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  #1  
Old 08-10-2013, 03:40 AM
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Location: Idaho
Posts: 378
life or death 300d knock

so i've been bothering this form for almost 2 years about this nasty knock in my 300d that i couldnt track down. Mysterious 1985 Mercedes 300D Engine Knock - YouTube
i know the injectors are nailing pretty bad but it sounded so... odd to be just injectors. i have the engine apart for a rear main replacement and found that the main bearings where pretty beat up pictures here crank shaft bolt.
could this cause that noise? should i dare open up the rod bearings for a look? there is no lose pistons or lose rod bearings that i can see but i will be turning it over a few times by hand when i get the new main bearings in. i honestly do not have a ton of money to sink into a crank grinding if its more that $300 plus new over sized bearings.
everyone i talk to has no idea what would cause this and still have a strong running car after 20k miles.
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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #2  
Old 08-10-2013, 04:15 AM
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Quote:
Originally Posted by benzdude42 View Post
so i've been bothering this form for almost 2 years about this nasty knock in my 300d that i couldnt track down. Mysterious 1985 Mercedes 300D Engine Knock - YouTube
i know the injectors are nailing pretty bad but it sounded so... odd to be just injectors. i have the engine apart for a rear main replacement and found that the main bearings where pretty beat up pictures here crank shaft bolt.
could this cause that noise? should i dare open up the rod bearings for a look? there is no lose pistons or lose rod bearings that i can see but i will be turning it over a few times by hand when i get the new main bearings in. i honestly do not have a ton of money to sink into a crank grinding if its more that $300 plus new over sized bearings.
everyone i talk to has no idea what would cause this and still have a strong running car after 20k miles.
In my opinion, where there's smoke, there's usually fire. IOW, there is likely connecting rod bearing damage as well. It would be prudent to check at the very least while you're in there.
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1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
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  #3  
Old 08-10-2013, 04:23 AM
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yeah i guessed that. just didnt have a 12 point that i felt safe putting on those connecting rods at the time. i'll have to grit my teeth and hope for the best, i believe i'm ok with the main bearing side of the crank, but who knows what those rod bearings will look like and what they have done to my crank
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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #4  
Old 08-11-2013, 02:38 AM
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Location: Idaho
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bump
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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #5  
Old 08-11-2013, 06:00 AM
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Location: Carson City, NV
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I've heard injector nailing sound almost exactly like a rod knock. However, watching the video, and reading that the main bearings are knackered, I'm thinking you have a bad rod bearing. Rod bearings usually will fail before mains if there's a general lack of oil pressure. Other things can go wrong to lunch a main or rod bearing with overall oil pressure still being ok. From what I've seen and read of your case, inspect all the rod bearings. One I'm almost sure is bad. Condition of the rest is what I'm curious about.

In the same situation, I would spring for a full engine rebuild, but I have a few bucks stashed away to pay for that. If you can't afford a rebuild, inspect the rod bearings and crankshaft, repair what really needs it, slap it back together and drive it for as long as it holds up.
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Anyone who thinks a 300D is fast drives too slow.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 357,xxx miles
08 Triumph Street Triple 24,xxx miles, lowered 10mm in front, Pirelli Angel GT tires, EBC HH brake pads, otherwise stock.
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  #6  
Old 08-11-2013, 10:05 PM
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Smile

Ordered the bearings today, the idle was about 950 rpms in that video and the injectors were not pop tested when rebuilt, being done now. I plan on buying a in rebuilt engine after college, just don't have the 8 grand to drop on it now.
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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #7  
Old 08-11-2013, 10:14 PM
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I'll post pictures on Friday of the bearings if I get the new ones quick enough. Can they be rolled in or is the only way to replace them a full crank removal? I can't see why not, but just checking
__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #8  
Old 08-12-2013, 11:08 AM
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Location: St. Thomas PA
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I have a friend on LI who is in the cesspool business who spun a rod bearing on his '81 Mack when he got stuck and accidentally stalled the engine and it restarted running backwards. His mechanic replaced the bearing, and it lasted one mile. Hopefully, your luck will be better, but don't count on it.
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  #9  
Old 08-18-2013, 05:07 AM
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rod bearings where fine, replaced them anyways though. crank cleaned up really nice with some brake cleaner and all the discoloration was gone. broke a connecting rod bolt when my toque wrench took a crap and am waiting on two new ones.
__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #10  
Old 09-06-2013, 03:04 AM
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Location: Idaho
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Still knocking but slowly getting better. Hope to have injectors balanced by the end of the month.
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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #11  
Old 09-06-2013, 03:54 AM
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Right on! Hooray for progress, albeit slow!


I have almost the same sound...

OM617 Knock - YouTube

It is encouraging to hear that the crank had no wear even with the bearing so gone!

How long has the vehicle been doing this? You mention ~2 years, how many miles and what kind of driving? What oil were you running?
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  #12  
Old 09-10-2013, 06:29 PM
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Around 15k miles. I've ran 20-50 15-40 50% Lucas and 15-40. Nothing works to slow the knock. Marvil mystery oil in the fuel does wonders though.
__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
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  #13  
Old 09-10-2013, 08:53 PM
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I was going to say 2 stroke oil in the fuel to quiet the nailing and see if you can further locate the knock. Does a (synthetic) oil change quiet the knock at all?
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  #14  
Old 09-11-2013, 01:25 PM
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Location: Idaho
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Haven't tried it yet. I've been using ATF and there is no knock when running 100%
__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
Reply With Quote
  #15  
Old 09-11-2013, 01:31 PM
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Join Date: Feb 2012
Location: Idaho
Posts: 378
The bottom of the pistons where fine, but one had what looked like paint on it. Took a week for 2cups of oil in each piston, room temp, to pass the rings. The wrist pin on piston 3 was silver looking compare to gold on the others. That might me bad wrist pin, I can live with that.
__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800
Reply With Quote
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