Side valve cylinder head caps

[davemark]

I'm trying to restore a 1927 600cc Douglas engine. Does anyone have any tips to remove very stubborn side valve screw-in cylinder head caps? All four are rusted solid and very corroded, so I don'd mind destroying them to avoid damaging the cylinder heads. I've tried lots of penatrating oil and a big spanner, but no luck. I'm happy to set the heads up on the mill and machine them out but as you can imagine this is quite time consuming, so I thought I'd ask the experts for any top tips before I bore them out! Are replacement caps available to buy before I start making four new ones?
Best regards.

[davemark]

After posting my first discussion on the site about Douglas cylinder head valve caps, I read a few comments on member location. It didn't occur to mention this and I have no problem saying I'm from Cheltenham UK.
Best regards

[eddie]

Dave,
           A suitable sized socket in an air ratchet will usually rattle them loose without doing any other damage.
                                         Regards,
                                                  Eddie.