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Old 07-17-2010, 06:33 PM   #1
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I had the head flange made at a local laser cutter when I had my manifold made. It was a very good price. I am now considering selling the things as there is nobody else here in the U.K. who is doing so, and I think I could make a little on each one and still offer a decent price.

When mine was made the fabricator gave it to me to make sure it fit, then I gave it right back for him to weld up the manifold. He clamped it down during welding to keep it flat. Well I recently had one made for a friend of mine (no profit this time) and he is going to do the welding himself. He has just emailed me to say that when it is laying on the workbench is is slightly bowed out. Measures 2mm gap in the center when laying on the table.

So the question is, is that an acceptable tolerance? Mine seals fine but I didnt think to check for this when I had it in my hands. (and I am damn sure not pulling it off just to check) As it is clamped down flat when welded would it make any difference anyway?

These are in 12mm mild steel BTW. I suppose the real question is, would this be an acceptable tolerance to begin selling them, or would you have a fit if you received it like this to use? As mine works and seals fine I am inclined to think it makes no difference, or when it is clamped and welded it straightens it out.

Those of you in the know with this sort of thing, please give me your thoughts.

Sorry for the novel
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Old 07-17-2010, 06:49 PM   #2
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Cheaper than this?
http://weirtech.ca/catalog/product_i...roducts_id=107

And yes, you need to weld it so that it doesn't warp or machine it flat after you have finished or it will not easily seal.
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Old 07-17-2010, 07:03 PM   #3
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When you ship things from the states to England, you combine the cost of the purchase with the cost of shipping (and U.S. company's ALWAYS pad the shipping internationally, they would most likely want around $30 to ship that) and take %10 of that number, and that's the import duty. Then you add all that crap together and %17 of that is the sales tax. And an extra 10 for the post office svc. charge to do all that math. So in U.S. dollars that would end up costing $80 or so when its all said and done.

I could supply these for 30 delivered ($50 ish), have it arrive in 2 days, and still make just enough to make it worth the trouble.

What I wonder is, is it common practice to mill the flange flat after welding? if that is the case a 2mm gap isn't going to upset people much
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Old 07-17-2010, 07:20 PM   #4
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In my experience the flange is going to try and warp as it being welded so 2mm probably isn't that big of a deal. I've always heard its good to bolt it up to a big piece of aluminum while you weld it so it will be relatively flat when finished. Just my take on it.

Michael
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Old 07-17-2010, 08:22 PM   #5
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2mm is a lot and definitely wont seal. Like Blaize said he could have it surfaced to alleviate the problem.

The heat has a tendency to shrink the metal or pull it towards the heat. Also welding a 12mm thick plate to relatively thin tube(compared to the plate) causes an issue as well. The different thickness materials heat and cool at different rates which means they expand and contract at different rates not as one piece. This means different amounts of torque applied in different directions at different times. Chances are none will be equal so it will deform to some extent.

Clamping it to a thick piece of aluminum will help to hold it straight plus the aluminum acts as a heat sink drawing the heat out as you weld. Or if it's convex, as your looking at the head mating surface, it may warp in the direction you want it to.

I would just try to get it close and have it surfaced. A belt sander that's longer than the flange or a mill will do the trick.
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Old 07-18-2010, 02:49 AM   #6
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I read somewhere a flatness tolerance of .040" (1mm), might have been my subaru shop manual. Factory multilayer metal gasket FTW. Also, keep it bolted to the head when you weld other stuff to the manifold after you have the head flange welded on...when I cut & weld the EWG flange onto my manifolds it tweaks the head flange otherwise. Just recently I added 4 EGT probes to a mani that I had already beltsanded flat...wasn't flat after welding the bungs on. This is with stainless which will be much worse than mild steel.
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Old 07-18-2010, 02:54 AM   #7
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Stainless is a finicky bitch. It likes to get harder as it gets hotter. Kinda like me!

Off topic: Tim you've been coming up with some trick stuff, looks good man!
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