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Thread: TIG Welding Aluminum Cylinder Head in Vehicle

  1. #1
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    TIG Welding Aluminum Cylinder Head in Vehicle

    Hello all,

    I am trying to get the opinion of some of the more experienced folks out there. I have a Honda VTX 1800 motorcycle with an exhaust stud mounting hole crack, pictured below (click to expand).
    Click image for larger version. 

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    I am concerned that after several heat cycles this crack will propagate and reach a place that will cause a leak like a water jacket, oil jacket, etc.
    I know that the right way to fix it would be to replace the head, or to weld it. From my research the right way to weld it would be to remove the head, preheat it in an oven, weld it, and allow it to slowly cool, possibly requiring machining afterwards.

    That being said, removing the head on this motorcycle is a REAL pain. I am considering dremeling away the area affected by the crack, preheating the head by running the motorcycle, and then TIG welding the removed material back up with filler, with the engine assembled on the motorcycle and wrapping it in a thermal blanket afterwards to slow the cooling. My concern with this method is that I may warp a critical component of the head. From my research most heads that are repaired by welding need machined, but all of my research is talking about welding cracks inside of the head, not on an outside surface such as this. There is plenty of distance from the crack to the head gasket. The exhaust valve is about a 5-6 inches away and the valve cover mating area is about an inch away.

    I'm including some pictures of the internals from another head in relation to the exhaust stud mounting holes to give you a better idea. Any advice/comments would be greatly appreciated. Thank you all.

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  2. #2
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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    Looking at the pics, you don't have much weld surface. I've fixed a bunch of this kind of thing before and never really had any distortion problems or need to pre-post heat. So the next question is how much of the crack can you see? Just the tip of the arrow on pic 1? Or is it on the top like arrow in pic 2 ?
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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    Hello. I can see a crack length of 0.2".
    The pictures with the arrows are just giving you an idea of where the crack is in relation to the critical components in the head. I included a picture of the actual crack in my original post. Did it not make it in there? I am putting another picture of the actual crack in this post, just in case it didn't make it in my original post. Click to zoom in on the crack.
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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    The size of the crack isn't that relative. Normally cracks like this the hole is completely welded up and then drilled and re-tapped. If you just weld the crack how do fix the threads? The casting has to be super clean for welding. May have to weld it to bring dirt out, grind it out again and re-weld. Might be good to talk to a shop that specializes in this type of repair if you've never done anything similar. I know a couple guys that weld up cooling fins on air cooled bikes that were involved in accidents with the engine still assembled but out of the frame. Can't tell it was ever damaged when they're finished but takes some very careful finish grinding. You might want to consider a threaded insert for stronger threads than the aluminum.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    If it were mine I would grind out the crack and tig weld it then use a grinder to clean out the threaded hole so a drill bit can be used to redrill the hole and put a helicoil in it. The stainless heli-coil insert will distribute the load of the new stud so there would be little to no chance of it cracking again. 200-250 degrees of preheat will help burn out any contaminants in the cracked area and also make it so that less amps can be used to weld it. There is little chance of warping but if you are concerned bolt the head to steel plate during the process and remove it after it has cooled. A quick sand blast of the cracked area will clean off the surface contaminants and or any paint in that area.

    Otherwise grind the hole open right through the cracked area and fill the whole thing with weld and redrill and tap the hole for the stud. If done this way no heli-coil would be needed.
    Last edited by thegary; 2 Weeks Ago at 04:42 PM.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    I want to start by saying that I am experienced with welding cast aluminum -- I have welded cast aluminum valve covers very similar to this cast aluminum so I think I can pull it off.
    I am planning on buying a scrap head to practice the job.

    Also, I like the advice about bolting the head to a steel plate to prevent warpage but unfortunately I cannot get the valve cover off without removing the engine.

    So it sounds like my plan of attack is going to be:

    1. Grind out the crack with a dremel until the crack is gone. This will also assist in getting me a cleaner surface for welding
    2. Clean it as good as I can with acetone and a wire brush (that is the best I can do for cleaning)
    3. Preheat the head (I am getting mixed responses from people and my research about welding heads -- Some of my research indicates that preheating will help prevent cracking in the heat-affected zone, but some say that preheating is just to make it easier to weld. In any case, it does not sound like preheating is going to help prevent warping unless somebody more knowledgeable than me can weigh in)
    4. Clean again with acetone and wire brush
    5. Weld the grinded-out area with filler
    6. Evaluate weld quality and determine if I need to grind and re-weld. If so, repeat steps 1-5.
    7. Clean it up with a dremel
    8. Drill, tap, install a helicoil and "let er eat".

    If we can agree that the above steps will work and that if I perform it correctly that I will not have to worry about warpage, then I have the following questions for you:
    1. Do you think I can weld it all up in one go or am I going to have to stop, let it cool, and then get back at it again to help prevent warpage? If so, how long do you more experienced folks think I will spend welding VS waiting on it to cool? Is there a good rule of thumb for this that someone can tell me?

    2. Preheating: to preheat or not to preheat. -- like I said in step 3, I am getting mixed responses from people and my research about welding heads -- Some of my research indicates that preheating will help prevent cracking in the heat-affected zone, but some say that preheating is just to make it easier to weld. In any case, it does not sound like preheating is going to help prevent warping unless somebody more knowledgeable than me can weigh in.

    Thank you all for your input, I really appreciate all of you!
    Last edited by TackLife; 2 Weeks Ago at 06:03 PM.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    There is no reason not to do it in one shot. I am in the group that says preheating will make it easier to weld and will have no effect on cracking. The heating will also remove oil from the casting if it is saturated. Just heat it until it stops smoking . Somewhere around 250 degrees should be plenty. Personally I do not like acetone for cleaning but your milage may vary. A good sand blast of the imediate area and heating until it stops smoking is all That is needed. Along with grinding the crack.
    Last edited by thegary; 2 Weeks Ago at 07:19 PM.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    Thank you so much for your feedback!

    I don't have any sandblasting equipment and I have some concerns that sandblasting will get sand past the valves and into the cylinder -- short of ensuring that this particular cylinder is in the compression stroke so that the valves are closed, are there any suggestions besides acetone or sandblasting?

    Also want to hear other opinions ... not that thegary's comments are not great, I am valuing everybody's input, I just wanted to hear what other people have to say because doing this correctly could mean the difference between an hour's fix and several days worth of work pulling the engine and replacing the head.

    Like always, thank all of you so much for your input!

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    I guess I am confused. Your pick shows the head laying on a clothe. Yet you talk of having to disassemble it ? Why would you put it together with a crack in the head? If you can not sand blast it then just use sand paper or a file to take the oxidised layer off in the area to be welded. Then grind out the crack .

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    My apologies -- the pictures on my original post are to show the dimensional relationship of the crack to the critical components in the head... The head with the crack on it on my motorcycle is still installed on the motorcycle and was never removed. I tried to make it clear in other posts so I apologize for any confusion. The whole point of my post was discussing me fixing the crack without taking the head off.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    I think you have plenty of advice for welding. The only thing I would add is if you need to use an insert to repair threads use a Time-Sert instead of a Helicoil.
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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    I'm thinking of this from a different perspective.

    1 - What was the root cause that resulted in the crack? Knowing this answer will help guide you to the repair.

    If the root cause was some type of force acting on the stud - then yes you'll need to weld it up properly.

    However, if the crack is not due to physical forces stressing it, then it seems to me that a helicoil would restore the threads w/o the problems associated with TIG welding.

    It is going to be extremely difficult to clean the area, and then weld the head while on the bike without getting some contaminants in the weld. Those will cause porosity, which will in turn lead to future cracks.

    Which brings us back to question #1 - what caused the crack in the first place?
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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    I will investigate the time-sert. Thank you!

    In response to the question about what caused the crack, the exhaust flanges were bent inward, signifying that the previous owner overtorqued the stud nut. This, along with the high heat in that area could certainly have caused the crack because the bowing-in of the exhaust flange would tend to exert a force on the stud toward the exhaust pipe. In fact, given the location of the crack I suspect that is what happened.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    Quote Originally Posted by TackLife View Post
    I will investigate the time-sert. Thank you!

    In response to the question about what caused the crack, the exhaust flanges were bent inward, signifying that the previous owner overtorqued the stud nut. This, along with the high heat in that area could certainly have caused the crack because the bowing-in of the exhaust flange would tend to exert a force on the stud toward the exhaust pipe. In fact, given the location of the crack I suspect that is what happened.
    In that instance I think that I would heli-coil it and reassemble with a flattened flange.
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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    Preheating the head evenly prevents a localized hot spot that could cause warping. You want the head to expand and contract evenly. Being it's on the exhaust is a good thing. Maybe you could weld up the crack and very carefully true the hole so it could be drilled accurately for an insert. Use a propane torch for preheat so you don't contaminate it more.

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    Re: TIG Welding Aluminum Cylinder Head in Vehicle

    I would grind and clean it well, no acetone or anything. And then slowly heat it, with a gas lens and plenty of gas, spend a minute or a minute and a half then fill it in, then lightly grind out the buga's in the threaded hole. You could probably run a blind tap into it and get it back to the original. Not sure if you have enough meat for a Helicoil.

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