Aluminum BMW Oilpan Crack Repair

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A customer who owns a car dealership had me repair a crack in an oilpan off a BMW he was working on, that apparently hit a curb.  It was from an inline 6 motor, so was a pretty long pan for automotive.The oil pan had all these weird spiderwebby looking, kind of fracture patterns ALL OVER it, but not apparently going deep into the metal (at least one would hope.)  The dealer dude (who services these things constantly) said it was normal, they "all had it", and not to worry about it.  I suspect this spiderweb like pattern all over the surface of the casting had something to do with the metallurgy BMW used for these pans.  I wonder if this is an example of "stress corrosion cracking", such as from alloys containing excessive magnesium, which are run at excessive temperatures.I repaired the fracture to make it "hold oil" again, as he asked.  I solvent cleaned locally (only in the area of the crack), veed the crack out part way with a carbide burr, hit it with a stainless wire brush, and TIG welded inside and out.  I went over it with low amps first to etch clean the surface additionally, before hitting it with the full "deep penetrating, metal melting" heat.  But aside from that, I did not perform any pre-heating using any heat sources other than the TIG arc.I used 4043 filler, and it welded up pretty nicely.  Except for the one crack that I missed and didn't vee out with the carbide burr during prep, that one had a little contamination float up and prevent complete weld bead fusion on the first welding pass, so in that spot I went over that branch of the crack a second time with the TIG torch to get the whole bead all nicely fused.  Aside from that it went smoothly.I can't remember the exact machine settings I used on this, as I did it a few weeks ago.  I welded it with an Everlast Super200P.  The thickness of this oil pan was about 1/8". Attached ImagesLast edited by jakeru; 12-05-2010 at 02:55 PM.
Reply:Did you check the flatness of the entire pan gasket flange--before and after?Clamping the pan down on surface plate during welding, helps.That has everything to do with 'holding oil'.Blackbird
Reply:Yeah from where it is it may have "Curled Up" after welding..How flat is it?If not then when you bolt it down.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Die-cast aluminum parts typically have that weird spiderweb looking pattern over them.  They aren't cracks.  I think it's from shrinkage as the casting cools in the die.
Reply:76GMC - that's interesting about that pattern being common on die-cast parts.  But, I can say I've come across a lot of die cast aluminum parts that didn't have this pattern.  I'll see if I can find it on future die cast parts I come across.Dave and Zap - indeed, flatness can be a concern when welding a structure like this especially with a long, flat machined mating surface.  I've totally warped the heck out of flat machined surfaces that were much shorter than this one, by welding right next to the flat surface too much, or too repeatedly. In this case of this oil pan, the impact seemed to have spread apart the metal along the crack a little bit.  Almost the perfect amount it seemed, based on my judgement, that welding it in a carefully sequenced manner would have returned it to its original "as cast" position.  (And I did sequence the welds to encourage bringing the metals back together, by welding from the outside edges of the crack toward the center.)A plate to restrain the work during welding was not available, not within the customers budget on this, and I don't feel was necessary anyway because of how the crack was spread apart.  Besides, a restraining plate to covered the pan surface wouldn't have allowed access to weld the inside of the pan anyway.Anyhow, I can say I never got a call back about it.  I have done a fair bit of wrench turning, surface flatness checking (block deck, head, manifold, and other sealing surfaces with a precision flat edge and feeler gauges), and flattening (mostly using flat files and rubbing with sandpaper+surface blocks.)  If I were the mechanic installing it, I'd have installed it using a fresh gasket and not expected any problems with it.Someone was borrowing my precision straightedge, otherwise I might have measured the flatness on this.Last edited by jakeru; 12-05-2010 at 09:48 PM.
Reply:I've seen the pattern on oil pans, turbo-hyrdamatic transmission cases, Honda dirt bike cases, Honda dirt bike hubs, and about 10 other places that I can't remember off the top of my head.  They were all die-cast, though.Hey, one thing about long objects like this.  It's impossible to keep them from warping.  But...  there are many bolts to pull it back flat once you install it on the engine again.  Even if it were 1/4 inch out, if there were enough bolts, it would be no problem to get it to seal again.Last edited by 76GMC1500; 12-05-2010 at 11:44 PM.
Reply:About 25 years ago I became slightly "airborne" in a Mercedes 350SL and came down hard on the oil pan.  I made it home OK, but there was a definite cracked area in the oil pan.  In those days, I didn't have Tig, so I waited for the next gun show and bought some of that magic aluminum rod that you see the guys welding up holes in the bottom of soda cans using a propane torch.  Long story short, the stuff actually worked after a LOT of heating with the propane torch, but you can definitely have a lot more faith in a proper Tig weld.  A couple of months ago I welded up a broken clutch cover on a Ducati street bike.  I had to add a sizeable patch to it to replace a missing chunk.  After fully welding it, I ran it across my flat granite surface block, and was surprised that it had no warpage at all.  I wish I had a large enough granite block to get something as large as a complete aluminum oil pan all resting on the granite at one time.  It's a good feeling to properly repair something that a non-welder would have to throw away.  Good job on the BMW.DougMiller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:Hi Everyone,I'm looking for some kind of advice. I have an Audi A4 that is leaking some oil. Perhaps up to a quart a week. THere's a smal hole/crack on the bottom of the oil pan. The stealership has quoted $670 for replacing the oil pan, but i've been reading that TIG welding may do the job just fine.If I decide to go this route, who would I call? An auto Body shop? a regular mechanic? Who would have such tools for welding? I would appreciate if somebody could point me in the right directionAlso, what should I expect to pay to have this done by a welding professional?Here's what the damage looks like.
Reply:I read about four of your duplicate posts to this one (on other threads), but have yet to see a picture of the damage of yours.As someone else mentioned in another thread, take the pan off, or have a mechanic do it, and bring it to a TIG welder who is interested in doing repair work.  If you want to make it easier on the welder, degrease the pan completely in the area around the crack so he doesn't have to.If you brought it to me, I'd weld it up for you no problems... just like the one pictured in this thread.  But I don't know if you are very close.Edit: just found in another one of your threads, that a replacement pan is available for only $100.  That's a no-brainer, just buy a new pan.  Not worth the hassle of involving a welder.  It's not going to be repairable without removing the pan and degreasing it anyway.  (Motor oil and aluminum welding do not mix.)Last edited by jakeru; 02-04-2012 at 04:01 AM.
Reply:If it is a big open flat area sometimes you can put a patch over the crack and weld while on the car (not full penetration). If you have to weld in the crack the pan has to come off.