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#1
01-03-2012, 08:38 PM
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M103 Head Rebuild
I need some specs if anyone has them.
Some of you may remember that roughly a year ago I completely rebuilt and tuned the CIS-E system on my 1992 300E 3.0 with 210k miles. Since then it has run quite well, averaging about 22.5 MPG in the city and up to 26 MP US gallon on the highway at just over sea level. I have noticed that the oil consumption has been about a quart per tank of gas and knew that I would have to get the head off at some point to fix that. A sudden drop in mileage forced the issue. I had to pull the O2 sensor (Bosch 13953 is the inexpensive replacement if you can solder the OE connector on yourself) that was new a year ago and torch it to get it working, though not perfectly, again. Oil contamination killed it until I brought it back from the dead. I have a new one, but did not want to put it on until I had the head repaired. Fuel mileage got better, but was not back to what it was a couple months ago. Notes on head removal: I did NOT remove the intake manifold If you can remove the exhaust manifold to head STUDS along with the nuts, you can leave the exhaust manifolds in place. Don't forget the Allen screw at the back of the head that attaches the EGR tube. Leave the cam gear in place, just unscrew it from the cam and note the position of a couple cam lobes. This will put the car right back at pre head removal cam timing when you just bolt the cam back in. NOTE: You will need to remove the Timing Chain Tensioner SPRING before you pull the gear off the cam. You will need a 12 mm Allen wrench (or better, socket) to remove the cap (passenger side of the front of motor) to get to the spring. If you forget to do this, the plunger (feeds one way only) will tension the chain and you will not beable to get the gear back on the cam at reassembly. You can solve this problem by removing the tensioner (17 mm Allen wrench) and popping the inner plunger through the outer plunger and then feeding it right back in the other side. If the chain has forced the tensioner arm down, you can carefully pry it back so you can reinstall the tensioner all the way in. IMPORTANT Remove the locating pin for the plastic timing chain guide by screwing in an M6 bolt about five turns and then wiggle/pull the pin out of the head. I pulled the cam out of the head before I removed it to make the head lighter. Watch out for the little shim/cups that sit between the rockers and the top of the valves and the crescent shaped spacer in the front of the head. The intake valve seals were hard as a rock. Notes on machine work: It took about 0.003” of surfacing to get the head flat. There was a slight dip in the middle on the exhaust side. Valve to guide clearances were about 0.0015 on the exhaust side and 0.001 on the intake side. I note this because I have read several posts about replacing the valve guides. I do not have the specs, but this kind of clearance on 8 and 9 mm valves with over 200k miles suggests very little or no wear. Two of the exhaust seats were still perfectly concentric, two came in after feeding down 0.0012, one took about 0.003 and the worst one took 0.0044. I took them all down 0.0012 beyond the initial cleanup. By the way, my Newen G2 is for sale if anyone is interested. I need a new pilot for the intake side, so I’ll have those numbers in a week. EDIT The intake seats had moved quite a bit more than the exhaust seats. Two required 0.014" to bring concentricity back. How much this changed my balance for compression ratios, I did not bother to calculate since this is a commuter. You performance guys might want to check all the combustion chamber volumes and then match them to each cylinder so you end up with balanced compression ratios. Parts I will replace:
While I am waiting for my intake pilot, can someone please tell me the valve to valve guide clearance specs. I do NOT want the wiggle test specs, though I can do the math to back into the clearance specs if that is all MB lists. Thanks!!! Last edited by KJZ78701; 01-19-2012 at 01:37 PM. Reason: INTAKE Seat Information 
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