Knock Knock, Who's that? My 87 300D. - PeachParts Mercedes-Benz Forum

winmutt · #1 10-09-2010, 10:44 PM

So I have had this car for 6 mos now and it knocks. Original #14 head. Its coming from number 1. Been knocking since I had it and the PO said it was doing it when he bought it. Compression isnt great but not horrible either at 310, probably 320 if I retested and was more meticulous. If you loosen the injector knocking stops. I have checked the tappets and they seem quite functional.

Today I have replaced the injector with 2 different used ones. Still knocks. Another symptom is lots of unburnt diesel in the AM great plumes. Well see if that is still going on tomorrow.

Suggestions? It is the #1 maybe someone screwed up the delivery valve when timing it? I don't mind replacing the head if that is indeed the problem. If it was a rod or wrist pin then I would expect it to be constant, injector injecting or not. Is that solid thinking?

layback40 · #2 10-09-2010, 10:59 PM

Its not an injector problem. When you loosen the injector, you remove the load from that piston etc. probably a bad piston/pin or bearing.

winmutt · #3 10-09-2010, 11:27 PM

It could equally be a deliver valve problem AND its def in the top end. I need to get a stethescope tommorrow and verify. There are alot of people talking about redoing delivery seals and getting knocking.

layback40 · #4 10-09-2010, 11:43 PM

Thats true, if its a delivery valve, it wont be a motor noise. steth will let you know where the noise really is. I would have thought the PO would have got it fixed if it was simple.

winmutt · #5 10-09-2010, 11:54 PM

Prechamber is always another possibilty. Trying as much diag as possible without spending too much. Its smooth as silk except for the heavy smoking in the am. A rod or wristpin would not account for the smoke would it?

layback40 · #6 10-10-2010, 12:49 AM

thats true. Smoke could be caused by a sick piston /rings though. Comp fig goes against this though. What are the other comps?
I hope it is the delivery valve.

sixto · #7 10-10-2010, 01:01 AM

What are the symptoms of a prechamber ball falling into the combustion chamber?

Can a failed head gasket dumping oil into #1 cause knocking?

Sixto
87 300D

winmutt · #8 10-10-2010, 08:22 AM

Missing prechamber ball will cause early ignition as well. I dont think its oil burning as when its warm there is no smoke.

winmutt · #9 10-10-2010, 09:06 AM

Lots of smoke again this AM. Going to pull the #1 line after it cools again and see if that removes the smoke.

vstech · #10 10-10-2010, 09:23 AM

Try a mv test on that pot

winmutt · #11 10-10-2010, 09:24 AM

Loosened #1 no smoke. A bit of diesel in the air but nothing I could see. I could hear injector nailing. I am going to peek down #1 injecot hole and look for the ball as well as try to retard the timing and see if that fixes it temporarily.

winmutt · #12 10-10-2010, 09:34 PM

Which way to I turn the pump to retard it? Away from block?

winmutt · #13 10-24-2010, 09:43 PM

Anyone know how to get to the lower bolt on the IP? What magic combo of tools?

Cold compression is just over 300, pointing again to the IP.

Hit Man X · #14 10-25-2010, 01:36 AM

Quote:

Originally Posted by sixto

What are the symptoms of a prechamber ball falling into the combustion chamber?

Can a failed head gasket dumping oil into #1 cause knocking?

Sixto
87 300D

Well my SDL has that issue with the HG and does not knock.

hsmith · #15 10-25-2010, 10:37 AM

My card did that. I replaced the little shock (to the left of the spring that pulls the belt tight) and now all I hear is a smooth idle.

Hugh Sr.

1984 190d 95,384

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