Technical Forums > Knuck/Flat Head

To weld or not to weld? That is the question.

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I know we all need pictures to make a more informed call so I'll try tonight to round up a couple to add to this discussion.

I have a set of knucklehead head castings that are extra, both of which have a crack.  Rear head has a clean crack that starts at the exhaust spigot and as far as I can see it goes inward as much as about 3/4 an inch or so visibly.  It's not opened up any and no material is missing.

The front head has a hairline crack looking from the right side on the right most fin about 1.5 in from the front.  While this extends the height of the fin it does not appear to travel further in the main casting where the front rocker tab is.

First inclination is to get them welded but I've had heads welded before and the heat tends to introduce new issues with new cracks or the one there opening up some.

Short of seeing what I'm dealing with what are your thoughts on this?



Here's some pics of the affected areas:


For the cracked fin I would pre and post heat and flow a little braze in the crack. No strength is really needed there as the fin isn't going to fall off. Just for cosmetics brass would be the safe bet. For the cracked port, weld with a NI rod with usuall pre and post heat. How ever you could probably get away with a braze there as well  but the Ni rod would insure the crack doesn't travel.

Thank you for the response.  There's not much traffic in the knuckle section.  This is a spare set that I had after gathering a few to select from.  I've decided to e-bay them rather than poking a stick at the snake.  The set I'm keeping had a head with a tab missing that was able to be attached rather nicely.  These two should be a good set too but I'm not wanting to put money into them at this point.  I appreciate the feedback.


Some of the Flathead Ford high performance rebuild shops have been having great luck with drilling a hole at the end of the crack, to stop the crack from traveling, then doing a preheat, then doing the weld. The old Flathead Fords always cracked around the valve seats.


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