1986 300E 103 Engine Valve Stem Seals
 

I'm way overdue to replace the valve stem seals in my 1986 300E (289k miles). I have all of the tools and parts ready except I do not have an air compressor and would prefer to use the rope method mentioned in several posts. It looks straight-forward, but I'd appreciate any tips or watch-outs. Has anyone out there actually performed the job this way?

Thanks.

Brent Smith
Snellville, GA
1986 MB 300E 289,000 miles
2003 BMW 530i 93,000 miles
2003 Boxster S 43,000 miles

Brent, the process works great; I've done it on several engines using an outboard motor pull-start cord (just stiff enough and a good diameter).
But...... it might be a bit "iffy" on the 103 engine due to fact that you will have to turn the engine backwards to lower the piston and get the cord out after the valve work is done. Turning the timing chain backwards against the chain tensioner is something some of the pros herein don't recommend. The tensioner and it's slipper are not the problem. But, the plastic guides get pretty brittle, and if the chain slacks just a bit coming off the lower sprocket backwards, it could possibly catch the end of the bottom guide. Could be a disaster waiting to happen. Probably wouldn't happen if you go slow and carefully, as the tensioner is strong and should hold the chain in place. but, if it did, you might not find out until the damaged guide jammed in the chain at 4000 RPM.
If you do decide to do it, have all the plugs out, the fan belt off, and of course the rocker arms will be off, and turn the crank very slowly and carefully when going backwards.
But to be safe I'd recommend the air method. Pressure adapters are under $5, borrow a compressor and do it that way.

Cheers,
DG

Oh, the exhaust and intake seals are slightly different - pay attention.

i used air compressor...and some whistle thing to get it at tdc...

the passenger side seal near the firewall is tough... one time i replaced all 12... the other time i just did 11....

i think i used a 27 mm socket to turn the engine.... it's been about 5 or 6 years since i did it...


others have used the rope method with no issues...

I did the job and ended up dropping a valve stem down into the engine. I panicked and was so close to removing the head....the valve was on the passenger side and so all I did was take off the exhaust manifold and the valve stem was right there. Plus I could see all the pistons. Thats just an FYI incase you do lose one, don't panic. Removing the exhaust manifold is easy.

Thanks, DG. What is the reason for removing the fan belt? Also, don't you remove the rocker arms one at a time as you do each cylinder? It seems that the rope method would be safer in that the rope is solidly up against the valves while it may be possible to lose the air charge and drop the valves.

Thanks, Ismalley. Were you using compressed air or rope when you dropped the valve? Why do you think that happened? What would you do differently? I'm not in any hurry to take the exhaust manifold off........:eek:

Thanks.
Brent

I also dropped a valve into the cylinder. My mechanic buddy came and rescued me with a small guage Snap On magnet through the valve stem guide. Valve came right up through the guide. Big relief!!

Thanks, Dennish. Were you using compressed air or the rope method when the valve dropped?

Brent Smith
Atlanta, GA

I used compressed air. Compressor was running and I turned it off to answer the phone. The one cylinder that leaked a little air is the one that dropped the valve. Without losing air, the valves should stay up. I think the rope should work without issue.

There are small pencil diameter cups between the lifters and rocker arms that are very easy to drop. Stuff the timing chain area with clean rags to prevent them from falling into that area.

Do not over tighten the rocker arm bolts they can strip the threads in the head very easily. There are upgraded/slightly longer rocker arm bolts to reduce the chance of thread damage.

At 289K does it leak any oil from the headgasket? Has it been changed? If it leaks or has not been changed consider replacing the headgasket and timing chain and any worn timing gears.

Good luck!

Thanks for the tips, Sugar Bear. I'll watch out for those things. I have the repair history on the car and have owned it since 1990 and the head gasket is original. Actually, the valve seals are too. The head gasket does not seem to leak. The main leaks are the front transmission seal (also original) and the valve stem seals.

Brent Smith

Brent, the only reason to remove the fan belt is to make the engine easier to turn by hand - don't have to do it. Same thing for the rocker stands, just takes more load off when turning the motor. Leave at least one on to hold the cam in place. All this is only recommended to be able to turn the motor backwards VERY carefully and precisely to avoid nicking that lower chain guide when going backwards. Again turning it backwards a bit to get the cord out can be safely done if you are very careful and SLOW. And yeah, I'd probably do it if I didn't have access to a good compressor. I just hate to wake up in the night worrying about something - OCD I guess.

And, as luck would have it, I changed plugs yesterday - and #5 was pretty oily.
Hope you're not a jinx - Ha.

Good luck,
DG