Rattling sound at idle - PeachParts Mercedes-Benz Forum

uranian · #1 08-03-2009, 10:03 AM

Back working on my trustry 1969 406D, and we now a nasty knocking sound from the engine at idle, which goes away when the engine is revved. Comes back again if it's allowed to return to idle, and occurs regardless of whether the engine has been running for hours or just started. We've had the rocker box cover off, thinking it might be tappet related, but the tappets aren't adjustable. I think the engine is an OM615 or OM616, but have never been able to positively ID it.

Next choice seems to be that the timing chain is loose, but there seems to be reasonable tension on the chain (as adjudged by a friend of a friend who rebuilt coach engines for a couple of decades). I don't know what the cause is, it's been suggested that the tensioner isn't putting the correct tension on the chain (or that perhaps there's some rubber cover between the tensioner and the chain, which has worn away), but as the oil pressure increases with the engine speed, it's sorting out whatever is knocking. The sound I can best describe as an irregular rattling, as if something is loose within the engine and knocking against the rocker box cover. Hard to tell where it's coming from, as the rocker box could be acting as a sound box, but it sounds like the back of the engine (closer to the driver).

Anyone have thoughts as to what might be causing this? I can upload a vid to youtube so that the actual sound is listenable to, if that helps.

Diesel911 · #2 08-03-2009, 02:11 PM

Get a Mechanics Stethoscpoe or use something like a Broom Stick to put against various parts of the Engine and listen on the other end and pin point where the sound is comming From.

Doktor Bert · #3 08-03-2009, 08:40 PM

Simple things first....

Check for a loose alternator or A/C compressor and/or loose bolts between converter and flexplate.

Hope this helps...Robert

FLYWULF · #4 08-04-2009, 03:30 AM

Yes, definitely the simple things first.

Is their enough oil in the engine?

Has the oil been changed recently? Correct viscosity will stop a knock sometimes. As an engine matures the tolerances will become larger. An oil with a higher viscosity may do the trick. What are you currently running?
If 10/40 then move up to 20/50 and see what happens to the knock. Their are additives avaialable that can even thicken the oil beyond that. I have used them in the past and it helps.

Give your engine an oil and filter change. Examine the filter for any debris. If their are metal threads or fines in the filter then it may be time for an overhaul (worst case scenario). More than likely the fresh oil will help lessen the knock if their is no internal damage done.

If the oil change helps then the next place I would look is the hydraullic tappets(lifters). They do wear out and get pretty noisy when they do. Might be time for a new set.

please keep us informed of your progress.

EddieE

uranian · #5 08-04-2009, 09:27 AM

Thanks for the thoughts. We tried the stethoscope (novel idea!), and it seems to confirm that the rattling sound is coming from the back of the engine, suggesting that is indeed one of the tappets. The guys who were helping me thought that the tappets were not adjustable, can that be right? The engine is either an OM615 or an OM616. It's definitely not a loose bolt or similar.

The oil was changed a few hundred miles ago, new filter at that point too, with no obvious debris in the old filter. I'm beginning to think it most likely is the tappets, but had been told by the ex coach guys that the tappets weren't adjustable. I'm also somewhat surprised by speaking to a local Mercedes garage, as they quoted 40mm and 60mm as the inlet/exhaust valve clearances when I quoted the chassis number to them. I'd been expecting 10 or 12 thousandths of an inch, not 60mm! Am I badly misinformed, regarding adjusting the tappets and that the clearance should be thousandths of an inch?

Youtube vid of the engine, where you can hear the knocking sound quite clearly at idle, going away when the engine is revved.

Regarding the viscosity of the oil, I'm now using a thicker oil than I had in the engine previously; we found that using mineral oil was making cold starts in the winter difficult, changed over to a thinner synthetic oil and that problem went away. Now the oil is back to the thicker mineral oil.

Diesel911 · #6 08-04-2009, 11:31 AM

I have a book and they say Intake= 0.004 inches and Exhaust= 0.016 for both 220D and240D.
Here is a metric converision site:
http://www.worldwidemetric.com/metcal.htm

In any event in use the Valve clearances get smaller not larger.

You might try exchanging #4 Injector for #1 Injector and see if the tapping sound follows the Injector. If it does you have an Injector Problem.

uranian · #7 08-04-2009, 11:48 AM

thanks for that. ridiculous that the merc garage quoted me incorrect figures when i gave them the chassis number.

it's a manual gearbox.

Diesel911 · #8 08-04-2009, 12:20 PM

Quote:

Originally Posted by uranian

thanks for that. ridiculous that the merc garage quoted me incorrect figures when i gave them the chassis number.

it's a manual gearbox.

I listened to the video and could not specifically identify any sound except that it did not sould like you have a Rod or Main Bearing Knock as I believe that sound would have increased as you reved the Engine.

It did sound like you have an intermitent miss at Idle Speed.

I would remove the valve Cover and Inspect the Valve Mechanism looking for loose, damage or worn out parts that would cause an increased clearance. Also check for a Broken Valve Spring.

The later models have 2 springs per valve and it is possible for 1 spring to break and the valve itself will stay in place due to the other spring being good.

On the later model Engines the Engine number is on the Fuel Injection Pump side at the middle top of the Engine Block.

Added pics:

uranian · #9 03-18-2010, 02:11 PM

Diesel911, a belated thankyou, we did do as you suggested and had a look at the valves. Regrettably we made little progress with that, but since then I think we've identified the problem, courtesy of a friend who is an ex-coach driver/mechanic. He has suggested that it's the injectors that are the problem, which ties in with the rattling sound (diesel giant have a good vid with an engine that needs new injectors, which sounds exactly like our engine), so this is what I'm going to try. When we start the engine, the sound is very up and down until it warms up, and the power is uneven all the time (particularly noticeable at lower speeds), suggesting the problem is related to the fuel system somehow. I read too that a lot of black exhaust smoke indicates that an injector is faulty, as there will be unburnt diesel in the exhaust.

I'm looking at getting Monark injectors, as I read good things and the company are based in Europe, as am I, so no VAT/import tax issues. Problem now is that I don't have a copy of the EPC, and I notice the Russian site is now down, so don't know what part number to ask for from Monark. I've mailed them to see if they can help, wondering if anyone here knows of an alternative online EPC/other way to ID the right part.

Relevant vids:

http://www.youtube.com/v/dseUEVVGsAw
http://www.youtube.com/v/wBfP7lGaUeU

Diesel911 · #10 03-18-2010, 04:18 PM

You sound like you are not in the US. However, we have a member C Sean Watts who sells both the complete Monark Injectors and Monark Spray Nozzles. You might PM him and explain your situation.
I believe he would be able to give the Monark Part numbers so that you could order from a local source. Also, even if the Russian site was still working it would not give the Monark part numbers.
If you live in the US he could rebuild them for you. But, again you need to contact him.

uranian · #11 03-30-2010, 11:27 AM

Thanks again 911. We just tried putting some injector cleaning fluid into the fuel tank, and while the problem hasn't gone away, it's much better than it was. I've discovered there's a local Monark dealership here in the UK, so will give them a go when I get round to fixing this properly.

uranian · #12 06-16-2010, 10:32 AM

turns out that the injectors aren't made any longer, not too surprising as those on my van are i think the original, 40 year old bosch injectors. so i've had a dig around and discovered a source for bosch nozzles (turns out they're a third of the price that monark's distributors in the UK are asking for a different brand), so i'm now waiting on the nozzles to arrive in the post.

question now being, does anyone know how important it is to calibrate the injectors when i've rebuilt them with new nozzles? are we talking a few % efficiency gained by doing so, or is it potentially a more drastic improvement?

useful stuff i've learnt along the way with this is that injector cleaner fluid is basically kerosene, which can be bought at a sixteenth the price! care of a bit of reading around forums, no-one has experienced problems by just using kerosene/paraffin instead, and indeed you can expect ~10% increase in fuel efficiency by using it. not recommended for every tank, as it makes the fuel burn hotter, and only 250ml/40l of diesel, but i plan on doing this every 1000km or so to keep the injectors in good nick.

edited to add that a quick search revealed this thread, which suggests that the calibration is definitely recommended. guess my next step is to try to find someone locally that can do this, and see how much it'll cost.

uranian · #13 06-16-2010, 11:09 AM

having just spoken to a specialist company, they advise me that the probability of the injectors being fine are the rebuild is ~85%. so i think my plan is to rebuild them, reinstall them, and see how the engine runs. they'll test them for free, if i do have trouble.

Diesel911 · #14 06-16-2010, 01:31 PM

Everyone has their own idea what Rebuilt means.

To me Rebuilt means that you use as many of the old good parts as possible while at the same time restoring the item to preform like new.

This is what we did when we Rebuilt Injectors when I worked in a Fuel Injection Shop.

Clean the Exterior of the Injectors and put them on a Diesel Nozzle/Pop Tester (sold on eBay) and did a quick test on them to compare them with the Customers complaint.

(The 2 parts that make up the Injector Nozzle need to be kept to gether as they are a mated set.
It is also best to keep the parts for each Injector with that individual Injector because it makes it easier to set the Opening/Pop Pressure and on the later Injectors there is 2 different body styles that the parts do not interchange on.)

The Injectors are taken apart and cleand. We used Carburator Dip and Solovent to clean them; today they most likely use a Ulatrasonic Cleaning Tank. We had an Ultrasonic Cleaning tank but use it only on Injector Nozzles.

The Precision Flat Surfaces inside of the Injector are Lapped Flat on a Lapping Plate. Doing this of coures allows the inside parts to seal properly and prevents that teltal leak between the Injector Nuts and the Uppper Body of the Injector.

Everthing is cleaned and blow off with Filtered Compressed Air. As the parts are assembled they are dipped in Diesel Fuel.

The Injector Nut is Torqued properly to the Injector Body.

After that the Injector goes onto the Diesel Nozzle/Pop Tester and the Opening/Pop Pressure is checked, the Nozzle spray pattern is checked, and you do a pressure test on the Nozzle to see if it will hold pressure without dripping too much.
If all of the above is within spec you are done.

If you are installing new Nozzles everthing in the above is likely to be OK with the exception of the Opening/Pop Pressure. When you tested them as in the above paragraph you wrote down the Opening Pressure for each Injector (number the Injectors or keep them in a specfic order so you know which Injector goes with which opening pressure).

If the Opening Pressure is low you take apart the Injector and add a thicker Shim/Spacer to increase the Spring Tension. If too high you do the same but exchange the Shim/Spacer with a thinner one.

Assemble the Injector and Test it again.

You repeat the above until the Injectors opening pressure is within specs and balanced within specs compared to eachother.

Now the Injector is rebuilt.

Notes on only swapping the old Nozzle with a new one. About 1/3 of the time you get a seeping leak between the Injector Nut and the upper Injector Body. This can be do to the parts not being lapped or more often dirt or rust getting between the precision surfaces.
The next problem is several members have cracked off the end of they New Injector Nozzle Pintels because one of the parts got shiffted or actually in back wards and when the Torqued the Injector Nut it cracked it off.
The way to prevent this is to first note how the Injector Nut looks on the Body before you take it apart. Next when you assemble it turn the Injecor Nut on by hand and take a look and see that the Nut has returned to the same position as it was when taken apart before you torque it down.

uranian · #15 09-05-2010, 02:15 PM

finally got around to fixing this, turns out 2 of the injectors were very caked up with carbon, 2 were not so bad. replaced all 4 nozzles, the engine now runs well again. no calibration, just whacked them straight back in (after a fair bit of struggling before giving in to the need for a 24mm spanner rather than an adjustable!), off we go again.