How to Measure a 4G63 head for thickness

[BogusSVO]

How a 4G63 cylinder head is measured for thickness.


This is a fairly simple thing to do.
This will also help in setting the timing belt and calculate combustion chamber size.

New head thickness is 5.200
The Mitsubishi factory manual says a combined total of .008 may be removed from the block and head.

AERA (Automotive Engine Rebuilders Association) says .015 can be milled from the head.

So by AERA specs the Min thickness will be 5.185


The tools needed will be few.

Something to use to clean the head gasket surface
And a set of venier calipers,
Paper and pen.

The first thing to do is remove the head from the engine.
Remove both the exhaust and intake manifolds.

Now on the work bench, remove the cam caps

The cams and followers.

Next roll the head over so the head gasket surface is up.

Now the head gasket surface needs to be cleaned of any old gasket material.

I use a stiff backed long body board.


Now roll the head so one port side is up,
I will start on the exhaust side.

Measure from the valve cover rail to the head gasket surface.
I will also use the cam cap mating surface on the top, it will help keep the calipers square.
Make a note of the measurement.
This is Exhaust Front
On this head it was 5.193
Next I will move to the rear of the head.

Make note of this measurement.
This is Exhaust Rear
Here I measured 5.190

Next roll the head over to the Intake side.

This is the Intake Front
The measurement is 5.191

Now to take the forth and final measurement.
This is the Intake Rear

This measured 5.188

So now with the 4 measurements.

EF=5.193 IF=5.191

ER=5.190 IR=5.188


We see the head is not parallel to the valve cover rail.

We can see that from side to side there is .003 difference
And the same .003 from front to back.

Note also this head was belt surfaced before.
This is not a badly surfaced head for being belt surfaced.
The combustion camber volumes will still not be equal.

 

[AllanL]

so this head needs to be milled?

 

[BogusSVO]

Allen yes this head was milled, for several reasons.

First it was belt surfaced, and that will not provide a good sealing surface or a good camp force.

Second it is not parallel front to back or side to side, tho not bad off, it is still not right.

Third, look at the third pic, and you will see low spots from the water ports to the combustion chambers, the dark spots are low spots. Just replacing the HG would still not fix this, the new HG would fail in a short period of time, and maybe as soon as backing it out of the driveway.

 

[toybreaker]

You returned that head to service?

 

[BogusSVO]

I would have to say so, I wrote this how to 2 years ago, and I can only recall junking 3 4g heads.

 

[iceman69510]

What about the damage in that one combustion chamber?

 

[BogusSVO]

Something got between the piston and the head. But it is inside the fire ring seal, so it will not hurt anything, just doesn't look pretty.

As long as any other associated damage was fixed, it will be fine.

If you think that is bad, you will enjoy this....

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