crankshaft has been raced since 2005.
I could have/should have had the rod journals bored out larger and fitted with high pressure alloy plugs as a weight saving; maybe next time.
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I honestly cannot recall exactly. I do recall somewhere around +17 lbs. -18lbs.
My guestimate is that with a larger bore through the rod journals I could drop another 0.75 lbs or more.
My guestimate is that with a larger bore through the rod journals I could drop another 0.75 lbs or more.
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RennieK said:
It would take someone from "The Island" to make an analogy about this crankshaft with FISH! I am truely hurt.
I would have thought Thor or something more noble or god like would have been more appropriate :lol:
Cheers
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