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duxthe1 · #1 05-04-2017, 08:55 PM

So I bought another coupe recently. Got it for a song on Ebay. Well there is no such thing as a cheap Mercedes and this one had a problem with the #4 cylinder leaking combustion into the cooling system.

So off with the head. Sure enough #4 has a slight line of corrosion through the fire ring that almost looks like a scratch. Minute enough the motor actually ran ok, but still enough that pressure would build in the cooling system. There is also coolant residue half way up the intake manifold from it. Pretty yucky.

With the head off I found some interesting things. This isn't actually the original head. The car was built 4/90 but this head is the post 11/90 head. Smaller diameter valve stems and the cam thrust bearing is the middle cam bearing instead of half moons at the front.

Well I'm never one to leave well enough alone. Looking at the head the ports are pretty darn nice as MB cast them. The only place I see room for improvement is in the chamber. About 15-20% of the intake valve is significantly shrouded at low lift. A die grinder may have done the job of adding some clearance but for the sake of consistency I made a tool that would cut the additional clearance around the valve seat.

I used an old head gasket to determine how far out I could go and locked the cutter at that distance. I started out by using a cheapo drill to spin the cutter but the interrupted nature of the cut didn't give a very good result. I switched to using a T-handle by hand and got a much better cut. After cutting to depth by hand I switched back to the drill to get a better finish on the side of the cut.

First picture is the damage to the #4 cylinder. Next is the tool in a port. Last is the clearance gained by the operation.