Broken Valve Spring ('91 300E)
 

Well I pulled into work yesterday (after a 40 mile drive) and the car lost power. Poped the hood and hear what sounded like a really bad lifter.

Got the car home, pulled the plugs and did a compression test. Everything was 170psi except #4 which was 0psi. Pull the valve cover and found that the exhaust spring broken. Why? Stuck hydrolic lifter?

Anyone have a good procedure on how to change the spring?

I'll probably change the spring, the cup, and the hydralic lifter.

Anything else I should change.

Anyone recommend a valve spring compressor that works on the M103 engine?

Thanks.

First, I'd be concerned that there may be further damage. Since the valve spring closes the valve, the valve and piston may have come in contact.

Possibly the spring itself just failed. Hard to tell without replacing the broken spring and checking.

Does the valve move smoothly in the guide? That should indicate whether the stem is bent.

Fit a new spring and test compression again to see if the valve still seats correctly. If compression is good you should be OK.

If problems show in the checks above the head will have to be pulled.

Hope it's OK for you.

You need to remove the rocker arm bracket on that cylinder & then connect at least 90 PSI air supply to that cylinder with spark plug removed. For just 1 cylinder you can use a screw-down(over-head valve) type of compressor from a regular parts store.

If you can use a generic compressor like the one described by Doc for one cylinder, could you not use it for all of them in order to change out valve stem seals?

I wonder this also because I am too cheap to pay someone to do the seals and I am too cheap to buy the 'good' tool.

Anybody?

Marty:

Yes indeed. I can't see paying 200+ dollars for a tool I may use just one time. If it will work for a single cyl. repair, then why not all of them?

Of course you can! Just takes longer to screw up-down than the factory tool!

Broken Valve Spring -91 300
 

A bad lifter would not cause total loss of compression which should be closer to 195 as per MB. The lifters are located on the ends of the cam followers and when collapsed add only a small amount of play.You can purchase a universal valve spring comp. from NAPA which will work fine. Some folks use and depend upon an air chuck to keep the valve from falling into the cylinder. I would strongly recommend bring the piston to TDC before starting the procedure. While you in there, replace your valve stem seal. MB has been known to use materials which prematurely harden.

Has anyone ever seen a valve spring break?
 

Has anyone ever seen a valve spring break? Anyone know why?

When you get the old spring out...

You can examine the pieces. I would guess either a nick or a rust pit and then fatigue until it finally gave up. Seen lots of coil springs, sway bars and torsion bars which die due to small rust pits/fatigue.


Michael

Fatigue!

Have seen at least 20-30 broken springs on various engines. The latest was 2 weeks ago on a 2001 S430!!!

On 1989 & earlier MB with M 103 engines MB suggests that valve springs should be replaced as a complete set any time they are removed!!

If you dont want a valve to fall in using the air method, You must be at TDC compression stroke for that cyclinder. Not to be confused with top dead center of the exhaust stroke which is 180 degrees out and has the exhaust valve and intake open. Other wise a valve could drop in. Of course if the valve is bent and hissing air out, it might drop in the cyclinder anyhow.
If its is just close to tdc but not perfect, the air could move the piston down and rotate the cam.
Funny as this sounds I "fixed" a slightly bent valve once by attaching a dent puller and slamming it home/closed. Worked good enough to make it run. Otherwise pay big bucks.

Humm,


I was not aware of it being a general problem- go to know. If they are designed and manufactured correctly-springs have an infinite life.
Ok- maybe resonance problem causing failure...

Look at the broken spring when it's out. See if the striations from the cracking start at a point(ie they should start somewhere and get courser and look fresher). That would be a way to see if it is a manufacturing defect.


Michael