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-   -   '82 Mercedes diesel knocking when dead cold (http://www.thedieselstop.com/forums/f33/82-mercedes-diesel-knocking-when-dead-cold-78569/)

frobozz 11-30-2005 06:05 AM

'82 Mercedes diesel knocking when dead cold
 
While my son is off at college I've been driving the 1982 M-B 300SD a lot... both to keep it in good condition, and to take advantage of the better mileage! When it's dead dead cold it makes a knocking noise that rises with RPMs. After just a minute or two of driving it goes away. I'm thinking it's a prechamber problem of one kind or another. 284K miles on the car, unlikely it's ever had prechamber work.

It sounds like a combustion knock, not a mechanical knock. The fact that the sound is different when running B100 vs now when running normal diesel (but very present in both cases) would seem to support that. It does it when the engine is dead cold, but but doesn't seem to be any different now that the outside temps are sub-freezing as opposed to when it was in the 50s or 60s overnight.

There is just a tiny trail of oil leading away from the prechamber collars on cylinders 1 and 2. Never seen any bubbling or oil flow there. I wonder if when dead cold there is air leaking *in* there, which could account for the knocking, in addition to fuel/oil leaking back out during combustion. Then as the head gets a little warm they seal up and no more evidence of a leak (knock or outflow.) Alternatively, anyone know what the symptoms are of old prechambers in need of replacement. The car runs quite nicely and (relatively) quietly under all other conditions.

And just to follow up on a bit of a thread from a couple of months ago: I'm now getting a very consistent high-25/low-26 MPG commuting on local highways. My son ran 320 of 386 miles of a fillup while he was home for Thanksgiving and it dropped to 23.3MPG. So the 13-15MPG he was consistently getting before was an indication of some serious problem. So something, or a bunch of things, I did during the period we couldn't calculate mileage (long story) vastly improved that to where it ought to be, and I didn't know because I couldn't measure it. So I apologize to the poster who was getting 30+MPG in his, for being so incredulous at that figure. Turns out they really *can* get over double the mileage I was getting!

Duncan

GreyHorse 11-30-2005 09:08 AM

Re: '82 Mercedes diesel knocking when dead cold
 
I would post this topic at MercedesShop.com if you haven't already. I would say run some diesel purge or other type of injector cleaner through it although B100 should have the injectors really clean already.

frobozz 11-30-2005 09:27 AM

Re: '82 Mercedes diesel knocking when dead cold
 
The injectors are also only a few thousand miles old so I hope that's not it! It's weird how it only does it when the engine is completely at ambient temps (regardless of what those temps are), but not at all after a couple of minutes of running.

I've posted to a couple of M-B forums before but the responses were nonexistent/worthless. I had somehow missed MercedesShop.com though, I'll have to try it, thanks for the tip! I know there a couple of M-B die-hards around here though too, so I thought I'd ask here first.

Duncan

Spencnaz 11-30-2005 11:13 AM

Re: '82 Mercedes diesel knocking when dead cold
 
Have you plugged in the block heater on the engine at night (if so equipped)?

Indirect injection diesel engines can be very loud when cold. Remember too that diesels will not warm up when at idle, they only start to put on heat when there is a load placed upon them.

Does this noise go away when running B100? I might have missed that part in your earlier post.

Also, have you considered having the engine oil analysed to check for bearing wear just in case?

cmichalik 11-30-2005 12:17 PM

Re: '82 Mercedes diesel knocking when dead cold
 
[ QUOTE ]
And just to follow up on a bit of a thread from a couple of months ago: I'm now getting a very consistent high-25/low-26 MPG commuting on local highways. My son ran 320 of 386 miles of a fillup while he was home for Thanksgiving and it dropped to 23.3MPG. So the 13-15MPG he was consistently getting before was an indication of some serious problem. So something, or a bunch of things, I did during the period we couldn't calculate mileage (long story) vastly improved that to where it ought to be, and I didn't know because I couldn't measure it. So I apologize to the poster who was getting 30+MPG in his, for being so incredulous at that figure. Turns out they really *can* get over double the mileage I was getting!

[/ QUOTE ]

That would be me. No harm done. Don't worry about it. It's good to hear that the mileage is moving in the right direction...Up.

Sorry, but I can't add anymore to this thread except for what's already been suggested. Post this over at Mercedesshop.com

Later,
Chris

frobozz 11-30-2005 01:19 PM

Re: '82 Mercedes diesel knocking when dead cold
 
[ QUOTE ]
Have you plugged in the block heater on the engine at night (if so equipped)?

Indirect injection diesel engines can be very loud when cold. Remember too that diesels will not warm up when at idle, they only start to put on heat when there is a load placed upon them.

Does this noise go away when running B100? I might have missed that part in your earlier post.

Also, have you considered having the engine oil analysed to check for bearing wear just in case?

[/ QUOTE ]

I now have a block heater in it (didn't have one originally.) Since it does it when the *engine* is cold even on warm days it hadn't occurred to me to try the block heater, but it's a simple enough test to do.

It wasn't doing this way back when we first got it (not sure exactly when it started since I don't normally drive it) so I think it's not a normal cold-diesel noise. It doesn't go away on B100, just changes, which is why I think it's combustion related (since a rod knock or whatever wouldn't change with fuel type.) I guess I probably should have the oil analyzed next change.

I have never ever seen a diesel turn oil this black this quickly, and I'm used to how quickly a diesel will do that! Of course part of the problem is that you're not draining the oil cooler when you do a change, so there's a fair bit of old oil left in there, right? But that's normal for this era diesel, as I understand it, so that hasn't been worrying me.

I'll sign up to the mercedesshop site and see what I can find out.

Duncan

GreyHorse 11-30-2005 06:11 PM

Re: '82 Mercedes diesel knocking when dead cold
 
The oil turning black (and I mean the blackest you've ever seen) in a few miles is normal for that engine..... oil cooler like you said plus I think it holds a little in there in a few other places too. Mine will clank a few times kind of like what you are describing on a cold start on a cold day, then it goes away after it warms up a little.

wanderer4x4 11-30-2005 07:42 PM

Re: '82 Mercedes diesel knocking when dead cold
 
worn prechambers & burned ballpins sound like ball bearings in a tin can - very tinny, and rattly, sort of like a gas engine pinging.

knock when dead cold is normal to a certain degree, but can be exagerated if the barometric compensator on the top of the injection pump is sticking, or mis adjusted. you have to dis-assemble part of the injection pump to fix this, but if you feel daring, PM me for detailed descriptions of R&R.

also to note, there are 'warm ambient temp', and 'cold ambient temp' specs for the valve adjustements. those engines are manual adjust only, and I've known a couple of instances where thick oil, combined with slightly mis-adjusted valves has caused odd knocking at startup. I can usually pick up a couple of engiens cheap after each winter when the tolerances tighten back up & they quit running [img]/ubbthreads/images/graemlins/grin.gif[/img]

leaking fuel at the pre-chamber collars is a worry: you'll need to determine if its coming from the collars, or possibly leaking from the overflow return lines. the overflow lines just push onto barbs on the injectors, and are prone to wear. a new set is pretty cheap, or you can just go buy the hose from a jobber supply, and cut it to length. leaking collars would require a full head overhaul

I wouldnt worry about the black oil - most old benzes seem to do that. they seem to get a lot of blowby at startup in colder weather, too, which makes it seem even worse ( mine turns the oil dead black within the first 50km at this time of year)

chris aka wanderer4x4

frobozz 11-30-2005 08:35 PM

Re: '82 Mercedes diesel knocking when dead cold
 
[ QUOTE ]
worn prechambers & burned ballpins sound like ball bearings in a tin can - very tinny, and rattly, sort of like a gas engine pinging.


[/ QUOTE ]

My knock sounds an awful lot like gas engine pinging, actually. What's a ballpin?

[ QUOTE ]

knock when dead cold is normal to a certain degree, but can be exagerated if the barometric compensator on the top of the injection pump is sticking, or mis adjusted. you have to dis-assemble part of the injection pump to fix this, but if you feel daring, PM me for detailed descriptions of R&R.


[/ QUOTE ]

I'm daring, though I'll probably wait until spring to do it, I hate working in the cold if I don't have to! I have a spare injection pump (used) with the compensator (is that the ALDA?) if that helps.

[ QUOTE ]

also to note, there are 'warm ambient temp', and 'cold ambient temp' specs for the valve adjustements. those engines are manual adjust only, and I've known a couple of instances where thick oil, combined with slightly mis-adjusted valves has caused odd knocking at startup. I can usually pick up a couple of engiens cheap after each winter when the tolerances tighten back up & they quit running [img]/ubbthreads/images/graemlins/grin.gif[/img]


[/ QUOTE ]

I adjusted mine a few thousand miles ago when it was warm out. I also measured the timing chain slack while I was in there and it was about nil, whew!!!

[ QUOTE ]

leaking fuel at the pre-chamber collars is a worry: you'll need to determine if its coming from the collars, or possibly leaking from the overflow return lines. the overflow lines just push onto barbs on the injectors, and are prone to wear. a new set is pretty cheap, or you can just go buy the hose from a jobber supply, and cut it to length. leaking collars would require a full head overhaul


[/ QUOTE ]

It's definitely coming from around the collars (besides which I replaced all the return lines with Viton because I'm running B100). Why a full head overhaul for leaking collars? I thought it was just a matter of buying *another* batch of pricey M-B-specific tools and yanking out the old prechambers and putting in new (though the whole sealing ring varying thickness part confused me...) Is there more to it than that? I really don't want to yank the head off.

Thanks for the info,

Duncan

wanderer4x4 12-01-2005 02:25 PM

Re: '82 Mercedes diesel knocking when dead cold
 
ballpins are the hotspot inside the prechamber. they're quite small, and the only piece of these engines thats remotely fragile. ether starts, and / or crank oil getting into the prechambers from excessive blowby can burn out the ballpins. the resulting knock is from delayed ignition - it'll still run, but without the hotspot, the timing is off/erratic.


[ QUOTE ]
Is there more to it than that? I really don't want to yank the head off

[/ QUOTE ] the lower portion of the prechamber assembly is a 'turret' ( for lack of a better term) that projects into the main chamber. when you replace prechambers, thre are spacers that go underneath that are supposed to set the depth of that turret. If you've replaced the chambers, and are now getting seepage, I'd suspect asomething got scracthed when pressing the chambers back in. ( weeping along the scratch)

I'll dig up my notes on the injection pump and barometric compensator, and forward them to your direct email tonight.

re: valve tolerances - I'm not taling about warm vs cold engine adjustments. there's actually a winter / cold climate spec for the valve clearances. if you did it 'while it was warm' that might be part of the issue.

also - whats your injection timing set to/ ( do you have a mercedes drip tool, or did you just wing it w/ static injection timing?)

frobozz 12-01-2005 03:08 PM

Re: '82 Mercedes diesel knocking when dead cold
 
[ QUOTE ]
ballpins are the hotspot inside the prechamber. they're quite small, and the only piece of these engines thats remotely fragile. ether starts, and / or crank oil getting into the prechambers from excessive blowby can burn out the ballpins. the resulting knock is from delayed ignition - it'll still run, but without the hotspot, the timing is off/erratic.


[/ QUOTE ]

If I buy new prechambers, do they come with the ballpins? (I need to go read my manuals more closely...)


[ QUOTE ]
the lower portion of the prechamber assembly is a 'turret' ( for lack of a better term) that projects into the main chamber. when you replace prechambers, thre are spacers that go underneath that are supposed to set the depth of that turret. If you've replaced the chambers, and are now getting seepage, I'd suspect asomething got scracthed when pressing the chambers back in. ( weeping along the scratch)


[/ QUOTE ]

I didn't replace the chambers (though it sounds like I may have to...) and they weren't weeping at first. It wasn't clear to me how you set the depth properly. Simply replace the spacers with identical ones, or are there manufacturing tolerances on the prechambers that require them to be adjusted on the fly? Is this why you say I need to remove the head to replace them?

[ QUOTE ]
re: valve tolerances - I'm not taling about warm vs cold engine adjustments. there's actually a winter / cold climate spec for the valve clearances. if you did it 'while it was warm' that might be part of the issue.


[/ QUOTE ]

Sorry, I wasn't clear on that one: I did it while it was warm *outside* (i.e. in the early summer a year and a half ago); the engine at the time was quite cold.

[ QUOTE ]

also - whats your injection timing set to/ ( do you have a mercedes drip tool, or did you just wing it w/ static injection timing?)

[/ QUOTE ]

I have a drip tool but I've left well enough alone because it runs so well. Stories of runaway diesels are enough to scare me off from messing with the injection pump unless I absolutely have to. I assume since the knock is so dependent on the engine block being at ambient temps, that it's not an overall timing issue, right?

wanderer4x4 12-01-2005 09:56 PM

Re: '82 Mercedes diesel knocking when dead cold
 
the ballpin is actually part of the prechamber. you cant adjust it, or replace it independent of the prechamber. setting the depth of the prechamber is to ensure a proper transision of the burn from prechamber, to main chamber. corrections in the depth are made by adding/removing shims under the prechamber during installation - you can buy sets of the shims from MB specifically for rebuilding purposes, but due to the amount of force necesary to install / remove the chambers a few times, most people find it more blood-pressure effective to have a certified shop do this job.

if its JUST doing the knocking when dead cold, you're probably best of not muking with too many fundamental bits. a ballpin would knock WORSE under load, so I suspect you're clear of that headache. checking / adjusting the injection timing wouldnt be a bad idea if you've got the tool - no chance of a runaway whiel adjusting the timing on a benz as the max fuel adjustment, and timing adjustment are completley independent of each other.(and if you want to gain some power, this is where you'll find it - OEM settings are for low noise, low vibration, NOT power, or economy) if you've got the manual, you'll know its the 3 screws that attach the IP to the block that you loosen to set the timing ( plus the bolt on the rear brace, if your car still has it) the external setting for max fuel is visible between the block and the IP - if you have someone floor the pedal ( with the motor off) you'll see the lever arm on that side of the IP bottom out on the adjuster screw. unless you've got a tach, i dont recommend playing with this one. [img]/ubbthreads/images/graemlins/grin.gif[/img]

the barometric compensator is the bell shaped pod on top of the injection pump. there should be a slot screw, and a 10mm nut painted over (usually its yellow paint, but I've also seen red, and black) if I recall correctly, counter clockwise on the adjuster richens the mixture, clockwise leans it. again - not too likely the issue given the full description and times.

offical ideas from my manuals:
knocking at idle - not a whole lot as its normal for a diesel.

knock @ partial, or low speed, esp when cold - fuel leak, air in fuel, wrong timing. ***possible also from too low of a cetane rating.


knock at partial load @ high speed - faulty timing chain tensioner, or faulty mechancial advance hub ( located behind the vacuum pump)

hard knocking / engine shaking - sticking injectors,

intake clearance 0.004" ( 0.006" in ambient temps below 5*F)
exhaust clearance 0.016"

with a warm engine, warm weather, intake clearance is 0.008", exhaust 0.018"

and just to confirm,doing it 'by the book', on the older Mercedes diesels, the measurement is taken between the rocker arm, and the cap nut, NOT between cam lobe, and rocker arm

failing any of this resolving the issue, you'd be back to swapping the injection pump or injectors to try and source the problem.

hopefully this at least gives you somewhere to start

chris aka wanderer4x4

frobozz 12-03-2005 09:12 AM

Re: '82 Mercedes diesel knocking when dead cold
 
[ QUOTE ]
the ballpin is actually part of the prechamber. you cant adjust it, or replace it independent of the prechamber. setting the depth of the prechamber is to ensure a proper transision of the burn from prechamber, to main chamber. corrections in the depth are made by adding/removing shims under the prechamber during installation - you can buy sets of the shims from MB specifically for rebuilding purposes, but due to the amount of force necesary to install / remove the chambers a few times, most people find it more blood-pressure effective to have a certified shop do this job.

[/ QUOTE ]


...and I can't just replace the existing shims with identical ones to set the height? And do it all with the head in the car? Drat.


[ QUOTE ]

if its JUST doing the knocking when dead cold, you're probably best of not muking with too many fundamental bits. a ballpin would knock WORSE under load, so I suspect you're clear of that headache. checking / adjusting the injection timing wouldnt be a bad idea if you've got the tool - no chance of a runaway whiel adjusting the timing on a benz as the max fuel adjustment, and timing adjustment are completley independent of each other.(and if you want to gain some power, this is where you'll find it - OEM settings are for low noise, low vibration, NOT power, or economy) if you've got the manual, you'll know its the 3 screws that attach the IP to the block that you loosen to set the timing ( plus the bolt on the rear brace, if your car still has it) the external setting for max fuel is visible between the block and the IP - if you have someone floor the pedal ( with the motor off) you'll see the lever arm on that side of the IP bottom out on the adjuster screw. unless you've got a tach, i dont recommend playing with this one. [img]/ubbthreads/images/graemlins/grin.gif[/img]

[/ QUOTE ]


Heh - well like I said it's running quote well, not smoking except on really hard acceleration, and getting good mileage, so I'm hesitant to fiddle with things like that anyway.


[ QUOTE ]

knock @ partial, or low speed, esp when cold - fuel leak, air in fuel, wrong timing. ***possible also from too low of a cetane rating.


[/ QUOTE ]

I was thinking air leak in past the prechambers...


[ QUOTE ]

knock at partial load @ high speed - faulty timing chain tensioner, or faulty mechancial advance hub ( located behind the vacuum pump)


[/ QUOTE ]

Again, since it doesn't do it all the time...


[ QUOTE ]

hard knocking / engine shaking - sticking injectors,


[/ QUOTE ]

I get a tiny bit of engine shake at idle, of course. I did replace the idle damper screw which helped a lot. The injectors were barely-used ones I got off of ebay, so there's some tiny chance there's a problem with them but they looked perfect and barely used, and the car runs so well...


[ QUOTE ]

and just to confirm,doing it 'by the book', on the older Mercedes diesels, the measurement is taken between the rocker arm, and the cap nut, NOT between cam lobe, and rocker arm


[/ QUOTE ]


Yep, that's how I did it.


Thanks for all the clues, at least I have a few places to look now, and it may not necessarily be the prechambers, which is a good thing. (Those suckers are expensive, never mind the cost to have them installed, or for the tools to do it myself!)

Duncan

wanderer4x4 12-03-2005 09:52 AM

Re: '82 Mercedes diesel knocking when dead cold
 
'air leaking past the prechambers"

air leaking around the outside, at least in great quantities, wouldnt be feasible. if too much air leaked, it wouldnt run at all, and since theres no throttle plates to restrict inlet air, it cant leak too much 'in'. the prechamber its self isnt 'sealed' - its just a controlled tolerance mini-chamber with a hot spot. its sole purpose is to propogate a clean, even burn, so the injector goes in one end, and the other end is open to the main chamber ( all the time ) in a DI engine, the injector its self would fit right through to where the port end sits in the main chamber. ( not too well known, but there are a couple fo old Daimler/Mercedes commercial diesels that were basically a 240D block with DI head - about 8% more efficient, and maybe the same % gain in power, but they have ~twice the vibration, and knock than what you find in the sedan motors.

oh - and the reason you cant just put new pre-chambers in without doing the shims is the same reason you cant just put new crank, or rod bearings in - its a high tolerance part, with a thousandths of an inch spec. You 'might' be able to just throw things in and actually pull it off, but you're more likely to make things worse.

re: advance hub - you might want to look at htis when you check the injection timing. the hub can get scored, or warped, and 'stick' at one timing setting. ( its just a giant HD version of the centripital advance found in a gas engine's distibutor) if it was in the middle of the range, it would still run acceptably once its warm...perhaps just feeling a bit sluggish at very low, and very high rpms, and maybe smoking a bit at select rpms....

chris aka wanderer4x4

hapaschold 12-06-2005 06:56 PM

Re: '82 Mercedes diesel knocking when dead cold
 
my 91 350 sdl warms up relatively fast at idle..... hopefully not a sign of problems !!!!!!!!!

any luck over at the mercedesforum.com ??


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