Sherak,

If your engine is worn out, you might want to check into having it "pinched". I know you're in the UK, but there is a guy here in the states that pioneered the technic and he's the best. He goes by OSRocket on ebay and for ~$20 USD you can have the sleeve pinched around the piston and get all of your compression back. I don't know what international shipping would run you, but this guy is worth it as he's the only one I'd trust my piston sleeve to.

I just sent my the piston and sleeve from my 8-port to him a month or so ago. I haven't run the engine yet (too cold), but when I put it back together, I my starter box can't turn it over because of the pinch it now has. It's insanely tight now.

Check out the other thread, you see nothing but kudos for OSRocket and his pinch process.

-RobH