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Old 09-16-2018, 11:06 AM   #1
BGarrett
 
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Default Crankshaft discoloration

I have a ďlow milesĒ engine from a wrecked Sprinter that Iím getting ready to install in my 04 T1N. The oil pan on the new engine is broken, so I pulled it off in order to replace it with my old oil pan. When I got broken oil pan off, I noticed that each crankshaft web showed some discoloration near each bearing cap, as if it had gotten hot at each bearing journal. Iíve never seen this before, and am wondering if it indicates a more serious problem. I pulled a main bearing cap and a couple of rod caps, and the bearings shells and crankshaft journals looked pretty good. My original plan was to just verify the bearing clearance with some plastigauge but the crankshaft discoloration has me concerned. Anyone seen this before?
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Old 09-16-2018, 12:00 PM   #2
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Default Re: Crankshaft discoloration

Maybe getting more history regarding the engine would be helpful. What came into my mind was the question of when the broken oil pan occurred. If the oil came out when the engine was running, the discoloration could be from heat. However, if the oil pan was broken in the accident, maybe the discoloration is due to some other reason. How long the engine was out of service after the accident could be useful information.
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Old 09-16-2018, 01:11 PM   #3
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Default Re: Crankshaft discoloration

That my friend is the evidence or action of induction hardening on production of the crankshaft.
Briefly the crank area is heated and quenched in oil ( although a plasma hardening process can also have the same) to induce a skin of harness to the crankshaft pins/journals without destroying its ductile nature, so important for crankshafts.
So in short nothing to worry about.
Advise!!!
If you are opening things up like crank/rod caps always use new bolts especially for rod and torque to spec --read important.
Dennis

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Old 09-16-2018, 01:50 PM   #4
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Default Re: Crankshaft discoloration

As Dennis says, that is completely normal, as each crank receives a hardening process.

https://www.eldec.net/applications/i...hardening.html

https://en.wikipedia.org/wiki/Induction_hardening

Cranks are subjected both to high stresses, and a very high cycle of them to boot. So creating a part with a non homologous hardness throughout allows for both toughness, resistance to fatigue failure, and high tensile strength.
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Old 09-16-2018, 10:30 PM   #5
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Default Re: Crankshaft discoloration

Whew, thatís a huge relief. I donít have any history on the engine, since it was sold to me cheap ďfor partsĒ, so I donít know how long it may have been run without oil. However, I am surprised that I havenít come across this heat treating discoloration before. I know for sure that the VW TDI engines of the same vintage donít have this crankshaft heat treating, as Iíve changed a number of low-hanging VW TDI oil pans over the years. But, I have had one VW TDI crankshaft break on me while driving down the highway, so maybe Mercedes is on to something. (I believe a bad fuel injector was the root cause of this failure). I will certainly use new rod bolts and main nuts torqued to spec on this engine. Do you by chance, have a vendor for these?
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Old 09-16-2018, 11:36 PM   #6
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Default Re: Crankshaft discoloration

Some cranks get a surface blasting or cleaning, which removes the discoloration. Almost all cranks get hardening at the journals, and fillets.
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Old 09-17-2018, 01:37 AM   #7
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Default Re: Crankshaft discoloration

Quote:
Originally Posted by BGarrett View Post
Whew, thatís a huge relief. I donít have any history on the engine, since it was sold to me cheap ďfor partsĒ, so I donít know how long it may have been run without oil. However, I am surprised that I havenít come across this heat treating discoloration before. I know for sure that the VW TDI engines of the same vintage donít have this crankshaft heat treating, as Iíve changed a number of low-hanging VW TDI oil pans over the years. But, I have had one VW TDI crankshaft break on me while driving down the highway, so maybe Mercedes is on to something. (I believe a bad fuel injector was the root cause of this failure). I will certainly use new rod bolts and main nuts torqued to spec on this engine. Do you by chance, have a vendor for these?
This is because in about 90% of ordinary engines in production the crank is a nodular cast iron unit; the most preferred OE' s due to cost and simplified production activities in producing the crankshaft. In short bringing a cheaper vehicle in sum total to the marketplace
Due to the torsional stresses on the FIVE cylinder crank it demands a forging application only! .

Consequently on production, the formation the unit being a forging it has to undergo extra production activities like the distinct evidence of hardening. That evidence of course you see on that crankshaft of yours .
Dennis
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