I have an 83' 300sd 198k. My engine has always run very smooth with all the right sounds. I just starting hearing a very loud knocking sound. I would describe the sound as being a bad valve. Because this is a 617 Diesel, I realize that may not be the case. The other new symptom that started with this sound is serious blow-by. I have checked my blow-by in the past and found that I had very little. Now that I heard this sound I decided to check it again. I found that it has a LOT of blow-by now. This scares me

I would like to know the proper steps for diagnosing this problem???

I have new glow plugs and my injectors are new as of one year ago. I have not checked IP timming. I have had a new timming chain installed and valve adjustment done by an MB shop about 6 months ago.

I would guess a cracked pre-chamber or, bad injector to be causing this knocking sound but, this new blow-by situation leads me to believe it may be something more serious.

Has anyone had a similar experience and found it to be something other than a bad valve?

Your advise please

__________________
Cousin Dave
83' 300SD 250k+ and going strong!

Take the best that exists, make it better!
If it doesn't exist, create it!
Accept nothing nearly right or good enough!

Sounds like a cracked piston or blown out rings.

What were you doing when you first heard this sound?

I agree with the piston and ring scenario! shut it down and pull it apart or get professional help. This is still salvageable!

I was driving as usual when I first noticed the sound. Oddly enough I have not noticed a loss of power. Still runs good!

Does that eliminate anything?

__________________
Cousin Dave
83' 300SD 250k+ and going strong!

Take the best that exists, make it better!
If it doesn't exist, create it!
Accept nothing nearly right or good enough!

Was it after any hard acceleration/hill climbing/overheating?

Has the engine been over 5000rpm?

Could it be a bad vacuum pump making the noise and introducing more pressure into the crankcase? Is the vacuum system working ok?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Normal city driving. I am actaully a very conservative driver... with exception of an itialian tuneup every two months or so.

I do not recall laying into it today at any point. I did not notice the sound until I came to a stop at home. From inside the car it is not to bad. Outside it is very loud. When I removed the oil cap from the valve cover it became VERY VERY loud. And of course, that is when I noticed the excess blow-by.

__________________
Cousin Dave
83' 300SD 250k+ and going strong!

Take the best that exists, make it better!
If it doesn't exist, create it!
Accept nothing nearly right or good enough!

It's alot better than the alternative! Glad you found it!

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

What about the blowby?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I did this test today and found the motor would run about 10 seconds with the hose capped.

Any other measurements out there to compare to?

__________________
MJMoon
'83 300SD 460,000 miles (+ 3 years w/odo not working)

Cap the valve cover breather hose while the engine is running. If the motor builds enough pressure to stop running in under 5 seconds, the theory is that the valve guides and/or rings are worn past their useful life.

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MJMoon
'83 300SD 460,000 miles (+ 3 years w/odo not working)

good point. In my excitment of finding the loud noise, I forgot all about the blow-by. I will do this test real quick and post the results.

__________________
Cousin Dave
83' 300SD 250k+ and going strong!

Take the best that exists, make it better!
If it doesn't exist, create it!
Accept nothing nearly right or good enough!

You know there's some danger of blowing out seals with that test. It's also somewhat unreliable because the quality of the test depends on having solid deals throughout the crankcase.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Diesel2theMoon, I did the test as per your instruction. I capped the breather hole on the valve cover and started counting. It took about 25 seconds for the engine to die. When I let my thumb off the hole a HECK of a whole lot of pressure was released.

So how does that score? Please tell me what this means please?

__________________
Cousin Dave
83' 300SD 250k+ and going strong!

Take the best that exists, make it better!
If it doesn't exist, create it!
Accept nothing nearly right or good enough!

Either you don't have a lot of blowby or you have a leaky seal.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13