Commando Crankshaft Porn

Jim I copied this from the BSA dirt bike link posted above -- "And the crank counter weight mass is in a much smaller diameter so the weight saving will be multiplied grately! -- I'd wondered about his before, but wasn't sure if it would really make a difference. rotating mass etc... We're seeing more and more tungsten bucking bars being sold and used in aviation, and so the thought crossed my mind -- what if,,, ,,, however, tungsten might not have the right properties to be spinning around in there. what are your thoughts (and anybody else's out there) on this ?

billet said:

Dances with Shrapnel said:

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

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I had a cam grinder grind me a couple of four lobe shafts with a different lobe on each position. I had picked out 8 different lobe profiles that I was interested in. [the cam grinder just happened to have a big surplus of VW cores]

Then I turned out a blank in my lathe and made a coupler to attach the VW shaft to the end of the new core with a vernier adjustment and used a follower on the second cam to control the grinder. It gave me the ability to change lobe centers and use different combinations of lobes easily. I also tried some different radius grinds on the follower which changed the lift rate on the new cam. I made and tested around 10 or 12 different cams back in the 90's.

The oil holes in my streetbike cam are 3/32 inch. I use a .017 inch orifice in the line that supplies the cam to limit the amount of oil fed to the center of it. Jim

cjandme said:

Jim I copied this from the BSA dirt bike link posted above -- "And the crank counter weight mass is in a much smaller diameter so the weight saving will be multiplied grately! -- I'd wondered about his before, but wasn't sure if it would really make a difference. rotating mass etc... We're seeing more and more tungsten bucking bars being sold and used in aviation, and so the thought crossed my mind -- what if,,, ,,, however, tungsten might not have the right properties to be spinning around in there. what are your thoughts (and anybody else's out there) on this ?

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There is no doubt that placing the rotating mass nearer the center reduces the momentum of the crank. Of course it takes more weight to provide counterbalance for the reciprocating weight so in the end all that moving weight to the center does is increase the overall weight of the shaft.

Generally speaking you would want to remove as much weight from the center as possible to reduce the overall shaft weight. Then if you wanted to reduce the momentum you would remove as much weight as possible at 90 and 270 degrees and leave only the counterbalance weight at 180 degrees and keep it as far as possible from the center of the shaft so less weight can be used. [in order to reduce overall weight]

In the BSA shaft he is obviously attempting to reduce the momentum as much as he can.

My thoughts are that reducing momentum is great in a shaft for 6 or more cylinder engines [or maybe very high speed engines] but single and twin cylinder engines need the momentum to efficiently transfer the power from the piston to the pto shaft. In a 2 cylinder engine there is only 180 degrees [the first half of each power stroke] of power feeding the crank for every 720 degrees of rotation. A crank of the right weight absorbs the power over the right amount of time and then releases it efficiently. Jim

Thanks Jim.

Well after spending 26 hours lost by UPS they finally delivered it. My centerfold has a nice suntan. I'm glad I left lots or extra material on the PTO shaft because it sure is crooked. Like 1/16 inch TIR...

Say What! ~1/16" ugh, but very interesting as similar mysterious amount of bending found in Peel crank after Ken checked it after it was nitrided, though with 'pretty' grey nitride not lumpy doodoo chocolate. Maybe something to do with both the heat soak rates and skin layer tensioning assymetric. Ken said mine was worst he'd seen no way to deal with it but scrap. Depressed I tracked down a Calif. Marine crank shop that put it right ~. 002".
Here's a start for me on predicting what may happen after mine is run.
https://www.google.com/search?q=metal%2 ... 3Aofficial

My crank has not been nitrided yet. It has just been heat treated. 1650 degree soak then oil quench and 1100 degree temper.
It is at 43rc hardness. The plasma nitride will be done after everything is finished. Jim

Well maybe the plasma nitride distortion will pull the alignment back closer? Peel's crank had been dynamic balanced prior to nitride so certainly it was pretty straight then so what bent it is still a mystery. Good crank shops never store cranks horizontally d/t risk of sag setting in. Peel's shaft ends were nitirided and prevented chrome to build up undersize shaft OD, so Ken copper plated to solve.

hobot said:

Well maybe the plasma nitride distortion will pull the alignment back closer? Peel's crank had been dynamic balanced prior to nitride so certainly it was pretty straight then so what bent it is still a mystery. Good crank shops never store cranks horizontally d/t risk of sag setting in. Peel's shaft ends were nitirided and prevented chrome to build up undersize shaft OD, so Ken copper plated to solve.

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Your crank bent because it had not been heat treated before it was nitrided. Nitriding involves temperatures around 1000 degrees which will cause the crank to warp unless it has previously been heat treated and tempered over that temperature .

Nitriding will not change my cranks dimensions. They are already changed by the heat treat. Now I will machine it back to straight before nitriding.

Attempting to straighten a crank after nitriding is not advised. Jim

I've often heard burring an engine block or other machinery casting for say 20 years allows all the stresses to stabilize and make for the ultimate condition.

Seems people are in just too big a hurry these days...

RennieK said:

I've often heard burring an engine block or other machinery casting for say 20 years allows all the stresses to stabilize and make for the ultimate condition.

Seems people are in just too big a hurry these days...

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Then the '39' Ford Flathead engine I pulled out of a field should be just right for a rebuild and long stress free life.

Casting and forging are heat treated which in the trade in called ageing as a general term. I work in a specialist steelworks we melt then remelt the same special alloy steel under vacuum 2 or 3 times then its reheated forged then aged. Then machine then heat treated another 2 times to harden it then machined by me. Every heating it bends and tho the forging can weigh over Q ton the shaft weights 220lbs when its sent to the customer (who are famous for posh cars) then they machine it to its finish shape and every machining releases stresses an it may bend further an be scrap.
So never underestimate what happens to any metal when you heat it or machine it Hobot we start with over a ton an the finish part can weigh less than 150lbs some less than 50lbs !!! Always add bit you can machine metal off but it hard to machine it back on ;-)

Toppy,
Do you think I need to be concerned about my crankshaft warping during plasma nitriding? The people I have lined up to do my nitriding tell me that as long as the shaft has been tempered over 1000 degrees then distortion will not be a factor. Jim

Your crank bent because it had not been heat treated before it was nitrided. Nitriding involves temperatures around 1000 degrees which will cause the crank to warp unless it has previously been heat treated and tempered over that temperature .

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Hm, Jim I will take your tempering-aging data points to Geoff Collins to see what he or rather his hired shops did but seemed pretty thorough. I'm a bit confused on the heat treatment bit in my crank though, are not the Norton cheeks already tempered-aged for the long haul and my flywheel steel plate also tempered ready to go. It all had to be welded up before the dynamic balance which I'd think would of found the rather obvious out of line issue Ken found. Nitride was last step w/o need to check alignment. I called world wide Nortoneers to rescue Peels already nitrided crank to be told by one and all its beyond hope trash. I then jumped fence to a place that fixed it fast and cheap so will see if it can take what is planned for it. Geoff covered the $300 recuse expense, a good part of that was shipping.

Toppy, loved your machinist scale and sense of elastic metabolism of hi class metal alloys in complex shapes. Can the scraps be recycled back to hi quality alloy or just something less tolerant. 3D printing can do some neat stuff in some metals but someday may be able to just direct the growth of large parts with some buffing to finish.

Hobot,
Well I got the same story from three different outfits who specialize in nitriding crankshafts plus it says the same thing about nitriding metal that has not been hardened in one of the articles you posted.

http://books.google.com/books?id=AfTLFd ... on&f=false

Stock Norton cranks are cast and not heat treated as far as I know. That type of alloy is not generally considered to be heat treatable.

Of all the types of nitriding, the plasma nitride treatment is supposed to be the most controllable way to get a deep nitride with little if any distortion. I guess I will be finding out. Jim

Go with what the nitriding firm tells you I worked for general engineering firm making repair and one off pieces nitriding was used a lot to harden jobs usually with complete success. If they are a good firm an give out correct information and if other heat treatment has been done correctly it should all be ok. But with any heating or machining there is always risk a fault in the original making of the steel may cause a problem now or in the future. The crank is subjected to Hugh forces when in use an large manufactures have vase resources to make an test such parts you are truly a brave an talented man to make your own from scratch an if you have been given right help an advise all should be well.
Yes Hobot after its washed remelted into small ingots the scrap is reused back a the first stage of the process it make new steel but even that is very carefully controled. Between 85% an 97%!! of the forging is machined away an at very stage the part may fail an be scrap. My firm has been doing this since the first jets where made an before that they made crankshafts for aircraft in fact some of the heat treatment plant was made for Spitfire engines!!! An we still struggle making this stuff so you have my full respect for your efforts

comnoz said:

Toppy,
Do you think I need to be concerned about my crankshaft warping during plasma nitriding? The thr people I have lined up to do my nitriding tell me that as long as the shaft has been tempered over 1000 degrees then distortion will not be a factor. Jim

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hello Jim. I agree with Toppy. however this is the important bit. tempering by itself induces stress because there is a quenching action.
Nitriding is done at a relativly low temperature, over what can be a long period of time. Distortion is solely caused by the release of residual stress
because of the long time in oven, any residual stress in the part will be released and show up as distortion. No residual stress is vital to no distortion.

To ensure minium distortion, the shaft needs, or must have NO residual stress before nitriding. The best treatment before nitriding is a low temperature long time stress relief. the data sheet on 4340 will give accurate temperatures for stress relieving after hardening..

The tempering operation is not a stress relief treatment. The tempering operation has no bearing on stress removal.

Again, the secret to no distortion is good stress relief before nitriding. Even so, with a part like a crankshaft, 1 or 2 thou runout after nitriding would be considered acceptable.


Corrections or additions welcomed Bradley

comnoz said:

Hobot,
Well I got the same story from three different outfits who specialize in nitriding crankshafts plus it says the same thing about nitriding metal that has not been hardened in one of the articles you posted.

Stock Norton cranks are cast and not heat treated as far as I know. That type of alloy is not generally considered to be heat treatable.

Jim

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hello Jim. here is some info that may be informative.

the stock crank should be an English steel, EN16S. EN16 is a manganese-molybenum alloy of .4 carbon having good elongation. . being .4 carbon, it will respond to heat treatment. its claim to fame is the fatigue resistant properties, but tensile strength is similar to 4140, 4340 etc.

the suffix number after the EN16 refers to the heat treatment applied to commercial bar. there are 5 suffixes. R,S,T,U,V. ruling sections apply here to. R gives 850 megapascals ultimate tensile, while condition V gives1150 MPA ultimate. the stock shaft would be condition S giving 930 MPA . As there is no aluminium in this steel, , I dont know if this steel can be nitrided. my guess is the stock shaft was heat treated to 60 tons roughly, and the big end journals then induction hardened. 60 65- tons is still in the machinable range for the rest of the shaft.. my crank has heat coloring indicating induction hardening of the big end journal. this coloring is on the inside of the big end bore and can be clearly seen.

jim, are you grinding the big end journals after nitriding. one thing to be aware of is that aside from being minimal distortion, there is size growth depending on depth of case. on a 20 thou deep case, 1/2 thou on diameter would be about right. I know these may not matter, but there is size growth that may matter in some instances
respectfully yours Bradley

Bradley,
I certainly appreciate the input. This has been a learning experience for me. The nitriding firm suggested double tempering over 1000 degrees to keep the shaft straight for their process. The heat treater said they double tempered it at 1100.

I do have a heat treat oven here that I could use for some extended soak if you think it would be a good idea. It is too large to fit in my inert gas oven however.

By the way, the music is good. Jim

Bradley does what you said mean that Norton cheeks are already heat processed enough not to be an issue on the nitride distortion? IRRC there's 7 tons crank/rod area fling force on 750's at 6000.