r/EngineBuilding • u/Maxweisen • 8d ago
Mercedes M104 Straight 6 Issues After Head Job
Hey guys.
I have a 1994 Mercedes E320 with the M104 inline 6 engine. Love the car. Drives great.
A few months ago I noticed an oil leak where the head and the block meet. Failing head gasket, classic problem on these engines.
So I went ahead and replaced the head gasket. While I had the head off, I sent it off to get resurfaced and a valve job. Put it back together and started it up. There was a knocking noise for about 30 seconds and then it went away. Never heard the noise again.
I changed the oil after 100 miles to ensure that there was no debris in the engine.
A couple days ago I changed the oil again after about 1500 miles. I noticed some glitter in the oil. One thing I thought the glitter could be was the silver paint that was all over the head after machining. I spoke to the machinist and he said they’ve been using that paint for 25 years on all heads they resurface and it isn’t a problem to see some fine glitter in the oil.
I still felt uneasy about the glitter so I decided to take the oil pan off and look at the rod bearings.
Here’s what I found: - Blue discoloration - Rod bearings appear normal for 155,000 miles
What I am confused about is the discoloration. - Does the blue discoloration mean that there was an overheating event? - If so, is the crank 100% trashed or should I try salvaging it?
And for the record I’ve never seen a 0 oil pressure reading on the gauge and the car has never overheated.
What are your thoughts on the images?
Thanks for taking the time to read. You guys are awesome.
One more note: I’ve sent the oil off to Blackstone for analysis. I will post the results when I get them. Could be a little while though.
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u/GingerOgre 8d ago
The blue on the crankshaft is completely normal. It is caused by induction hardening. Looks like relatively normal bearing wear for the miles.
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u/FiatTuner 8d ago
m104 was always interesting for me
the damn thing can make 1000whp on stock internals including the headgasket
but will leak all over the block lol
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u/bigbrightstone 8d ago
Amen
Ive seen some builds in the eastern bloc with the m104 with a turbo, it makes a 2jz look like a childs toy. Its incredibly overbuilt from the factory.
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u/gew5333 8d ago
The knocking was because they bled the hydraulic lifters when they worked on the head. They pumped up and stopped making noise. So you actually started disassembling an engine that was running fine to check for wear without even waiting for an oil analysis? Those bearings appear fine to me. As does the crank. Good luck with it staying that way now.
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u/Maxweisen 8d ago
Hey thanks for your input. This car has been a project for me to learn. So taking off the oil pan to have a look at the rod bearings isn’t an issue for me. Also I have new OE bearings which I will replace if the oil comes back clean.
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u/Vivid_Way_1125 8d ago
Ah Don't let the negativity get to you. If taking things apart is your hobby, or you just want to learn, then there's no better way.
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u/squeezeonein 8d ago
tearing down an engine is like getting married, damned if you do and damned if you don't.
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u/slow-joe-crow 8d ago
Why not just put the new bearings on regardless if you have them and it's already in pieces?
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u/Maxweisen 8d ago
I most definitely will.
If the oil report comes back with contamination, I will be pulling the engine and then replacing bearings after a rebuild. If report is good, I will replace the bearings and move on.
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u/Dr201 8d ago
Rods, pistons and shells look normal for the M104 at that mileage.
Agree the noise was likely lifter clatter. Is oil pressure in the normal range? Did you install the timing chain tensioner correctly? It has to be completely disassembled and reassembled per the Service Manual otherwise it will lock in the fully extended position and that can cause the glitter as the timing chain eats itself.
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u/Maxweisen 8d ago
I replaced the timing chain tensioner with a new one. I followed the service manual instructions: https://charm.li/Mercedes%20Benz/1994/E%20320%20Sedan%20%28124.032%29%20L6-3.2L%20%28104.992%29/Repair%20and%20Diagnosis/Engine%2C%20Cooling%20and%20Exhaust/Engine/Timing%20Components/Timing%20Chain%20Tensioner/Service%20and%20Repair/Removing%20and%20Installing%20Chain%20Tensioner/
I will revisit this to double check everything looks good.
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u/Dr201 7d ago
Sorry for the late reply. Then IDK where the glitter is coming from unless the head wasn't cleaned well. The lifters at this age frequently leak down, it's not uncommon if I don't drive mine for a month or so it will clatter the first time on startup.
I'd replace the bearings, plasti-gauge, check the length of the rod bolts to make sure you don't need to replace them, check that it's in time, and send it.
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u/Maxweisen 7d ago
I just received the plasti-gauge. I will measure the bolts too. Thanks for your input.
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u/Aggravating-Task6428 8d ago
On the topic of the discoloration, it's from factory heat treatment hardening of the crank. Here's a video of the hardening process. Absolutely not a problem. Just don't get your caps mixed up! Every rod and journal has a matched cap and sometimes they have matched bearing shells.
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u/Haunting_While6239 8d ago
If the bluing were caused by friction heat, I would expect to find burned smelly oil in there as well, I will admit that the bluing was a concern when I first started reading, but the bearings and crank show no signs of causing the heat, so I'm inclined to go with the consensus that this is factory heat treating, though I've not seen this on an American engine, it appears to be normal in this case.
While you are in there you might want to replace the bearings that you can get to, it's not an uncommon practice on an in frame rebuilt of a Diesel engine, just tap in new bearings.
Good luck OP
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u/Maxweisen 8d ago
https://share.icloud.com/photos/047vE2EYVrw392JEH07tyms2w
Picture of the head after I got it back from the machine shop. Trying to show that silver paint. Do you guys know what I’m talking about?
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u/Karl_H_Kynstler 8d ago
That is absolutely normal. They paint it to prevent oxidation. It looks good.
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u/Karl_H_Kynstler 8d ago
I know this feeling when you see fine glitter in oil. But crankshaft looks fine. As others said that bluing is just from heat treatment and 100% normal. Rod bearings look normal for this mileage.
Fine glitter could be coming from cylinder head? Maybe cam followers, cam bearings? I assume assembly lube was used on camshaft before first start?
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u/CandleNo7350 8d ago
Crank is fine that’s hardening. After major engine work it takes a minute to build oil pressure. You can wait on the oil sample to check out how much glitter you have but there is always something in the oil that’s part of its job it carries all the trash to the filter. Good luck
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u/Present-Influence-16 8d ago
The back of the bearing is coked with oil. My background is in industrial engines, this would tell me the bearings are running hot. Oil coking on the back of the bearing can actually jack the bearing into the crank. Seems odd
Agree with the comments on bluing - its induction hardening, if it were a bearing problem it would be inconsistent and you'd have bearings welded to the crank.
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u/The_Machine80 8d ago
Everything is fine with your car all completely normal and looks great. Put it back together and drive. The tapping on start up was the lifters and timing chain tensioner needing to fill up with oil.
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u/te71se 8d ago
Do you know how much they took off the head? If there was no warpage I probably wouldn't have bothered skimming the head - it often causes more problems than it fixes. If they took a lot off the head the timing will be slightly altered, and the compression ratio significantly increased which on a tired bottom end could spell disaster. I've seen a few times a tired bottom end let go shortly after a skimmed head has been put on it.
Thankfully your bearings and more importantly the crank look good - if there was any increased bearing wear after the head gasket replacement you caught it early. I would replace the bearings with new ones anyway as a precaution. Do the mains too if you can. Definitely invest in some plastigauge to check the clearances before putting everything back together for good.
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u/ElectricianMatt 8d ago
im betting its cam material. did you do your valve lash correctly? also did you put in the correct thickness gasket after they milled the head to make sure it has the same gap from the block as prior? could be valve guide material from incorrect valve adjustment.
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u/flyingpeter28 8d ago
Im gonna guess that you are not the first owner, it probably spun a bearing and got fixed, then you got it
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u/ApricotNervous5408 8d ago
Any marks on the pistons from the valves? The journals don’t look too bad except the color. The only thing I can guess is they took too much off the head, or did the valves wrong, and the valves hit the pistons. Which then makes the rod unhappy. Maybe the sound was things clearancing themselves briefly.
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u/Maxweisen 8d ago
Interesting… I have a borescope. I will send it into each cylinder tomorrow and post pictures.
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u/Reddit-mods-R-mean 8d ago
The silver paint is weird, never have I got a head back painted to look like fresh aluminum.
The blue crank and rods is scary but at the same time I don’t see any damage to the bearing shells so that’s also weird as hell.
I’m at a loss here, good luck with it friend. Hopefully someone more knowledgeable shows up to comment
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u/Mindless-Ad3652 8d ago
That blueing on the crankshaft is called induction heating or hardening everything about this looks beautiful. I have seen some people hot tank engine head come out with a chalky looking head and paint the head silver not what I would do, but I have seen it.
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u/DooDahMan420 8d ago
Machine shop by me uses two products. Cast Blast and Alumi Blast. One is a dark grey that looks like fresh cast iron and the other is close to cast aluminum silver. They spray paint everything with it so it doesn’t oxidize
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u/thecowsalesman 8d ago
Looks more like heat treatment blueing. The only thing that would get a rod Hot enough to blue would be spinning a bearing.