Why NOT to let your head be belt surfaced
 

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.

This is the surface finish left by a belt sander

https://www.miataturbo.net/attachmen...ine=1332296046

This is how the surface looked after I milled appox .002
https://www.miataturbo.net/attachmen...ine=1332296046
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.
https://www.miataturbo.net/attachmen...ine=1332296046
I made another pass of about .002
This is how it looked.
https://www.miataturbo.net/attachmen...ine=1332296046
I made another .002 cut
And was to this
https://www.miataturbo.net/attachmen...ine=1332296046
So one more pass to clean the gasket surface, and proper clamping force will be kept on the head gasket.
https://www.miataturbo.net/attachmen...ine=1332296046

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.

Happy to see a shop give a F--- and measure things. Now if I could just find a local place to do machining that wasn't full of morons I'd be set.

lol @ ghetto machine shops.

That is pretty lame. BTW, see if you have a macro mode (flower icon) on whatever camera you're using. It would help tremendously with your photos. Bring it into a well-lit area if you can. More light=better focus, shorter exposures, and more depth of field.

and turn off the flash when taking pictures of shiny stuff.

a belt sander?
jesus

I have an old Fujifilm Finepix 4 mega pixel camera I use around the shop.
From what I can remember I did not use a flash, I just have alot of lights up and on in the shop.

phillyb.. It is a belt surfacer, but it is nothing more than an overgrown belt sander, alot of machineshops have them and use them, they can do OK for a cast iron head with a composite gasket.

They are cheap to buy $10k and under new, and take very littler training to use, and they are quick to use.

But they mangle alum heads 99% of the time.

unbeleivable. that is janky as ----.

A couple of internet pics of belt surfacers.

Bogus, any reason you aren't a vender on the forum? You seem to pretty competent at your craft, something I think alot of people struggle to find locally.

What is your plan for the valves that are now exposed? In one of the pics before they were removed, it looked like there was a bit of contact with the mill and valves.

Luke..... I just came here to learn about the 1.8l, and share some of what I know and do. I am a small one man shop.

Maiter.... Honestly, I can not say what I did to fix the 2 valves that I tinged, it has been a few years since I orginaly wrote this.

But knowing what I do of hot spots and trubos, I proberly pitched the valves and grabbed a coupple stock used replacements and seated them in.