is200 cylinder head problem

All that has to be removed is the least amount that will remove any un -eveness to the lowest point across the engine block. Very often just a few thou. Any more and you are in big trouble.

First question, Does it really need skimming? Any automotive machine shop will usually know how much they can take off. The fact that no-one seems to know, I find dubious. Can you get it measured by a third party?

Are you sure the head is warped? if the distortion is small you can use two head gaskets. Worked on an old chevy of mine many years ago.

What you need to do is take a stiff straight edge and run it diagonally across the head in both directions down the length of the head. While the straight edge is against it run a feeler guage under it between it and the head. If you don't have a gap any larger than .005 - .008 at any location on the machined surface there is no need to have it machined. If the gap is greater that that you have to choices. You can either use 2 headgaskets as mentioned above, or you can have it machined. The amount to be shaved will be equivalent to the lowest spot found with the feeler guage + .001.

Hope that is helpful.

You posted previously about running the bad gas didn't you? You gotta love people, like the "guest" whom claimed you should never disconnect your battery when you perform service.

Excess detonation (bad gas) can cause overheating which can warp your head. Do you have coolant loss? Visible seepage around the gasket and maybe white smoke in the exhaust? I take it you're getting low compression (rough idle) too? That would be your head gasket.

Like everyone else has mentioned, maybe all you need to replace the gasket (or add 2.) The mechanic probably wants to play it safe and plane the head so you don't come back with a reoccurring problem. I would say a local garage (not "stealership") would charge $200-400 for that job. That is in the US anyway.

A good automotive machine shop would know how much can be removed without potentially causing interference between the valves and the piston. Check a FACTORY service manual for maximum removal amount (not Haynes or Chilton!!!). Be careful doing this as the compression ratio can go up significantly on some engines. I suppose the valve timing could also be affected as the head moves closer to the crankshaft.

It depends on the damage done to the head by the leaking joint. A Vauxhall Astra in the family had minor cylinder head damage due to a leaking head gasket, and the remedy here was to carefully weld excess material over the affected area and grind back flush. 75 Pounds Sterling including carriage and delivery was considered good value. With a repair, the compression ratio is unaffected.

If the head is warped then replacing it may be an alternative to skimming it, thereby avoiding the problems of compression ratio change following the skimming.