M20 Valve Grinding

This short article describes how to grind valves for the M20 engine. Valve grinding is neccessary if you fit new valves, or if you had the valve seats serviced, or both. The purpose of grinding the valves is to make a closed valve perfectly air-tight by grinding the valve edge against the seat.

What you need
You definately want to have a valve grinding tool. I tried grinding a few valves without it, and I soon realised I had no choice but to buy one. Imagine I have taken the pictures below while using a valve grinding tool :)
You will also need grinding paste, or grinding powder and a fine kind of oil (such as knitting-machine oil).

Apply grinding paste on the valve edge, like this:


Now, insert the valve onto its seat and turn it in a back-and-forth rotating movement by holding the valve grinding tool between your hand palms and rubbing your hands. To properly grind a valve, you will have to do this for a while with each valve.

Once you believe the valve is properly grinded, remove it and clean all remainings of grinding paste carefully (or your valves will keep grinding on and on). Pressurized air is useful for this.
On this photo, you see what a grinded valve looks like. The valve on the right has not yet been grinded and has a smooth shiny edge. The grinded valve has grooves along the edge which match the valve seat for that particular valve.

It's important to fit the valves in the same seats you've grinded them into, so don't mix them up.