On further inspection, once the old valve seats had been machined out of the cylinder barrels, we found a number of cracks at the base of the valve seat bores.
To ensure the water jacket is sealed from the combustion gases we had to repair this. The ideal method of repair would be gas fusion welding at a cast iron specialist, but this would entail the casting being exposed to 800°+ temperatures which would potentially distort it, so we opted to try and repair the cracks with braise.
At first glance the braise repair looked quite hopeful. We carefully remachined the valve seat bores to size, but it became clear that the braise hadn’t filled the cracks as well as we had hoped.
We had another go at braising it, but it just wasn’t penetrating the cracks so the only option we had left was to send the barrels off to a cast iron repair specialist.
To prepare for the extreme heat it would be exposed to, we removed the new liners and valve guides etc. The barrels were away for 3 weeks, but once they returned we machined them and they were spot on. They had however distorted as we suspected might happen, which meant we had to remanufacture the liners to fit the bores.