Why NOT to let your head be belt surfaced/sanded

[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




































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.

 

[prove_it]

Damn. So how can we guarantee that when we get head work done that it's done right?
I never knew the difference in head machining.
I trust my guy completely, but as for others on here.....

 

[BogusSVO]

That's the reason I post, so others not in the field will have an idea what to look for.

Ask questions, how long the machinist has been doing it, what kind of equipment is used.

 

[Wizardawd]

I only have one machine shop in my town and the next closest is literally almost 1.5 hours away. And so many horror stories from this shop. Flywheel resurfaced, but they didn't do the step, and tried to say we didn't know what we were talking about. A couple heads that were pulled off running cars that just needed a gone through and valve/seats cleaned. Next thing you know, the head has been shaved to below spec and was told that was the only way to get it straight. Of course it wasn't warped in the first place. And of course the bead blasted head that had beads all up in the oil galleys in the head.
I hate this shop and because of them, I have assembled every motor over the last 10 years on my own. I cringe anytime I need to take anything to them and pray it comes back ok. And the guy wonders why his son's Eclipse with 10k into it only made 304hp at the wheels. Yeah, you know, the kind of power a 16g makes with a bone stock motor.

Anyways, thanks for the info Bogus. I have run into the head situations before. The best is when you take in a warped head from an overheated car. They say they can just shave it to straighten it. And when you try to explain why that doesn't work, the look they give.

Wiz

 

[BogusSVO]

I hear stories like that all the time. Even in my town with 7 or so machine shops, you hear horror stories. most over surfacing issues and MLS head gaskets.

Some shops still run wore out equipment, or just out of date. I was picky when I was buying my shop equipment. The head shop and surfacer mainly. My boring bar stand was another I stressed over.

One of my main sayings are "Not all shops are equipped equally."

Do I have all the newest latest and greatest machine equipment on the market? No, I know I do not. I bought what would fit in my budget and still do a good job and fit with my knowledge base.

There are a few shops I know of that I wish I could buy out and just shut down. Lotto dream ??? lol

I just hope some learn from my posts, and have a better idea what to look for and what to ask.

 

[mitsuturbo]

If you had all the latest/greatest/newest/best equipment, you'd be having a hard time with getting customers willing to pay what you'd have to charge in order to cover your overhead, or recoup some investment losses. This is why a good machinist doesn't need all the newest/best stuff. They know what they can get by with, and what is absolutely required.

Your posts are informative and clearly well meaning. I appreciate seeing stuff like this posted. A lot of guys don't know the difference between a surface prepped for MLS gasket vs a composite gasket. Maybe you could also illustrate how rods are balanced to one another, and the different methods used. Especially on the big end. Some grind the bottom of the cap, some take material off the area around the bolts. Whenever you get either back from the machine shop, often there are questions such as "why does this one look perfect and the other 3 had to be ground on?"