Knock, Knock... - PeachParts Mercedes-Benz Forum

Cadin · #1 08-25-2013, 02:54 AM

Hey Gang,

I have a OM617 that is knocking pretty well. I took it to the local Mercedes guys for a listen, and they think it is in the top end somewhere. They doubt that it would be the block.

It sounds to me like it is coming from around #1. I loosened each injector to see if the sound disappeared but to no avail.

I have done the diesel purge, and added some Lubro High-Test.

It is more noticeable at idle when warm, and when revved with no load, quiets a bit. Revved with load is VERY noticeable.

Does this data help, or shall I post a vid?

Later,
Nater

benzdude42 · #2 08-25-2013, 03:06 AM

When did it start? What were u doing? I have loud knock in my mercedes, took it apart found nothing. Turned out to be an injector that just chooses to knock like a rod going bad. Having them pop tested when I complete my pop tester

vstech · #3 08-25-2013, 08:59 AM

crack the line nut and see if the knock stops. if it does, then that's it.

if you move the injector to another cylinder, and the knock moves then it's an injector, if if does not... it's either the pump, or the piston...

Cadin · #4 08-25-2013, 06:52 PM

I did open each injector to check, and the sound persisted.

Could this be caused by timing chain stretch throwing of IP timing?

Pressure is at 1.3-1.5 bar @ 90C @ idle ---> 3.0+ bar at 2000rpm with 5w-40 Mobil 1 Turbo Truck Juice.

I understand that poor bearings would cause lower oil pressure than this, is this true?

eatont9999 · #5 08-26-2013, 10:05 PM

Have you performed a valve lash adjustment to factory spec?

Yes, timing can cause knocking but usually when it is too advanced. Timing chain stretch retards the timing; not advancing it.

If your valves were severely out of adjustment, you could get a tapping sound.

Oil pressure depends on a lot of things like temp, oil viscosity, filter, and oil pump condition. Low oil could produce a knocking. Just ask anyone who has driven an older Chrysler low on oil. Same with a Diesel. Too low on oil and lubrication does not get to all necessary components.

Cadin · #6 08-26-2013, 11:30 PM

I am currently figuring out how to make the 14mm bent wrenches to adjust the valve lash. I am using .014" for the Ex and .004" for the intake. What do you guys use for TDC? 90*(deg) to the rocker pad?

It knocks at all temps, 5w-40 oil, Oil level has at the high (full) mark the entire time, just replaced filter, I don't know the condition of the pump. This 617 has ~170k, and seems to run fine otherwise.

ROLLGUY · #7 08-26-2013, 11:30 PM

Smell your oil. If it smells burnt, you most assuredly have a rod knock. A nailing injector usually causes a miss. If your engine runs smooth, it probably is not an injector nailing. My first CD developed a rod knock, so I replaced the engine. I got the replacement engine running, and it had the EXACT same sound. I found out the replacement engine had a bad injector, so I changed them all. The knocking sound was gone. I thought I had 2 bad engines in a row! The first engine had burnt smelling oil, and the second did not. The first engine ran/idled great, the second did not. Let's hope yours is just a bad injector....Rich

Cadin · #8 08-26-2013, 11:43 PM

Hey RollGuy,
I have smelled the oil, and it doesn't smell burnt, but would that happen with synthetic? (Which is what I'm running). I've done the loosen injector test more than once, and it doesn't effect the sound.

Does that eliminate piston-slap as well, or just the injectors? I have heard from a few folks that piston-slap is not an unusual culprit. What say ye?

cooljjay · #9 08-27-2013, 12:13 AM

People with disagree with me....as it happens alot....

Sometime synthetic oil can cause damage to an engine that only ran dino....plus you went to 5w-40...synthetic is pretty thin already on its own....

What I would do is switch back to 15w-40 diesel! Rated oil...and replace the two o-rings on the pipe that goes into the oil filter...

http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1640962-oil-filter-shaft-o-ring.html

Synthetic oil, does a very good and sometimes to good of a job cleaning out the engine, your filter may be clogged and the orings hard as a rock....both with effect oil pressure and can lead to oil starvation I would think...

I would do the valve adjustment as soon as possible....because they may very well tight as can be....again with synthetic...

5w-40 oil is only recommend for climates that reach below freezing...

ROLLGUY · #10 08-27-2013, 12:17 AM

Quote:

Originally Posted by Cadin

Hey RollGuy,
I have smelled the oil, and it doesn't smell burnt, but would that happen with synthetic? (Which is what I'm running). I've done the loosen injector test more than once, and it doesn't effect the sound.

Does that eliminate piston-slap as well, or just the injectors? I have heard from a few folks that piston-slap is not an unusual culprit. What say ye?

I believe piston slap sounds different than a rod knock or injector nailing. Does the engine idle smooth out in between loosening of each injector nut? Yes each one should make the engine stumble when loosened, but it should go back to idling smooth if the injectors are good. If you rule out a bad injector or injectors, then the only thing left a problem in the reciprocating assembly. I am not sure if synthetic would smell burnt or not, but dino oil will definitely smell if a bearing was bad. You might want to try changing the oil to 15-40, and adding some Lucas oil stabilizer. If your noise goes away or is lessened, you know where the problem is...Rich

eatont9999 · #11 08-27-2013, 12:24 AM

I want to see a video. Sometimes people mistake knocking for the true nature of an OM617.

Unless you live in a really cold climate, there is no reason not to run only 15W-40 oil. You don't need Synthetic. Running light oil in a Diesel will make them sound like they are knocking more than usual.

You can buy valve adjustment wrenches if you want. They are not too expensive. Get the valves right before you do anything else. Also, get some correct oil in there. Some people may disagree but I see no reason to run synthetic oil in an older Diesel engine. I don't run it in any of mine and I do not plan to. The engine was designed and ran on dino for many years. Changing that adds variables I do not wish to explore.

cooljjay · #12 08-27-2013, 12:28 AM

Oh another thought, post your location.....maybe a follow member close by would be happy to listen and loan you the valve adjustment wrenches....

Cadin · #13 08-27-2013, 02:16 AM

Location added! I will add a video ASAP, though it may not be until tomorrow evening.

I have been waiting on most things to do a proper valve job first to get an accurate baseline. I have a pyrometer and boost gauge (exhaust pressure would be interesting). I don't plan on "dialing up" until she is "dialed in". Though I would like to hear settings that work for folks.

I hear the not changing variables advice; in my 22re I would never dream of running a synthetic; the dino is now part of the engine!

When I looked into the oil, a lot of folks had very good luck running it (5w-40 Mobil 1 Turbo) in these motors and saw very good soot retention, possibly (unknown) better flow to the turbo and of course the engine instantly fires. Since this oil was far from cheap, I would like to run it with perhaps the stabilizer to increase surface retention and a slight increase in viscosity and see how that alters the knock. Would this suffice? (Hey Rich, do you know if the Lucas is compatible with the synthetic?)

As far as wrenches go, I grabbed a couple of 14mm from $ears and I found a dimensional sketch on one of the forums, I will likely build a set, but if anyone local has a set, I would love a physical reference!

Thank you all for your input, it is appreciated!