Have a pesky tapping/nailing sound coming from my 1981 240D. I know there are tons of threads already in existence about this, but after looking through them I am still stumped, curious to see if anybody has some wisdom to share.

Here's what has been done so far:

1) Valves adjusted
2) Oil changed
3) Vacuum pump checked. Was replaced by PO and ball bearing look almost brand new. Ran engine briefly without VP installed and noise persisted. Almost certain it is innocent
4) Alternator, water pump, power steering all checked for bearing play and anything else that could make a cyclic sound
5) Injector hard lines loosened one at a time looking for a change in the sound, no change heard
6) Inspected the rocker arms and valve springs for excessive play and/or broken spring
7) Run the engine with the valve cover off to look for obvious problems with the valve components. Did not notice anything, and oil flow was good. The only thing I noticed was white smoke coming from the timing belt compartment. Not sure if this is normal or not.
8) Measured the frequency of the tapping, found it to be ~6 taps per second, which seems to be valve speed rather than crank speed.


After doings the above and still not knowing the nature of the sound, I splurged and bought a mechanics stethoscope at HF.

Using the stethoscope I narrowed the noise down to the valve train or timing chain. Can't pinpoint a specific cylinder, the sound seems to be fairly uniform all across the valvetrain. Noise is not coming from VP or IP. Sound does not change when the engine warms up or when it is cold, and is proportional to RPM.

All signs seem to point to the noise coming from the valves, I just can't figure out why. If a valve had dropped or a spring had broken, it would be pretty obvious by inspection or when adjusting the valves right? Is there something else I should be looking at?

Another idea is the chain guide or tensioner or some other part of the timing chain is worn. Would that cause the 6 taps per second frequency though?

Maybe an intake manifold leak? Or multiple nailing injectors, which is why the injector line test didn't work?

Here's the link to a YouTube video of the noise, maybe that will help.
https://www.youtube.com/watch?v=ssPsRr6qgZA



Any ideas?

Check the big balancer bolt on the crankshaft and the small allen head bolts on the crankshaft belt pulleys.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Possible worn cam shaft/rocker.

Thank you both for your replies!

I checked the 6 allen head bolts and the big crankshaft bolt, all are tight and the crank and pulley seem to be rotating smoothly.


Here's an update to the source of the tapping:

After some more digging I found that the upper chain guide and the idler gear of the timing chain both have a lot of lateral play in them. These are 85 and 98a in the picture, respectively. Running the engine with the valve cover off revealed that the idler gear visibly moves back and forth, in the direction to and from the radiator.

My question is, would the play in this idler gear possibly the culprit for the tapping sound? If so, what is the procedure to changing only one of the timing chain gears? Haynes has this, but only for a complete engine teardown.

I probably need to check the chain stretch as well.

Thanks!

The image I attached may not have gone through, hopefully it made its way to this message at least.

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Yes, check the chain for stretch, I've seen several break on 240's and it snaps the cam supports at a minimum. If you change the chain use the crimp link style, replace the rails 85, 89 and the chain tensioner.

Also there is a sector shaft type gear that drives the oil pump under the large nut/plug between the front of the injection pump and the block. It is where you would expect an ignition distributor to be if this was a gasoline engine. The bushing in that gear wears out, it is worth checking.

About the idler movement fore and aft I think that is normal. If you change the idler gear it would be a good idea to lock the injection pump in place/time but this requires a special tool.

Remove bolt 94 and see if it is chewed up on the end, if it is the chain is probably loose.

Keep us posted and good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

We’re you able to find wrong?

Sugar Bear, any more info on what to check on the oil pump drive bushing?

I’m just getting started on this job(parts hunting). If anyone knows the part numbers for the intermediate shaft bushing & sleeve it would be helpful.
Anyway take a look at video. About 8-9 minutes in the guy gets into this so you can get a good visual of what’s going on.
After cleaning up the pump valves and gasket it was pretty obvious that the pump was in good shape and an unlikely culprit but to confirm this I removed the cam plate to cancel the pressure against the gear/shaft and pump arm assembly and reinstalled the pump housing. The ticking was more noticeably more prominent at idle. According to Ken Bergma of **************, no shaft play should not exceed 1/16”(1.6mm). I was theoretically within tolerance but it’s clearly the source of the noise.
Note: After watching the video I learned that the FSM states a zero tolerance policy for shaft play I.e. 0.00mm, zilch, nada, niche, rien. I can’t completely rule out the pump assembly as a contributing factor. I don’t have specs for the armature spring height and not the bearing and cam have a visible travel history but the bushing and perhaps sleeve are being replaced when I find the parts. I may look for a cam plate with a few less miles and perhaps a new roller bearing for the arm.
I’m actually pretty excited to tackle this. I’ll report back on my results.

I’m just getting started on this job(parts hunting). If anyone knows the part numbers for the intermediate shaft bushing & sleeve it would be helpful.
Anyway take a look at video. About 8-9 minutes in the guy gets into this so you can get a good visual of what’s going on.
After cleaning up the pump valves and gasket it was pretty obvious that the pump was in good shape and an unlikely culprit but to confirm this I removed the cam plate to cancel the pressure against the gear/shaft and pump arm assembly and reinstalled the pump housing. The ticking was more noticeably more prominent at idle. According to Ken Bergma of **************, no shaft play should not exceed 1/16”(1.6mm). I was theoretically within tolerance but it’s clearly the source of the noise.
Note: After watching the video I learned that the FSM states a zero tolerance policy for shaft play I.e. 0.00mm, zilch, nada, niche, rien. I can’t completely rule out the pump assembly as a contributing factor. I don’t have specs for the armature spring height and not the bearing and cam have a visible travel history but the bushing and perhaps sleeve are being replaced when I find the parts. I may look for a cam plate with a few less miles and perhaps a new roller bearing for the arm.
I’m actually pretty excited to tackle this. I’ll report back on my results.

I just went through a concerning ticking noise similar to yours on my 82 240D. I checked everything you checked and even sent an oil sample out for analysis to make sure there wasn't an elevated metal concentration in the oil. to make a long story short the noise vanished after about 3k miles... so bizarre!!

That’s encouraging. Thank you. I completely disabled the vacuum pump and I’m just using it to cover the hole. Sound is still present. I’ll figure it out eventually... hopefully.

and was not able to resolve the stray noise issue.
New chain installed with proper peening tool
replaced timing device bushing with NEW part
Back in engine today, replacing front seal
Apparently there are varying opinions circulating about ID of spacer- mine came off with surprised fingers, rotated around crankshaft like a pinball machine decorative device, it served not a lot more than for entertainment purposes
Entire end of crankshaft looked factory new, dowel pin holes perfect, crankshaft bolt hole FSM picture-perfect
The only sensible thing to do i completetly overhaul the front of the engine. Most of the cars are approaching 400,000,000,000 miles and the FSM was not expected to cover the cumulative wear of all components and the results of such wear.
Replace timing chain and all sprockets
We all like to talk about the timing chain replacement as if it cures all. It doesn't. All of the sprockets the timing chain rides on ALSO get badly worn; unfortunately this also includes the TIMING DEVICE SPROCKET being a integral part of the system. New chain, new guides, new sprockets and tensioner all the way around will restore the front of the engine to as-built specs, and will result in no noise.
Some hotshot metalurgist out there may be able to CNC and heat treat a replacement timing device sprocket ring because new replacement timing devices were costly years ago and i don't know if they are even still available from Mercedes. When the last one is sold out of the Alpen warehouse we are all facing the same destination.
The timing device is another trillion-mile part that is dead simple and wear-resistant by design. 4 years ago Mercedes still sold the coiled counterweight springs which get side wear like the tensioner spring.
The design of a bolt-on ring sprocket gear would correct the TD sprocket problem.
I ridden in new cars and dislike the senstion of the entire body flexing, something that screams cheap. Not that we get cheap cars, but it is as if quality has been completely engineered away from them and they are designed to appeal to our strangley insipid sense of what a good car should be. Shouldn't be too long before we can play VR games with out cars.
My money and my time is on the W123 design. The return is more than the time and money spent. If you do a half-way job, expect to return to the job as a rescue mission later.
Just do it; do all you can do. These cars respond well to proper repairs and will reward work well done.
I will look up the timing device bushing #. If I recall correctly mine arrived from Greece via ebay. I actually got 2 new ones for less than the price of one. I am probably good for another 75,000,000,000 miles. When you rmove it you can FINALLY accurately measure the bushing wear. If you are in there, REPLACE IT. Taking out the accumulative slack will make your engine run quiet.
Yesterday I installed the seal properly. For wahtever reason the upper oil pan DOES NOT align with the block, it is set back about .020". Today the lower part of the seal gets acetone and sealant and it will not be touched further for 24 hours.

When I installed the spacer I read it should be heated to 250° and slipped on. Ha. Got it to 276° with soak time and it stopped right on the crank snout so I pulled it right back off like poision and back into the toaster oven to 296° soak time and it went right on, straight back to Timbukthree. (if it gets to Timbukthree, you know you have made it to Timbuktu).
Not a good idea to drive this on as you will pare away at the intended clearance of the parts. Maybe just enough to let it ride loose, or loosen with time. The only advantage to this is the continuous external block washing from the profuse oil leak.

I've been in here. If you have any questions I can answer them. I will also tell you if I do not know.



Cheers,


Stan

I believe this is the correct part: 617-052-01-06
Photo attached $47 is reasonable. It’s on the way.

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I have a main seal and spacer on order as well. Not looking forward to doing this in cold weather but the final result should be with it. Thanks again for your informative reply.

oil pump bushing #
6151800044
cheers

Stan