Valve adjustment info

[claymore]

Lots of posts on other sites about guys adjusting the valve clearance and everyone is wondering why the intake gets looser and the exhaust gets tighter.

The reason the exhaust valve clearance gets tighter is because with no lead in the fuel now when the valve closes against the seat there is nothing (this is where the lead used to be) between the seat and the valve to cushion the closing.

So what happens is the valve actually BEATS itself against the seat and being the exhaust valve the valve is HOT so it starts to bend (slightly) and it hits the seat so hard the seat starts to wear away.

The end result is the valve bends with the spring pulling it farther upwards and the seat recedes further into the head so the valve tip EXTENDS further upward away from the combustion chamber resulting in a valve tip HIGHER than it was. And that means the space between the valve tip and the cam followers is LESS than it was so you now have a tighter space to measure.

Now with the intake valve being colder it doesn't bend so the height doesn't change from bending. But why it is looser (more clearance) you ask ...the valve tip gets hammered on by the cam follower every time the valve is opened so it gets mashed down or worn away causing more space between the tip and the follower so the clearance is bigger. This also happens to the exhaust valve but the bending causes more of a difference so the opening up of the clearance is offset by the bending which is larger.

But bottom the line is THIS IS NOT UNUSUAL and that is why the valves are adjustable so you can manually adjust for these phenomenons. The amount of wear and bending is really very small and in itself will not cause any problems.

However with the clearance so tight on the exhaust valves you could have a problem with the valve spring binding in on itself because the coils are forced closer to each other causing coils of the spring to collide with each other. And even worse if you let it go forever there could come a point where the clearance is so tight the the valve doesn't close all the way and that will lead to a burnt valve.

The problem on the intake side is far less severe and the opening of the clearance means the valve isn't being forced open as far so you loose performance and get the noise.

So when you set your clearances I would recommend using the LARGER end of the specs on the exhaust side because it's going to close up. And the smaller end of the specs on the intake because it's going to open over time.