Joined: Aug 2017 Posts: 2,748 Threads: 31
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23-05-2021, 11:46 PM
(This post was last modified: 24-05-2021, 10:16 AM by Bob Culver.
Edit Reason: expanded
)
Steves comments of considerable interest but had me a bit perplexed too. 4140 is EN19. EN40/EN40b is not equivalent but the alternative esp suited for nitriding and for consideration.
From the above if P20 is superior to EN40/EN40b (presumably same) i wonder why EN40 has become so established for nitrided cranks.
Anyone know what Phoenix use?
My interest in this stems not just from Seven experience but years of involvement with Javelins which had cranks of various forms and material and hardening process, many of which were prone to failure, some sooner than later. En12, EN 16, revised hardening, revised shape, drastically revised shape, finally nitrided .
The practice here was/is to linish after niriding but dimensions are somewhat variable. Most sources indicate a final fine grind (which adds to cost) Curious as to how Phoenix finished, esp as the journal dimensiosn are critical.
Experience has presumably increased but recondtioners here ruined many nitrided cranks by introducing grinding crarcks.
The Companion gives original cranks as 1% chrome moly so possibly EN19, 4140. 60 tsi is claimed; hard to beat.
The high performance versiosn of the Rootes 1500/1600 engine 1957-65 had EN16 sfafts, the ordinary but notably rugged models something lesser.
To recap somewhat; EN40 is specifically suited to nitriding so when it is mentioned in relation to cranks, most in the business would assume nitriding is intended. I dont know when the process became established. I vaguely recall Merlins were treated. It was certainly used for sleeve valves in WW2. If not nitriding, so without its very considerable gains in fatigue resistance, you are basically in much the same territory as were Austins. Unforged billets may be more sutable now than as available then. Any attempt to make cranks more robust often tends to stiffen the webs and concentrate bending stress in the crankpins. However if counter balanced the bending due rpm is much reduced.
Is the demand fo very high rpm high output engines expected to continue? Probably a requirment for reliable cranks for slightly raised cr and sustained but modest revs will .continue.
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I was not suggesting 4140 is the same as EN40b but it is of similar properties. P20 is very much used here in NZ as it is available in flats and plate which 4140 is not. P20 has superior stability and can be nitrided to .3mm in its supplied state after machining . It may prove wise to stress relieve before grinding and nitriding after machining.
Austin cranks were not very hard (fileable =57 Rockwell C) The Austin drawings state A2 as the material. This could be an internal material reference-maybe the same stuff as steering arms?
My experience has shown P20 nice to machine and finish.
What is important is to cut down the number of operations to finish the Billet with the view to affordability, wire cutting and water cutting give good results but are very expensive. I have had multiple quotes for 700 pounds (NZ$1400 ) just to profile the billet by waterjet.
I would comment that the prices paid for Phoenix ,Barlow etc cranks in the past leave little room for profit, having done my own cost analysis.
I think that Tony is doing due diligence on suppliers for good reason- Good luck and thanks to him.
Cheers Steve H.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
In the Companion there is some info about materials. Frint axles EN16b and cranks .35-.4C and !% Cr Mo whatever that might be to 60 tsi. EN8 is a relatively modest material. Every 10% increase raises the fatigue limit about 4%, which makes a huge difference to life if limit regularly exceeded as Seven cranks obviously do. Conversely a slight reduction (say 50 tons to 45) is very detrimental to life in cycles, as many cranks heated at the taper have proven. I have a Remax after market crank but it is cracked like all the others.The EN8 one woulds seem notably inferior to the original.
Early Javelins with a tough but not surface hardened shaft used EN12. Many lasted to 150,000 miles whereas the more exotic (defectively) surface hardened ones often went at 40,000! EN16 was used for the high performance versions of the 3 bearing 1600cc ohv Rootes motor although these were notably robust in the lesser versions and much used in racing prior the lightweight Cortina.
If Austin had beefed some parts slightly lesser materials would have done.
