Some ideas on a OM617 Knocking/Tapping/Nailing?
 

Here's the story so far:
The car in question is a 1982 300D, has around 200k+ on the clock.

I bought the car with "low oil pressure", turns out it had a bad turbo drain seal and dumped the oil on the PO and they drove it home and possible around more with "low oil pressure"

I put oil in it and it has excellent oil pressure, so I drove it home.
Fixed the turbo drain so it stopped barfing oil everywhere.

It drives great, except has a different sound that my other 82 with the same engine, and my now sold '80 300SD with the same engine

It has a metallic tappy knock type sound you can sortof hear in this video:
https://youtu.be/zzLLIDDYk4o
I'll get one of it warmed up soon.

The car has excellent power above about 1500-1800rpm, a little flat and shaky under that, idles kinda lopey when its warmed up.

Heres what I've done so far:
Adjusted valves twice.
Replaced injectors with a known good set (out of my other car, new crush washer heat shield thingys)
Replaced glow plugs with new Bosch duratherm or whatever they're called.
Fixed turbo oil leak.
Checked compression with cold engine (350psi ~10psi on every cylinder)
Ran on a straight can of seafoam
Biobor treated the tank
New fuel filter (and tank strainer)
New air filter
New oil and filter
Flushed nasty green coolant out and replaced with proper kind
Center driveshaft bearing
Flex discs
probably more other unrelated stuff

Notable things to mention:
It was driven for a while with very low/no oil pressure
The Camshaft has some wear on a couple lobes (see attached picture for an example of one)
The car idles rougher, shaking around in the engine bay and knocks louder once its warmed up
It uses no oil or coolant, or negligible amounts
I have a brand new gold rack damper pin bolt thingy in case that is the cause of the lopey idle, but I feel the sound and idle may actually be related


I'm planning on digging into this shortly, and I'd like some ideas on starting points.

is that cam wear definitely going to cause a problem? its not huge but still there is a noticeable lip that will catch your fingernail at least several thousandths of wear.

I may have a spare cam (haven't torn engine down to inspect it, its been in my garage for a few years now) I could drop that in depending on how difficult it'll be/likely that is a cause

Thanks for your help!!

It's very interesting that you posted this thread. I had logged in to post a similar one regarding my '86 SDL (OM603 engine).In my case, the car sat for years and has been getting slowly brought back to life. Not a whole lot of info on the history.

One issue I've been chasing has been an irritating nailing and intermittent soft-miss at idle when the engine is hot. Very similar to yours, with a couple of exceptions - my cam isn't worn and I don't have any reason to believe the car was run with low oil pressure. Otherwise we're in the same boat - known-good injectors, new glow plugs, inspected prechambers, balanced compression (350-360-350-350-360-340), etc.

Mine starts extremely easily, even in the cold weather, and idles smooth until it's warmed up. As the temp starts coming up, so does the nailing, followed by the soft-miss at idle. Anything over 900 RPM and it's smooth as glass. No shortage of power and my 0-60 time is ~12 secs - right about where it should be. Just that irritating nailing and soft-miss.

Very interested to see where this thread goes. We've both kind of tried the same things and are at the same point with a very similar problem, but on different engines (617 vs 603).

I think you've found your problem. That definitely needs to be fixed with a new cam.

I'd suspect the delivery valves in your case. I would install fresh springs, copper washers, and O-rings in all six. Note the special tool required and the special torque procedure: Torque to 30 Nm and release; torque to 30 Nm and release; torque to 30 Nm, and then torque to 35 Nm and install lock-down tab.

I was doing some reading last night after posting and largely came to the same conclusion. I did the DV's on the previous 2 IP's I had on the car (both duds) and decided to skip it on this one just to rule out a variable. Used IP, no weeping diesel on the top plate, but who knows, perhaps someone changed the O-rings in the past and reused the crush washers. I think this will be my next step. New washers, O-rings, and springs. We'll see.

I agree with needing the cam replaced, but would that cause the detonation/knock issue he's having? I'd buy it running rough as a result of that, but the knock is usually a symptom of timing, unless it's something mechanical :(

I have purchased a couple cars with knocking sounds just like yours, and it has always been a bad wrist pin, rod bearing, or even vacuum pump (any of which could be caused by running with little or no oil pressure). Your cam looks suspect, so I would do the easiest thing first by replacing it AND the followers. A wrist pin or rod is a different story, but let's hope either one is not the source of the noise.

I'll see about swapping the good cam I have in sometime soon as that's likely an issue.

A few more notes:
We've driven the car as-is for probably somewhere between 3-5k miles and it has not changed at all. not gotten worse, not changed at all, which makes me inclined to believe its not something catastrophic coming apart or anything.

after I got the grey car put back together I decided to investigate the blue cars knocking before continuing to drive it, and havent driven it in several months waiting to get freed up enough to look into it.

I have been suspicious of the vacuum pump, but it produces vacuum as expected and seems ok.
I may pull it off just to ensure its not destroying stuff behind it.

If replacing the cam doesn't solve it, I guess I'll be digging in further.
it did have some oil, but maybe only a quart or two at most, none on the dipstick, as it took nearly a full gallon to get it back up into the notches on the dipstick. so I'm hoping the bottom end is largely undamaged.

Its sounds like what my vacuum pump sounded like went when it went south , this will be your easist fix so I would check it first .Its very sensitive to oil and what I was hearing (exactly the same sound) was the tappet of the vacuum pump rolling along the ride that creates vacuum without the bearings.The casing that those tinney tiny bearings are encased in are of a hardened plastic ,it would not take long with no oil to seize the bearing for failure .If you ask what happens to the bearings? they end up in the oil pan ,12 , along with the mangled casing ,all to be found once the pan is off. Consider it a fishing expedition without the fish ,just minnoes.

Or worse yet. it causes the timing chain to jump time and then break the cam, chain and other parts. If you find the pump bearing to be bad, it will take out the "roller coaster" or cam that the pump arm bearing rides on. It may need to be replaced as well.

It seemed fine ,that is the roller coaster piece ,the piece that lost the battle was the tappet ,it had a nice groove being made ,if driven another few weeks it would have surely sent those parts into the chain.My guess would be 140 miles I had put on it till I got back from my road trip ,it still made vacuum so dont feel that its not the culpreit because of this sign.Their is some detail also to be aware of on the vac pump , the allen bolts ,when pulling the unit it will give you false hope that you can use a socket on all the bolts ,the clearance on a few will only allow for the L shaped allen due to clearance.

Good to know, that'll certainly be easier than swapping the cam, which will likely still get swapped out due to the wear, and my spare engine has a good cam with no odd wear patterns, but that's a big job from the look of it.

I can probably at least remove the vac pump today. it does still make vacuum, but who knows about the bearings like you said.

the car has such good power, better than any om617 I've driven until I put the 4 speed and new turbo into the grey car.

the rough idle is probably the cam or rack damper bolt, which I should be able to swap out today.

Thanks for all the ideas guys! I'll try to get some stuff done on it today and see what I find and let you know!

I wonder that bad camshaft lobes could make such a sound. People on a classic Mopar site I visit often fail cam lobes during startup, due to high-lift cams w/ high spring pressures, plus the low-zinc oil today. Those failed lobes look much worse than yours, yet people report no significant noise. Of course, those cams ride down in the block (push-rods). I had a failed OHC once (Dodge 2.5L) when a drive service delivered the car cross-country w/ oil light on and 1 qt of oil left in the pan (did oil change & left drain plug loose, clueless driver). It made just a slight tapping sound, and the lobes were very worn. Indeed, the ridge you speak of appears to be in the axial direction. If true, that could be just normal wear from where the follower doesn't touch the lobe. The path the follower rides looks smooth.

As post 11, I had the vacuum pump follower bearing failure a year or so ago in my 1985 300D. My son only drove ~100 miles from when he heard the noise begin, but the follower arm was cut half thru by dragging on the roller-coaster. A little more and all that would have slid into the timing chain!!! I still had good vacuum, and couldn't pin-point the noise, but removed the pump to see. It was a tapping sound you could hear in the cabin.

I took the pump off yesterday, the bearings were OK but not good if that makes any sense.

They were all there and in decent shape but the follower piece was extremely hard to turn with my fingers.

Interestingly the pump has no markings, no part numbers, nothing to identify where it came from.

I pulled the pump off my spare motor which after a good cleaning could see it was an OEM Mercedes and had pierburg logos, and the bearings were also nice and tight, no discernable play anywhere, but extremely easy to spin the follower.

I put this pump back on the car, and it's hard to tell but the sound still appears to be there.

I figure I'll try swapping the cam and followers the next chance I get some decent weather, as the spare engines cam has no discernable wear, and all the lobes look identical, none duller or shiner than the others. Which is impressive as I believe that engines has as much or more miles than the one in the blue car. (Just probably didn't get driven around with no oil as often)

I'm unsure if the cam will make this kind of noise or not, the car runs amazingly well, started up nearly as soon as I hit the key yesterday. But stranger things have happened I suppose.

I'll update my findings as I find more things to update about!

I usually use the followers, cam and towers as a unit when changing (replaced because of broken cam and/or timing chain), but that involves new head bolts. Although I have never done it this way, you should be okay just replacing the cam and followers, and leave the cam towers in place.