I had a clean head in the garage that failed a crack test so I thought I'd have a go at making a port mold using silicon sealant. It says it can flex +/- 25%.

The head is from a Ford 2L SOHC Pinto engine  as found in the Capri, Escort, Cortina and Sierra. 

James decided use grease to stop the silicon from bonding to the port and kept the valve closed, I went with gear box oil and put some lift on. 

We used cable ties to hold the valves in place.

Because i had some lift my port cast will have to come out the cumbustion chamber. I'm going to try and pull the valve out before I pull the mold out.

I put a lump of sealant on to a card so that I'd have a way to check that the silicon sealant has cured fully. The tube says that it takes 72 hours to cure....

It's time to pull the mold out. It wasn't as easy as I hoped, The valve ripped out even though I i tried to peal it out.

Doesn't look flash parts of it were still liquid.

I don't think oil is the right substance to stop the RTV sticking to the head here's the left overs....

The grease seems to have done better.

Both attempts.

I actually think this might work. I'm going to try it again tomorrow. I plan on greasing her up good and leaving the valve out.... update not so soon ;-)