Welding VW heads??

My buddy, Vic Giles, has this Sonerai homebuilt airplane. It uses a VW engine for power. He's giving me lathe lessons today and shows me some of the VW heads he has that have some cracks in them. The cracks are all in the same place, inside the spark plug hole in the threads. The crack runs from the top of the threads to the bottom and is very, very small as far as width goes. It appears that the crack does not go beyond the threads in depth, although there is some blow-by coming from the combustion chamber, up through the crack showing up by the side of the plug. Vic has redrilled and machined the heads to accept a second plug for each combustion chamber and these holes do not crack. He asked me if I thought I could try to fix these heads up (they cost about $300 a pair with valvetrain). I said that I wasn't sure and that I might ruin them. He said "they're no good now, so how much damage could you do?"
My question is, these are aluminum (I don't know what "flavor") ..my thoughts are to use a carbide burr and grind through the threads and create a U shaped channel where the crack is, then fill the crack with filler, grind it down a bit and rechase the threads for the plugs. Does this sound like a reasonable approach? If I mess it up, Vic doesn't care and I figure the experience might be good. I don't know what filler to try or if there might be a trick to this.
Any thoughts would be appreciated.
Thanks
J

Shops that rebuild VW aircooled heads have to weld virtually every head that comes in. It is a super common practice. Plus, there are loads of performance mods to these heads that require building up aluminum in spots and machining back down.
There have been many articles in both Hot VW's and VW Trends magazines about welding heads. The rebuilders have a large oven that they preheat and postheat the heads in. I forget the preheat temp, but I seem to recall it is 600 degrees F. I also recall seeing Miller welders; in one picture they had a Syncro 350, in another a Syncro 500. I believe you need a lot of power, as the aluminum is really thick in that area.
They ground all of the crack out with burrs, and built it up, followed by machining both the spark plug holes and the valve seats.
Bottom line; you need a good preheat oven, a massive TIG welder, good machine tools, and the capabilities to do a good job. Suggest you check out back issues of aforementioned mags, and contact some rebuilders for advice.
Jeff
James Arnold wrote:
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VW tended to have good castings for their heads. They are pretty easy to weld, compared to bell housings. You will have to grind out the crack to get down to clean metal. You will have to preheat the whole piece up to about 600 degF. This can be done in an oven at it's highest roasting temp.
You will need some good thick blankets, wool or welding blankets, to wrap around it to handle it and protect yourself from the heat.
You willhave to run your machine at it's maximum output with the biggest tungsten you can fit.
As far as alloys go. 4043 can often work. I prefer 4047 for castings. The higher silicon content of 4047 gives it a lower melting point, much better wetting and less shrinkage. If you need some I can send you some. I had to buy large quanitites last time I went looking for it.
Keep it wrapped up while you work on it, and when done, bury it in a pile of vermiculite to keep the heat in.
An Argon/Helium gas mix can help a lot too. For something this heavy I would go for at least a 50/50 mix, maybe even a 75% Helium/25% Argon.

I can get about 225 amps out of my HTP Invertig. Do you think that will be enough to get it done with preheat?
Thanks
J
On Tue, 14 Oct 2003 03:08:28 GMT, Ernie Leimkuhler
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If the aluminum is hot enough you might just get it to melt. You should max out the frequency on your arc to help more, and cheat your AC wave balance towards max penetration.
Give it a shot.
I think your machine might be too small, but it might just make it with the higher frequency.
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Ernie:
Sure, send me a few pieces. Let me know what you need in return ($$) and I'll get it to you (paypal??)
Thanks
J
On Tue, 14 Oct 2003 03:08:28 GMT, Ernie Leimkuhler
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James, Ernie has given you some excellent advice but I would add just one thing. Drill a small hole just beyond the end of the crack to stop it from going any further into the cast body. Then complete the job just as Ernie has told you. Harry

I had thought about drill stopping the cracks, but I don't think I can get a drill in there to do it!! Pretty tight..I'm going to have to extend the tungsten quite a ways out to get into the hole to weld up the crack as it is!!
Thanks a lot for the help.
Jamie
On Tue, 14 Oct 2003 18:32:43 +0100, "Harry Culshaw"
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Perhaps you didn't read or comprehend the implications of my post. Welding the crack will do no good, as will just drilling the ends. The rebuild shops I mentioned earlier have lots of experience on what works; please respect that. You need to totally grind out the area and build it up, then machine. Trying to weld the crack will result in the crack still existing in the bowels of the head, and it will crack again once hot.
Jeff
"Jamie Arnold (W)" wrote:
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What he mentioned earlier sounds like grinding and machining to me.
Jamie Arnold (W) wrote: ..my thoughts are to use a carbide burr and grind through the threads and create a U shaped channel where the crack is, then fill the crack with filler, grind it down a bit and rechase the threads for the plugs.
Jeff answered: You need to totally grind out the area and build it up, then machine. Trying to weld the crack will result in the crack still existing in the bowels of the head, and it will crack again once hot.

Jeff:
Please read my orignal post. I described how I intend to grind out the crack, then fill the area with weld, grind that down and remachine the threads.
J
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