Monday, 4 November 2013

Welding the crack of dawn...

.. Impossible!! welding cast iron, it can't be done.. etc, etc... So the engine block had been pressure tested and showed up 2 or 3 hairline cracks which needed fixing (there were actually 4). Having spoken to several 'engine shops' around and about, none of them were willing nor even dared to try and fix a cracked engine block!! I knew it could be done, and I've seen it done. So I took it to the only engine shop in town that would.. my own!

Having done my homework, and preped for this, I decided to give it a go, after all this IS the original Mercury engine and I'd really like to use it, plus trying to find a replacement period flathead unit is really going to be tough.

First things first. Preparation! Clean out the crack, identify the beginning and ending of the crack and carefully drill two holes to help stop and start the weld, 'plugging' the weld run. I'm using a dremel, an angle grinder and cold chisel to 'temper' the weld once done.. basically beat the weld with a chisel and hammer right after welding.

Cast iron will crack if too much heat is applied. But if you work in small short runs the block itself works as a big heat sink and dissipates the weldling heat quickly. To ensure decent adhesion, weld in small parallel strips.

You can see the crack, grind a 'valley' out to weld in and drill the plug holes.. and keep it super clean!!

Welded, grinded, and sanded... difficult to show, bit it's a solid fix.... The two other holes are required 'stud' holes. Repeat the process for the other 3 cracks and she's looking good!.. This took day to do, but well worth it. Next, send off for pressure testing again and chemical clean ready for rebuilding the engine.

Two of the cracks were on the flat sump matting face which made them easy to get to fix.

The other two (thought there was only 1) were on the inside block wall, but fortunately easy to get to and treat. Here the holes drilled and valleys ground out ready for stitch welding.

Finished!.. all 4 cracks flattened out and polished flat. Hope this does the job, time will tell : )

1 comment:

  1. i just picked up a flathead with the same cracks as yours. do you have any more detail on your welding process?? tig? stick? what filler?? you can email me at

    cool project btw!!
    Kevin in the U.S.