hello, i am an ase master tech with a 1979 300d. i work in a euro shop and decided to rebuild the engine in this car about a year ago. i had new bearings, new liners installed, and new 91.00mm pistons as well. the engine was fully rebuilt and assembled by a very experienced machinist that does all of the machine work for my shop. the engine always had a bit of an irregular noise to it, i always figured it was related to the 5 cylinder layout. after the rebuild, the irregular noise was still there, but since it had always been there, i again thought it was normal.

over the past few months, the noise has gotten louder. it is a very pronounced knock with that seems to happen every power stroke. the noise can be pinpointed with a stethascope to the #1 cyl, on the pass side of engine, right where the wrist pin is at TDC. it sounds loud at low idle,and it seems to quiet with load, although as the accelerator is backed off, it gets louder. i have removed the piston/rod assy for inspection and had the machinist replace wrist pin bushing (after finding out it was not replaced during rebuild) and rod bearings (just because i had an extra set) and verify the clearance ok. after install, noise is still there. cracking the injector line to #1 quiets the noise, but not completely. i am very frustrated by this, so if you think you can help me i would appreciate it. if you know what would cause that exact noise, i want to hear from you.

side note: why is the factory spec for cyl #1 bore .010mm larger than the rest? i'm not 100% sure this was done.

thank you
eric

have you tried running the engine with the injector out?

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1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.

what would that accomplish exactly? what do i do twith the fuel line? could you be more specific on what to look for with this process? i am not opposed to the idea, i just had never thought of doing something like that. i imagine there would be a lot of whistling involved.

eric

did you do any work on the head during the rebuild?
prechambers? valves?
it may be "nailing" from a bad injector or prechamber.
I would have the injector poptested/balanced. instead of driving without the injector installed, how about switching #1 with #4 and see if it moves to #4...
also while you have the injectors out, visually inspect the prechambers of the two, and see if they are the same visually. shine a light down there and see if both have the same ball/rod assembly.
John

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My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

A 4 stroke NA engine should knock on intake, but not the power stroke.....if your problem is in the piston pin.......

The piston pin us under load during compression, power, and exhaust.....and under slight vacuum during intake.....on a Naturally Aspirated engine.....

On a turbocharged engine, this noise would diminish as the turbo begins to load up the intake stroke......

Could you be having a little piston skirt slap?? try parking the car in an incline...side to side.....and running it, see if the noise changes some.....

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
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'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG