Cylinder Head M130

[MikeSimon]

I am sure there has been discussions about that, but it is difficult to find:
The lower limit for milling a head is given with 84mm.
What is the critical issue for giving this dimension?
Can it be addressed by using two head gaskets?
I have a SE/A head that came off a running 280SE and measures 83.4-83.6. At the very rear it is only 82.9.
Why is the head scrap? The car was running.

[ja17]

Milling of a warped head, causes the compression on the end cylinders to get higher since the volume in the combustion chamber is reduced with each milling. Normally the head warps downward on the ends. The volume of the end combustion chambers becomes smaller, the more the head is cut. I have seen compression on some end cylinders as high as 230 psi while the center cylinders were still around 170psi on a severely, over-milled head. Correct ignition timing would almost be impossible on an engine like this. End cylinders might have ignition pre-detonation (pinging) while the inner cylinders were fine. A radical, dangerous fix might be to measure combustion chamber volume and remove some head material from the combustion chamber in the head until all combustion chambers are equal. However since the valves are moving closer to the pistons after each milling, you could have problems with valves and pistons crashing into each other. In addition reducing the thickness of the head slackens the timing chain by twice the amount. Best to stay in spec. and you'll sleep better at nights!

[MikeSimon]

Thank you, Joe. One open question is still, would a double head gasket help in this case here?
The car was running fine. No issues with valve/piston interference

[ja17]

It would not even out the compression if that was a problem. I heard of people using two head gaskets, but I never tried. The cylinders are soo close together on the M130 engine. The 190SL group came up with a good solution. They have solid copper 1mm shim plate made which is cut out exactly like the head gasket. The 1mm shim plate along with a new head gasket and you are back to full size factory specs!

[MikeSimon]

I think I know who makes the 190SL shim plate (Cometic?). I talked to them regarding another project and the technician talked about something they made for the 190 group.
The shim plate is essentially a copper head gasket that goes on top of the deck under the normal head gasket?

[ja17]

Yes, I assume, but the copper plate is a lot more stable then stacking two head gaskets. It is probably precision laser cut. This might be a worthwhile project to do on M130 engines.

[stickandrudderman]

Many years ago I fitted a 2nd head gasket (at customer's request) to overcome the loss of material.
The car has run perfectly ever since.
Trouble is can't remember if it was a 230, 250 or 280.

[Benz Dr.]

As pistons move up and down in the cylinders they actually have to stop to change direction as the crankshaft goes over center. At 5 degrees ATDC the piston and intake valve are at their closest during the four cycle progression. However, the camshaft never stops turning while the engine is running.

I turn the crankshaft to 5 degrees ATDC on number one piston and then I use a small pry bar to lever the intake valve rocker arm down until I feel it touch the piston. If I can fit a .040 feeler gauge between the cam and the rocker arm the engine is within spec. You could use a dial indicator but this is just as effective and easier to do. 

[MikeSimon]

Next time I am out at Cometic I will try to get a quote for a M130 copper gasket. Then again, we have two versions. Wonder if there will be enough interest to justify the investment.