Hi All,

I was changing a tappet shim in my gs when I noticed a hissing sound coming from around the left exhaust valve. I've adjusted the valves on this engine a few times before and I don't remember this sound. Is it normal for air to escape when turning the engine by hand? The sound happens around the time the exhaust cam contacts the shim. I kept the original shim in with a clearance under .04mm and the engine is running normally.

Hi Trey, welcome to the forum!

Folks generally consider it safer to have exhaust valves on the higher side (around 0.08) to prevent valve seat recession. If under .04, Id think of opening it up

As per your sound, as soon as the cam touches the shim the valve starts to open so air compressed by the compression cycle should escape the valve at that point. I normally take my plugs out when adjusting shims to make it easier to turn the engine so I've never heard that noise before.

Thanks. Now that you mentioned it, I don't remember if I removed the spark plugs like I usually would. That would cause the compression that I was hearing. I also have have a size smaller shim that should put the exhaust valve in the correct spec around .08mm.

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