How To Resurface a 4G63 Head for a MLS Gasket

[BogusSVO]

How to resurface a 4G63T Head For a MLS head gasket.



I use a Comec Auto I 1000 High Speed Milling Machine with CBN insert for Cast Iron OR a PCD Insert for Aluminum Heads
This machine is double adjustable, I can adjust the spindle speed and the table travel speed to achieve the surface finish that is required.
Auto I 1000 CBN Surfacer


The first thing to do is check the valve cover surface for any burrs and remove them.

Next is to mount the head in the machine and check the level of the head in both directions.

Then the other way, this head was not out that bad from the last time it was milled.

I did a “getting to know you” pass of .002 to see how square the head was. This was done on a faster setting.
Notice the upper and left side of the head is dull, this is a low spot. The head was not index properly and did not maintain a proper “square” to the valve cover surface.

I made another cut of .003, I sped up the cutter, and slowed the table speed.

This is the end result.

Another different view.

Now with a proper surface, and the head re-squared, The customer will have no issues with a MLS gasket sealing, and also having a closer to equal combustion chamber size.


this is a good vid to watch, it shows BOTH the belt sand method, (NOT TO DO) and it shows the method I use, A high speed milling with a .500 insert. (THE ONE TO USE)

YouTube - Resurfacing an Aluminum Cylinder Head

 

[Barnes]

Very informative post. I didn't know about the belt sander method.

I do have one question. It seems the way this is done, the valve cover mounting surface is considered the datum. Is that because it *is* the actual datum? Or because it has not been altered since it was made in the factory it is considered the most appropriate feature to use as a datum?

 

[BogusSVO]

On the head everything will be indexed on the cam center line, much like a block is all machined off the crank center line.

Since the VC rail is machined on the center line of the cam journal bores it is simple to set up off the VC rail. This also keeps the HG surface parallel to the cam journal center line.

 

[Barnes]

Ah, I see. I forgot that the VC mounting surface is machined, probably in the same step, as the cam cap mounting surface on the head. Thus it can be used as the mount so your HG surface is now using the cam centerline as the datum. Nice to know.