Brazing a cast iron engine block
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  1. #1
    Join Date
    Nov 2006
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    Phoenix
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    731

    Brazing a cast iron engine block

    Hello all,

    I would like some opinions on a project that has been presented to me. I have been asked to repair a cast iron engine block that has broken mounting points. I haven't yet gotten the pictures but from the description two mounting "ears" have broken off and one has some metal missing and needs to be built up, drilled and tapped.

    I have learned to stay away from cast iron engine block repairs as my success is 50-50 using the traditional ni-rod approach with peening. However I have started using brazing rod for repairs on the perimeter of the block where expansion and contraction is free as opposed to expansion and contraction somewhere in the main body of the block where expansion or contraction can lead to a crack as the stress is "locked" in by surrounding metal.

    I have done one engine mount using brass and so far it has worked fine. However, I am unsure if this is safe as brass is softer than cast iron and I wonder if I'm exceeding the mechanical properties of the braze metal.

    When I worked in the steel mills as a maintenance welder years ago we routinely repaired huge, I mean huge, heavy machine bases and parts made from cast iron using brazing rod with total success. The procedure involved pre-heating the part with propane torches for hours to get it dull red and then beginning the brazing process and keeping the heat on while the repair was being performed. Then it was covered with asbestos blankets and left to cool slowly, sometimes for a day or more.

    However, unlike an engine mount, these bases were static and load bearing, not subject to pull, push forces. They were subject to impact type forces leading to the break in the parts. Generally speaking I use brazing quite a lot for some types of repairs (such as on bike frames )and have never had a part I repaired returned for a rework.

    So, am I safe using brass to repair an engine mount? Is a ni-rod approach a better solution? Attached are pictures of the repair I spoke about. Any and all opinions will be welcome and appreciated.

    Thanks,

    Tony
    Attached Images Attached Images    

  2. #2
    Join Date
    Sep 2008
    Location
    Louisiana
    Posts
    746

    Re: Brazing a cast iron engine block

    Hi Tony
    I repair a lot of engine stuff for the local junk yards like this. Those pads you built up were protruding enough that heat input into the block was probably low enough not to cause trouble. Bronze filler (depending which one you used) usually exceeds the tensile of the cast iron. Many engine castings fall in the 40,000 lb tensile range, the low fuming bronze I use has a 60,000 tensile, and a nickel silver (brazing rod) I use is 80,000 tensile. So you should be good for strength if weld cross section is same as iron. Bronze for iron blocks is the method I prefer, especially on a bare block I can heat in oven. I do not usually weld braze assembled engine because of heat input. On that repair I would have turned and tapped some cold rolled stock and tigged it in using a high ni rod.
    Peter
    Equipment:
    2 old paws
    2 eyes (that don't look so good)
    1 bad back

  3. #3
    Join Date
    Nov 2006
    Location
    Phoenix
    Posts
    731

    Re: Brazing a cast iron engine block

    Hi Peter,

    On the repair I sent pictures on, do you think over the long haul, the bronze threads will fail? I was somewhat concerned about it but since I only know to do these repairs with ni rod or brazing, it didn't occur to me to TIG some iron on the block.

    What do you think? Will the brass hold up? The shop that had me repair the engine block has not heard from the client that sought the repair indicating that the repair is still holding up. It has been almost two years ago.

    Thanks,

    Tony

  4. #4
    Join Date
    Apr 2010
    Location
    Galesburg, il USA
    Posts
    1,644

    Re: Brazing a cast iron engine block

    Castweld didn't say they would fail, he mentioned that the bronze is likely 1/3 stronger than the block material.

    As for the tigging he said using a hi-ni (prolly n90-n99), just drill & tap a piece of cold rolled, V things a bit and tig the gap. The stretchy high nickel filler lets the steel and ductile live happy together.

    Matt

  5. #5
    Join Date
    Nov 2006
    Location
    Phoenix
    Posts
    731

    Re: Brazing a cast iron engine block

    Hello Matt_Maguire,

    your right, I didn't quite complete the thought process. Thanks for the clarification.

    Tony

  6. #6
    Join Date
    Sep 2008
    Location
    Louisiana
    Posts
    746

    Re: Brazing a cast iron engine block

    Tony
    You should be good to go with the bronze. Looks like you did that in place? That must have been a fun repair in frame! Most repairs like that I do on bench, which is much less of a challenge.
    You might want to cover that fuel line, and I am sure a fire extinguisher was just out of the foto's frame.
    Peter
    Equipment:
    2 old paws
    2 eyes (that don't look so good)
    1 bad back

  7. #7
    Join Date
    Nov 2006
    Location
    Phoenix
    Posts
    731

    Re: Brazing a cast iron engine block

    Hi castweld,

    I do keep a fire extinguisher handy whenever I'm working. Those lines however are transmission related and posed no threat. The repair was done in position and as a result took three hours to complete. I often get called to do in position repairs by shops in the area especially aluminum cracks and damage to engine blocks.

    Phoenix is a car haven for dealers and people who are looking for deals as there are a lot of auto auctions here. As such car haulers travel from far away to take back loads of cars with them. The auto transport business is big here. Auto repair is a huge business here and one market focuses on the buying of cars involved in accidents to rebuild them and put them back in service.

    Often a shop discovers that a tranny or engine block has been damaged in the accident and that's when a welder gets called in to repair the damage before the car can be salvaged. The attached pictures is one of the most extreme repairs I have been called on to do for a shop. It was all done in position and took me six hours to complete. The repair saved them from having to scrap the block, locate a replacement and reinstall it.

    It was not fun though.

    Thanks for your help and you too Matt_Maguire.

    Tony
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  8. #8
    Join Date
    Dec 2009
    Location
    Las Vegas, Nevada, USA
    Posts
    484

    Re: Brazing a cast iron engine block

    Quote Originally Posted by therrera View Post
    It was all done in position and took me six hours to complete. The repair saved them from having to scrap the block, locate a replacement and reinstall it.
    ..
    Tony
    Tony, that's quite a job. I will ask.. without clean access to the underside of that block, did you draw file the bottom to ensure it was flat to get a good oil pan seal? How were you able to drill and tap the oil pan bolt holes where you welded up the block? Remove vehicle subframe, while holding block up from top? How do you keep heat away from critical seals near the weld repair area?

    that is a tough repair.

    --zip

  9. #9
    Join Date
    Nov 2006
    Location
    Phoenix
    Posts
    731

    Re: Brazing a cast iron engine block

    Hi zipsit,

    I did have access from the bottom, not to weld, but to line up the parts. I was able to clamp a piece of flat stock on the bottom flange. This kept the parts and build up on the same plane while they were tacked into place. The only seal near the weld area is the one where the gear select shaft protrudes, a relatively easy replacement if needed.

    Regarding the holes: The shop said they would take care of grinding and cleaning the over-weld. Also they took care of the bolts but I suggested that they don't try and match the holes exactly but rather to drill fresh holes and then use self tapping screws to make new treads in the block's repaired flange. There was access for a drill from the top.

    This was the second most extensive repair of this type I have attempted and using hind site, I don't think I would recommend it. After consulting with a mechanic friend who owns a shop, he told me that in such accidents that would cause this type of damage, there is a high risk that cracks may have resulted inside the transmission where oil lines are cast into the case. Thus even though mechanically the parts are whole again and mate on the surface, below there could be extensive damage that will prevent the transmission from operating.

    I have wanted to drop by the shop where I did the work to see how the job turned out. The in position jobs are very hard to do and I have a tendency to underestimate the time it takes and bill accordingly. I usually have them bring the part to me and I do it on a bench, much easier and less strain on the body, especially at my age .

    Attached is probably the most extensive repair I have done on a part and another example of an in position repair on an aluminum trans-axle, but I am taking the discussion in another direction. Sorry,


    Tony
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