Mercedes Diesel Misfire After HG Replacement

[cptbarkey]

Back from your original post, you took it in for coolant in the oil, and the now retired mechanic broke the cam somewhere in his repair and was likely dishonest in the process. You do not know how long he ran it that way either unfortunately. I would still not trust his cylinder head work, and plan for that as well.

 

[JHZR2]

I'm just now seeing this thread. My condolences on the hacks who worked on your car, and broke the cam...

Personally, I would want new lifters with a new cam. It's also good practice.

I don't know what parts might be OE quality, or counterfeit junk. Hopefully someone still in the auto repair business, and familiar with classic MB's, can give some insight on that.

Yeah the Febi Bilstein is interesting for the price. Maybe German made, may be Chinese anymore.

A good used one is probably the best bet. These cars aren’t known for cam issues. The 3.5L is known for HG because they bored the block too far.

Back from your original post, you took it in for coolant in the oil, and the now retired mechanic broke the cam somewhere in his repair and was likely dishonest in the process. You do not know how long he ran it that way either unfortunately. I would still not trust his cylinder head work, and plan for that as well.

he had a machine shop do it. I don’t really have a reason to doubt his work on that, but point taken. I was in his shop today. He has 50 years of old cars, parts, etc. Even some old Ferraris in there.

Not justifying anything but knocking on wood all else is fine.

 

[mattd]

While this is an excellent find, I still go back to your leakdown results with a large volume of air into the crank case.

Change the cam and see what happens, but be aware there still may be an issue.

 

[snarl]

So with a used cam how do you know they took it out correctly?

 

[JHZR2]

So with a used cam how do you know they took it out correctly?

Because it isnt cracked???

 

[JHZR2]

While this is an excellent find, I still go back to your leakdown results with a large volume of air into the crank case.

Change the cam and see what happens, but be aware there still may be an issue.

Define large…

This has boggled me a bit too, so it’s a great point.

I’ve read some leak down is always expected.

I saw in a cold engine with a bit of oil in the cylinder 66/72 = 92% in cylinder 6. Cylinder 1 I saw 72/74 = 97%. So yes, some difference. Hopefully some operation like this didn’t wear/damage the rings too much.

There wouldn’t be stoichiometric air in the cylinder. So I’m not sure if any combustion was going on. There could be cylinder wall wash down. That’s my biggest concern.

I did note from the start that the oil smelled kind of like diesel fuel, so this would correlate.

Back from your original post, you took it in for coolant in the oil, and the now retired mechanic broke the cam somewhere in his repair and was likely dishonest in the process. You do not know how long he ran it that way either unfortunately. I would still not trust his cylinder head work, and plan for that as well.

I’ve been digging into that.

Man, not following the FSM - how many guys on this forum brag about not needing the service information for a car - look what happens when you "assume" that you know it all...

Actually, I found errata in the FSM.

Note the difference:

W126 FSM

W124 FSM

FWIW.

 

[mattd]

If it’s enough to blow oil out of the dipstick tube, I consider that large. A leak with a slight hiss audible through the fill cap would be consider small. At least in my opinion

As I previously stated, replace that cam and see what happens.

 

[JHZR2]

If it’s enough to blow oil out of the dipstick tube, I consider that large. A leak with a slight hiss audible through the fill cap would be consider small. At least in my opinion

As I previously stated, replace that cam and see what happens.

It didn’t blow oil out until I plugged the main breather. And that’s to be expected with >60 psi and the dipstick tube below the oil surface…

I assume any surface rust is a no go for a cam? There is just Chinese new and not great used thus far…

 

[Trav]

Photos of the carnage:

View attachment 229220View attachment 229221View attachment 229222View attachment 229223View attachment 229224View attachment 229225

That was the bearing that the break was under. Note the scoring.

For reference, here is bearing #7:

View attachment 229226

Should I find a new bearing too?

I have not been following the thread much, things got real busy.
Too late now and not a criticism but if you would have pulled the valve cover to check the cam timing you would have found this quickly but would have, should have, could have but didn't is how we learn, and I am still learning every day.

I suspect they tightened the cam improperly or dropped the cam and cracked it, this is super common with MB cams going back as far as time. Rough handling on the bench can cause a crack, but they are really durable and wear resistant. I wouldn't put anything from Febi in any engine, they are crap parts, if it were mine new OE if available with new lash adjusters and cam bearings shells if they are removable and not cast in.

 

[JHZR2]

I have not been following the thread much, things got real busy.
Too late now and not a criticism but if you would have pulled the valve cover to check the cam timing you would have found this quickly but would have, should have, could have but didn't is how we learn, and I am still learning every day.

I suspect they tightened the cam improperly or dropped the cam and cracked it, this is super common with MB cams going back as far as time. Rough handling on the bench can cause a crack, but they are really durable and wear resistant. I wouldn't put anything from Febi in any engine, they are crap parts, if it were mine new OE if available with new lash adjusters and cam bearings shells if they are removable and not cast in.

I think they’re cast in.

Not being argumentative, but I’m not sure if I would have seen it just from pulling the VC. I needed to turn the engine over, and I didn’t pick up on any of it until I thought I should see the valves moving when doing the borescope…

But what’s interesting/part of the learning process is this: would you, as a pro, have removed the VC as the first step? You probably would look and do things differently than I would given experience. And that thought process you have is super valuable to learn.

I think I’ll try to do OE but start it on a junkyard cam just to turn the engine by hand and then start it up. Just in case there is some other issue. Removal of the cam is a 30 min job.

Then get the whole car back to normal, and put in a new OE cam and new lifters…

 

[Trav]

I think they’re cast in.

View attachment 229711

Not being argumentative, but I’m not sure if I would have seen it just from pulling the VC. I needed to turn the engine over, and I didn’t pick up on any of it until I thought I should see the valves moving when doing the borescope…

But what’s interesting/part of the learning process is this: would you, as a pro, have removed the VC as the first step? You probably would look and do things differently than I would given experience. And that thought process you have is super valuable to learn.

I think I’ll try to do OE but start it on a junkyard cam just to turn the engine by hand and then start it up. Just in case there is some other issue. Removal of the cam is a 30 min job.

Then get the whole car back to normal, and put in a new OE cam and new lifters…

I would have removed it first after I got the low compression reading just to check the cam timing and to make sure all the valves were moving when the engine was being turned over

 

[JHZR2]

I would have removed it first after I got the low compression reading just to check the cam timing and to make sure all the valves were moving when the engine was being turned over

That’s helpful for instructing and learning.

TBH I guess I probably would have to verify timing too once I verified the IP (I have the tool I just hadn’t done it yet, and wanted to start with soaks since I was guessing the ring was the obvious issue). And, since it’s an interference engine, if it was off much it would have destroyed valves, which the borescope and all didn’t show. My logic just flowed a little different. But I’m learning…

This info is helpful. Thanks!!

 

[JHZR2]

Well, I got a “junkyard” cam today. Had a tiny bit of pitting on one lobe, and two fingernail deep rides on the same bearing that mine snapped at. Otherwise smooth.

I installed it per FSM, I realize that if you don’t go to the install subsection to specifically read the order of install, and instead install in reverse of removal, without good comprehension, it could be installed in a way to snap it. I slathered every surface in red assembly lube.

I had a bit of a time getting the cam back on the gear. From tightening it the cam timing went off around 10 degrees. Because I was going to watch with a camera and only turn by hand, I turned the engine to aid in installation.

I turned it twice over and all was perfect. The TC is new. So zero degrees off. FSM says they wear two degrees in the first 20k. We’ll see.

No breaks, no issues. And we have valves!

I feel like they are a little dirty up there, for a new clean head. But I saw the head redone and fully bare.

Some other time I’ll install the prechamber and injector, double verify IP timing, and start it back up…

There was obviously diesel wash down of cylinder 6, the oil smelled bad. The magnetic plug caught a lot of junk.

Illl run a few short intervals of cheap HDEO.

Then I’ll find a proper good used cam, and install it with new lifters and all…

 

[JHZR2]

We were able to work on it a bit after work today, despite 100 degree conditions.

Put the prechamber back in, then the glow plug. Did a compression test. Wasn’t even seeing 100psi! I had treated the cylinder with a bit of HPL EC30 a few days ago to coat the walls.

But then we cranked it again and got compression!!

Right where it should be!

Put the injector in, closed it all up, and it fired!

Drove it a few miles and seems to be ok again.

Now to re-baseline all fluids, and take it on a real drive! Probably need tires too. They’re dry rotted.

But it works!



It isn’t perfectly smooth like originally at idle, I wonder if the mounts got moved too much with the misfire. It’s smooth as glass and plenty powerful once moving.

I did find when I had the cam out, that about half the lifters move a few mm while the other half don’t. So at some point I’ll pull the junkyard cam and replace with a new cam and new lifters.

 

[Trav]

Nice one! Compression is good. Give it some time, things sometimes need a while to get things run in.

 

[Sam_Julier]

Well done! Your persistence is admirable. I’ve learned so much from this thread.

 

[JHZR2]

I knew the water was low when I picked it up. I didn’t realize it must be only water. Good thing it never froze and cracked the block!!!

I started flushing with distilled. I guess I should have have started with a hose!!

Yuck. It didn’t seem to get cleaner as we flushed. I think it’s going to need some chemical treatment.

I had some G-05 laying around, and I wanted to stop for the Olympics, so I filled it with 50/50 to help stop the corrosion.

What’s the best additive to clean this? Not sure I need a citric acid flush, I don’t have scaling and not sure I want to use it with aluminum. But I want to get this garbage clean and clear!!

 

[JHZR2]

The saga continues.

Had an excessively busy fall, so I didn’t mess with the car much. Today I went to install a decent low mileage cam I got from Latvia, with all new lifters.

I removed the junkyard cam. No issues. Put in the new lifters, lubed everything up, put on the replacement cam.

I started to tighten the cam tower bolts by hand, then started the half turn regimen by ratchet. When that felt tight, I got the torque wrench set at 18 ft-lb. When I got to bearing 4 (iirc) I tightened the next half turn, could feel the torque, and then bump! A weird jolt. I continued doing the towers per the FSM. Later I was torquing #7 to completion and, pop!



Ugh. I snapped my cam.

Twice in fact.

Unbelievable. Stupid tax for sure.

So now I’m shopping for another late model one with low mileage. I think I have a lead…

Beyond frustrating though!!

I’m trying more than anything to reconcile what I did wrong. This is the third cam install I’ve done. I haven’t snapped any others on install or removal.

I see it could be one of two things:

1) the new lifters all got dunked for a second in fresh oil just to coat all surfaces. I didn’t work them or try to purge them. Could I have gotten excess oil someplace that made them not want to give?

2) on all the other jobs, I started the loose bolts and screwed them all in at the same number of turns. This time I was a bit more casual with it, thinking that if I just started torquing together when the bolts were down at the caps, it would be ok. Maybe I got the caps sort of crooked relative to the cam (one of the two bolts was turned in more) causing a misalignment and stress even though the cam was pretty well tightened in.

I’m leaning towards #2. @Trav eo you have any thoughts on this? Im disgusted at the mistake and waste of money and time. I don’t want to let it happen again.

 

[KrisZ]

Ouch, that sucks.

I take it that the cam rests with at least one lobe pressing against the valve spring? If that’s the case, it was likely the cause of the cam not sitting all the way in the bearings before you applied the final torque.

 

[meep]

Years ago I lost the order of bearing caps while installing a crank. Granted i didn’t break it, but upon assembly, prior to dropping it back in the car, I put power to the starter and noted that the engine wouldn’t turn. After brainstorming a bit (I was 15 and this was my first rebuild that wasnt on a tecumseh) it occurred to me that I was uncertain at that step. So I separated it from the trans, put it back on the stand, flipped it over, and tried to resequence the bearings. Lesson learned - start testing to make sure it rotates and doesn’t bind while torquing down. Idk if this is a good idea from the pros or not, but it stuck with me.

Maybe it didn’t seat in the bearings, maybe the caps are out of proper sequence, perhaps a lifter was supposed to compress and didn’t, is this an interference engine?

By the way - I’m so sorry - you are doing wonderful work on an amazing classic, with less available information than say a gasser. Labor of love (or car disease, depending on perspective!)