Work process, Osmo

The process of porting a four-stroke cylinder head

About porting

Porting cylinder heads is something you do to achieve a better fuel consumption and in some cases gain horsepower. There are many ways of porting your cylinder head but in this text I´ll focus on beginner porting. "Beginner porting" is when you dont do racidal changes to the cylinder head and mostly just clean up the head. There are 5 steps to port a cylinder head correctly. These are: inspection of casting errors and restrictions, counting the right valve to seat ratio, counting the optimal size for the channel, evening out the intake gasket, and last but not least reshaping the valve seat and removing the casting errors.

The goal for this process is to have a better flowing cylinder head and reshape the channels. 

Preparing the work

First start off with checking for bad casting marks and restrictions in the channel. The biggest restrictor is at the valve seat and this will most likely be the biggest flow restrictor. After the casting marks and restrictors are checked you can move to counting out the optimal valve size. This is achieved by counting the amount of percentage the valve is compared to the size of the valve seat. This percentage should be somewhere between 85-95%, If less it needs bigger valves which is a whole new story. The tools that are needed are a marker or some tape, a small grinder and some bits to that. The bits that are required are sanding rolls between 80-400. I highly recommend using safety glasses because the grinded material flies at high velocity while porting the head. this job can be done on a regular table or even on the floor.

The process

Start off by taking a valve and rubbing the sealing surface with valve grinding paste. Then place it in the valve seat, rotate the valve a couple of times and check for the sealing surface. Now that we know the sealing surface you can either paint it with the marker or apply tape to it. This is done so that we accidentally don´t hit the valve seat while modifying the channels. Then slowly start removing casting marks with the 80-grit sandpaper bit and slowly go up to the 400-grit paper. While grinding it is very important to keep a cirkular movement in the bit so that the channel is even in all directions. When doing this to the valve seat area be extra careful so that you don´t hit the valve seat. The goal is to have good shaped cylinder channels and not a shiny finish. When the surface of the channel is even and looks even the job is done, you can now clean the excess material with brake cleaner and compressed air. Any metal left in the cylinder head will go directly to the cylinders which means huge engine damage.