valve stem seals
 

hello, i have been told that the valve stem seals in my australian
gas powered w116 6 cyl need replacing. No smoke at this stage out of the exhaust mechanic has told me to watch the oil level and not to worry till the blue ?? smoke appears. car has 340000km and goes hard and strong on the open highway. what experiences do others have on this subject. thankyou for your help sugestions in advance

340,000 kilometers is about 211,000 miles, and that is a significant amount of miles if you are still running your original valve guides and / or valve seals.

I think your mechanic is right in that oil might be leaking down your valve seals and you are simply burning oil.

If the usage is more than 1 quart of oil / 1,000 miles ( you do the quart / mile to metric conversion), then it's time to replace the valve guides and / or valve seals. Valve stem seals and valve stem guides will wear - it's just a matter of when they are worn out and how the wear takes place.

The question is this: how does your mechanic know whether the problem is worn valve guides or valve seals?

The primary wear areas are between the valve stem and the valve guide, and between the valve and the valve seat.

Every valve moves up and down: once for every two revolutions of the crankshaft. The valve stem is lubricated by a light film of oil that gets by the seal at its top.

Depending on your driving technique, it is not unusual to have to replace valve guides as early as 75,000 miles to as much as 150,000 miles. If you use large throttle openings at low rpm's, the valve gets hammered into the seat, which is what causes premature wear.

Your mechanic should first do a compression test and a cylinder leakage test, to make sure whether or not your problem is due to cylinder bore wear.

The cylinder leakage test requires pumping air into the cylinder with the piston at top dead center, and then measure how much air leaks out. Your mechanic should also remove one valve spring and valve stem seal, and wiggle the valve in the guide to see how much free play (wear) exists. An experienced mechanic can tell whether or not the guides are worn.

If the valve stem guide clearance is within specs, the engine may need only valve stem seals. In this case, you are in luck, because the head does not need to be removed to replace the valve stem seals. The head does need to be removed to replace valve stem guides.

Putting in new seals may keep your engine another 75,000 to 100,000 miles, depending on how you have taken care of the engine. This is where frequent oil changes pays off. The more you invest in oil changes, the less you'll pay for engine repairs.

If your guides are worn, then the head comes off, and it is probably a good time to look at all the other parts of the head: timing chain, timing chain sprockets, timing chain rails, timing chain tensioner, cam lobe wear and bearing surfaces, rockers, followers, lifters, valves, valve springs, etc.

Sugi,
Thanks for the thorough description of stem seal and guide issues.
On my 4.5, obscene quantities of smoke pour out the tail pipe on most every start-up. The guides/seals must be so badly worn that oil just dumps into the cylinders. Also, there is usually very visible blue smoke wafting out the back on leaving a stoplight. My friend on following my car commented "There's so much blowby that George Bush could declare your exhaust system a natural resource for drilling exploration"
I guess its high time for a compression and leak test (probably like a seive).
Well at least I only paid 500 bucks for it and got my moneys worth out of it but I'd hate to put an old benz to death.
I don't think it smoked that badly when I got it a year ago. I'm beggining to wonder if the leaky radiatior which leads to occasional high temps has made matters worse. It never boiled over but got almost to the red a couple of times. I watch it like a hawk and drive it easy.

joshhol: I am going to say YES on that one: my parents changed the oil religiously on our 4.5 and it only had ~40K miles on it when they got it in the late 80's, and the rad developed a leak - in its years before we parked it (before I did all the work on it and got it running) it never overheated, but did get hot a few times. My cams and rocker arms were a MESS. This is the only thing I can attribute it to. Therefore, I am going to guess that these engines suffer severe damage to the top end when they get too hot!
If your 4.5 isn't rusted at all, I'm sure plenty of people here *cough*me*cough* would gladly buy it off you for $500 - even if it smokes as badly as my dad's GMC p/u with 180K miles! :D

Well Tomguy,
I would like to see it survive in some way. I'm not one to send an old Benz to the crusher unless it's wrecked or rusted beyond all hope.
This one, however has several problems:
Cosmetically rough
Interior very humble
Front end shot (probably to include saggy front springs)
Toasted exhaust
Window regs toasted
Rusted trunk
Rear tires with negative camber possibly due to low sagging front end (no hydro-compensator here)
No hubcaps for that urban assault look
and on and on.
One of the reasons I wanted it was to take something rough into San Francisco and not worry about it. But when I turn the engine over, the hippies give me dirty looks. I don't blame them. That and exhaust filters into the car if the windows are open.

Just curious what you might be able to do with it? Would you pull the heads and re-guide and stem it to see if it stopped belching smoke? Not to mention the geographic obstacle.
I'll report back on the compression/leak down test when I get around to it.
I'd keep it for a beater if I could eliminate the hot running, smoke belching and exhaust poisoning in the passenger cabin. However if I can find one cheap enough that is in better shape, I could go for it. When that happens, ol bilgey might be headed to Silver Star Recycling in Sacramento.

Well, if it had a good body and frame, since mine is rusted badly and I'm going to eventually have to get it welded if I want it to survive a few more winters here (and the underbody sealed as well), and mine is mechanically sound, I'd swap the engines from them and the interiors as well as anything else that needed to be, then if I had the time I'd try to fix the engine up on the "bad" one and get it running well and get the frame and body welded/repaired so that it would be a good historical car... and I wouldnt mind having 2 108's, a daily driver and a show car ;)

Well, that's a heck of a lot of work, but nothings wrong with that.
There are much better candidates out there for donor engines. The cosmetic shape of this one disqualifies it. For one thing you've got the pathetically replaced ugly solid brown cloth headliner that hangs down in the back and was cut to close enough spec. The dash is cracked, the wood is a joke, rust bubbles under the paint in various places. I wish I had a digi-cam.
This thing really is a beast. It definitely has the warrior spirit though.
I'm sure between the factory manuals and this forum, there's a lot I could do to keep it going.
I'll let you know the compression/leak specs when they come out.
Late,
Josh