W123 knocking sound diagnosis

[guyonabuffalo]

Hi folks,
Sorry I havent posted anything in a while but have been reading a bunch of threads and learning. Been doing a lot of work on the car, slowly but surely. There seem to be quite a few threads on knocking sounds and their different sources and non have definitive conclusions. So I though I d post a video and share here to see what folks with similar issues have to say.

https://youtu.be/95xmxp2XzMQ

This past weekend, decided to drive from Los Angeles to San Francisco (approx 800 miles round trip) so I changed the water pump, radiator hoses and got rid of the A/C compressor belt since it doesnt work anyway. She drove perfectly, got me there and back in 2 1/4 tanks.
Upon returning, I started noticing a knocking sound from the front. Could it be the new water pump? Or maybe because I took the compressor belt off, there is some kind of vibration happening from the lack of tension? All the belts are tightened to spec, the car drives fine, just the knocking at idle is a lot louder than I ever remember. Took a video this morning to show what I am talking about. This is after about 15 minutes of city driving.

I am a little worried that it could be something serious but a mechanics stethoscope suggests its coming from somewhere in the top. Could tightened valves cause this? I did a valve adjustment a couple of months ago (first time ever). Cylinder 1 was extra tight and I didnt want to strip the nuts so i did it as best as I could. The rest were easy and the engine runs much quieter since then.
I will try a diesel purge today and see if it makes a difference, maybe another valve adjustment as well.
I would really appreciate if anyone with a similar experience can chime in or provide suggestions on what I could reasonably try/look for etc.

Thanks in advance.

[DeliveryValve]

To me that sounds combustion related..

I would crack open each injector line while the engine is running to see which cylinder is making the noise. Loosening the line nut at the injector effectively shuts down the cylinder. Then you can determine if the knocking goes away or not.

So it could be fuel related.. You can swap injectors with a good cylinder once you determined which cylinder is bad. If it doesn't improve, it could be the IP.

Also think you are on the right track on checking the valve clearances. Poor compression on one cylinder can cause a combustion knock.

That is pretty much I would start with in the investigation.

[guyonabuffalo]

Thanks a lot for the info. I will try this tomorrow. I did a diesel purge today just to be safe, sounded better to me but it might be ear fatigue and/or just psychological. I will start it tomorrow morning and take another video for comparison. Thanks.

[Maxbumpo]

I don't think it sounds too unusual at all.

2.5 tanks = 40 gallons? = ~20 mpg? That is pretty miserable mileage!!! You should have been getting at least 25 or more. What is the engine temperature once the car is fully warmed up? What fuel are you using?

[guyonabuffalo]

Hi everyone, sorry I havent updated sooner.
First off, I checked all the valve clearances and they were acceptable, the slightly tight ones I adjusted. The engine sounds different, almost like an older gas engine. That knocking sound near the front is still there.

@Deliveryvalve, thanks for the suggestions, I havent had a chance to try the disengaging injector yet since I didnt have a wrench that was the right size and didnt want to use anything else in fear of damaging anything, I will try it this weekend.

@MaxBumpo, I use diesel, specifically from Shell stations since they are close to my daily routes and sometimes have competitive prices. I always look at 300Ds' for sale and the ads all claim 25-30 mpg. I always felt like they were exaggerated based on my experience. To be more precise about my trip, I took the PCH back, which is a much longer and slower way down. Lots of twisty roads, hilly sections etc. The whole journey was realistically 850+Miles and from my experience, with just city driving (through traffic and occasional highway) I get approximately 385 - 400 per tank of diesel which comes out to about 23.5mpg. Is this unreasonable? I figured since it revs so high at highway speeds (60 - 70mph) it gets poor economy than suggested. IMHO

As for the current problem, I am still worried that the knocking could be something serious. I will report back over the weekend once I ve had my local indy mechanic check the valve clearances, injector lines etc. On a different note, theres is a deep bass drum like knock coming from the air scoop. I have heard the engine with the air cleaner housing lid off, the intake has a deep almost metal drum like sound but with the ld on, its usually unnoticeable. Since my valve adjustment this past weekend, this deep thrum seems to have gotten louder, could a leak in the intake path (from air scoop to manifold) cause this?

I accept that I have recently gone slightly insane trying to tame the noise in and around the car and that all this could just be my noise control obsession on edge; playing havok on my perception. On the other hand, I cant help but notice that somehow my car is a little louder since all the recent events.

[Maxbumpo]

Check your air cleaner mounts / bracket. Could be the source of your noise.

[BillGrissom]

Posts 4 & 5 are pretty squirrelly ways to determine mileage. First, nobody would run a tank to empty. You must use the pump (calibrated) to measure fuel input, from full-tank to full-tank. Repeat several times since the full cut-off point varies. But then most people say, "I went a long ways on 1/2 tank". I have yet to see a car where the 1/2 tank mark isn't ~1/4 tank left. Manufacturers might do that purposefully so a potential buyer is thrilled by the assumed mileage from a test drive.

For distance, validate your odometer against mile markers on the highway, Google Maps, and/or a GPS. On the highway, I get ~26 mpg in my 1984 and 1985 300D's, driving 65-70 mph, but I haven't taken many long road trips to measure.

I can't view youtube at work. I had a strange rattling sound that turned out to be the alternator fan blades slightly hitting the bracket. I agree w/ checking for combustion-related noise. Another test is to try B20 or the new HPR (CA only) since most report their engines running much quieter, especially at idle.

[guyonabuffalo]

Thanks for the suggestion Bill, I will check out HPR. You are right about the measuring mileage process. Based on my 1.5 years of owning and driving this car, I ve consistently gotten approx. 400 miles on a full tank (aka needle at the last mark). I know that's not 26 mpg even with what I assume are atleast a gallon or two left in the tank. I know some improvements were made to 300Ds from 1980. Since mine is a 78, I always assumed its high revving at highway speeds was normal for something of its time and was contributing to my sub par mileage. Besides all this, it gets me everywhere. I have bigger tires than factory (205-75-14), which could also contribute to my mileage I suppose? I ve been slowly working on it, trying not to go crazy over budget or time. Should I consider an injector nozzle replacement?
Thank you all for your suggestions and advice, I will post back on the weekend after some more checks/testing etc.

PS. In case it is a rod knock, what are my options? Worst case scenario?

[cooljjay]

Honestly I cannot hear any issues in the car. The mileage has me concerned but my car has had seen everything from the full tank to the injectors gone over...

This car I can see has been neglected as the original primer pump and loop style glow plugs...it tells me this car hasn't seen much in the last thirty years of maintenance.

What does the oil gauge do? Does it style pegged or does float down at idle? Its possible the car is seeing the issue that non turbos have with the thrust piece that holds the gear onto the oil pump...but that is really the only thing besides engine knock that will cause a loud knock...

[charmalu]

Use a 17mm open wrench to loosen the Injector hard lines. Any auto supply will have one.

Your year 300D has a 3:46 Differential ratio. So yeah, you will rev a bit high at hwy speeds.

Checking fuel mileage when the pump handle clicks off isn`t a good way to calibrate mileage. Each station and pump you use, the pump handle will not click off at the same amount of gallons.

Diesel foams up when if goes into the tank. after it clicks off, you can squeeze a bit more fuel into the tank. squeeze the trigger to slowly fill to the brim, you will have to do this several times. I rock the 240 and burp it to get the air out and fill a bit more.

Get a receipt. Write down the odometer mileage on the top. the next tank fill the same and get a receipt, write down the mileage. subtract the difference and divide the gallons used. this will be the MPG for that tank.
Do this each fill up, city, highway, combined driving will get you a true story of your cars MPG.
Don`t believe CL and E-bay exaggerated claims.

Use a GPS, that will give you the most accurate figures. Only if you turn it on each time you drive the vehicle.


Charlie

[Maxbumpo]

Check the air cleaner mounts / brackets. They are notorious for breaking and making noise.

[guyonabuffalo]

Thanks a lot Charlie, I will try and remember to do this from now on. I know about the differential issue. I considered putting an 85 turbo or W126 differential in but the prospect of accelerating slower than my current blistering pace stopped me. If I ever find a 5 speed for sale and have the necessary funds on hand, I might consider it seriously. Plus, since my A/C doesnt work (hence disengaged) I drive with the windows down and the loud revving is drowned out by wind/traffic noise anyway.

M.Dillon, I am well aware of the failing mounts, most are made of really soft/pliable rubber. I even managed to twist one into two halves by hand. Either way, I try to keep a set handy since they suck so much.

Cooljay, you might be right and all this search for quietness might just be in my head and its making me do things to the car that dont need done. The oil pressure needle drops down one mark at idle but climbs to full and stays there under throttle.Is this normal?

Either way I will check a few other things suggested by members here and another forum before this goes to rest. You are also correct in assessing that she has been neglected. The odo says 72K, which based on wear and tear is a damn lie. More like 2/372K. Either way, I didnt know any better (new to diesels -especially old mercedes diesels) and paid $2000 for it 1 year ago. Since then I ve grown to realize that it had numerous rubber seal leaks that let water in and bits of floor pan rusted-which they covered from underneath with a license plate. Parcel shelf and rear seat back horse hair rotted, the engine ran pretty rough, all suspension parts were original (as in 37 years old. given how the rest of the car was treated, i doubt the previous owners would have replaced anything with original MB parts).

[cooljjay]

Originally Posted by guyonabuffalo

I drive with the windows down and the loud revving is drowned out by wind/traffic noise anyway.

Cooljay, you might be right and all this search for quietness might just be in my head and its making me do things to the car that dont need done. The oil pressure needle drops down one mark at idle but climbs to full and stays there under throttle.Is this normal?

I personally think you have a lot wrong with this car that your just not aware of. The noise being so loud from the engine to not hear traffic, bad mileage and acceleration tells me you have some things wrong with the transmission as well as the engine...normal luxury age issues in all reality...

For the oil pressure gauge I would read over this thread I made. ALOT of people driving non turbos don't realizes there are bushings that wear that drive the oil pump.

Clank Clank when cold....new engine time??

You also sound like you have typical issues coming from the transmission associated with the early all mechanical driven automatics. There are half a dozen bushings that fail apart in the linkages that tell the transmission what to do. When these go bad the transmission does not know how to operate in sink with the transmission.

The fluid in the transmission also has to be spot on for this transmission. It cannot be dirty, low, overfilled and it MUST be DEX III or dex/merc fluid. Must be checked at the exact moment the engine is warm idling in park.

There is also a kick down switch under the accelerator. The car DOES NOT start off in first gear, the car is only put into first gear when the accelerator hits the switch or when manual switched. If this button or solenoid does not work it will cause the car to hold gear to long, not kick down or not up shift.

All the linkages to the transmission also need to be the adjusted to the FSM...no ifs or ans...there is also a bowden rod that controls the transmission that has a well over looked bushing in it also that will cause transmission issues.

Even worn out transmission and engine mounts will cause shifting issues on these years..

This car has a grand total of 77 horsepower! and weighs near two tons. Despite being a diesel these cars need regular maintenance and with a very fine tooth come...

You don't EVEN! want to know about the evil servo climate control system...I commend you for paying that much for a 78!!!!!

I say that because NO ONE will ever give a non turbo a second thought...I think its sad as I love mine but they just suffer the more rotten end of the stick...I can also say that I have found out most everything I know about this through research and lots or reading....there is not many people on the forum that have really good knowledge on non turbos...and I will be the first to tell you that there is a LOT of difference between maintenance of a non turbo and a turbo..

[guyonabuffalo]

CoolJay, thanks for response. That thread is great! I m starting to suspect that the knocking from the front could be as you say.
Thanks to this forum, I ve actually been able to get my transmission working pretty well. Changed all the bushings etc. I however have yet to check and adjust all the linkages to spec. I only adjusted the bendy control lever (passenger side)that connects to the rods for the transmission close to 327mm, which dramatically improved shifting (after I also changed the fluid and filter). This weekend, I plan on adjusting all linkages to fsm. Unfortunately I had to cut off both the idle speed cable and cruise control cable because some clown before me messed with them and left them tangled. I thankfully discovered this while driving on an empty street when my throttle jammed at moderate throttle. Put it in neutral, pulled over, in a fit of panic and rage cut both cables off like aforementioned clown. I and the car live to search the Internet for replacements.
When I say its loud, I'm comparing it to gas cars, so my standards are unreasonable. Also, because of a lack of insulation on panels, the inherent vibrations cause quite a bit of low end noise, which I ve been remedying with MLV and other insulating material. My hood pad is also rotten.
I know these cars were slow even back then, but I guess I could really put all my problems into perspective if I could drive another 300d from the same year and preferably in properly maintained condition, for comparison.
Thanks for all your help.

[toomany MBZ]

I don't hear anything unusual myself.

You're comparing apples to oranges when you state a comparison to a gas powered car.

You don't have a Bowden cable, as you have adjusted the bendy control lever, same thing. Later cars switched to an easily adjustable cable.