Crankshaft grinding service (passenger car)

[carl0s]

Hi all,
I have the crank out of a BMW N57 straight-six diesel (306hp one - the one that tends to spin bearings).

5 out of 6 rod journals are rough and need a grind, number 6 might just need a polish.

Mains are all OK - might need a light polish, but main bearings were all good and not spun which is a rarity when this happens - we have been lucky and the block is safe.
I guess this means the crank is likely not bent either, since all 7 mains are good - I was going to rig up a stand and check it but probably got other things I could be doing instead.

Does anyone know of a firm that could do the work and could be trusted to do it well? It is a forged crank, and I imagine it might be nitrided or induction hardened, so I would want that back as it should be.

I have not measured the journal diameters yet but will do if I get chance this week. I measured the worst but can't remember what it was. I will measure and write down properly.

A replacement crankshaft from BMW is looking like about £1,700, and we are resigned to going for that, but I just thought I would ask here first. I have assessed the aftermarket and decided it's a no-go.

crank can be seen here:

and here:

Any thoughts / ideas?

Thanks,
Carl

 

[Memmeddu]

You can't grind 5 out of 6, it's pointless.
Grind them all and use the same size bearings on all the connecting rods
Check the block for warpage in the machine shop where the crankshaft will be machined .
They're aluminium and they are prone to get out of alignment very easily.
Remove all the plugs and clean all the internal passages.
Try to understand why it starved for oil .
And check piston rings too.
It would be a shame if after assembling all you'll find out the engine is an oil pump

 

[mr haynes]

Seem to remember Diesel Pump UK doing N57 builds.....find out who they use?

 

[carl0s]

You can't grind 5 out of 6, it's pointless.
Grind them all and use the same size bearings on all the connecting rods
Check the block for warpage in the machine shop where the crankshaft will be machined .
They're aluminium and they are prone to get out of alignment very easily.
Remove all the plugs and clean all the internal passages.
Try to understand why it starved for oil .
And check piston rings too.
It would be a shame if after assembling all you'll find out the engine is an oil pump

Yes I did think that about grinding all to the same size.

I am going to thoroughly clean and check everything, although I wasn't going to bother checking block for straightness given that the mains are all OK, but I suppose I can do.

It was neglected of oil changes and the oil was congealed like jelly. This is why I think it failed.

 

[minimutly]

If the be has spun, you need to check the piston and gudgeon pin (no need to say the rod is scrap).

 

[dave h 2]

Yes I did think that about grinding all to the same size.

I am going to thoroughly clean and check everything, although I wasn't going to bother checking block for straightness given that the mains are all OK, but I suppose I can do.

It was neglected of oil changes and the oil was congealed like jelly. This is why I think it failed.

Did think about it????? bearings come in sets so to save one bearing you spend on an extra full bearing set.

I've seen 2 jellied oil motors, a Triumph PI motor where the springs were invisible due to jellied oil, stank of petrol and needed each plug blow lamping for 5 minutes to clean them before it would run. The choke may have been a good place to hang a handbag.
The other was a sb chevy with a cracked block like a road map, the sump on that one was full of set oil.

I'm not convinced you can get a nitrided crank ground and then redone without it cracking. It's also possible that the crank may be cracked already, make sure the grinder crack tests it.

 

[carl0s]

Did think about it????? bearings come in sets so to save one bearing you spend on an extra full bearing set.

LOL, calm down. What I meant was "it had crossed my mind that it might make sense to get them all done the same if I do have a regrind".

BTW Autodoc sell the Glyco big end bearings in pairs and same for BMW OEM.

As I said at the beginning, I am mostly convinced that a new crankshaft is the way to go but just wanted to discuss it a bit. Not in a great rush on this job. Father in law (it's his daughter's car!) keeps pushing me to send to a machine shop to have crank inspected and ground etc but I keep saying I think I'm just gonna buy new and don't want to risk a less-than-new oem-quality crank.

 

[bricol]

Recommendation for nitrided Lancia cranks was not to regrind. More than likely go through the layer. Might get away with it, might not. More than likely to fail again.

 

[Anguz]

how much for engine from a scrappy?

 

[carl0s]

£4500 upwards for working ones that would still need a strip down.

 

[oldbikedavey]

You might do a lot worse than give Gosnays Engineering in Romford a call.
If it can be done, they can certainly do it.

 

[Memmeddu]

£4500 upwards for working ones that would still need a strip down.

Buy an entire donator car if you can.
Anyways we do grind BMW crankshafts at work.
I'm enough confident to say that we work mostly on BMW's engines.
We do Caterpillar, Kubota, Tohatsu, Iveco, Penta Volvo, Mercedes, crankshafts and engine blocks mostly , those are heavy diesel engines.
About car engines we do a good 80% BMW's (drift school nearby and Mini's), the remainings are Fiat multijet and JTD's and a lot of Suzuki's (1000cc ) , Mitsubishi's and Subaru WRX's
The rest of the engine machining are just head and block skim .
I'm not a motorist, I mostly work on the milling machine and on the lathe so I'm not sure about codes but I'm sure that it's possible to save your engine.
We do a lot of Fiat 110's and 126's engines too for racing applications

 

[Erie Fred]

Recommendation for nitrided Lancia cranks was not to regrind. More than likely go through the layer. Might get away with it, might not. More than likely to fail again.

IIRC there are shops that can nitride after grind.

 

[bert]

I can't suggest anyone near you but any engine reconditioning should be able to either grind or get it ground. It's pretty normal for competition engines and have them nitrided once ground

 

[MetalMonkey]

I've not used them personally, but Ivor Searle are a big outfit that do a lot of rebuilds and I believe crank regrinds.

 

[Popcorn]

Park Engineering in Malton

Park Engineering | Engine Reconditioning Specialists | Yorkshire

Welcome to Park Engineering, the region’s leading independent engine reconditioning company. Based in Malton, North Yorkshire.

www.enginereconditioninginyorks.co.uk

 

[Trevorleach]

I've not used them personally, but Ivor Searle are a big outfit that do a lot of rebuilds and I believe crank regrinds.

Seen many of their recon engines fail, some before they even left the workshop!

 

[bricol]

Much published photo of a reground Lancia crank showing the micro-cracks formed in the nitrided layer:

As an engineer, I wouldn't hesitate to specify nitriding for a new component . . . re-nitriding something that won't cost personally cost me money (ie for work) I'd think carefully about . . . for something I've invested my time and money in, I'd buy a new one.

 

[steveo3002]

Seen many of their recon engines fail, some before they even left the workshop!

was thinking the same , they talk it up but read between the lines they sound like bandits

 

[8ob]

As I said at the beginning, I am mostly convinced that a new crankshaft is the way to go but just wanted to discuss it a bit. Not in a great rush on this job. Father in law (it's his daughter's car!) keeps pushing me to send to a machine shop to have crank inspected and ground etc but I keep saying I think I'm just gonna buy new and don't want to risk a less-than-new oem-quality crank.

I wouldn't discount aftermarket, a lot of them would be made for OEM and wont be carrying the price tag.
As for engine re conditioners, worth wandering around the workshops and checkout the footwear, if they are in sandals/flipflops run.

Bob