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  #1  
Old 02-01-2009, 08:50 PM
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New valve stem seals installed

For the past few years my 300SD has been giving the big puff of smoke on cold starts and I have been fumigating the the poor buggers behind me in stop and go traffic.

Well today, finally, I got around to replacing the valve stem seals in the hope that this was the cause of my unwanted smoke screen. I was glad to see that all 5 of the exhaust seals came off in pieces, so I know those were leaking big time. The intakes were all intact but hard and not pliable.

I'll will be watching in the mirror closely over the next few days to see if there is a noticeable drop in oil smoke out the back.
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  #2  
Old 02-01-2009, 08:54 PM
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An overlooked, yet cheap and effective maintenance item. Congrats. It would be nice to hear an update in a few months.
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  #3  
Old 02-01-2009, 09:04 PM
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Ether..

How big of a hassle was this job to do? I've never replaced valve seals, and wonder if I shouldn't, just since what's there are 25 years old..

Has anyone done a writeup on this service??

AJ RN
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  #4  
Old 02-01-2009, 09:20 PM
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Here is a thread with a nice write up.

Replaced Valve Stem Seals - My experience

Since I had never done this before I paid a bit more than I needed and bought a kit with step by step instructions and a special tool for seating the seals. I'm glad I bought the kit but after doing the work I see know that this is a fairly simple job.

Took me about 5 hours start to finish but I took my time and that includes a trip to the store for a socket I was missing. For me the hardest part of the job was getting the old seals off. That and having to redo the exhaust valve clearance when I realized that my helper had been using the intake gap distance by mistake. Doh!
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1980 300SD - 495k miles - 'The Ambassador'
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Former Family Members
95 C280
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  #5  
Old 02-02-2009, 06:54 AM
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I would really be interested to find out if oil consumption drops appreciably. Since diesels don't develop a vaccum , I wonder if it matters that much.

Rick
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  #6  
Old 02-02-2009, 05:13 PM
Dionysius
 
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I did this job on a 617 engine ten years ago. I was not happy to find that there was no appreciable change in oil consumption.

Let us know your experience. The oil consumption problem is multi-faceted but on high mileage engines I believe it is mainly due to ovaling of the cylinders.
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  #7  
Old 02-02-2009, 05:44 PM
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I removed the head on my 81 SD and had valve guides and new seals, valves ground, about five years ago. Oily smoky mess and it cleared that up nicely. Went from using a quart of oil every 500 miles to quart used in about 1600 miles.
Cost was $300 total, and I did the labor to remove and install the head. Shop showed me where the guides were worn badly. When we unlocked the valves they slid down and would rattle around. They are supposed to be tight against the guides in there.
New seals are not a bad cure for most of the problem though.
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  #8  
Old 02-02-2009, 05:47 PM
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Quote:
Originally Posted by rs899 View Post
I would really be interested to find out if oil consumption drops appreciably. Since diesels don't develop a vaccum , I wonder if it matters that much.

Rick
I was always told they dont matter that much with a diesel, this will be an interesting follow up ("not that much" doesn't mean not at all)
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  #9  
Old 02-02-2009, 07:43 PM
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My oil consumption has been about 1 quart per 1k miles so time well tell if that changes. I will keep close track on that and report back.
I can say based on today's commute that my cloud-o-smoke upon acceleration after sitting in traffic or at a stop light is gone. Or at least reduced to the point that I no longer see the billowing cloud in my side and rear view mirrors that I had grown accustomed to.
Also, the morning cold start was smoke cloud free as was my start leaving work this evening. Typically, my car would send an oil cloud rushing to the exhaust fans at the end of the parking garage every afternoon, but not today.
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Former Family Members
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  #10  
Old 02-03-2009, 12:37 AM
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I can't speak for oil consumption.

But it is quite possible that accelerated valve guide wear could be avoided (primarily on the exhaust valves) by not allowing oil to burn on the valve shaft after the exhaust stroke.
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  #11  
Old 02-03-2009, 12:24 PM
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Has anyone seen a reduction in Blow-by after replacing the Valve Stem Seals?
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  #12  
Old 02-03-2009, 06:37 PM
Dionysius
 
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Quote:
Originally Posted by Diesel911 View Post
Has anyone seen a reduction in Blow-by after replacing the Valve Stem Seals?
A great question. I would be highly surprised to see an observable reduction but I will always defer to actual results. The seal would yield to any appreciable up pressure IMHO.
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  #13  
Old 02-03-2009, 07:11 PM
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Quote:
Originally Posted by jt20 View Post
I can't speak for oil consumption.

But it is quite possible that accelerated valve guide wear could be avoided (primarily on the exhaust valves) by not allowing oil to burn on the valve shaft after the exhaust stroke.
This is a very true statement but as you will see there are many design compromises and the net result is less that great.

If clearance is insufficient oil will not penetrate the interstitial zone between the valve guide and stem. The friction which results will cause wear and heat. This heat will cause the stem to expand making the clearance even tighter. Valve sticking may now occur which will result in abrasion and scoring. This is referred to as 'galling' which is a bonding and breaking loose process. This can procreate more damage as new high spots are created which give rise to more galling as the valve oscillates up and down.

So with this in mind it is a good thing to have sufficient clearance....but how much is sufficient. The valve stem has a significant temperature gradient and the sodium filled valves do try to equalize this some, or so I think. All in all it is a very complex set of conflicting forces. Clearance will give way to oil consumption since a differential pressure exists along the guide and a supply is present. Some deflector type methods have been used to reduce the supply of oil to the top of the guide. All in all the reciprocating piston engine is an abominable design but it was the first and so we have made it good enough after one hundred years of engineering and billions of dollars of R and D. I wish that investment had been made in rotary designs. Incumbency is not a great thing when it comes to politicians and poor designs.
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Last edited by Dionysius; 02-03-2009 at 07:17 PM.
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  #14  
Old 02-03-2009, 07:52 PM
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The valve stems are textured - not smooth. I imagine this is to help lubricate between the guides and stems...? - it allows a film of oil to remain.

Can a valve stem seal ever truly be designed with the sole purpose of restricting all oil from entering the 'interstitial zone'?

As nature would have it, and as you mentioned, heat is going to cause the most harm w/respect to the stems and the guides; and the exhaust valves are all the more critical to keep sealed. The two engines of this era I have dismantled both had clearance primarily on the exhaust valves. Easily explained by heat, but, surely, exacerbated by friction. How can we make claims against burnt oil? I have some valves laying around.


the reciprocating engine is truly outdated.
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Last edited by jt20; 02-03-2009 at 08:27 PM.
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  #15  
Old 02-10-2009, 09:06 PM
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After 9 days and about 500 miles I can report one interesting observation.

My oil cap has always leaked a bit of oil on to the top of the valve cover. I've replaced the cap, the gasket, tried tightening the tabs, but all to no avail. It has always leaked for the 7.5 years I have owned the car.

Well, this evening I took a close look under the hood for the first time since I put it back together and to my pleasant surprise the top of my valve cover is clean as a whistle. I've also always had some oil seepage under the valve cover gasket but that area is clean as well. Previous to the seal replacement there would have been oil within a day of driving so that's pretty cool.

I can only assume that there is now less pressure under the valve cover than before and that's gotta be a good thing.
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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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