One crankshaft rod journal is out of specs, - journal resizing question

[Bimmer525e34]

Hello, i have s52 crankshaft and one rod journal had spun bearing, it's out of manufacturer specs. (44.965) all other journals are fine (44.976+)
i want to resize for 0.25mm bearings only this defective journal and not all of them, is it correct way? if not, can you tell me why? i have this question because i see everyone is resizing every crankshaft journal even if it's not needed for other journals and why?

P.S sorry if it's a silly question, this is first time i have a deal with defective crankshaft

[jclausen]

No the correct way is to install a new rod or resize the rod end and repair the crankshaft with two tons of force on the connecting rod and bearing win the spark plug fires nothing but the best repair will work or change the crank out with a good used one and one connecting rod.

[mechanicalzen]

Because the cost difference is miniscule compared to the expense involved in removing the crankshaft, and most would replace all the bearings if doing all that work. Would be tragic to reassemble and find that another bearing or journal was on the verge of failure. only get a new crankshaft if you can find one for less than the machining cost.

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[Bimmer525e34]

Because the cost difference is miniscule compared to the expense involved in removing the crankshaft, and most would replace all the bearings if doing all that work. Would be tragic to reassemble and find that another bearing or journal was on the verge of failure. only get a new crankshaft if you can find one for less than the machining cost.

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other bearing journals are perfectly fine, we measured it and all of them are in specs.
one journal repair is very cheap compared to whole crankshaft repair.
it's very hard to find good used M54B30/S52B32 crankshaft in my country.

one rod journal repair is about 20$ equivalent in local currency
all journals repair is about 250$

[mechanicalzen]

I would machine all 6 rod journals for $120, if the rest of the car has any life left in it. Good luck...

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[Substance D]

I wouldnt go mix matching bearing, get oversized and clean up the whole crank

[digger]

do them all for consistency even if strictly speaking it will not harm anything, at some point someone will change bearings down the line and may not detect one being different.

[Matt Cramer]

do them all for consistency even if strictly speaking it will not harm anything, at some point someone will change bearings down the line and may not detect one being different.

That is my take too. You've already pulled the crank out, the other journals probably already have some wear even if they're in spec, and reusing the old bearings sounds like a classic case of false economy. Might as well get all the journals machined as a matched set even if it's an extra $100 (and ordering the bearings one at a time in individual sizes is likely to cut into the savings). This doesn't sound like a case of "I pulled the oil pan to change a rod bearing with the engine still in the car and just want to get another year out of the motor before I scrap it" sort of halfway measures.

[someguy2800]

I would just replace the entire crankshaft with a good one from an M54B30 since they are cheap. If I had to have it fixed I would have only the damaged journal ground and leave the rest of them alone. There is nothing wrong with the other journals so there is no good that can come from grinding the rest of them. Its just introducing more opportunities for something to get screwed up.

[Def]

I would just replace the entire crankshaft with a good one from an M54B30 since they are cheap. If I had to have it fixed I would have only the damaged journal ground and leave the rest of them alone. There is nothing wrong with the other journals so there is no good that can come from grinding the rest of them. Its just introducing more opportunities for something to get screwed up.

This is what I'd do. Grinding the other journals is just money spent doing nothing but hoping they don't screw up.

I guess BMWs don't have it, but I know many Japanese cranks are nitrided which gives them a very hard/strong outer layer which adds quite a bit of fatigue resistance. Grinding them usually makes them break in a higher HP application fairly quickly since the stress state goes up from reducing the area, and they lost proportionally much more of their stiffness than if everything was uniform. The harder nitride layer also helps slow crack formation/propagation.

[someguy2800]

This is what I'd do. Grinding the other journals is just money spent doing nothing but hoping they don't screw up.

I guess BMWs don't have it, but I know many Japanese cranks are nitrided which gives them a very hard/strong outer layer which adds quite a bit of fatigue resistance. Grinding them usually makes them break in a higher HP application fairly quickly since the stress state goes up from reducing the area, and they lost proportionally much more of their stiffness than if everything was uniform. The harder nitride layer also helps slow crack formation/propagation.

BMW cranks are also nitrided which is the reason I would rather replace one rather than having it ground. The nitriding is pretty amazing. I had a chunk of debri go through my #1 main bearing once that completely trashed one half of the bearing, but the crank journal was still perfect. The anti corrosion properties are pretty impressive too. I have a bunch of bmw cranks sitting on my shelf, some of which I have had for 15 years with no oil on them and they don't have even the slightest bit of corrosion on them I have one that I threw on the ground behind my shed 2 years ago and its not even rusted.