Metallic sound coming from engine front - PeachParts Mercedes-Benz Forum

steeleygreg · #1 02-16-2012, 06:17 AM

I have an 82 240D. When I start the engine a strange metallic sound is coming from the engine compartment. After the engine warms up, the sound goes away. Could this be timing chain stretch ?

Greg

Aquaticedge · #2 02-16-2012, 07:05 AM

It's possible. could possibly be injector nailing too. when you say grinding what does it sound like? is it like if you dragged a necklace across a plastic or metal surface? or more like bearings being dropped on the floor. if you could record the sound/make a video that could help. I would also check your chain stretch, someone will chime in I'm sure with the procedure

t walgamuth · #3 02-16-2012, 07:13 AM

It also could be your vac pump. If it is you want to stop driving the car until it is rebuilt or risk major engine damage. If parts in the pump fail they are free to drop into the engine and often will break the cam chain, resulting in pistons hitting valves and all sorts of bad things.

Stretch · #4 02-16-2012, 07:37 AM

If you can make and post up a video with sound or a sound recording then there's a chance you won't be sent round the mulberry bush too many times!

steeleygreg · #5 02-16-2012, 11:54 AM

Thanks guys. Sorry for not being more detinative with my explantion. The sound produced is a clacking/rattling type noise, like something is hitting an alluminum surface. I suspected at first this was piston slap as it would be in a gaser but the pitch is to high.
Tonight I'll record the sound and pick up a stethoscope at habor frieght in attempt to localize noise. I'll report findings.

Aquaticedge thanks for the comment. Since I'm new to the diesel's, I didn't think injectors made noises.

Greg

Diesel911 · #6 02-16-2012, 12:12 PM

I do not have the same Engine but when mine rattled up front it turned out the Blot for the little Chain Guide was loose; the one that easy to see when the Valve cover is removed.

steeleygreg · #7 02-18-2012, 11:06 AM

Tonight when I get home, I'll listen to the engine with a surgical stethoscope and let you know what I hear. The clacking noise happens predominatley when it's cold. I'll let you know what I find.

Going back to a comment Aquaticedge made about injector nailing, research indicates this is from the spring within the injector. Now since I've never rebuilt injectors, this may be a stupid question. Isn't that part of the nozzle?

Diesel911 · #8 02-18-2012, 11:22 AM

Quote:

Originally Posted by steeleygreg

Tonight when I get home, I'll listen to the engine with a surgical stethoscope and let you know what I hear. The clacking noise happens predominatley when it's cold. I'll let you know what I find.

Going back to a comment Aquaticedge made about injector nailing, research indicates this is from the spring within the injector. Now since I've never rebuilt injectors, this may be a stupid question. Isn't that part of the nozzle?

How to Rebuild Injectors
http://vincewaldon.com/index.php?option=com_content&task=view&id=20&Itemid=28

Diesel911 · #9 02-18-2012, 11:56 AM

When something happens that upsets the time and place where Fuel Burns it can cause abnormal Diesel Knock.

Worn Injector Nozzles that do not atomize the Fuel well or inject the fuel into the part of the precombustion chamber they are supposed to, low Compression = low heat to ignite the Fuel, low Opening/Pop Pressure allows the Fuel to be Injected early and does not atomize the Fuel as well, late or too much advanced Fuel Injection Pump timing, and Air in the Fuel system.

While the Engine is running and knocking you might loosen the Fuel Injection Hard Line Nut or the one at the Fuel Injection Pump for that Cylinder. If when you cut the Fuel off the knock/rattling sound goes away you have an issue in the Cylinder or the Injector.

If remove the Injector and swap positions with another Injector and the problem follows the suspect Injector to the new position you have an issue with the Injector.

Aero Diesel Engines | Shell Aviation

What actually happens in a diesel engine is that when the fuel is injected there are 3 stages to the burning process.
Phase 1
When the fuel is first injected into the very hot air in the cylinder, it does not ignite immediately. The fuel is actually in the form of very fine droplets at this stage, and initially the drops start to evaporate to form a vapour. This vapour must undergo some chemical reactions and also mix with the surrounding air before any combustion can occur. This initial period is commonly known as the "Ignition Delay" period. As we shall see, a short delay period is preferred.
The delay period is primarily a property of the fuel being used, but can also be affected by the temperature of the cylinder contents, and also other factors such as whether the fuel is sprayed against a hot surface, or there is a lot of turbulence in the air / fuel mixture. It is a measurement of the delay period that is classified as the Cetane rating of the fuel - a high Cetane number results in a short delay period.
Phase 2
After the delay period, there is a period of rapid combustion of all the fuel which has had time to evaporate and mix with the surrounding air during the delay period.
The rate and extent of burning during this period are closely associated with the length of the delay period, as a long delay will result in all the majority of the fuel having evaporated and become mixed with air which means that there will be a rapid increase in pressure as all of the fuel burns in a short space of time. This is undesirable as the pressure rises can be very large and cause damage in the engine or, if less severe, can be heard as a noisy "knocking" sound in the engine. (See Chart 2)
One way to alter this is to use a fuel with a short delay period - or high Cetane rating. If the delay is short, then it is possible to still have fuel injection occurring whilst some of the fuel is starting to burn. So part of the fuel charge is in stage 2 (rapid combustion), whilst some fuel is still in phase 1 (delay). In this way the rapid combustion phase is spread out over a longer time and, as not all of the fuel charge is burning at once, the peak pressures are greatly reduced. (See Chart 1)
If we consider the things that effect delay time other than the fuel, then cylinder temperature tends to increase delay. This is why diesel engines tend to be much noisier when started from cold, than when they are running at operating temperature. With a cold cylinder, more of the fuel will evaporate before combustion starts, so there is more fuel burning at once, so the pressure increase is larger which is heard as a knocking sound.
Phase 3
The Third phase of combustion is the period from maximum pressure to the point where combustion is measurably complete. If the delay time is longer than the injection time (which we have seen results in large pressure increases in Phase 2) then there is comparatively little fuel remaining to burn in phase 3. Phase 3 is characterised by a decreasing pressure in the cylinder and only the fuel which has not found enough oxygen to react with in phase 2 remains to be

foolio · #10 02-18-2012, 12:02 PM

Fan hitting fan shroud? As motor mounts age this can happen. Sometimes you can adjust the shroud a little to stop it.

steeleygreg · #11 02-20-2012, 10:06 AM

Well, I've listened with a stethoscope taking sounds from the top of each injector, but no clacking noise. So I was unable to locate which injector is causing the noise. Sorry for sounding so vague. I'm going to replace the injectors for these are probably original and the car has over approx 200k miles. The noise shows itself driving down the road at various rpm's. I agree it might be that the injectors may have the pop points to be far enough out to cause this intermitent noise.
Thanks for the fuel Cetane information. This sounds similar to the octane ratings for gas engines which result in engine ping. This in gas engines about 30 years ago was controlled by either adjusting the mechanical distributor or changing to a higher octane gas. I guess it's the same in a diesel. Correct me if I'm wrong, but engine timing is controlled by the timing chain. If stretch exists in this chain, it can be compensated by both a key and/or minor IP adjustment.

lutzTD · #12 02-20-2012, 12:32 PM

check your balancer and balancer pully also. have you even touched the big crank snout bolt? If so it could be lose. get it now or if it is the issue it will ruin your crankshaft

Diesel911 · #13 02-20-2012, 02:41 PM

#89 in the pic was loose and rattling when I first got my Car.

steeleygreg · #14 02-23-2012, 07:23 PM

OK, I think I found the problem. My son said that the noise was coming from the passenger side, so that isolated the issue. I had a hard time believing it was such a low tech problem. The other day I was replacing a starter on the engine. When removing the air filter I noticed a small metal nut from one of the rubber dampers which support the air filter housing. It had broken off at the bottom and was rattling around in the case.

Diesel911, thank you for the front component diagram. Due to millage on the car I will be replacing the timing chain in a few months. That will give me time to line up the necessary tools.

Greg