Weld a Boat Exhaust Manifold: Boat Manifold Welding Tips

MuggyWeld customer testimonial:

“I hope you don’t mind, Mark (I guess I am giving away your secrets!), but I thought it might be helpful to Mike to outline the procedure used to fix the manifolds.

Mike, I am Mark’s neighbor and helper. Here ’tis…

We opened the crack from end to end with a grinder, flap wheel, Dremel… Stop drilled end of each crack “leg” with .1875 bit. As the cracks were in the water jacket only, we decided to use 77 rod for machinability.

The manifolds were pre-heated to 450 degrees in oven for 2 hours. We used a PowerCon 350 DC welder at about 70 amps, and welded 1 inch at a time. Immediately after the 1 inch of weld, we “shot peened” with air hammer and pointed chisel. This removed the slag and left the surface of the new weld dimpled. (golf ball-ish!) This was repeated over and over until parts of the weld were “proud” to the rest of the manifold.

The high spots were removed with a flap wheel… This made the low areas very visible. We kept a Dremel with a  grinding disk handy, and if we saw any little cracks, we ground them out and re-welded. Each weld was followed by peening.

As soon as the welded area was flush, we peened entire welded area and let the peening overlap the cast iron about .75 to 1 inch. This was to stress relieve, but had the added effect of giving the weld the appearance of a sand casting! Serendipity. Then immediately back in oven at 450.

Repeated for second manifold. (When old Mark busts a manifold, he busts ’em both!). After both were in oven, we decreased oven thermostat about 50 -100 degrees per hour and NEVER opened oven. After “cooking” overnight, they were done.

Hollar if we can be of any assistance…”

Learn how to weld cast ironCast iron repair techniques are demonstrated.


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