I was just about to take the heads off the barrels and sure enough they're stuck fairly fast, in the past I've used a bit of heat and a rubber hammer and sometimes included a piece of wood and selected expletives, I'm sure someone must have a better trick that skins less fingers and breaks less fins :-O

You could try a soaking with penetrating oil or some diesel around the head joints,having left them to soak over night , slacken off the tappet adjusters so the valves stay closed, then with the plugs in turn her over with care.You do need to be careful not to have the barrells lift .I've done this on other engines but not a 2cv. and see if the compression will pop em off. Make sure your coil is disconnected though I assume you have undone everything .

Thanks Banjo, the engine is on the bench, heads and barrels off but stuck together, I'll get em separated tomorrow, just thought there might be other more elegant approaches

As before a soak with penetrating oil or diesel but now you can stand them on their head over night,then a suitable length of wood up the barrel and a smack with a Brummie screwdriver should see it done, making sure your heads don't fly off and get damaged.

Happy persuading

Use a bit of 2"x2" balanced upright or in the vice, and drop the barrel over it, repeatedly. Heat really is the key though, wait 'til the good lady's had some wine, and pop them in the oven. Though best use the welding gauntlets to take them out rather than the oven gloves.