Valve seal job on '72 280SEL 4.5L - PeachParts Mercedes-Benz Forum

#1 11-03-2003, 05:44 PM

What tools do I need to replace the valve seals, also what tools will I need to adjust the valve seals? I am just doing the valve seals right now, and I am going to see what will happen. Do I need the same kind of wrenches that you need to do this on a diesel? Could I do this basically with metric wrenches and sockets? Does anyone know of a website that has a how to guide on how to do this even if it is in a different Mercedes-Benz? I would imagine that most of them are the same. I will probably get a Chilton's guide to see if they have it in it.

Thanks for yor help
Tim

psfred · #2 11-03-2003, 10:04 PM

Tim:

You MUST have a special crowfoot to adjust the valves -- adjuster is an interference thread "post" on the opposite side of the cam from the valves. Not absolutely necessary to replace valve seals, but nice. DO NOT use a standard crowfoot, as there is a radius on the edge of the working part, and the nut is very thin on the adjuster -- a standard crowfoot will almost always round off the nut. It is supposed to be fairly hard to turn.

You can make one if you need by grinding the bottom side flat, but the 'special' one isn't very expensive.

To replace valve seals you will need compressed air and a spark plug adapter to hold the valves closed and a valve spring compressor. Force the rocker arms off the adjuster stud and remove them from one cylinder. Apply compressed air to that cylinder through the spark plug hole, then remove the valve spring and pull the old seals off. Use the little plastic cover over the valve stem when installing new seals so the retainer slot won't cut them.

Re-install springs and retainer before venting the air pressure or the valve will fall into the cylinder! Replace rocker arms in original position.

Also, get a complete set of the plastic clips that hold the cam oiler tube on and replace them when you are finished with the seals, you will break the old ones (very brittle) when you bump the oiler tube.

The only Chilton's manual for this car available today (if it still is!) is almost useless. Get the CD manual on this site, or go to eBay for a factory manual.

Start engine with valve cover off and VERIFY that you have oil delivery out of the oiler tube BEFORE driving the car, or you will be getting a new cam or two if the oiler leaks!

Peter

Tomguy · #3 11-03-2003, 10:11 PM

FYI: I was able to use the Sear's 17mm crowfoot w/o any issues. I did have to use an extension though.

300SDog · #4 11-04-2003, 01:48 AM

You also want to set each piston at TDC when you pressurize the cylinder with air..... just in case you drop a valve - it can be retreived using a magnet.

Find TDC by probing spark plug hole with pencil while turning the crankshaft.

joshhol · #5 11-05-2003, 01:07 PM

In the factory manual, it talks about removing the valve cone halves with a special tool magnetic lifter. I was going to ask about this step since I need to do this job as well. Can anyone shed light on this step?
Thanks

psfred · #6 11-05-2003, 07:29 PM

Any "retriever" magnet will work, smaller is probably better.

The rational is that the "keepers" are small, smooth, and oily -- easy to drop and then you've got to fish them out of the spring seat area in the oil standing in there.

Going back in they will be clean and dry.

Peter

#7 11-11-2003, 07:10 PM

Are there any how to websites on doing a valve seal job on a 4.5?
Thanks
Tim

WANT '71 280SEL · #8 11-13-2003, 09:42 PM

I will be accompanying Tim on this adventure. How do you get each piston at TDC with a pencil? I don't understand that. I am looking on fastlane and don't see anything about cam oiler clips. It speakes of cam oiler kits but I think that is the hose or pipe itself, but that's it.
Thanks
David

psfred · #9 11-13-2003, 11:11 PM

Remove spark plug, and feel for the piston to stop moving through the hole.

If you use compressed air after removing the rocker arms, the piston will "motor" to BDC, but the valves will stay put from the air pressure. If you use 50 psi or so, you won't be able to push them down. If the intake or exhause hisses while you pressurise the cylinder, the valves are burned and you need to do a valve job.

I will probably be in Fr. Wayne over Thanksgiving, we should get together. Won't be driving the 280, alas, the heater doesn't work well enough and I don't trust the cracked block that far yet!

Peter

300SDog · #10 11-13-2003, 11:58 PM

Probing through spark plug hole will measure piston's up stroke.... eraser side down will not scratch anything and grip piston crown..... when it approaches TDC the piston pushes the pencil out. Naturally you dont want to break the pencil and should readjust it and turn the crank very slowly. Easiest method is pull ALL the spark plugs then work from the cylinders that are closest to TDC. With all the plugs out you can practically turn the crank by hand yanking on pulley and belts........ this comes from one-time experience with 220Sb.

IMHO, valve seals fall into DIY labor of love category - not the easiest job, but not the toughest either...... probably a "6" on degree of difficulty scale with things that can go wrong - not something for the mechanically challenged, but fun way to lose yourself for at least a full day if you enjoy working on your own car. Poking and pulling out old valve seals was toughest for me. Was lucky to have a very good spring compressor on loan.

WANT '71 280SEL · #11 11-14-2003, 08:08 AM

When valves are burnt don't you have to put new ones in as well as have guides done? Will the air try to leak around the piston rings or is that only if they are in bad shape?
Thanks
David

psfred · #12 11-14-2003, 06:19 PM

If the valves aren't too bad, they can be ground and the valve seats resurfaced, but usually by the time MB valves leak, they are so worn that they need to be replaced. Valve guides are usually worn by this time, too, so the head comes off and you do all of it at once.

Not cheap, sadly, but if you have less than 250,000 miles on it and the valve guides aren't worn, new seals will fix you right up. I've seen it any number of times -- oil consumption goes from a quart in a thousand miles to zip, no more blue smoke on startup.

Peter