The Place

Hello,

I have a GSX R-600 K7 engine, the head has been skimmed and we seem to have zero valve to piston clearance.

I have removed the shims, and the valve clearance is around 0.4mm. With the thinnest shim being available 1.2mm. So If I put the thinnest shim in, I will have no valve clearance.

Is this just a case of getting a thicker head gasket? I basically need to replace the thickness that was removed when the head was skimmed.

Thanks in advance

Not good news, when you skim a cylinder head you automatically decrease the piston to valve clearance. I presume this was done to increase your compression ratio ? In order to re gain this clearance you must now machine the valve pockets in the pistons,one again this will lose you some of the comp increase you have just gained ! It's usually the inlet valves that cause the problems,,before calculating the amount to be removed you must take into consideration the correct valve clearances and factor this into your clearance calculations.
It's a simple error but it has caught many people out and sometimes with expensive consequences. If you get stuck a good man to talk to is Geoff Bell.He knows his stuff does Mr Bell.

Shim size won't change the valve to piston clearance though

The valve is resting against its seat

What thickness gasket are you using?

You might be able to use a standard gasket and get the clearance if you have skimmed head and thin gasket at moment

Hi,

I think I was confused when I wrote this post. It is bucket to cam clearance I was talking about.

The head was skimmed as it was warped Lee.

This clearance can be set with the head off, so I don't think head gasket thickness is going to have any effect.

The only thing I can think of is that the valves seats have been cut too low. Even with no shims in there is only 0.4mm clearance on some cams, so I need to get some tinner shims, or shorter valves, or something....

Ok,The thinner the shim the less reliable it becomes. It may be possible to achieve the clearance you require by having the head or top of the valve stem precision machined. Remember you must get your measurements correct as once the material has been removed from the valve stem head you cannot put it back on !!!!! This type of work should be undertaken by a precision engineer who has an understanding of high performance motorcycle engines,to be honest any cylinder head Specalist should be able to sort it out.Once the cam clearances are set do a dummy build and check your piston to valve clearance.

More likely the valve faces are worn. Also if they're that worn the valve seat may also be damaged.
Get the head to someone to replace the valves & make sure the seats are O.K.
Usually the valve spring is a bit weak & can contribute to premature wear. A good mod is to use the 750 springs as they're a bit stronger.

Once the hardening surface of the Titanium valves wears , or if someone has tried to lap the valves in, in the past, the clearences will vanish in a few miles. Try to get a decent 2nd hand set Dave. A new set costs as much as an engine .