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#1
11-01-2023, 08:28 PM
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1980 300SD W116
Hi all,
just got a 300SD that I always wanted. I was told by the previous owner that his friend drove the car for a while in third gear at high speeds. I was told that this is why the engine now has a knock. I haven‘t started the car yet, because I have to replace the lift pump (he took it for his other car), but I was wondering if driving it at high speeds in 3rd gear would damage the engine. I figured I‘d need to do an engine swap before I bought the car, but I just thought I‘d shoot this out to the Mercedes Diesel experts to see what you all thought about the previous owner‘s story. Think this‘ll definitely be an engine swap? Thanks, Nick
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1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd. 
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#2
11-01-2023, 10:08 PM
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Hi RPM probably wouldn't hurt it but running it low on oil would in a hurry. I'd suggest figuring out what is causing the knock AND doing a compression test after adjusting the valves.
How many miles?
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"Rudeness is a weak man's imitation of strength" - Eric Hoffer
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#3
11-04-2023, 04:29 PM
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Thanks as always, Sugar Bear! When I checked the oil level, it was good, and the p.o. said it didn‘t lose oil, and he wasn‘t just saying that, either, because he was the one who told me that the engine would need to be swapped. And, that‘s why I came here! I figured the high rpms wouldn‘t hurt the engine like that, and I was wondering if it could be something else! I have an injector tester, so I can test the injectors when I pull them out for the compression test, but what else should I look for, and what else should I test?
Thanks as always!
__________________
1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd.
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#4
11-04-2023, 04:45 PM
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Quote:
Step #2: Listen for knock. Then ask how to proceed.
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#5
11-04-2023, 06:03 PM
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Sounds good! I will start the engine in a couple days time, listen to the knocking, and come back to the forum, and by that time, I‘m sure someone will have been gracious enough to post some helpful information to help me - a person who has not dealt with engine knocks before, and does not know how to diagnose them - precisely why I came here seeking information in the first place. I did not see a problem with asking early, I simply wanted to get some thoughts of what I should do once I got the engine started, rather than start it up, listen to it knock about, and shut it off again.
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1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd.
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#6
11-04-2023, 08:42 PM
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If it knocks, it could be broken air cleaner mounting cushions, broken/loose bolts (6?) on the crankshaft belt pulley, a bad injector, a cracked flexplate OR...an internal engine problem.
If it knocks due to an internal engine problem do a compression test before condemning the entire engine, it may need only a crankshaft and bearings. That is way better than needing a full rebuild.
__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer
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#7
11-04-2023, 09:20 PM
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Quote:
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#8
07-30-2024, 07:43 PM
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So I finally got around to moving the car to my house and started to dig in… It‘s definitely quite a knock. I swapped over some good injectors I had on hand, tested and all, the knock did not quieten. I also did a valve adjustment today in preparation for a compression test, and while the engine seemed to run better, the knock is still loud and clear.
https://youtube.com/shorts/L8-AVgU0G2c?si=lVCGWoqPRMjvFeNc That is a link to the sound the engine is making currently. I plan on doing a compression test within the next few days, I just wanted to come back here and update this thread as to what I‘ve done thus far. I know it‘s not a crazy amount, but I wasn‘t sure if some of those with more experience than I have wouldn‘t be able to tell what I might be looking at here. Thank you all for all your help!!
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1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd. Last edited by DieselMercGuy; 07-31-2024 at 05:09 PM.
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#9
07-30-2024, 09:14 PM
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Does the knock change if you crack open an injector line? Use caution when doing this, wear eye protection and gloves. The injection pump is generating very high pressure, don't use bare hands on the nuts etc. use wrenches. The pump makes enough pressure to easily put diesel fuel through your skin. If the knock changes when cracking a line open it is probably piston or rod bearing related.
__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer
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#10
07-31-2024, 06:18 AM
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Thank you, Sugar Bear, for reminding me. I did exactly that when I first got the car back and started working on it, and the knock did not change regardless of which injector line I loosened… I figured this meant a deeper engine problem, but I was wrong in my thinking?
__________________
1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd.
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#11
07-31-2024, 07:35 PM
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So I performed a compression test today… The results were as follows:
cyl 1: 250, cyl 2: 360, cyl 3: 320, cyl 4: 340, cyl 5: 280. The three middle cylinders are fairly decent with the outer two not being so stellar…. Especially cylinder 1. I certainly wasn‘t glad about that… The engine starts and runs smooth and seems fine, outside of that knock. With these results, though, am I correct in thinking that this engine isn‘t salvageable outside of a full rebuild?
__________________
1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd.
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#12
07-31-2024, 09:06 PM
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Remove the belts and start the engine for a minute or two (don't let it overheat) to rule out accessories making the noise. The compression #'s could be better but IMO don't necessitate an immediate rebuild. Use a stethoscope to try to pinpoint the knock location.
Are the air cleaner mounts good?
__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer
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#14
08-01-2024, 12:00 PM
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The old quote is: "When all else fails, read the directions".
In this case read the title of the thread.
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#15
08-01-2024, 06:39 PM
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It is indeed a W116! I took all the belts off and ran it quickly without the accessories, and that didn‘t stop the knock. The air cleaner mounts are all good, I actually removed the air cleaner to get at the upper alternator bolt, and visually confirmed they were good. I guess next I‘ll check the bolts on the crankshaft pulley, but it sounds more like the knock is coming from the engine. I have to get a stethoscope to confirm that, but that‘s what it sounds like with the naked ear…
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1979 300D, sold 1984 300D, totaled 1984 300D, sold 1982 300TD, sold to Dad 1976 240D automatic unfortunately; gone, but not forgotten. 1974 240D manual, sold 1981 300D, sold 1983 300TD, no rust, sold 1979 240D manual, rear-ended 1965 200D, four-on-the-tree 1982 300SD 1985 300D 1984 300CD „Rusty“ 1980 300SD 1982 240D 4-spd. Last edited by DieselMercGuy; 08-01-2024 at 06:54 PM.
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