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  #1  
Old 07-21-2004, 03:18 PM
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Thumbs up W126 Valve Stem Seal replacement DONE!

Well, here it is the day after the BIG JOB, and I canít believe I DID IT, and it's a smashing success! For a bit of background, Iíd been getting the blue smoke on start-up for the 2 years Iíve owned the car, and figured (correctly) that it was valve stem seals. I paid little attention until this year, when the oil started fouling the plugs and affecting the idle, badly. So, I bit the bullet and took 2 days off work, finishing last night.

The project was a success in large part due to the search on this forum and the many posts/tips learned herein. It was also a success because of careful planning, the right tools, and that old standby, luck. So I thought Iíd share a few tips that didnít show up in the searches, and certainly werenít in the MB shop manual.

To begin, the valve spring compressor I used is home-built from a copy of the real MB tool that my friend made up when he left Mercedes to go on his own. I found the geometry of my version a bit off, so that made pushing straight down on the spring retainer (to get slack to remove the %$^&*$# retainers/keepers) difficult. If I had it to do over, Iíd probably get a buddy to do the pushing down while I used both hands to get the retainer halves out.

To hold the valves up when the springs are out, I followed procedure and used about 100lbs air pressure. I made up a fitting by smashing out the ceramic and all internals of a used plug, then brazed an air line fitting to the plug casing. Unfortunately, the female air coupling wonít quite fit the plug recess, so I added a 4Ē length of hose and another fitting to get it out beyond the exhaust manifold. Turning the hose by hand works fine, no wrench is needed to seal the air connection at the spark plug hole.

Tip no 1 is about getting the air pressure inside the cylinder without moving the crank and carefully positioned cam lobes (now in TDC. I chose to do each valve completely, 1 by 1). First, turn off the air and connect the fitting, then reduce pressure to about 40lbs. Turn on air, then slowly increase to 100 lbs. I mashed a finger when the socket wrench jumped as I connected at 100lbs, so that was when I changed my method. Plus, if it moves the cam too far, you've got to start all over to get back to TDC.

Tip 2 is all about my previous post about watching the crank damper markings and finding TDC. It is MUCH easier to go 1 cylinder at a time, 1 Ė 8, doing each valve completely before moving on. By sticking a 12Ē piece of wire, bent at about 8Ē or so, into the spark plug hole, I put a bit of white tape lined up with the edge of the valve cover seat on the head where the TDC position of the piston is. This is about the same for each one, so I just turned the crank until it was there, removed the 2 rockers and shims, then did each valve in turn completely for each piston. (springs off, old seal out, new seal in, springs back in, return rocker arms before moving to next cylinder).

I used tweezers to pluck the keepers out of the retainers, but found that magnetized ones work best to get them out, but are a pain to put them in because they arenít easy to release with one hand (other hand is holding the spring compressor. Be ready for mighty sore muscles next day!).

Use rags, lots of them, to cover as much of the exhaust area and especially oil holes, as possible, for when one of those little cone halve keepers bounces out of your tweezers, or hemostat, which I also found useful for returning them to the spring retainer. But, Tip 3, watch that you donít get the rag caught in the cam gear when turning the crank over to get to TDC! (You canít turn the engine backwards either). This is easy to do when your attention is on the rear cylinders.

Tip 4 is from another post, but a small magnet sitting between the valves will catch the wayward keepers some of the time. I was very lucky, and only Ďlostí 1. It ended up on the floor, just waiting to be picked up!

Iíll end this with a question for those whoíve been there. One of the hardest steps was actually detaching the old seal from the guide groove. I used a flat blade screwdriver levered on the head for most of them, but every one was a ***** to pry loose because thereís no room to work. Especially on nos. 4 and 8. Those I used a trianglular scraper on, levering the point with the handle.

But is there a special tool or trick to getting these off? Pliers donít grip at all.

All told, it took 8.5 hours to fabricate the air fitting, remove and mark all vacuum lines, fuel lines, plugs and wires, valve covers, and complete the seal change on numbers 1 - 4 . The keepers on no. 1 took me ĺ hour alone! The change on cylinders 5 Ė 8 took only 3 hours. Add another 3 hours to put everything back, including new plugs and an oil/filter change, and you have the DIY amateur verson of an $800.00 job. But, my engine purrrrrs now..... ....and my wallet is only out $80.00 for seals.

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Old 07-21-2004, 06:07 PM
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Thanks for the write-up!
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Old 07-21-2004, 07:11 PM
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valve stem seals

I just did the same on my 190E since I was shipping the head off for a rebuild, but I did it before I knew I would be shipping it

It is a 4 cylinder engine, and I found an amazing spring compressor for $12 at princess auto, it works like a charm, never slipped, always fit right in and made spring work a breeze.

I was able to pull the seals off with some pliers, I'm not sure if they are the same on my car, but I was very surprised they came off so nicely compared to other heads I worked on, but prying them up with a flat screwdriver also helps, just make sure not to scratch anything

Very good DIY job, I also had the cylinder head off, so I did not need pressure to keep the valve in place, but fabricating a fitting from a spark plug, that's pure genius, I would have never thought of it

Great work Don keep it up

xp
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Old 07-21-2004, 10:23 PM
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Well Done!

It was truely a pleasure to read your post. I already have a spring
compressor, the one from Sir Tools. Other than the spring compressor and fitting for the spark plug hole, was there any other special tools that would make the job go easier?

Some day I hope to be as brave as you and undertake the job. I have a few years to find the courage and plan the job, since the seals were done about 2 years ago.
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Old 07-21-2004, 10:50 PM
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Good job! Sounds like it was a real pain. I tried the compressed air method before, I had a compression tester that could be simply plugged in to my air line. Unfortunately, even with 150psi it was never enough to keep the valve in place. So I just put the piston at tdc and let it hold the valve for me.
So what are you going to do with all the money you saved?
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Old 07-22-2004, 12:57 AM
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Hey Don!
Congrats again to your achievement. I had to do the same thing on my 82 380 sel. Unfortunately, I had to replace the head gaskets too. If I ever have to replace seals in another future project v8, I would just pull the heads. At least you know the head gaskets won't leak oil for another 100k. So after complete seals, head gaskets, valve adj, chain rails-guides, and h20 pump, the car purs... and gets an honest 21.5 mpg. Not bad for such a huge car and 126k. les
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Old 07-22-2004, 07:52 AM
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Cigar Havana posted
Quote:
Other than the spring compressor and fitting for the spark plug hole, was there any other special tools that would make the job go easier?
Yeah, I forgot to mention (Tip 5) the slightly reamed out thick washer that I used to push the seal onto it's seat on the valve guide. The seals for my 116 engine have a steel casing with a small protrusion of sealing material that retains the tiny circular spring. A washer that just sits over the protrusion and right on the edge of the steel casing is dandy for pushing down hard to seat the buggers using thumbs and/or fingers. Beats the pricey pushing tool from MB.
Chevota:
Quote:
So what are you going to do with all the money you saved?
Tip 6: Don't brag to the wife about it, as she will instantly find ways to dispose of said savings!
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Old 07-22-2004, 10:33 AM
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I heard of using rope instead of compressed air to hold the valve closed, sounds like a good idea.
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Old 07-22-2004, 03:28 PM
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air pressure

I do not understand why the air pressure method is used by so many people when replacing the valve seals. If you work on one cylinder at a time, and set the valve on the cylinder being worked on at TDC and secure the wrench holding the crack so it will not move, shouldnt this be enough to assure that the valve will not fall inside?

thx
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Old 07-22-2004, 04:19 PM
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emmydotnet: I believe the correct answer to your question is this:

The valves need to remain on their seats, not merely be kept from dropping into the cylinder, in order to replace the seals and then replace the springs and retainers, keepers, etc. Having the valve on the seat is imperative so that the full length of the valve stem is available to allow work room when the spring is compressed to do the refitting of retainers and such. Springs only compress a small amount beyond the normal valve lift before coil bind occurs. If the valve drops only one-eight inch onto the piston top at TDC, that one-eight inch becomes very important when holding down the compressor with one hand and fitting the other small bits with the other hand, all while sweat is running into your eyes and colorful curses drift from your lips.

Just a thought from one who has a developed a very broad vocabulary of colorful curses while doing these sorts of things just to save a bit of $$.

Cheers,

230/8
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Old 07-22-2004, 06:16 PM
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Don, I'm looking at doing the same job on my wife's 560. Did you find much valve guide wear when you had the springs off? Wife's car is starting to use a lot of oil (not fouling plugs yet!). I had always heard the valve seals were kind of an early point for oil leaks. I just don't want to pull the heads if I can help it.
Thanks
BobK
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Old 07-24-2004, 02:01 PM
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Quote:
Did you find much valve guide wear when you had the springs off?
Well, I took the time to wiggle some of the valve stems just after removing the spring assembly and old seals. I couldn't detect any perceptible play. However, as the air pressure was holding it up on it's seat, that alone may have prevented my feeling play if there was any.
At any rate, I know when this engine was last rebuilt, and the rebuilder is a friend of mine, so I'm guessing that in my case, since the car sits in storage Nov - April, and doesn't get much mileage when it's running either, I believe my seals just plain dried out, moreso than wore out. There was a noticible difference in the internal diameter of the seal, old to new.

Quote:
secure the wrench holding the crack so it will not move
230/8: Well phrased answer, 100% agreement, but I don't understand what 'wrench' and 'crack' emmydotnet is referring to? As far as I can see, there is no way to slip the new seals onto the stem unless they are completely bare.
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Old 07-25-2004, 01:12 AM
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230/8:
thx for the clarification....now I see why I would need the valves seated why I work on the seals.

what size of a compressor would do the job?


donbryce
the wrench is what you would use to turn the crank pulley.

thx
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  #14  
Old 07-26-2004, 12:27 AM
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valve stem replacement insitu guides too

My older brother replaced the valve GUIDES on is 450sel several years ago without pulling the heads. One of the old pne was floating in the head and he had to install the biggest oversize guid he could get. Chilled em in his wife's deep freeze and then in dry ice/gasoline mix just before installing them. Worked like a champ and ran another 100K miles without anymore problems.
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Old 07-26-2004, 08:18 AM
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This technique deserves a post of its own.

Wow. Now there's a procedure we'd all love to hear more about! I can possibly see how one might extract the old guide from the head, leaving the valve stem sticking up through the hole. How did he do this?
Then, I gather the chilled replacement was pressed into the hole, pushed over the valve stem? How did the chilling process not also make the valve stem bore in the guide smaller as well?

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