Why NOT to let your head be Belt Surfaced

[BogusSVO]

Why not to let your head be belt surfaced/sanded

The subject head is a Mitsu 4G63T from an Evo VIII

This head was in very good shape to start.

The head was pulled due to a bottom end problem.

It was not overheated.

It was taken to another shop, NOT mine.

The customer was told it was surfaced .003-.004

It was then run and the bottom end failed, Then came to my shop.

The first thing I did was to check the thickness of the head.

I know a belt surfaced head will not be parallel nor square along with not having the proper surface finish for a MLS head gasket.

HN#
Date
CAST#G6EW
NOTES:
IV stock
New thickness 5.200
EV stock
Min thickness 5.185 (AREA SPEC)

EVO 8

Cam Gears

Combustion Chambers

Bolt Holes

4

3

2

1

5

4

3

2

1

10

9

8

7

6

Head Thickness 5.187

Head Thickness 5.184

Head Thickness 5.189

Head Thickness 5.188

If you look at the 4 corners, you will see how the head gasket surface is not parallel to the valve cover rail.

It is close, but still off

This is the surface finish left by a belt sander

This is how the surface looked after I milled appox .002

It did cut most of the surface, but it was still low at one corner, and it would happen to be right around the oil feed port to the head.

I made another pass of about .002

This is how it looked.

I made another .002 cut

And was to this

So one more pass to clean the gasket surface, and proper clamping force will be kept on the head gasket.

I measured the head again, and it was 5.183 at all 4 corners

When I cc’ed a combustion chamber it was 44cc

I also did “oil port mod #1” before I surfaced the head.

This head is now .002 below AREA min spec, but is still a useable head.

[CarPsyco84]

LOL who ever thinks belt surfacing is a good idea on anything that needs to be even close to flat is high.

[twack]

Originally Posted by CarPsyco84

LOL who ever thinks belt surfacing is a good idea on anything that needs to be even close to flat is high.

i know,! ive beEn using a dremel

[Goat Blower]

I just beat it flat with a large hammer.

[turbotalon1g]

I just like to beat it.
I belt sanded my turbo fitting, works great for the last year.

[blackrosenova400]

Aww come on that just the wrong way of doing things. OYu should use a brass malet!

Originally Posted by Goat Blower

I just beat it flat with a large hammer.

[BogusSVO]

Originally Posted by turbotalon1g

I just like to beat it.
I belt sanded my turbo fitting, works great for the last year.

I would think there is a bit of diffrence between the surface needed for a turbo fitting (oil return I would guess) and the finish needed for a head gasket...