valve stem seals- 4.5 engine - PeachParts Mercedes-Benz Forum

rix116 · #1 06-08-2004, 12:50 AM

On a 74 450 SEL is there any way to replace the valve stem seals
with the heads still on the engine.? I'm guessing no, but
wanted to ask the more knowledgeble ones on the board.

Tomguy · #2 06-08-2004, 01:15 AM

YES!

Get a valve spring compressor that'll fit around the cam and you can leave that on too (I'd have to take the cam off with the type I got but it was all they had that fit/worked). Just MAKE SURE to turn each cyl to TDC BEFORE you attempt to remove the spring and retainers, lest the valves fall into the cyl and you need to take the heads off to retrieve them. Some people say to get a fitting for an air compressor that you put in the spark plug hole to keep the cyl pressurized... but looking at the head, if the cyl is at TDC, you really shouldn't need this IMO. You might have to turn the spring compressor a bit more but thats all.

1) Set the cyl to TDC
2) Remove the rocker spring clips and the rockers
3) Compress a spring, remove the retainers (I'd imagine magnetized needle nose pliers would work well for this), then remove both inner and outer springs, and the bottom rotating part
4) Remove old seal, put new seal on
5) Reinstall in proper order the rotator, inner spring, outer spring, top piece, and retainers
6) Uncompress the spring
7) Move to next valve and repeat 1-6
8) Set the next cyl in line to TDC and repeat steps 1-7

joshhol · #3 06-08-2004, 02:01 AM

Tomguy has it covered. Air in the cylinder is optional. Forcing the valve to bottom out against the piston is good since it forces the top piece to push down past the keepers, exposing them and making it possible to get them out. They can be a bit of a pain. You'll also want to put a socket on the crank and with a breaker bar attached, bungee cord the bar to something like the radiator neck so the crank cant move. You don't want to drop a valve.
The factory manual has specs for which piston is TDC at different degrees.
I'll have to go look it up and get back to you.

Also, on the old stem seals, there might be a wire or something coiled around it to keep it tight. Pry that off of there before you try to pry up the seal or you may have a hard time getting them off.

Good luck.

joshhol · #4 06-08-2004, 02:07 AM

Sorry, I'm about 10,000 miles away from my shop manual right now. But I imagine if you go by the firing order and position of the rotor, you could figure out where the piston is. Also double check with a pencil eraser in the spark plug hole.

Tomguy · #5 06-08-2004, 03:24 PM

1: 0°
5: 90°
4: 180°
8: 270°
6: 360° - 0°
3: 450° - 90°
7: 540° - 180°
2: 630° - 270°

Note that the first set is what the actual degrees will be, the second is what the balancer will read. But you will have to turn the engine 2 complete times to do this, so cyl 6 won't be at TDC when cyl 1 is... it MIGHT be possible to do them at the second set of degree markings on the first rev but I'd think the cam lobe would be in the way.

And I'm assuming that 0° on the balancer is TDC for cyl 1... I would sure hope so!

psfred · #6 06-09-2004, 07:40 PM

Ah, but #6 IS at TDC when #1 is. It's just not on the intake stroke, so getting the rockers out would be a pain and risk gouging the cam.

This is all fairly straightforward, just a PITA. Don't drop the keepers down an oil drain, and don't put the springs on upsidedown.

I'd check the valve clearances after getting all the new seals in. Basically, if the back of the cam lobe is brown, you have adequate clearance (that is, the heel of the cam isn't running on the rocker). If they are shiny, they are too tight. However, you will need to roll the engine around a couple times after putting the rockers back in to get them settled down. Otherwise, they tend to sit a tiny bit crooked, and that takes up all the clearance.

Peter

Peter

Tomguy · #7 06-09-2004, 07:57 PM

Quote:

Originally posted by psfred
and don't put the springs on upsidedown.

Crud... are you sure there's an upside-down and, if so, how do I tell which side is up and which is down? I already put 7/8 of them back on my "new" left head and would like to do the right properly to avoid doing what I now must on the left, if there is a wrong way

This goes for both spring too - which way does the inner one go too?

WANT '71 280SEL · #8 06-09-2004, 10:43 PM

When you look at the spring, I think the part that has the coil closer together is what goes on the bottom. I double-check that though.
David

rix116 · #9 06-09-2004, 11:09 PM

You guys are great. I just got back into town after a 2 day bus.
and had all these responses. That gives me hope that I can solve the problem w/o taking the heads off which would be a PITA
in my car, and my rings are still pretty good.

What about (as backup to air compressor) the other old shade
tree mechanic's trick of stuffing clothes line down thru the spark plug hole into the cylinder, thus stuffing it so the valve can't drop?

KyGuy · #10 06-11-2004, 11:57 AM

This procedure work on the 6.3 m-100 engine?

Tomguy · #11 06-11-2004, 05:05 PM

David and Peter: Well, I looked at the springs - both the outer and inner - and they look identical on both ends. The outer spring is wound counterclockwise, and the inner one clockwise. Holding it upside-down does not change the winding direction either. I think I'm safe. Maybe some other engines have 1-way springs but not this one (I've worked on a 1-cyl engine or 2 that had one-way springs)

psfred · #12 06-11-2004, 10:52 PM

The valve train on the M100 is almost identical to that on the M117, so yes.

Peter

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