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Old 09-20-2014, 03:59 PM
cmac2012's Avatar
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Location: Berkeley, CA
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Rod knock in my 300 SD

This is an old issue. My car has sat for some time waiting for me to fix it.

I let the oil level go down to the lowest level, the add line, once or twice. Not smart but what made it a real problem is that the rubber neck thing attached to the steel oil port in the crankcase, the rubber neck that went down to the bottom of the crankcase had a tear about 3/4ths the way around at the point it attached to the steel pipe. This I found out later. I had been working in the Oakland hills for weeks before the problem and spent much time powering up steep hills. My guess is the angle and the torn rubber neck deprived my engine of oil.

So what I'm wondering, if I can determine that compression is acceptable, would it be possible to change rod bearings, etc. from below w/o taking the heads off? Would eliminate a good deal of complexity. The engine would still need to be pulled of course. I'm not that stupid.

This engine ran pretty well before the incident. The death symptom was a loud rod knock. Doesn't mean that oil starvation caused no damage above in the piston/rings area I realize. I was running bio-diesel during most of this and I gather that it's good lubrication so maybe the valves and rings were spared.
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1986 300SDL, 305K
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Old 09-20-2014, 04:48 PM
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Location: Long Beach,CA
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If you are able to remove the Oil Pan and have room to get at the Rods and Mains it is not hard to roll in new Bearings.

If you to to the Library and they have some old Motors or Simlar Manuals it may have some hints on roling new Bearings as that was more common back before 1975 then it is now a days.
It also used to be done frequently on Big Trucks and other equipment were making Money meant keeping the Vehicle on the move.

No need to remove the Head as long as it is the lower Rod Bearings.

On a lot of Engines the castings below the Piston prevent you from pulling the Piston out from below and in fact on some they will pull out fare enough for some rings to pop out but the Piston will not have enough room to come out completely and you are sort of locked in Place and it takes some carful manipulation safely stuff/compress the Rings back in and and get the Pisto in.
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Old 09-21-2014, 02:42 PM
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Usually number one or two rod bearings are the issue on the 617. Unfortunatly not always and the possibility also exists they all might be somewhat damaged in your case..

If you can remove and find by loosening injectors it is one of them. You might be able to roll in bearings on either of those rods with the engine in place.

Hopefully the crank is not marred. Using plastigage to check the bearings or if possible setting up a dial gauge and moving the rods back and forth sideways to check for existing bearing clearance if there is room and you are uncertain. Although if you establish it is limited even to one cylinder you have to do something.
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Old 09-21-2014, 04:42 PM
cmac2012's Avatar
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I'm not a man of great experience on engine rebuild, did one once years ago. Is it pretty common to have brass sleeves on the crankshaft to rod connection? I know this thing was making a hell of a noise when it went, and like a fool I limped it home about a half a mile. Might have damaged the crankshaft right there.
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