decking the cylinder?

[rugerpooch]

I would like some info on " decking the cylinder" for more performance. I am familiar with the term, but I always thought it refered to mating the head to the cylinder ( flat surfaces ). But I have read some forums detailing anouther procedure. What is actually involved to check the "decking " on my quad, and what is the benefit to changing the gaskets or machining to achive this?

[R3Concepts]

Off of what bike?

[rugerpooch]

It is on a stock 1999 400ex.

[R3Concepts]

When you get a 400ex really hot the head has a tendency to warp. Decking or surfacing makes the surfaces true and flat. On four stroke it doesnt provide any power gains, besides jacking up the compression a little bit, which might make it blow head gaskets if the surfaces arent flat. Downsides especially on a 400ex is the when you deck either the head or the cylinder, the cam chain will get looser because it will have a shorter throw. You can get away with a few thousands but I wouldnt go big on decking. This isnt something I would be doing on a 4 stroke, decking is mainly for sealing purposes.

[cals400ex]

yeah, i would just run a thinner head and base gasket.

[K_Fulk]

I wouldnt bother doing it unless your having head gasket problems. Sure you might get a little more compression, but then your cam timming gets messed up.

If you have to deck it for sealing issues, you could run 2 base gaskets to put the cylinder back up a little higher.