OM617 N/A main bearing problem- I'm baffled - Page 5 - PeachParts Mercedes-Benz Forum

vwnate1 · #61 07-08-2015, 05:10 PM

I did see it was galled across the wrist pin .

I guess I'm learning , I'd still never re use a piston like that .

Audible piston slap is normally from the skirt area .

Please keep posting and sharing this info , it's getting to where there are too few hands on Mechanics anymore .

Stretch · #62 07-08-2015, 05:32 PM

Quote:

Originally Posted by ROLLGUY

...

EDIT: Yes Stretch, I will have a look at the oil pump shaft as well.

It will just be nag nag nag otherwise!!!!

(Good on you for finding the piston information though)

Has the connecting rod been checked for straightness?

Stretch · #63 07-08-2015, 05:35 PM

Quote:

Originally Posted by vwnate1

...
Please keep posting and sharing this info , it's getting to where there are too few hands on Mechanics anymore .

Huh it has long been the case - I know we're all guilty of arm chair mechanicing here because we're on a forum giving advice to someone about something we can't see - However I imagine only a hardcore few have engine dirt under their fingernails when they are typing!

Dan Stokes · #64 07-09-2015, 08:35 AM

Quote:

Originally Posted by Frank Reiner

Actually, piston cam grinding produces a greater diameter across the skirts than across the pin bores. The greater mass of metal in the pin bosses results in greater expansion along the pin axis, and hence requires greater cold clearance than across the skirts. Remember that piston clearance is always measured across the skirts, not the pins.

10-4, Frank! At least, that's what they taught me at school in 1966 and so far it's worked for me. That piston scuffing at the pin bore definitely means that it's lost lube, gotten hot, and expanded in that area. I'm surprised that the pin didn't seize in it's bore but there must be enough lubricity in the piston metallurgy to keep it moving. Good to know.

Dan

vwnate1 · #65 07-09-2015, 02:43 PM

Quote:

Originally Posted by Stretch

Huh it has long been the case - I know we're all guilty of arm chair mechanicing here because we're on a forum giving advice to someone about something we can't see - However I imagine only a hardcore few have engine dirt under their fingernails when they are typing!

Don't forget the scars and broken finger joints Stretch

.

I always wash up before touching the computer .

Engine work is fun and rewarding , I'm still at it , I have several lined up in my back yard....

Still and all , reading about how others , professionals or DIY'ers , do things and approach situations and problems , is always educational .

I'm never too old nor too proud to learn .

DeliveryValve · #66 07-10-2015, 12:21 AM

Hopefully the replacement piston will do the trick and hope you are using new rings for it too.

Quote:

Originally Posted by ROLLGUY

...
EDIT: Yes Stretch, I will have a look at the oil pump shaft as well.

Important, be sure to pull the helical shaft also. You'll see the most wear there. I think the metal is softer compare to the oil pump shaft.

Stretch · #67 07-10-2015, 02:32 AM

I agree - by drive I meant from pump to top cap - and the intermediate shaft deserves a bit of attention too

ROLLGUY · #68 08-10-2015, 03:28 PM

I finally got the replacement piston in, and the engine back together. It seems to have no rod knock anymore, hooray! There is another issue that I have not looked at, and that is that I could see a little smoke coming out of the coolant hose (heater) fitting on the rear of the head. I had to break away from the project as soon as I knew it ran quietly (well, at least as quiet a a Diesel should be), but the smoke concerns me.....Rich

vwnate1 · #69 08-10-2015, 03:44 PM

Sounds like you've turned a corner here , do keep us posted .

I need to dip into overhauling my 240D's engine and tranny both .

t walgamuth · #70 08-10-2015, 03:47 PM

Quote:

Originally Posted by ROLLGUY

I finally got the replacement piston in, and the engine back together. It seems to have no rod knock anymore, hooray! There is another issue that I have not looked at, and that is that I could see a little smoke coming out of the coolant hose (heater) fitting on the rear of the head. I had to break away from the project as soon as I knew it ran quietly (well, at least as quiet a a Diesel should be), but the smoke concerns me.....Rich

Is there a hose attached to it?

ROLLGUY · #71 08-10-2015, 04:07 PM

Quote:

Originally Posted by t walgamuth

Is there a hose attached to it?

No, just the nipple sticking out of the side of the head by the filter stand.

funola · #72 08-10-2015, 04:36 PM

Quote:

Originally Posted by ROLLGUY

I finally got the replacement piston in, and the engine back together. It seems to have no rod knock anymore, hooray! There is another issue that I have not looked at, and that is that I could see a little smoke coming out of the coolant hose (heater) fitting on the rear of the head. I had to break away from the project as soon as I knew it ran quietly (well, at least as quiet a a Diesel should be), but the smoke concerns me.....Rich

How can smoke come out of a coolant hose fitting? Was the coolant hose not connected to it? You ran the engine without coolant???

ROLLGUY · #73 08-11-2015, 10:38 AM

Quote:

Originally Posted by funola

How can smoke come out of a coolant hose fitting? Was the coolant hose not connected to it? You ran the engine without coolant???

The engine has been out of the car and on a stand, or on the ground. There is no harm running an engine for a short period of time without any coolant. Since I had the head off, I assume the smoke is just coolant residue heating up and making a vapor that can be seen. It is that I don't remember seeing this before when I started the engine to determine which cylinder the rod knock was coming from.....Rich

leathermang · #74 08-11-2015, 11:16 AM

As to why one piston might overheat....
be sure to check the oil squirters....
and I think you have to open a plug at the rear of the block to be able to physically clean out that oil galley which feeds them..

funola · #75 08-11-2015, 11:32 AM

Quote:

Originally Posted by ROLLGUY

The engine has been out of the car and on a stand, or on the ground. There is no harm running an engine for a short period of time without any coolant. Since I had the head off, I assume the smoke is just coolant residue heating up and making a vapor that can be seen. It is that I don't remember seeing this before when I started the engine to determine which cylinder the rod knock was coming from.....Rich

That depends what is a "short period of time". How long did you run it? Without water flow, hot spots can develop very quickly in thin areas of the head.

I personally would not run an engine without water flowing through it for more than 2 seconds, especially aluminum head engines. When I had to run it longer (a VW diesel engine on the ground for about 10 minutes) I ran water through it open ended with a garden hose and let the output spill onto the ground. I was surprised that output water was warm immediately after engine started.