Engine Knocking - Help
 

On my way to work this morning, as I left from a 4 way stop, I heard this horrible knocking noise. It can not really be heard at idle, it starts at about 1200 rpms. I limped it home and tried to make sure that it was not as simple as an exhuast manifold leak, I pulled the valve cover off and and ran it up for a couple of seconds. It sounds to me that it is coming from Cylinder #1 (furthest front - new to mercedes not sure what order). Is there a typical problem with the 85 300SD engine that I should look to? I am looking for a manual and figure on pulling the head off and starting with a possible valve problem.

Also has anyone downloaded any of the workshop manuals from www.workshopmanuals.co.uk ? This is the only one I have been able to find and it is downloadable.

Thanks for the help.

Search for ' skinnerbox' on this site... should be an engine manual downloadable there...

This appears to be a MAC site only??? Do you know of any that are for MS OS? Thanks

I have paper manuals and am on a slow dial up... so I have never tried to access that site... but I would be surprised if it was only Mac accessible...

Welcome to Mercedes diesels! :cool:

Assuming good oil pressure, and no bearing damage, which is not too likely since the bearings are quite long-lived and rugged unless oil flow or pressure has been lost, it's possible you are hearing 'nailing' or combustion knock.

You are corrrect, #1 cylinder is in front, #5 is in back. A few quick diagnostic tests regardless which cylinder sounds noisy...

Grab a 14mm open wrench and a paper towel. Loosen the nut on top of the suspect injector that holds the fuel injector tubing. This will create a pressure leak and that cylinder will not 'fire.' If the noise decreases, you have confirmed that #1 is the source. You can operate the throttle linkage to rev the engine and listen for the nailing... When finished, re-tighten the nut, firmly to stop the leak but don't overdo it. Wipe up the diesel drool with the paper towel. ;)

Go ahead and try other cylinders to be sure. It's like pulling the spark plug lead on a gasser to find a bad spark plug, just not nearly as dramatic since you don't get the high voltage shock from holding the spark wire! :eek:

You can also swap the suspect injector with another. If the nailing moves to the new cylinder, there is an injector problem and it might need to be cleaned and/or rebuilt.

Swapping injectors requires a 27mm deep socket. The special injector socket is deep to avoid knocking off the fuel return line arms, but other sockets will work if deep enouth. You will also need a new heat shield for each injector, shaped like a conical crush washer and about $1-$2 a piece at your friendly dealer, and a torque wrench for tightening.

Oh, while you are ordering the heat shields, get one meter of braided fuel return hose, since your hose is probably old enough to crumble when you remove it from the injectors. One meter (3+feet) will replace all of the braided hose on your engine, a quick and easy job once the old hose is off of the injectors.

Before all of this, try the the pulldown Search feature, and look for 'nailing' which will give you hours of reading. Basically, it's a result of a problem with injectors such as a bad spray pattern, bad pressure, dirty injector, etc. that sounds like, well, a hammer hitting a nail into the block...

Sorry if I rambled...

Best Regards,
Jim

Jim H - Thank you for your advice - I tried each cyllinder, in fact I disconnected the fuel line completely at each cylinder. The knocking noise did not change on any of them. Is there another typical issue with the 617 diesels that I should look at? It is loud enough that I do not want to drive it anywhere. Thanks

Also the skinnerbox site has multiple dead links, I can navigate to the point where it would pull up a pdf file and it can not find the page??? All of the menus work, but then they dead end.

Now I'll take a wild guess. Check the Vacuum Pump, in front of Injector Pump, in the area of #1... It might be making knocking noises, as in going to fail soon. If so, replace/repair SOON!

Best Regards,
Jim

Use the W123 indexing for reference.

not to be pessimistic, but that knocking noise appeared on my friend's 300CD while driving along the highway. it was VERY loud and coming from the front of the engine. I told him to drive slowly and not to over rev it. He managed to make it about 10 minutes more, but of couse the idiot he is, didn't listen to me and was going uphill doing at least 65mph.

You can see the results below, hope you had better luck than he did. :eek:

New info on same problem
 

OK - I now have the engine partially disassembled and am looking for some guidance before going too far.

I have manifolds removed, fan and shroud are out fo the way fuel lines removed, valve cover off, CC module off etc.. preparing to remove head and see if I can find the source of the knocking.

What should I look for in a vacuum pump to determine if it may be knocking?

How loose can a timing chain be, also why can I not find a master link on the chain? If I am not going to replace the chain, do I need to split it in order to remove the head.

When I cycle the motor by hand I get this wired creaking sound (like an old box spring) but only seems to be on exhaust stroke for #1 and #2??? Otherswise I do not see, feel or hear any other strange noices...

What size Torx is on the head? T60 was the largest I have.

There were two sizes, on the latter years I beileve they were 12mm 12point torx. Hazet makes a tool to fit it.

This link is the best around for rebuilding the vacuum pump:
Click Here
Most of the parts won't do harm if they fail but it the bearing goes it could be catastrophic.
Also, if you do need a rebuild make sure you build that plate they talk about. It makes the job so much easier.

This link here is for checking timing chain stretch:
Click Here

Danny

Thanks - a couple more questions
 

Thank you for your help so far. A couple more questions -


What should I look for in a vacuum pump to determine if it may be the cause of the knocking?

When I cycle the motor by hand I get this wired creaking sound (like an old box spring) but only seems to be on exhaust stroke for #1 and #2??? Otherswise I do not see, feel or hear any other strange noices...
Any ideas as to what that might be????

That vaccum pump is not too hard to pull. I would remove from engine and inspect it but also turn over engine with it off to see if bedspring noise gone if nothing visual found. It would truly be a shame to pull head if thats what it turned out to be. Not possibly a good choice but one of neccesity as you stated noise was around #1 cylinder and was not relieved by releasing injector fuel line pressure. :) Perhaps waiting till further more experienced post opinions come in prior to actual head removal would be a good thought as well. :) (never had to split the gas merceds chains to remove head and diesels probably simular.) (if you are suspecting # 1 rod bearing the front portion of oil pan can be removed to access #s 1&2 journals plus you may audibly pick up the location of that noise down there with someone tuning over engine by hand or starter. But again I would wait till more posts show.)

Thanks again Barry123400 - Sorry I started a different post, since it was a more specific issue I figures it might be easier to find the answers. Thanks again.

yikes!
 

i would never start tearing an engine apart without experienced people telling me that the noise warrents it. you can very easily cause more damage than good if just tearing things apart to look around. this sound is impossible to diagnose over the net. it could be anything from nailing to vacuum pump to a piston coming apart. did you do a compression test? did you pull the valve cover and inspect the valve train?

Yes and Yes, Everything looks good so far. At this point it is a 3rd car and not needed. I would have to tow it about 80 miles to a real diesel mech, as I can get by, but no proffesional.

I was out of options without going this far, it seemed with a scope that it wasn't the vp when it was running, but now that I can hear an odd noise while cycling the engine, is making me 2nd guess, which is why I stopped at pulling the head, I too do not want to pull more apart than what is needed.

Thanks

nailing I eliminated by shutting down 1 cylinder at a time, no real change on any of them.

Do you think 1/16th of inch play on the bottom end of the connecting rod is too much??? :eek:

I found the problem on cylinder #1. Now the question is, do I fix it or junk it???

I guess we will see. Thanks to everyone who repsonded and for the help.

Glad you found it. I just remove the bearings to run my engines so they cannot wear out. :D Really hope the journal is not damaged. Have noticed majority of complaints seem to be in number one area on these engines. Wonder why? Oil passage sludging up? Fatigue failure of bearing since you mention sudden onset? Bent rod? I would probably just plastigauge # 2 and if within reasonable tollerence just check journal and rebearing the number one rod after making sure oil passage seemed clear. Checking with plastigauge of course. :)

I was starting to wonder that myself. both of the engines i've seen throw a rod were both cyl 1. what the hell!

Johnhef, I suspect mercedes knows the answer. Possibly no tech note ever issued because it is basically unavoidable. A little less oilflow or last point lubrication arrives at eventually takes it's toll over time. First engine of this series that I totally take apart will be sure to have a good look. Will report anything that I think may contribute. Same on their diesel fours as far as i can tell. Also suspect green castings for engine block may let front bore run a little off square after casting seasons with time providing just enough to run rod slightly off square with crank. Primary cause being the inability to have metal at same temperature inside mold when pouing for whatever reasons. Not enough to bind but just enough to provide a little more loading on the number one bearing. For years they did not appear to get their casting temperature consistent on their camshafts either as always was number one lobe that wore away eventually and it did not appear to be oil related. :)

Haven't checked real close, but is it feasible to pull out #1 without pulling head (from below)? If not, no big deal I have already removed everything - again - to remove head. I wasn't sure if the oil pump assembly (once again didn't look real close yet, but I think that is what I was reaching around to check #1) is in the way of dropping that straight down, or if that would be too difficult to replace piston into the cylinder.

If I do too many things, than I might as well rebuild the whole thing, as there are probably a 100 things that may be on the edge of giving in - who knows, but for what I paid, I am just interested in getting it road worthy again.

Thanks again.

I will let you know what I find once pulled out - just for your reference later.

possible rod knock
 

go with Barry 123400's advice,if the vacuum pump checks out O.K.

You may or may not get a metallic screeching equivalent to fingernails
on a blackboard just prior to "Spinning a Bearing" on the crank end of
the rod.

Do not ask how I know.

Thanks for the post, but I am suspicious that you did not read page 2 - I am to the point of knowing that it is the crank end of a rod bearing, if you can help me with my last question that would be great, otherwise - thanks.

Wish someone with more experience this engine type would chime in. If journal checks out I would think you can rebearing #1 rod without pulling head or piston assembly out. Most important is that the journal is not scored up or rough and still appears pretty good. I do not suspect rod end has stretched to any degree. Also try to get a good look at bearing shells to try to determine type of bearing failure that occured. The reason I would try to plastigauge #2 is just to get some indication of other bearing wear and to see if #1 was an isolated occurence. Of course #2 is going to be nowhere near as bad but will help you have perhaps a little more confidence in engine if still not at outer limit of specs. :)

bearing wear
 

first, 1/16" sounds like a lot of play. it will probaly be necessary to pull it out and go through the engine. if one is worn that badly i would not think that fixing it alone will solve the problem. the bottom ends on these engines are about bulletproof. we have pulled engines out with hundreds of thousands of miles on them and found the bearings have no measurable wear. usually we put new ones in anyway but sometimes we have not. it doesnt seem to matter, if they mic out.

if you have a bearing badly worn, there is the possibility also of the bearing material getting into other places and causing other problems.

my advice is to pull it out and pull it down to see what is causing the problem. most likely your other bearings are worn too, and the oil pump and the chains and guides, and on and on. bearing failure in the 240 or 300 motors is just unheard of. it probably means at some time it was run out of oil or on very dirty oil or very low oil levels.

i have owned about 30 mb diesels and have rebuilt at least six, having bought them blown up and done the fixing. i dont do it myself but have a very good friend who owns an automotive machine shop. i have participated in the process to different levels through the years but lately have pretty much participated in decision making and writing checks. i found that even though i love tearing an engine apart and putting it back together it comes out much better if he does it.

Thanks for the input, my struggle is that this happened 3 weeks after buying it and I do not intend now to keep it. I have already replaced the vehicle. I pulled #1 and #2, since I can do that without pulling the engine. I am not sure if I can pull the main oil pan without pulling the engine (anyone who can tell me, please do) But there was a major difference between #1 and #2 bearings, there was a little scoring on #2, but #1 was destroyed. I can feel any play in 3-5 using a non-metalic tool to reach them.

Anyway if I pull it and replace everything that needs to be, which I know with 310k on it I will find plenty I am volunteering to spend money that I will not get back....if I do that I am better of junking it between time and money.

I thought if I can get it in runnig condition and everything else looks decent, that someone who only drives 10-15k miles a year. it would not be a bad deal to spend 2500 bucks for a MB that lasts for 2-3 years.

Not sure - a lot of things to consider.

Thanks