OM617 Engine Knock

[Casey]

Okay, okay, this is a W123.  But as it's the exact same engine as the 300SD, I'm hoping somebody could give some advice on what might be wrong with my engine - the last day I drove it it started making this horrible knocking sound.  Since then I've changed the oil and done a diesel purge, to no avail.

Car seems to still perform very well, but I'm not driving it much like this.  Any advice very welcome!

http://www.youtube.com/watch?v=LUUnLepAT50

[TJ 450]

I've no idea what that is, but I would get a stethoscope and try to pinpoint the sound. It might be an idea to remove the rocker cover and have a look.

There must be a huge amount of play in whatever it is, rod bearing perhaps?

Tim

[Casey]

Surely you can't mean an actual stethoscope, as I imagine the sound would be quite deafening.  Do you mean something like this?



...or is there some special product for cars you can buy?

[calvin streeting]

I use a big old flat screw driver, great to use on a 280E before and after valve adjustment. get one and put the handle against your ear and the other on the engine, in different places.... just gets tricky with a realy bad idle

[Big_Richard]

sounds like a seized hydraulic valve element - if the diesels have them i've no idea, but i'd be inspecting the valve train.

[Casey]

sounds like a seized hydraulic valve element - if the diesels have them i've no idea, but i'd be inspecting the valve train.

Would this be by taking of the valve cover, and having a look at what's underneath?  If you could point at some pictures (on any engine) of what you're talking about or give me a "for dummies" breakdown I'd appreciate it.  I've got no almost no experience with engine stuff yet.

[Big_Richard]

I've never seen one of those engines in my life so I wont be able to help you 

It does however sound exactly like a company car i drove many years ago which had a sticky hydraulic valve compensating element and sounded like a sewing machine on steroids until it free'ed up usually after 5 - 10 minutes from cold. Hence my thoughts that its absolutely valve train related.

perhaps not a task for the uninitiated, might be worth getting a in independent mb specialists opinion.

[Big_Richard]

I just looked at the epc, those engines look about as simple as simple can get.

there doesnt appear to be any kind of hydraulic valve compensation, it looks like the valves are adjusted manually by nuts on the stems ?

I'd take the cover off and rotate the engine by hand if possible from the front crank nut (running direction only!) and see WTF is going on in there. should be pretty obvious with that much racket.

[TJ 450]

Surely you can't mean an actual stethoscope, as I imagine the sound would be quite deafening.  Do you mean something like this?



...or is there some special product for cars you can buy?

There are mechanic's stethoscopes available, but the old screwdriver trick is just as effective of course.

MT, surely the nuts are lock nuts on tappets? 

Hopefully the camshaft hasn't suffered and it is in fact just a tappet/lifter issue (easy fix).

I would suggest googling or searching on YouTube for "adjusting tappets", or whatever to get an idea of what it's all about.

Tim

[wbrian63]

I'd start with the top of the motor. Remove the camshaft cover and see if anything looks out of place.

Adjusting the valves is easy, even for a non-mechanic. Here's a link to a set of instructions that are well done:
http://dieselgiant.com/valveadjustment.htm

If you don't find anything out of place under the cam cover, you can check to see if the issue is deeper in the motor with a fairly simple test.

First, get a good line wrench and loosen and retighten each injector line at each injector. There will probably be some diesel spray or leakage during this part - wear eye protection and have rags present.

Then, start the engine and allow it to come up to operating temperature.

With the engine running - fit the wrench to the first injector line, then cover wrench and line with a wrag. Crack the line open just a bit. Diesel will spray out around the loose connection, but the key is it won't spray into the engine, so that cylinder will go "dead." If the knocking is a rod, or wrist pin, the noise will go away when you get to the cylinder where the problem is.

To me, the sound appears to come from the top of the motor. Hopefully you'll find the cause when you get the cam cover off.

[Casey]

I'd start with the top of the motor. Remove the camshaft cover and see if anything looks out of place.

Adjusting the valves is easy, even for a non-mechanic. Here's a link to a set of instructions that are well done:
http://dieselgiant.com/valveadjustment.htm

If you don't find anything out of place under the cam cover, you can check to see if the issue is deeper in the motor with a fairly simple test.

First, get a good line wrench and loosen and retighten each injector line at each injector. There will probably be some diesel spray or leakage during this part - wear eye protection and have rags present.

Then, start the engine and allow it to come up to operating temperature.

With the engine running - fit the wrench to the first injector line, then cover wrench and line with a wrag. Crack the line open just a bit. Diesel will spray out around the loose connection, but the key is it won't spray into the engine, so that cylinder will go "dead." If the knocking is a rod, or wrist pin, the noise will go away when you get to the cylinder where the problem is.

To me, the sound appears to come from the top of the motor. Hopefully you'll find the cause when you get the cam cover off.

Thanks a lot for the clear instructions/suggestions wbrian63...somebody else also suggested the injector line check - I will try it tonight.

[Casey]

Today I finally got around to trying the injectors - every one was the same - I'd disconnect it a bit and the engine would start hesitating and stop if I didn't reconnect it immediately.  In no case did the sound go away and it seemed there wasn't any injector that acted different than the others when disconnected.

I also removed the valve cover - I don't have a clue what I would be looking for but I don't see anything obviously broken.  Sorry I don't have a camera any more, but I can record a video if need be.  Any suggestion of what to look for/try now?

As a side note, I was replacing all the Bosch injectors on the 300SD with Monarks, and broke one of the new ones in the process.  So now it's got 4 Monark's and a Bosch, and as a result sounds rattly, though a more random uneven sound than this one.  So now I have two rattly 617 cars. :/

[1980sdga]

How did you break the injector? 

[Casey]

How did you break the injector?

With stupidity.  The internal parts weren't lined up correctly so the little pin on the top of the injector snapped when I went to bolt the injector back together.  I've got a new one already though - Might see about getting them installed tonight.  I've actually been running this week with the 300CD injectors transplanted into the 300SD, as that gives me a pretty smooth engine.  But pretty soon it'll be the original injector housings with all new Monark nozzles fitted.

[1980sdga]

Stuff happens, it's how we learn sometimes   

Did you pop check them and all that stuff? Didn't you get one of those testers?

I'd be interested in hearing about that!