Procedure for welding aluminum cylinder head

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Hello all,I have been asked if it was possible to weld a crack on an aluminum cylinder head.  I have never done an automobile cylinder head before, only motorcycle heads when they have stripped bolt holes.Attached is a picture.  I did a little reading on this topic in older threads and on the Net and the procedure seems to be to preheat the part to around 450 degrees, weld it and allow it to cool slowly.  Also to grind out the crack prior to welding it.I don't know how I would preheat such a part.  Could it be done in a BBQ grill?  Maybe its time to invest in some form of heating apparatus?Anyway, to those who routinely may do these types of repairs, how would you go about doing it.  It wasn't clear what rod to use as it seems to depend on the material of the casting.  I saw in an earlier thread how some manufacturers stamp the material into the part making it easy to identify the needed filler material.The person who showed me the head pointed to what he thought was a crack between the two new valves.  You can see a line going between them.  However after looking at the pictures again, I think the damage is the pitting that is evident under one of the valves.If that's the damage, then its a build up situation.  If it is a crack then it needs to be ground out, etc.Thanks for any help,  I may walk away from this one simply because I won't have a way to get it to temperature.  If it is a build up issue, do I still need to preheat it in an oven?  Will a torch do?  I realize that the valves need to be taken out of the cylinder to be repaired in either case.Thanks,Tony Attached ImagesLast edited by therrera; 06-26-2011 at 11:59 AM.Reason: for clarity
Reply:Before being welded a leak down test and a pressure test should be done before any welding , until then not worth doing.
Reply:Originally Posted by Jay OBefore being welded a leak down test and a pressure test should be done before any welding , until then not worth doing.
Reply:Checkered pattern, BMW?
Reply:I think if it is just the pitting I would take a chance and not preheat. I looks like it chunked out when the seat was staked.
Reply:Thanks for your feedback.  How is a leak test done?  Are we talking here about testing for leaks in the water channels?  It sounds like on the surface that I may need to invest in some equipment to tackle this type of repair.  For example a propane weed burner that I can use to heat the part.  Maybe even a BBQ grill that has enough room for a cylinder head, etc.  I have a heat resistant blanket that can be used for covering it so it will cool slowly.When you say preheat might not be necessary for repairing the chip that is visible under the valve, do you mean to just build it up and then smooth it down?Thanks,Tony
Reply:Originally Posted by therreraWhen you say preheat might not be necessary for repairing the chip that is visible under the valve, do you mean to just build it up and then smooth it down?Thanks,Tony
Reply:Well if you just thought you could weld this with everything in place...Sorry..'aint happening..Like stated disassemble first because the damage may be more than you think under the valve..To each their own but I have fixed many alum race heads that were pretty bad and never pre heated anything but do it whatever way you want.It MUST come completely apart and then major reconstruction will be needed on that port because the seat will have to be re-machined and that means a bead around the old seat area and a complete re machining of the seat needs to be done..You will never line up the old bore trust me.These are never easy.No matter how "small" it may look.....zap!Last edited by zapster; 06-26-2011 at 04:59 PM.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:That part number on the head comes back to a M50 or M52 BMW.   Straight 6 engine.Miller 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:Thats a BMW I have done a few. Its not a leak down test, you need to pressure test it to find out if it is repairable. Close off all water ports and introduce air pressure in water jacket. Check with soapy water or submerge in water tank and look for bubbles. Then after welding do it again to check weld and possibly again to make sure machine work did not go into water jacket. I do BMW's with A356 filler.No welding on top the crack, it will fail. As others said- cut seats out, grind to water jacket, remachine seat bores, new seats, and straighten head because welding will warp it  (so cam bores are aligned) and then surface head along with valve job.Pre and postheat at 350 but no open flames touching head. I weld a lot of heads and if you don't preheat it one will eventually crack, I know this because I have cracked a few when I first started and was not heating them. Some worked but why take a chance?Good news is that head is expensive and worth repairing.PeterEquipment:2  old paws2  eyes (that don't look so good)1  bad back
Reply:http://weldingweb.com/vbb/showthread.php...acked+bmw+headEasy as pie.PeterEquipment:2  old paws2  eyes (that don't look so good)1  bad back
Reply:Originally Posted by Mick120Peter,Great link to the old thread.As an ex mechanic thats seen a LOT of cooked heads over the years, that made intersting reading.I don't miss spanner swinging tho, my back forced me out of the trade in '98.
Reply:Hi everyone,OK.  First step is to pressure test the water jacket and identify any leak sources.  If the damage is just that chip that shows in the close ups, then I can just weld over it without the need for pre-heat, post-heat.  Weld it and smooth it down.If there are cracks, they must be ground out to the bottom, which may mean opening up the area so I can get my torch in there.  Then preheat to 350 in an oven and weld it out, then post heat it at 350 again and let it cool slowly at ambient temperature.  How long do I post heat it?I need to take the valve seats and valve stems out.  The seats can be split with a cut off wheel and taken out.  The stems I believe can be punched out.Questions:1. should the entire head, valve seats, stems be disassembled in order to test for leaks and inspect thoroughly or is it enough to test first and THEN take apart to repair?2. I don't have an oven to heat with.  What can I improvise to accomplish this?  In the steel mills we used to  point weed burners at a part and heat it in the open and use temp stiks.  Especially since they type of stuff we would repair in this fashion was large cast iron machine bases that had broken or cracked and would not fit in any oven.Could I build a BBQ grill for just this purpose.  I routinely build them for sale out of old water heaters.  They are fairly large (48" long x 16" wide).  Could I put the part in there and fire it up with charcoal, close the lid and take it out when it reaches temperature?  Or could I make openings in it to put in weed burner heads and fire them up to accomplish the same thing?3. If the flame shouldn't touch bare metal, how do I arrange the torch to heat the head?  How does the heat get to the head if I need to deflect the flame?4. The filler rod selection is based on ???  I have never used A356 rod.  Is this a special rod designation for this type of alloy in this head?  Is it expensive stuff compared to standard 4043 rod?  Is it the type of stuff that is reserved for this type of repair only?  Where do I get some. I did a quick search on google and didn't come up with a source, only information on the rod.5.  Should I approach a machine shop for the machine specific work (press out the valve guides, re-cut the valve seats, drill out and tap filled in holes, true up the head, etc. before taking on this type of job?It sounds like apart from the logistical hurdles (oven, machine work, etc.), the repair is pretty straight forward.  Test for leaks (soapy water), disassemble, cut out cracks to the bottom, heat, weld, heat and cool slowly and turn over to machine shop to finish repair.Since I won't be actually doing the project from start to finish, only the welding and necessary prep work, what kind of bill should this job generate, in general terms?Thanks for your input, ideas and tips.Tony
Reply:Hi All,I think maybe the moderator should blow this guy out of the water.  He is a spammer and his junk will go to everyone following this thread and who knows how many more threads?Tony
Reply:You don't need to reassemble the head to do a pressure test.The alum flows heat pretty good, so whatever feels good for preheat time. A simple burner is what I use, with a steel flame deflector. A BBQ style heater would work. Charcoal? That would be a new one on me, but why not.Now I don't use A356 cast for filler, only on parts that require a good color match and I have A357 for that. Corvette guys are picky that way. Even then I still use 5356 in the seat contact area, lest they may fall out. But you can chose what ever you feel is right. I chose 4043 in the crack areas because it resists cracking and is cheap. I don't reheat the weldment after, just cover and let cool slowly.Yes, I would line up a machine shop before hand. Best to be prepared for the worst.If I had to plan for the worst, with full valve job and resurfaceing, I think off the top of my head $700. But that is just a guess, and I hate to guess. I think rates in you part of the country are much better than Los Angeles.
Reply:Originally Posted by therreraHi All,I think maybe the moderator should blow this guy out of the water.  He is a spammer and his junk will go to everyone following this thread and who knows how many more threads?Tony
Reply:Ahhhh Yes I know what you are typing about now..I gave him the  yesterday!...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:Hello all,I appreciate all your comments and I feel much more confident going into a job like this as a result.  I told the client (a repair shop that does high end cars) that we need to coordinate with a machine shop so that the welding is done as part of the repair/rebuild process and not as a separate task in and of itself.He told me that the head WAS repaired by a machine shop and that once they assembled it, it leaked (compression, I think) so they had to pull it again.  Not only that but that they found three more cracks (but didn't mark them).So I have a lead on a neighborhood machine shop that deals almost exclusively with heads.  I bought a pair of rebuilt heads from them for a car that had blown a head gasket I repaired for myself.  I am going to talk to them about working together on repairs that may come my way.  If they go for it then that will be the missing piece so I can venture into this arena.By the way, I had read about the BBQ grill/charcoal idea for heating parts years ago in a backyard machinists forum that specialized in promoting back yard, home made, do it yourself machining.  They had plans for building forges, machine tools, etc. that could be hand built and then used to produce highly accurate products.  They are tied into the Lindsay Publications outfit and have a lot of interesting books on home brew made technology and keeping old craft work alive.  http://www.lindsaybks.com/prod/index.html I'll report on how my first head project works out.Thanks for your help/advice,TonyLast edited by therrera; 06-29-2011 at 02:50 PM.Reason: to add more information
Reply:Hi there!I created an account solely to learn about the progress of what happened with this? Do you have an update at all? We have a machine shop that specializes in this exact head repair and recondition and I was curious how things turned out with the repair. It would be interesting to hear about such an accomplishment.
Reply:Hello Autohead,I'm sorry to report that I never put my hands on that project.  Once I told the shop that had called that I needed to partner with a machine shop, they more or less dismissed the project being in my hands as I had no way to follow through with it.Work took over and I put getting in touch with a head shop on the back burner.  It isn't until I read your post that I realized that I had meant to talk with them about partnering.  I will do that this week and will be able to report on repairs like this one when called  upon to do them.Part of the skill set besides the welding is being able to detect the cracks so I will have to learn how to use dye detection products along with visual inspections.I wish I could say more.Sorry,Tony
Reply:I got a oven with a non working burner top for free that I set up in the corner of the shop for pre heating parts like this. It is great because of the adjustable temp, I can set the temp and forget about the part and not worry about it overheating. Plus it is an even heat, I am very very paranoid about heating sections only especially with heads, engine blocks, cranks, cams, etc.Everything else seems so be explained very well in this thread.You mentioning the head being repaired once and leaking right away after assembly would scare me a bit as well. If it were me I would like to find out exactly where was repaired besides the obvious and inspect very very thoroughly. Also it doesn't look like any machining was done after the initial repair besides cleaning up the chamber. Any previous half a$$ed repairs can become your problem if things don't go right when the motor is assembled again.
Reply:Hello Tony,Thanks for all your information.I don't have much idea about this.But will you please help me to know more about this.
Reply:What is all this bit about not touching the head with flame? Ive welded literally dozens of heads and preheated every one with a rose bud.  You just cover the head with carbon black from your rosebud, then start heating the head with the rosebud. the whole head evenly,  that means moving the torch around a lot.  eventually the carbon black will start to burn off. when it starts to disappear the head is ready to weld.  Pour the heat to it with your tig and get the job done, then immediately cover with insulation.   Always works fine. Mac
Reply:I am assuming the head is prepared before you start preheat and the weld is peaned thoroughly after welding.  Mac
Reply:Tony,Here is a small explanation (ok a large one) on using dye penetrant and developer to make cracks visible to the naked eye: http://en.wikipedia.org/wiki/Dye_penetrant_inspection. I pressure tests heads rather by attaching plates to seal off the whole water system then pressurizing the internal chamber with compressed air and using soapy water to check for bubbles / leaks.But for cracks that are clearly visible, this dye allows us to see the extent of the crack. I can attach a few pictures so you can see the dye work (the first pic is a diff cracked head to the second and third, but it explains the concept).1.  The first is the red dye sprayed onto the cracked area and allowed to soak for a few minutes.2.  Then the red dye is cleaned off with brake cleaner or something along those lines. This crack didn't really need dye, but works for explanation purposes.3.  Finally, the developer is sprayed on the same area and given a few minutes to draw out the dye to make the crack clearly visible.Hope this is helpful SheldonLast edited by Autohead; 09-28-2011 at 01:34 PM.