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Tig Welding Water Passages shut on bmw motor?



bradler451
12-28-2009, 03:17 PM
I have changed lots of head gaskets on my BMW 87 m20 motor. The motor is turbo and low compression. A common mod to the head is to weld the water passage shut then to drill holes so coolant can still get pass. How would this be done with out warping the head and how does it look like they completed this task. This is a picture of a companies head they welded. Some they cast over the whole hole then they deck the head. Any suggestion???

Hamstn
12-28-2009, 04:16 PM
Looks like those heads are Aluminum? If so then tig welding them would be the way to go. I would thing it would take lots of heat to warp the heads but not taking a chance I would weld in short sections at a time. If a shop done those welds I think I'd only weld what they did or maybe just on the inner side of the passage to give a bit more room between it and the cylinder. Another way to look at it would be to lay the head gasket on there and weld it all up to match the size of hole in gasket. Sort of what you would do to port an intake/exhaust port.

Does the gasket blow between the passage and cylinder or passage to outside of head? May have to do same on the block. At any rate then the head will have to be decked to smooth out your welds.

junes
12-28-2009, 04:57 PM
Your not going to warp it if you know what your doing. Heads get hot no matter what so don't worry about that. No way around it just get them decked. I would use a copper backing strip behind the weld to make it a bit easier to build up the material.

Gadget
12-28-2009, 05:02 PM
You are going to have to have the head surfaced when done anyway. Even if you did have some warpage it would be corrected by surfacing.

junes
12-28-2009, 05:05 PM
Thats a good point gadget. You don't have to worry about it too much.

bradler451
12-28-2009, 06:45 PM
ThanKs every one sounds good. What is a copper backing strip??? Where do u get them?? I shouldnt build it up with aluminum???

junes
12-28-2009, 07:29 PM
The copper backing strip is just a piece of copper that you place on the back of the weld. Since the weld will not adhere to the copper it acts as a starting point. You can just start building up from that point. Just makes life alot easier since aluminum doesn't have much surface tension making it tough to fill holes with no backing on it. I always use it when building up or filling in holes in aluminum. I hope this explains it a bit better. Why do you want to do this anyway. What's the bennifits?

bradler451
12-29-2009, 05:01 PM
these water passages are a common weak point for the head gasket. I want more surface area on the head gasket so i dont have to keep changing the gasket. The bmw is turbo and under boost even a multi layer headgasket seems to warp then crack at these passages. So its really i am just trying to save time and money. If not u have to keep untorquing the head bolts which are like star socket and getting new gaskets.

NoRdO
12-30-2009, 12:32 AM
I think he means a strip to place under the gap that you are welding on so it is easier to get the weld pool to travel to both sides.

Gadget
12-30-2009, 10:57 AM
I think he means a strip to place under the gap that you are welding on so it is easier to get the weld pool to travel to both sides.

Welcome to the forum NoRdO, when you get a chance please post an intro in the introduce yourself forum so we can get to know you.
Thanks for joining us,
Dan

junes
12-30-2009, 03:47 PM
Kind of it's so you have something to start with and it gives you a nice flat back.