Crankshaft usable or not?

[Oldskoolbaby]

I have a rather nice Cooper S crank on a shelf that has a very very small amount of damage/pitting on number 4 big end facing toward the middle. The mains have been ground +.030 but unfortunately the ends are at +.040. Am I looking at a scrap crank or is it reusable? If I could get +.050 bearing I wouldnt be too fussed. Any suggestions guys? I used to throw stuff like this in the skip but am hesitant these days.

[Spider]

0.060" Undersize bearings are available, but I don't have a listing for 0.050" for the Big Ends.

0.040" are available of course for the Mains.

Be aware that at those sizes, the Nitriding that was originally applied has gone, it's only around 0.012 - 0.015" deep at the very best.

While the crank is well undersize, for a street car it will be fine, but not something you'd want to take to the track with.

[rich@minispares.com]

but I don't have a listing for 0.050" for the Big Ends.

you can/could get 50 thou big ends, as I have a set in my collection, but they are really rare - 60 thou are quite easy and common to find.

the biggest that they ever did was 80 thou, those muthas are REALLY fat!

[Spider]

Yeah, I have seen the 0.080's. They should just say 2 mm!

[mikep]

I have a rather nice Cooper S crank on a shelf that has a very very small amount of damage/pitting on number 4 big end facing toward the middle. The mains have been ground +.030 but unfortunately the ends are at +.040. Am I looking at a scrap crank or is it reusable? If I could get +.050 bearing I wouldnt be too fussed. Any suggestions guys? I used to throw stuff like this in the skip but am hesitant these days.

Have had many cranks that have run journals repaired by submerged arc welding, mind these are a bit bigger than mini cranks but principle must be the same so phone around and ask.

[abri]

Cut it and have it re-nitrided. The crank may bend slightly from stress release due to heat, but good engineering places can straighten it. Then have it crack tested, polished and assemble. I did exactly that recently on one of my S cranks.

[Oldskoolbaby]

Cut it and have it re-nitrided. The crank may bend slightly from stress release due to heat, but good engineering places can straighten it. Then have it crack tested, polished and assemble. I did exactly that recently on one of my S cranks.

Tbh, this is exactly what im planning on doing.

[Rich997]

Interested in the comment made by abri re. Straightening crankshafts

I believe you can recover a warped crank with a particular type of grinder (adjustable offset) but thought this was rarely seen nowadays.

Does anyone know who might be able to sort out such a problem?

Ideally in North West area

[abri]

Rich 997, my crank was warped by 3 thou on the center main and about 1 thou on the front one. The engineering place used a cold press method to straighten it. I asked them specifically if they used heat and they said no, just press. Crack tested it afterwards and it was ok. That doesn't help you however as mine was done here in Cape Town, South Africa.

[mk1]

Most decent engineering shops should be able to straighten a bent crank. I have only heard of it being done with a big press like Abri says.

M

[Spider]

Most decent engineering shops should be able to straighten a bent crank. I have only heard of it being done with a big press like Abri says.

M

That does seem to the the most common way. I had one once 'stress relived' following Nitriding, it was done by grinding the 'right places' on the crank. It was scrap after that.

[mk1]

I had one once 'stress relived' following Nitriding, it was done by grinding the 'right places' on the crank. It was scrap after that.

Sounds like an invaluable exercise

[Spider]

I had one once 'stress relived' following Nitriding, it was done by grinding the 'right places' on the crank. It was scrap after that.

Sounds like an invaluable exercise

It was a very long time ago.

We live and we learn!

And I did say 'once'.

[251 ENG]

With EN 40B competition cranks the correct method is grind crank to correct any damage to journals , fillets and thrust faces etc . Then nitride heat treat and then finish grind .

The crank will then be straight .

Most people don,t do this because it is difficult and slow to grind after heat treatment because the crank is so hard .

When you do it this way you just have to " kiss " the thrust faces and radi which saves damage to the grinding wheel .

[Supersonic]

I have a question to ask? Why would you not build a engine using a new design crankshaft? A friend has built a new engine using an EN40B DC5 crankshaft, H-beam steel con-rod set, billet piston set and flywheel assembly balanced from Swiftune. It runs as smooth as a baby’s bum for being 86 mm stroke and is one powerful engine. This set-up is light years ahead of original S type engines.

[Oldskoolbaby]

I have a question to ask? Why would you not build a engine using a new design crankshaft? A friend has built a new engine using an EN40B DC5 crankshaft, H-beam steel con-rod set, billet piston set and flywheel assembly balanced from Swiftune. It runs as smooth as a baby’s bum for being 86 mm stroke and is one powerful engine. This set-up is light years ahead of original S type engines.

Lets face it, that is a HUGE ammount of money to throw at an A seires. Especially after factoring the price of an 8 port build on top.

So as it stands, my crank is +.040 with a very very fine bit of damage. Not ideal but cest la vie. If i regrind it +0.050 to remove the said damage, then nitride the crank and finally regrind to +0.060 using shells from Minispares I'll have a very much usable crank once again?

[251 ENG]

DC5 kit from Swiftune is £3988

Minispares are listing new EN 40B forged cranks in latest MCR mag at £1638.

[Spider]

With EN 40B competition cranks the correct method is grind crank to correct any damage to journals , fillets and thrust faces etc . Then nitride heat treat and then finish grind .

The crank will then be straight .

Most people don,t do this because it is difficult and slow to grind after heat treatment because the crank is so hard .

When you do it this way you just have to " kiss " the thrust faces and radi which saves damage to the grinding wheel .

Yes, when I have had them done subsequently, that's how I've asked for it to be done. There are a few shops about though who grind it to a few 10's of a thou undersize and then have them Nitrided, that first shop I went to many moons ago seemed to be of that school.

[Supersonic]

I have a question to ask? Why would you not build a engine using a new design crankshaft? A friend has built a new engine using an EN40B DC5 crankshaft, H-beam steel con-rod set, billet piston set and flywheel assembly balanced from Swiftune. It runs as smooth as a baby’s bum for being 86 mm stroke and is one powerful engine. This set-up is light years ahead of original S type engines.

Lets face it, that is a HUGE ammount of money to throw at an A seires. Especially after factoring the price of an 8 port build on top.

So as it stands, my crank is +.040 with a very very fine bit of damage. Not ideal but cest la vie. If i regrind it +0.050 to remove the said damage, then nitride the crank and finally regrind to +0.060 using shells from Minispares I'll have a very much usable crank once again?

I do appreciate the high cost but they are something else and the car I refer to runs a 5-port cylinder head. I remember an old friend saying years ago that once a EN40B crank is taken below -0010 a 1300 GT crank and rods are a better option. I raced with the 1300 GT cranks with 8-ports heads and never had a bottom end failure. My problem was always gearbox related

[Oldskoolbaby]

To be honest, if this was a 1275 crank sitting infront of me then I'd not think twice of getting something else. Unfortunatly it a 970s so I'd like to keep a usable spare sitting on the bench. The problem with spending out on all new custom parts is at what point do you stop and maintain some sort of period modifications.