Broken N55 Crankshaft

doublespaces

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Oct 18, 2016
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Thank you to @GhassanAutomotive for sharing these photos, but it appears there has been another case of a broken crank in the N55. It seems the cast crank can't withstand certain conditions, I'm curious what happened to it.
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Dmak

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It broke at the front main bearing which it drive the chain/cams/hpfp/etc. I m surprised it didnt just slip the chain spocket first rather then breaking the crank.
 
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Bnks334

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Thank you to @GhassanAutomotive for sharing these photos, but it appears there has been another case of a broken crank in the N55. It seems the cast crank can't withstand certain conditions, I'm curious what happened to it.

This looks more like what happens when you grab the wrong gear lol. I asked Ghassan what the crank journals and main bearings looked like and he said they were fine. How do you flex and break a cast crank from power yet do 0 damage to the main bearings? The rod journal is the only one that is damaged. I am no expert just asking for genuine explanation because these pictures have already taken on a life of their own... Good driver of traffic for Ghassan but misleading to make inferences about an engine based on one instance of failure.

It's hard to tell from the pics because these cranks have bluing from the factory heat treatment but some spots near the broken rod journal look blackened from heat.

Poor castings do also happen. Sucks but what can you do.
 
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GhassanAutomotive

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Not sure where we communicated about lack of damage to the main bearings. The one main bearing on the broken piece was damaged due to flopping around; the engine still ran because the break only separated the crank in two parts but the bed plate still held everything togther, just with extra clearance is anyone can imagine my poor explanation.
 

Bnks334

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Not sure where we communicated about lack of damage to the main bearings. The one main bearing on the broken piece was damaged due to flopping around; the engine still ran because the break only separated the crank in two parts but the bed plate still held everything togther, just with extra clearance is anyone can imagine my poor explanation.

You replied to a facebook post and you just stated again that the one main bearing side looks like some light wear post failure. Rod side looks chewed up. My point being that a pre-failure crank issue would've produced more main bearing wear, no? Could've just been poor casting. Looks like it happen pretty abruptly for whatever occurred.
 

Bnks334

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Yes, apparently cars getting the OFHG services are seizing up after having the work performed for whatever reason. What does that have to do with the crank shaft though? The crankshaft isn't the cause of the failure... The broken crank is the result of other failures that cause the rods bearings to seize and stress the crank... cause/affect.
 
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Rob09msport

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I know what happened it thought it was an n54 lmao

Just joking before i get slayed I have an n54 and n55 and must admit the n55 sounds better and for stock turbo def breathes up top nice .
Anyway on topic I had a gsxr 1100 that the crank cracked in half like that and it ran as well . I think cast parts just are more prone to breaking as opposed to deforming so why wouldnt a misfire or detonation do this without destroying the bearings?
 

fmorelli

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We had problems like this on one of our GT cars ... after busting twice, we were able to determine a front oscillation/vibration issue was the problem. Forged just has more headroom for less than adequate circumstances.

Filippo
 

Turtle

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Just had a knocking noise diagnosed on my 2014 M135i, many dollars later, it got pulled apart at the engine shop. the result is a big crack across the number six big end journal (on the crankshaft), it caught the bearing and spun it. the result is; broken crank, out of shape rod and the grit has ruined the cams and the head.
just wondering if this is common with the N55s, my mechanic said that he has seen it before mostly on the 2012-2014 models.
 

Bnks334

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Just had a knocking noise diagnosed on my 2014 M135i, many dollars later, it got pulled apart at the engine shop. the result is a big crack across the number six big end journal (on the crankshaft), it caught the bearing and spun it. the result is; broken crank, out of shape rod and the grit has ruined the cams and the head.
just wondering if this is common with the N55s, my mechanic said that he has seen it before mostly on the 2012-2014 models.

Cause/effect... spun rod bearing likely like underlying cause as it likely was in the OP of this thread. Friction from the spun bearing possibly even seizing up the engine as it happens in many cases.
 

e92_n55_

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Apr 8, 2020
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Any updates on the n54 crank swap on the n55? I had no clue this was even possible šŸ˜± Its so hard to find an m235/m2 bare crankshaft for sale.
 

F87Source

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Oct 14, 2019
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Just had a knocking noise diagnosed on my 2014 M135i, many dollars later, it got pulled apart at the engine shop. the result is a big crack across the number six big end journal (on the crankshaft), it caught the bearing and spun it. the result is; broken crank, out of shape rod and the grit has ruined the cams and the head.
just wondering if this is common with the N55s, my mechanic said that he has seen it before mostly on the 2012-2014 models.
how was the maintenance on this car? Did you warm the car up properly before going hard? Did you track the car? Also did you ever do an oil filter housing gasket change?