Crankshaft re-grinding of a different kind.....any ideas???

[Brett]

Ok guys this is a long shot. I'm after a specialist that can weld/thermal spray and regrind the journals on a couple of crankshafts I have. This is not to repair a dodgy crankshaft but to add material to them so I can offset grind them and re-stroke the cranks to a smaller stroke. I have a very good engineering shop just outside our village which can do pretty much all my machining work to re best of standards but I'd prefere for this to be done by one person to save hassle. I know of shops in the states that do it but I don't fancy sending my stuff across there tbh. The cranks are made from EN40B and EN16T steel.

Any help or ideas will be great :approve:

 

[rustedandrotten]

Try John Noble in Chesterfield as he has done loads of strokers over the years Inc en 40b s cranks, he used to use Beckitt & Garners, other option is to get a bespoke crank from Gordon Allen billet en40b, much stronger as plasma deposits can be porous and spall, sounds like a mini motor on the build, 1500+cc?? Metro Turbo block cheat!? :approve:

 

[Brett]

Haha Your nearlly there Simon. I'm going the other way to 1500+. I'm going sub 1000cc. I'm looking at £1500+vat for an Arrow crank but its a lot of money to push past the 9500-10500rpm mark on a regular basis. I'm thinking of going 998 A+ with over bore and less stroke which I know can sit at 9000 most of the day. I'm aiming for 120+hp with the use of a crossflow head.

Does John Noble have a website Simon. I know what I want to do can be seen as not quite the best way to do it right but cranks are classed as disposable when dealing with these revs in my opinion. Once my first season is out the way I shall be tracking a genuine 970s to make the real deal.

 

[Matt]

http://www.noblemotorsport.co.uk

Only down the road from me mate if you needed me to go in for you. Good guys there that certainly know their stuff as Simon says.

 

[rustedandrotten]

Ok, in Rome at the minute but back mid week, will speak to John when I get back, in the meantime what stroke are we looking at as short stroker motors are easier and I might be able to find some Shardlow blanks that could fit the bill.

 

[Matt]

Simon, do you know if they service Atoms at noble?

 

[rustedandrotten]

Would imagine that it would not be a problem as they are Caterham and Noble approved amongst many others some of the best engineers you will meet (not a fitter to be seen!) Again will ask when I ring John.

 

[Matt]

Thanks pal. :approve:

 

[Brett]

http://www.noblemotorsport.co.uk

Only down the road from me mate if you needed me to go in for you. Good guys there that certainly know their stuff as Simon says.

Thanks Matt I will give them a buzz tomorrow mate :approve: There are certainly very few shops that are prepared to even consider this process. I just rather go by word of mouth recommendations instead of handing cash over to a chancer.

Simon a 61.9mm stroke or less with 1275 main bearing dimensions will be preferable but thats a hard to find part! As it stands I'd like to short stroke a not so special 998 purely as if it goes wrong, it will cost peanuts to replace compared to original Cooper S parts. So I'm wanting to offset gind one way beyond 76.2mm. Ill drop you a pm fella.

 

[rustedandrotten]

Ok,see where you are going,you obviously realise that plasma cannot be nitrided and due to stress can be unstable,normally only used for a couple of millimetres before the stress breaks the weld bond, particularly when grinding.

 

[Spike]

Brett, slow getting in here,
I am just having a quote done for a ducati crank at the mo, i would be happy to ask them about your job.
A consideration for you is to possibly undergrind the crank but offset it negative and use a rod with a smaller big end, if you are spinning to 9000 rpm you must be looking at a custom rod, if so from where as i may be able to help there also.
The secret to success with building the crank up is the temp and time it takes to cool, i think due to the amount of cranks that are done in the USA the oven time is much longer there, we seem to rush things with disasterous results.
I would be happy to help.

 

[Brett]

Thanks Spike.

The under cut option is by far the easiest and one that is done on a regular basis with these engines. Its made easy by there being two different off the shelf big end bearing sizes. Unfortunatly the size crank that i want to use doesnt have that option. Reason being by the time you do offset grind the journal it would have so little material left on one side it wouldnt be safe past 5k let alone 9. Hence why i want to add more meat to the journal. I can get away with using oe Cooper S rods at the 9krpm limit as they are very well made. There are loads of off the shelf H section rods though from the likes of Arrow, Cosworth, Seinz etc etc. All of which should be good for 12krpm.
The temperature management is exactly the problem im having in the uk! I know of two shops in the states that can machine weld up to 7mm extra material to both en16t and en40b cranks and only allow the surrounding areas get up around 170*c thus not effecting any of the crucial temping. The crank will need re tuftriding but only to add life to the bearing face.

 

[Spike]

Brett,
The process i know of is submerge weld the crank, then oven at around 900 deg (i may be out on the temp but cherry red ) for 48 hours to de stress the whole assembly, it seems its the lack of flexibility in the weld that gives the problem.

 

[rustedandrotten]

This is a more than interesting problem, EN40B is a forging steel that is used for items that need to be nitrided to achieve a high degree of hardness and surface compression, this means that it is resistant to wear and has good properties when flexing to not allow crack propagation, just what you need in a crank. Also as it is a forging steel it is hammered from bar stock to the required shape and the ductile working of the forging defines the structure of the crystallography of the metal, the stress lines 'flow' through the crank creating immense strength compared with the brittle crystal structure of cast iron.
Welding is just a glorified casting process and will never have the strength of properly wrought/forged steel. You cannot weld more EN40B to an item so you will have an inferior, hybrid journal, made worse by the fact that it is not a perfect geometry but off centre so nitriding will not be an option. if you are cooking at cherry red you will indeeed stress relieve the crank but you will also remove all the beneficial stress that the forging process has built into the crank.

Very careful! this is reason I used to use forgrd billet EN40B to machine cranks from, not perfect but pretty indestructible!

Simon

 

[Brett]

Spike, i cant remember the name of the machine these two companies use but the part is constantly sprayed with some type of solution whilst the weld is being applied. I'm not 100% sure what the crank undergoes after that process either. I was very much against this process and completly turned my nose up at it as ive never seen it done in this country. They assure me that because it is not a repair process where by you are trying to fix a weak link ie add strength to a crack or the like, it works perfectly given time. The extra material is used only as a surface for the bearing/shell face.
Like you say Simon, the grain of a forged EN40B crank is one of its big advantages. Its one of the reasons ive never been a fan of billet cranks machined down by a big bit of steel. Im with you on the fact that it could be very silly to do this process with an EN40B specced crank. Especially given how special the OeM stuff was that was built by Rolls Royce. If i can short stroke a cheaper and lesser EN16T crank using this process then it sort of makes it a more practicle process.
Let me know if you can get hold of any blanks Simon at not too silly money. Its my prefered route but money is the issue as i want it to be cheap(ish) to fix or replace.

Thanks guys

 

[Fred]

I've got a trade account with Arrow