The chance of new crankshafts and rod etc

[Paul N-M]

Hi Tony,
Is 722M24 not generally available then? I thought this was widely available and commonly used for crankshafts machined from billets. 
This is meant to be the same as EN40b as far as I am aware.

I'd appreciate comments on this from those in the know.

Paul N-M

[Stuart Giles]

Using EN40B for crankshafts (less memorably called 722M24 in the more recent British Standard) seems to be a UK thing.

With a view to getting a crank made, I was talking to a USA manufacturer of custom crankshafts a couple of years ago; All their products were machined from 4340 material -which we would know as EN24T, that also happens to be the material used to make the billet conrods by Phoenix etc. Having said all that, the nitriding is supposed to increase fatigue strength so I have always gone for Nitrided cranks for the couple of one offs I've had made for old motors until now.

The fatigue strength imparted by nitriding is probably less important on modern engine crankshafts because they always have multiple main bearings and large diameter and narrow (by old motor standards) journals along which along with their short strokes have an inherent high degree of beam strength and torsional rigidity.

[Tony Betts]

interesting stuart.

we had taken into account modern cars having more jernals, also a smaller throw. and staggered jernal cranks.

here are the materials we were offered.

ASTM 4340 used for, engineering structual. used as require good toughness. high strength. as well as the important conditioning of large size. heavy machinery such as high load of axial, turbineshaft. larger than 250mm helicoptor rotor shaft. turbojet engineshaft, blade. high load of transmission parts. fasteners of the crankshaft, gear etc.

OR.

ASTM 4140 used for, many applications as forgings for the aerospace and oil and gas industries. a myriad of uses in automotive, agricultural and other defence industries, typical uses are forged gears and shafts, spindles. fixtures, jigs, and collars.

thanks tony

[Charles P]

If I was to make a crank at home (as you do) I'd probably use 4340 (EN24T)
I know of one A7 crank made "at home" from a slab of this and it's fine 25 years later

c

[phillips]

Hi Tony. I will be looking to build up a new engine this coming winter, and if you do go ahead, I will be in the market for a new crank, metric or imperial, you will not see the crank, anyway. S&P

[Tony Betts]

hi stuart,

as ive called a hault on them for now, i wouldnt be able to get them in in that time. sorry.

although they are made overseas, we have to go through all the stages of manufacture. as we are trading with higher quality companies.

so if i accepted the material spec, and signed my lifes savings and some dept. to intent of manufacture.

the company has all the blueprints, and although i pay nothing up front. they would make the forging tool. machine it. and send me a sample. the thing that makes a large saving, is that things are really and truelly put on a slow boat from china. which means id get a sample around christmas time

quick costs ALOT OF MONEY.

if the sample is good, i sign that i accept it, and they go into manufacture. this may take another 90 days, if there is no further corona virus. and a further 90 days delivery.

the finished item is then quality checked in the uk against what we agreed to. and I signed for if ok. rejected if not.

and finally sent out to me. when i have to pay.

i put this on the forum before that a friend has hanging in his office.

you are welcome to pick two of the following three.

quality, fast and cheap.

if you picked quality and fast, IT WONT BE CHEAP.
if you picked fast and cheap, YOU WONT GET ANY QUALITY.
if you picked quality and cheap, IT WONT BE FAST.

needless to say we pick option three

tony.

[Bob Culver]

The recent manufacture crank which failed; was it of a steel suited to nitriding, heat treated correctly, nitrided, never dropped on end? The vagaries inside a racing motor are considerable. With stresses going up as the square of revs a burst of astronomic revs, esp with closed throttle, could start a crack which in a racing engine could proceed rapidly.
The merit of Phoenix cf original seems to be primarily that they are nitrided. Other replacements like Remax seem much as the originals.
Any basic text on metal fatigue points out for complex shapes the potentially huge gains in fatigue life by processes which place vital areas in compression; ie rolling as moderns, and nitriding. For complex shapes the gains for nitriding far exceed an extra 10 tsi or so in strength. AS EN40B is especially suited to nitriding its use has become legendary. If not nitrided other ht steels would be comparable but likely little better than the original.
I dont know about the latest but in the 70s and 80s many cars used cast malleable iron cranks of modest tsi but, as above, these were adequately supported. And not 1 5/16
(A colleague here has just had turned from a billet a new crank for a 4 cyl 2 brg flat four Jowett 10. All cranks traceable in the world were broken or cracked to a lesser or greater extent (mostly the latter!) The orig crank is very modest,  short, and the centre two big ends share a crankpin. All done by a keen home engineer with a bigger lathe, more spare time, and more skill than me!).

[Tony Betts]

sorry bob,

much of that was jibberish or yidish to me.

i have a better knowledge than most, learnt through actually doing it. and working with companies that are experts in there field and learning from them.  rather than reading the correct blurb from a book. learning nothing but how to repeat it.

after that if im not sure, i ask experts with more knowledge than me. and learn from what im told.

and i retain my knowledge of things well.

so unless you use laymans terms, im lost.  as most of the forum will be.

are you saying only EN40b should be used.

tony

[Bob Culver]

Sorry Tony
Here is a translation
Cranks fail from fatigue. In general the higher the final as finished tensile strength in tons per square inch (tsi) the greater the resistance to fatigue. But for complex shapes processes which place the surface layer in compression have a further greater effect. ie shot peening. On modern cars the fillets are rolled. Nitriding another method. The absorbed nitrogen compresses the surface layer.The effect of the latter on fatigue life is very considerable. But only a few steels are ideally suited to nitriding. EN40b is one. Hence its wide use for high performance cranks, and so its legendary status. If not to be nitrided no gain over other steels of same finished strength. But nitriding is very advantageous.
Most basic texts on metal fatigue include a graph comparing life of nitrided items with others. The gain is considerable and presumably expalins the success of Phoenix.
I am not trying to interfere but seems to me the basic decison is to adopt nitrided or not. Most else follows

[Tony Betts]

thank you bob,

thats alot clearer for me.

the tensile strenths will then be close on all three 655, 670, and 680 on en40b.

but it doent help the ignorance of expecting cranks to be made on en40b.

tony