Commando Crankshaft Porn

hobot said:

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.

Click to expand...

Gidday Mate. I will try and explain succinctly. the cheeks are cast or forged. then normalised. the stock cheeks are then heat treated to about 60 tons tensile. this is still soft enough to be machinable .it is not hard enough to need grinding.

this now is the normal condition of supply as if you bought a bar of commercial steel.

the shaft is now roughed out leaving diameters oversize

the big end journals would then be induction hardened to at least 50-55 Rockwell.

you now have a shaft that has a core strength of at least 60 tons tensile that is machinable , with big end journals that are harder then the rest of the shaft.

all diameters may now be finished machined and the big end journals ground.

As I dont know exactly what the factory does, there is a bit of speculation here on my part regarding the process. but it will not be too far wrong.
So firstly, a stock shaft is heat processed to be tough and have hard big end journals.
Secondly, for a stock shaft, the big ends are not nitrided as I think the steel is not capable of being nitrided, so nitriding is irrelevant here. all finish machining is therefore done after all heat treatment is finished therefore eliminiating distortion. have a look at the inside bore of the big end journals. u could see the heat rainbow left from induction hardening.

Jim's shaft is being made from a different grade and is another story completly.
Hope his helps explain the process Bradley

I have sliced up and tested a stock crank. It tested 48rc everywhere- cheeks, shafts and crankpins. I have not seen any sigh of post cast heat treatment. Jim

Ok, ugh, what does the above imply for Peel crank survival odds after all its faults pointed out and bent back?

hobot said:

Ok, ugh, what does the above imply for Peel crank survival odds after all its faults pointed out and bent back?

Click to expand...

That is a 6 million dollar question. You will have to let us know. Jim

So what is the maximum runout one can allow on this type of crank?
Is there the opportunity to grind true a small amount after nitriding?
My Terry Prince crank came to me with 4 thou total indicated runout. This was deemed too much by the local experts. Fotunately it is the style of crank that can be beat back to true, to some extent (press fit crank pin and main shafts)
Dan Smith and I spent the afternoon beating on it with an 8 pound lead hammer, the flywheels sitting on a thick lead plate. After many hard hits, it moved about 1/2 thou closer to true. We had it in the press up to 10 tons, no movement. Dan was afraid to go higher with the press as he had a press accident some years ago and still bears the scars. The setup in the press was somewhat unstable, pushing diagonally on the flywheels, as was necessary.
Finally he gave up on it and suggested I run it as is.
After watching his truing methods all afternoon, and realizing how to go about it, I had another go at it with the large press in my shop. It took seventeen tons to move it, and now the drive mainshaft runout is one half thou , timing side is just under one thou. I have thought about trying to reduce that further, but likely will leave well enough alone. I need to move the drive side 1/4 thou to get to zero, I could easily move it five thou by accident instead.
The bible on the subject, Paul Richardsons 1950s book, suggests that anything less than 2 thou total indicated runout is good. There seems to be a couple of ways of defining total indicated runout. Some suggest it is the greatest amount of runout measured, in the case of my flywheels, just under one thou. Others add the runout of the two mainshafts, so in this case 1/2 thou drive side and close to one thou timing side, so 1.5 thou would be the TIR using this definition. Either way it is under the magic number.

It strike me that with these billet cranks, there is less opportunity for adjustment, should the crank take a "set" as machinists say.

Glen

The hardened layer from nitriding is a very thin almost surface effect. It depends on the material having a nickel content. The biggest problem that I can see is that if the steel is 'dirty' i.e. has sulphur asnd phosphorus contents above 0.01% there can be inclusions or a 'pipe', especially in the centre of bar stock where the mainshafts might be. The usual way of detecting this is to cut a disc off the end of the bar, grind it to a fine finish, then do a 'sulphur print' using hydrochloric acid and photographic paper. I've been greatly involved in making gun barrels and rocket motors. Typically barrels are alloy steel of carbon 0.2 %, 3% nickel, 1% chromium, and the sulphur and phosphorus must be down around 0.007 % each (i.e. similar to very clean 4130). Unheattreated the material is about 70 TSI, and 90 TSI heat treated. If you can find an offcut from a large billet, it is a better way to go than using barstock, and vacuum degassed steel is better than from an arc furnace. I think that in Australia, the only easy source is Bola Steel, our own manufacture is garbage.
If I was making a billet crank, I'd find a bit of barstock which was way too large in diameter, put it in a four jaw chuck and offset it as much as possible to get away from the centre of the bar. I'd do the nitriding after grinding the journals, but a layer of chromium plating is a much better option - requires grinding twice. I had wear problems with the billet crank from my short stroke Triumph, even though I'd had it nitrided.. So I had it ground, then took it to work and had the big end journals plated in the gun barrel chromium bath which was a very good bath with low contamination. When I had it reground, the grinders said it was the best chromium they had ever seen. I used Cooper mini minor big end bearings which are a very hard grade of copper lead. After a race, the oil pressure indicator button used to stay right out for ages.
If you are in the UK somebody involved in making gun barrels will be able to help you source decent material (try a metallurgist at Woolwich Arsenal laboratories for advice if they still exist).

acotrel said:

The hardened layer from nitriding is a very thin almost surface effect. It depends on the material having a nickel content. .

Click to expand...

Is mention of nickel for nitriding your red herring for today, or a dodgy memory without checking your 'facts' ?

http://www.keytometals.com/Articles/Art117.htm

"Nitrided steels are generally medium-carbon (quenched and tempered) steels that contain strong nitride-forming elements
such as aluminum, chromium, vanadium, and molybdenum."

You really should use google to check facts BEFORE posting bad information ??

comnoz said:

I have sliced up and tested a stock crank. It tested 48rc everywhere- cheeks, shafts and crankpins. I have not seen any sigh of post cast heat treatment. Jim

Click to expand...

JIm,
I went and actually checked the data sheets and I was close in my figures but not spot on. these math are pretty close allowing for conversion of MPA to short tons and conversion of the hardness scales.

Your crank measures at 43RC.

for 4340 data sheet says 34RC= 67tons(short) tensile. 46RC = 90 tons max tensile. your shaft at 43 is at least 80 tons. plenty there.

stock shaft EN16 condition S 30RC= 65 tons. there seems a discrepancy between the EN16S data sheet and the hardnessof the standard shaft you cut up. this is a puzzle. the one you cut up seems harder by a bit. .

now, if your made shaft at 43RC and 80 tons, and the standard shaft you cut up is 48 RC there are only 5 points difference in hardness.

your made shaft at 43RC and 80 tons and factory spec shaft (EN16s) at 34 RC and 67 tons then your shaft far exceeds the standard. nitriding will give you at least 60Rc or more

just a thought that nitriding may not be necessary. Respectfully, Bradley

Rohan said:

acotrel said:

The hardened layer from nitriding is a very thin almost surface effect. It depends on the material having a nickel content. .

Click to expand...

Is mention of nickel for nitriding your red herring for today, or a dodgy memory without checking your 'facts' ?

http://www.keytometals.com/Articles/Art117.htm

"Nitrided steels are generally medium-carbon (quenched and tempered) steels that contain strong nitride-forming elements
such as aluminum, chromium, vanadium, and molybdenum."

You really should use google to check facts BEFORE posting bad information ??

Click to expand...

Rohan, Would you please nominate the steel specification and supply source of an appropriate sized billet for a Norton crank ? Also should be a manufacturer with a process which produces 'clean steel' without the sulphide inclusions. I suggest what you are talking about which gives the appropriate properties is pretty rare. The priority is core toughness, not the hardness after nitriding.

Rohan,
The grade of steel I mentioned as being used for gun barrels had about 0.1% Al, 0.2% C, 0.005% S, 0.005%P, 0.6%Mn,3% Ni, !% Cr, O.2 % Si. 0.2%V. It was pretty much the ultimate about 30 years ago. It is not even listed here:
http://www.thompsonsteelco.com/page191.html
Very close to this:
http://www.interlloy.com.au/our-product ... ing-steel/
However the carbon and manganese are higher.
and it seems common practice to not even list the aluminium contents, so what do you do if you are looking for a nitriding grade with appropriate mechanical properties ? Talk to a practicing metallurgist and forget google for a while, you are misinterpreting it.
Perhaps we need more stoichiometry ?

The balance factor will actually determine WHEN it shakes . It would be wise to have it best balanced at high / max revs , where imbalance is amplified - increaseing loadings and robbing power .
We Dont Care if your fillings fall out on the Start line .

We need to rob neuclear submarines and destroyers of their propellor shafts , fot the optimum material . :lol: :wink: before theyre melted down & turned into Hondas .

That is exactly the situation I have Matt, although at idling on the start line the bike rocks. It is quite bearable. If the imbalance happens at 7000 RPM, the situation is worse in the extreme. The relationship between revs and accelerations applied to internal components is a squared one ? So as the revs rise the forces due to imbalance are squared, not linear with respect to the revs.

The imbalance is still happening at 7000 rpm,and the maximum imbalance (thus stress) is even greater with a high balance factor.With a high balance factor,you've only caused the maximum imbalance to be in the horizontal plane,where it's less noticable to the rider (but not less noticable for the crank).

This discussion is about low alloy steels for crankshafts, not carbon steels for ship building. It happens that aluminium is added to carbon steels to deoxidise it, not to render it suitable for nitriding. It just happens that it improves the properties in that way. I suggest the reason low alloy steels can be nitrided is more about the relatively high nickel content. The aluminium content is very usually low:

'Killed steel is steel that has been completely deoxidized by the addition of an agent before casting, so that there is practically no evolution of gas during solidification. They are characterized by a high degree of chemical homogeneity and freedom from gas porosity. The steel is said to be "killed" because it will quietly solidify in the mould, with no gas bubbling out. It is marked with a "K" for identification purposes.[3]

Common deoxidizing agents include aluminium, ferrosilicon and manganese. Aluminium reacts with the dissolved gas to form aluminium oxide. Aluminium also has the added benefit of forming pin grain boundaries, which prevent grain growth during heat treatments. For steels of the same grade a killed steel will be harder than rimmed steel.'

Rohan is right about my memory, there are things about that time in my life that I had shut out. There were two deaths back in those days. One was when a group of our customers were being shown how gun barrels are made. While they were watching a worker threw a shovel load of ferro managanese into the arc furnace, and a stream of molten metal came out and killed him on the spot in front of the visitors. The other was when a worker fell backwards into a mould full of molten steel.

Does a flywheel run more smoothly (vibrate less and do less damage to bearings and supports) when it is in balance ? I suggest the additional offset weight on a racing crank is there to counteract the increase in centripetal force due to the greater accelerations of the rods, pistons, rings and gudgeons (a squared relationship) , so that at higher revs the crank is closer to being in balance. It's primary purpose is not about rider comfort. If that was a major issue all two stroke racing bikes would have rubber mounted motors. As I've said before, the most successful TZ350 Yamaha on the IOM was the Charlie Williams / Dugdale Maxton. It had a rigidly mounted motor and a schraeder valve to check for frame cracks after races. You might like to justify the silly 58% balance factor of the commando crank, however it is still wrong. It was done in an attempt to keep up with the CB750 in smoothness. I suggest the result is that if you rev a commando 750 engine as much as you can safely rev an Atlas 750 engine, you are likely to cop the hard lesson.

http://www.iomtt.com/TT-Database/Events ... de_id=4923

http://davestestsandarticles.weebly.com ... _tz350.pdf

A 53% balance factor places the least load on the crankcase and bearings at any RPM. The counterbalance weight increases at the square of the rpm just like the reciprocating forces.

Increasing or decreasing the balance factor from 53% always increases the vibrating forces regardless of RPM.

The only thing RPM has to do with balance factor is the fact that a frame and engine mounting assembly may resonate less at higher RPM if the engines plane of vibration is shifted from vertical to horizontal. Jim

Bradley,
I must say I was a bit skeptical about the need for further stress relief on my shaft. But I went ahead and recut the centers on the end of the shaft in line with the main journals. Then I ground the mains to within .25mm of finished size and the ends to within around .5mm of size. Then I put it in the oven at 260 C. for 4 hours and let it slow cool. Then I checked it and found .004in TIR.
So thanks for the advise. The shaft is back in the oven at 250 C. for another 15 hours. We will see if it moves anymore. Jim

Jim, just to clarify, the 1/16" runout afer initial heat treating became .004" after stress relief?

Glen

comnoz said:

The only thing RPM has to do with balance factor is the fact that a frame and engine mounting assembly may resonate less at higher RPM if the engines plane of vibration is shifted from vertical to horizontal. Jim

Click to expand...

That is stating, in a somewhat roundabout fashion, that frame and ancillaries and rider may well vibrate MORE at higher RPM,
with a low BF ( 53% ish), if the frame resonances are not suitable. ? !!?

In fact it was found, from the 1920s even, that BFs had to shifted above a 50ish % to higher % factors,
to shift the vibes more into the fore-aft plane as engine rpms rose,
to give the rider and cycleparts a less tortured ride....

worntorn said:

Jim, just to clarify, the 1/16" runout afer initial heat treating became .004" after stress relief?

Glen

Click to expand...

No, I had recut the center holes and reground everything true and straight. I had left plenty of metal to remove in case it warped a lot in heat treatment -which it did.

The straight shaft became .004 out after stress relief. Jim