TheSamba.com :: View topic - Pre-Heating Heads Before Welding

Wed Nov 23, 2011 8:47 am

Anyone preheat heads before welding?
Anyone ever welded aftermarkets like Competition Eliminator or SCAT.
What were your experiences/thoughts?
What TIG filler Rod are you using?

Wed Nov 23, 2011 9:03 am

When we used to cut the chamber floors out of s/p heads and reweld to the lower fin(kinda hard to explain) I would always preheat. Without it took forever to get a good puddle going. And I believe I used 4043 rod

Wed Nov 23, 2011 9:05 am

I thought preheating all aluminum head was a nessissity,and normal.

Wed Nov 23, 2011 9:17 am

mark tucker wrote: I thought preheating all aluminum head was a nessissity,and normal.
It's more of a necessity with Magnesium.
Ambient temperature and equipment make a difference too.
I am also assuming we are all talking about TIG welding and not torch welding or spool/MIG.

Wed Nov 23, 2011 10:48 am

I would also think that preheating the heads will reduce the chance of any warp from heat-build.

Wed Nov 23, 2011 1:35 pm

I have a 1/2" thick aluminum plate about 12" in diameter that I set on top of a hot plate to heat things I have to weld or expand collars or gears to fit over a shaft.

Casey

Wed Nov 23, 2011 2:28 pm

mark tucker wrote: I thought preheating all aluminum head was a nessissity,and normal.

X2! I preheat any 1/4" and thicker aluminum using whatever means I have available (propane torch, Oxy/Acetylene torches, BBQ, or oven) and if it's over 1/2 or 5/8" thick and a larger area needs to be welded, I just stick it into an oven or BBQ that has been preheated and leave it on the top shelf with a plate/pan under it. When it's no longer pink in the center, remove and serve! :shock:

Andy

Thu Nov 24, 2011 7:55 am

yamaducci wrote: I would also think that preheating the heads will reduce the chance of any warp from heat-build.

Pre-heating..any metal really...will make it take the weld better. This practice decreases cold-welds. NOn-ferrrous are particularly prone to cold-welds as they dissipate heat out pretty good. In other words, you have a better chance of making a good puddle when they parts are warm.

Your weldor should know this if he has been trained properly. Or if you are not sure, read some welding books.

Warping is part of welding. That area you just welded will shrink!! :lol:

Depends too if what welding you are doing. Are you attaching parts or building up an area??

Also w/ non-ferrous, the prep-work in cleaning is very crucial. Oxides will readily form if not clean and no amount of welding current will break through all that. TIG-welding alum or non-ferrous takes a LOT of current. The machine has to be big enough..at least 250 AMP...or you will just be tickling the metal.

Fri Nov 25, 2011 12:45 am

When my buddy TIG welds heads, he pre-heats them for 15-30 min on a hot plate, then welds them on the hot plate.

Fri Nov 25, 2011 8:05 am

Bruce wrote: When my buddy TIG welds heads, he pre-heats them for 15-30 min on a hot plate, then welds them on the hot plate.

That's exactly what I've done in the past.

Fri Nov 25, 2011 8:49 am

Mark....or anyone for that matter: Do you have a pic that is closer in of the ares after it is welded? I'm getting ready to have mine done up. The guy I'm having weld them is a phenominal welder, and welds SS and aluminum all day long, but has never done VW heads. I would like a good pic to show him what I am needing done so that he has a visual. Thanks

Fri Nov 25, 2011 10:23 am

No I don't. That was done about 7 months ago on my airplane motor. Dropped the CHTs a ton.

Fri Nov 25, 2011 2:03 pm

nsracing wrote: Warping is part of welding.
Not if you know what you're doing.

Sat Nov 26, 2011 8:15 am

Pre-heating helps tremendously.. Post cooling is what I consider to be just as important..

Sat Nov 26, 2011 8:22 am

There you go!! No one really mentioned post weld scemario scept jake

True , its quite important , atleast to the heads and chambers we weld here :)

Sat Nov 26, 2011 10:18 am

Bruce wrote: nsracing wrote: Warping is part of welding.
Not if you know what you're doing.

You obviously have NOT done that much welding then, or maybe read thru the whole welding process. If you are just putting a tiny spotweld, then sure. But if any extensive heat application on the part WILL most surely warp that part. Machine shop will have to remachine most aluminum extensive welding repairs.

It all depends too on how thick the part you are welding.

By all means, don't cook the part if you are TIG welding. Hence you have to pace and time yourself if concetrating heat as you CANNOT stay there too long. If you are welding multiple areas in the head, you have to alternate the welding areas to control the heat.

On the VW head, if modifying the plug areas to take smaller diameter plugs, these kinds of welds are small. But if reconfiguring chambers, this is extensive welding. And you most certainly need to pay attention the excessive heat.

As already pointed out, the post-heating most certainly is very important to address the stress. Unless you do lots of work on aluminum heads, I do not think one will have a pre/post-heat oven just laying around.

I use temperature sticks to let me know if the head has reached preheat temperature. A small propane stove is all I use to preheat and turn the head often in minute increments. After awhile you have a good idea how long it takes for a VW head to reach the temperature. For welding just the plug areas, one preheat is plenty to do both holes.

Hope this helps the original poster.

Sat Nov 26, 2011 10:20 am

I think if you can control the cooling rate, you can eliminate a gross amount of the warpage.