Hi guys,

I'm soon going to be pulling my M103 open to replace the timing chain and tensioner, and while at it I am thinking of doing the valve stem seals. Motor has 153,000 on it. I've got a little adapter that I've made to inject air into the cylider to hold up the valves(using compressed air from a "scott" bottle from the firehouse) and I saw that the manual has some special tool for compressing the valve spring to remove the collets. I have an "overhead valve spring compressor" the Lisle type from another car. Will this work on the MB, or is the special tool absoulutely neccessary. Any other hints and tips on these two jobs would be greatly apprciated.

Thanks
Evan

Don't know what a "scott's" bottle is but you will need a tremendous amount of air. There will be significant air loss through the rings for all the time the jobs take. It's going to have to be a big bottle.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

The kind of valve spring compressor that hooks on the camshaft should work. I'm not sure there's room for the kind that grabs the lower coils and pulls them agaist the upper retainer.

Is there a reason you're replacing the chain and tensioner? M103s are not knows for throwing chains regardless of mileage unless foreign objects are involved.

I don't know what a scott bottle is but it might be easier to stuff rope in to the combustion chamber to keep the valves in place. Make sure the rope isn't the kind that sheds. The manual says to give it 5bar which is around 70psi.

Sixto
91 300SE
87 300SDL

As Sixto stated, there's most likely no reason to replace the chain if you're doing it for preventive reasons. If you've been changing your oil regularly, you will likely find the chain in excellent condition with little or no stretch.

Do replace the tensioner rail and guide however, if this has never been done.

Good luck!

~Paul

_____________________
'91 300E, 215K miles

A "Scott" bottle is short for a Scott Air Pack or SCBA - self contained breathing apparatus. It is that yellow bottle you see on firemens backs that contain the breathing air for use when they are going into an area full of smoke. In addition, they are located throughout facilities where you may come in contact with noxious fumes and/or gases and you need to carry your own air. Not sure how long it would keep the valves in place but the bottle does have an indicator on it to alarm you when it is starting to get low.

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Jim

I really think you'll want to use a tank with compressor arrangement, not just a tank. A normal cylinder leak-down for an engine like this would be in the 20% range.
Gilly

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I used the Lisle compressor - it worked but it was a battle all the way. I wouldn't use it again on the M103. The type that hooks on the camshaft would make life much easier.

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Oupa
1988 300e

Thanks for all the info guys!!

Everyones right about the Scott bottle, it is an SCBA bottle. I hadn't thought about the leakdown through the valves, the bottle does hold lots of air, enough for me to breath for almost and hour(if breathing regularly) it at about 4500 psi, and I have a tool regualtor to bring it down to any pressure I want with air tool type fittings on it. I've run an air ratchet constantly for over 45 mins on one, but like you guys said since I haven't done this before I guess I'll try to get my hands on a compressor. As for the valve spring compressor, thanks to whoever said the "lisle" style didn't work to good. I know performance products sells the MB style, I wonder if anyone rents them. Anyone know of any other good ones??? The consensus of opinion is that I don't need a new chain, oil had been changed religously at 3000 mile intervals, no noise or such coming from it even when cold. I had just always heard to replace 'em at about 100k -120k.

Thanks guys
Evan

V8 chains should be replaced periodically since the direction changes present a tougher environment.

Just about any auto parts store sells the kind of valve spring compressor that hooks on the cam. I have one that cost about $20.

Sixto
91 300SE
87 300SDL

I replaced my M103 valve springs seals about 6 months ago using compressed air and an overhead type valve spring compressor. Everything went smooth. I used 100 psi air pressure. My compressor has a 20 or so gallon tank and it was cycling about every minute (lots of air). I wouldn't risk the possibility of dropping a valve by using the Scott bottle.

A couple tips:

1. When compressing the spring, give the collet a sharp rap with a small hammer to unwedge the keepers. If you don't do this the valve will start to open and your air will come rushing out.

2. Temporarily cover the oil drain holes around the valves so if you drop something it won't go inside the engine.

3. Use a small magnet to remove the keepers and the round shim between the valve stem and rocker (these are the parts that can get lost in the engine). A set of picks also comes in handy for maneuvering the keepers in and out of place.

4. Use prelube or heavy weight engine oil on the new valve guides and when reassembling the rocker parts.

5. I also brought each cylinder I was working on up to TDC so if I did drop a valve for some reason, it would hit the piston and not drop into the cylinder. This takes some care in doing because you have to turn the engine slightly beyond TDC, until the piston just begins to go down, and then hold the crankshaft with a good size socket braced against the garage floor. The socket keeps the engine from turning due to the air in the cylinder. Note that the direction of rotation of the crankshaft will tend to loosen the crankshaft nut, although the torque is not enough to actually do that.

My car(89 420 sel) was burning oil and thru this site I realized it was the valve stems(and not other things) and instead of paying $2000 or more I found out that the parts cost $50 and it took 2 1/2 hours work, so I paid $280 and my benz is not burning oil anymore ! The timing chain is the same way, you just need to change the guides and not the chain.

The chain is less than $70 and replacing the chain will take a seasoned pro less than 30 mintues while addressing the guides. Seems like cheap insurance.

... on an 89 420SEL, that is.

Sixto
91 300SE
87 300SDL