namasgt

hello
Im sending my heads out to get repaired. the drivers side has 2 corrosion spots but their not that deep, with a little welding it should be fine if resurfacing doesn’t take care of it. but the passengers side has 8 corrosion spots, 4 of them are nasty deep, one of them is 0.053 inches deep. the machinist said if they weld they could warp the head and they will not be responsible for it, its my call if I want to weld. they have not seen the heads yet.
what should I do ? I personaly think 8 corrosion spots is too much.
the car is a 88 S4 with 95000 miles on it.

blown 87

My machine shop has done several for me over the years, and every one of them had to be put in a jig that can be twisted and then the whole thing goes into a big oven to relive the stress, then they are put on a surface mill before the valves are done.

On a head you have to head you have to heat it before you can weld it, so they should have a big oven all ready to put it in.

That is my understanding of how it is done correctly.

namasgt

pics

6.0-928S

Cast iron, to be done properly needs to be heated. Not aluminum. I had one of my exhaust ports welded & the head is fine. But if I was having the gasket surface welded I'd definately have it resurfaced afterwards.

Hammer

namasgt

hello Greg
he did say they pre heat it. but if this one head is going to take alot of money to repair I will just get another one. the corrosion on the gasket is horrible.

blown 87

Any aluminum over 1/2 inch thick needs to be heated to weld.

It conducts heat to well to get a good weld if it is that thick or over if it is not heated.
Trust me on this, or ask any welder who does much AL work.

blown 87

Many times that is the cheapest way to go.
I do have one suggestion, find a really good machine shop, stay away from any that does not have a surface mill to do the heads, many have what looks to be a large belt grinder and it does not make for a good, lasting job.

6.0-928S

The baseplates for my ITB intakes are 1/2" thick & did not have to be heated. They were welded by Ed Quay & he IS an expert. I agree that large aluminum (over 1/2") objects would have to be heated to weld properly but is a 928 head that thick?

Hammer

RyanPerrella

Those are some really nasty heads

Those must have been sitting for ages, or had original fill coolant for the life of the car.

blown 87

Yes, in places it is that thick and it is a large part.

I would not even try to weld on something close to 1/2 inch thick in aluminum with out preheat it.

No doubt that Ed is a better welder than I am, so that may be the difference.

DR

IF you can find someone who TIG welds aluminum all day long, everyday, this is nothing. The problem is almost every machine shop you go to (or at least in my experiance) always seem to have someone who say they can weld aluminum..they always did more damage than repair. This is what prompted me to get my own TIG years ago.

I'm with Hammer, I pre-heat my aluminum with my TIG, my oven is for powercoating. I can put more heat into an aluminum part with proper modulation in no time at all before actually attempting the welds. In my experiance, when you see those "aluminum welder guys" grab a propane torch to "pre-heat" the aluminum ... grab your part and RUN...even if it burns a little :-)
I could have saved literally thousands of dollars if someone had told me this 5 years ago. :-(

As always, everyone's experiances are different.

blown 87

The guys that do my machine shop work have been voted the number one machine shop in the US at least once in the last 15 year, they are really good.
They have repaired many heads for me and I have never had a issue with any of them.
But I agree that you have to know what you are doing to do good work.

I do not do enough TIG work to be good at it, but I still am better than a lot of "Welders" so I do understand where you are coming from.

DR

Another thing we have in common

namasgt

The name of the machine shop I was told to take them to is "Pete’s machine shop". they are in Haltom City close to Forth-worth. Apparently they did work on one or two 928 heads as I was told.
Tomorrow I will find out.
Im definitely learning a lot about engine maintenance, had no idea not replacing the coolant will do that to the heads.

blown 87

So will using some tap water, I always use distilled water and check for any voltage to ground with the engine running and hot, from the coolant to ground, anything over .3 volts is bad.