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  #31  
Old 02-12-2009, 10:27 PM
KAdams4458's Avatar
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The seals are just supposed to hold back oil. That's what has me so very interested in this thread.

I know that poor piston sealing is the major contributing factor to blow-by. My 300D did, in fact, have some seriously clogged up rings. The first time I soaked the cylinders with MMO, it all drizzled right past the rings and in to the oil. After several weeks of soaking, oil changes, test runs, and more soaking, they eventually stopped leaking, and will hold MMO for a long time. Once I sorted out some other compression leaks, I can report having between 320 and 340 PSI on all five cylinders, and yet, I can still watch a trickle of oil run from the valve cover vent hose and in to the intake manifold. (Not the vacuum pump, it's new!)

My engine was pretty neglected, and had such tight valves for so long that it ate the soft cast camshaft lobes up pretty badly, so the valve seats are obviously suspect. Admittedly, I have not run the engine long enough to give the valves a chance to really pound back in to their seats, but given my current compression, I feel that they could make a decent recovery.

Now, I've had the top end far enough apart to wiggle the valves, and the valves didn't have any perceptible movement to them. They could still have massively worn guides, but I was only trying to rattle them by hand. For the most part, they all slowly would creep down from the closed position when gravity had its way, and the exhaust valves slid at least three times as fast as the intake valves. They didn't feel bad at all, but they didn't feel or look to be well sealed, either. (I didn't have any replacement seals on hand because the local parts store FORGOT to order a set for me, and I had no time left to wait on parts before putting the car in to storage. Boneheads!)

The question I'm hoping this thread will answer is this; Will valve seals alone contribute to less oil being vaporised in to the valve cover area? I know they're mostly intended to keep oil in the valve cover area from getting sucked in to the motor, but if air is leaking past valves under cylinder compression, and they do to some extent on every engine, will fresh valve seals prevent so much oil from being blown in to a mist by escaping compression that it creates an oil mist that escapes through the vent hose and subsequently gets sucked in to the intake? Basically, I wonder if they work both ways.
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'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
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My '77 300D progress thread

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  #32  
Old 02-12-2009, 10:50 PM
Ether's Avatar
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My little maintenance project sure has stirred up an interesting thread.

As I noted in my original post the exhaust seals were all shot with the tiny rings all broken or missing. I too would think that bad seals would be a minimal contributor to pressure inside the valve cover. But lacking any real way to measure that pressure before and after the repair I can only rely on the visual evidence that I have reported.

Maybe 500 miles is to soon to properly evaluate seepage. We shall see, as I will continue to report my observations. Stay tuned.
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  #33  
Old 02-13-2009, 10:02 AM
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Quote:
Originally Posted by KAdams4458 View Post
The seals are just supposed to hold back oil

The question I'm hoping this thread will answer is this; Will valve seals alone contribute to less oil being vaporised in to the valve cover area? I know they're mostly intended to keep oil in the valve cover area from getting sucked in to the motor, but if air is leaking past valves under cylinder compression, and they do to some extent on every engine, will fresh valve seals prevent so much oil from being blown in to a mist by escaping compression that it creates an oil mist that escapes through the vent hose and subsequently gets sucked in to the intake? Basically, I wonder if they work both ways.
I have not read all this enough to give any sort of total answer..
but would suggest that you look at the FSM pictures and descriptions of the valve stem seals... 05.4-270/2 in my manual...
To summarize... the valve stem seals at one time came in two lengths. Only the shorter are available now... the shorter ones have a ' gas tight lip' in addition to the oil lip... Someone has probably posted this a picture of this page in some discussion in the archives....
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  #34  
Old 02-13-2009, 10:25 AM
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Post Oil Cap Leakage

This is a good thread ! .

As I'm too busy (or lazy) to do this repair on my , my brothers or SWMBO's 310,000 mile Mercedes' Diesels , I use another method you won't belive works until you try it :

Clean the cap gasket and rockerbox mounting surfaces perfectly dry before replacing the oil cap ~ this means a few minutes with several sheets of toweling every time you add oil but folks always ask how the heck my engine is so clean and I only wash it once or twice a year (I hate oily engines) .

So , if that black gooey mess around the oil cap bothers you , give it a try .

I do this to the cylinder head's deck every time I adjust the valves to and the rockerbox doesn't leak either ~ this on high milage OM617 engines that use a quart of oil every tank of fuel.....

I know I should just replace the stem seals but what the heck .
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  #35  
Old 02-13-2009, 11:23 AM
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Oil cap leak...
I am not the first to mention this... but the main cause of oil running down from the oil cap onto the top of the valve cover is making the mistake of turning the oil cap upside down when having it off the valve cover... keep it in the same position it is used in and you will have a cleaner valve cover and probably worry less about blowby ... since it won't look so much like oil is being blown out of the top of the valve cover by ' excess pressure' .
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  #36  
Old 02-13-2009, 01:35 PM
KAdams4458's Avatar
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Quote:
Originally Posted by leathermang View Post
Oil cap leak...
I am not the first to mention this... but the main cause of oil running down from the oil cap onto the top of the valve cover is making the mistake of turning the oil cap upside down when having it off the valve cover... keep it in the same position it is used in and you will have a cleaner valve cover and probably worry less about blowby ... since it won't look so much like oil is being blown out of the top of the valve cover by ' excess pressure' .

My oil cap was leaking because the gasket was completely hardened and rotting away. I guess more than 480,000 miles will do that. I did notice some time ago that turning the cap upside down let oil run run in to the top side of the cap that would later dribble out over the valve cover later. Your tip is a good one.
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'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work


My '77 300D progress thread

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  #37  
Old 02-13-2009, 01:45 PM
KAdams4458's Avatar
Mmm! Diesel!
 
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Quote:
Originally Posted by leathermang View Post
I have not read all this enough to give any sort of total answer..
but would suggest that you look at the FSM pictures and descriptions of the valve stem seals... 05.4-270/2 in my manual...
To summarize... the valve stem seals at one time came in two lengths. Only the shorter are available now... the shorter ones have a ' gas tight lip' in addition to the oil lip... Someone has probably posted this a picture of this page in some discussion in the archives....
I'll be darned... You are absolutely correct. The updated seals do have a gas tight lip. I wonder how much of an improvement over my old "tall" valve seals that will make.
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- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work


My '77 300D progress thread

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  #38  
Old 02-13-2009, 04:27 PM
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Quote:
Originally Posted by KAdams4458 View Post
I wonder how much of an improvement over my old "tall" valve seals that will make.
I remember my indy/friend in PT mentioning that "the intake and exhaust seals used to be different". that was about five years ago when I was rebuilding my 616 in his shop and we were ordering parts.
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  #39  
Old 02-13-2009, 04:29 PM
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the set I bought came color coded for exh / intake although the FSM states there is no difference after a certain date. The sizes were visually identical.
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  #40  
Old 02-13-2009, 08:19 PM
KAdams4458's Avatar
Mmm! Diesel!
 
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The seals actually changed dimensions to the shorter versions back when they up-rated the NA engines with the chilled camshafts and chrome rockers/valve cap nuts, according to the FSM. Increased valve lift was the reason for the decreased height.
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- K.C.Adams

'77 300D Euro Delivery
OM617 turbo / 4-speed swap
404 Milanbraun Metallic / 134 Dattel MB-Tex

Current status:
* Undergoing body work


My '77 300D progress thread

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  #41  
Old 02-14-2009, 08:51 AM
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The seals...
Attached Thumbnails
New valve stem seals installed-valve-stem-seals.jpg  
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  #42  
Old 02-14-2009, 01:56 PM
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Quote:
Originally Posted by Shawn D. View Post
You know, folks, that blowby comes from rings as well. In fact, rings are probably the major culprit in almost every case.
Quote:
Originally Posted by Dionysius View Post
If the Seals make a noticeable reduction in Valve Cover pressure what I am saying is that it will be difficult to explain. The challenge here is to keep an open mind and analyze the data we get from Mr Ether who is doing a great job in providing us with the data.
I wasn't denigrating Ether's input, and he obviously understood and addressed the point I brought up. Valid points that don't support the gist of a thread shouldn't automatically be considered attacks on other posters. Keep an open mind about that, OK?
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  #43  
Old 02-14-2009, 04:27 PM
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Often in a thread people's attention gets focused on something to the exclusion of the bigger picture... I thought your reminder was a good one.
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  #44  
Old 03-10-2009, 10:53 AM
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Ok fellas, sorry for the delay in getting back to this thread but I had some brake issues that took my attention and parked the car for a while.

Got the brakes squared away and finally got around to evaluating my oil usage. I went a bit over my 1k mile check point but at 1250 miles I THINK I can offer a fairly accurate observation.

It would appear that my oils usage is less than I have been experiencing. I was down about half a quart as opposed to the typical quart or so prior to the valve stem seal replacement. I can also report that the top of my valve cover remains free of leakage from the cap as does the area around the valve cover gasket.

Disclaimer: Far from a scientific analysis this is merely my observation of oil consumption pre and post seal replacement.

I will be taking the old boy on a road trip to Orlando this weekend. I am curious to see if oil consumption is different with extended highway driving as opposed to the mix of stop and go & highway of my daily 60 mile round trip commute.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1980 300SD - 495k miles - 'The Ambassador'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

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