Replacing a Cylinder Head Valve
It’s not the cylinder head valve you replace in the engine, but the cylinder head valve seat. It’s not something for the inexperienced mechanic to undertake as it’s involved and you need to be exact in your work.
Step 1 - Why You Need To Replace
There can be several different reasons why you’ll need to replace the seat on a cylinder head valve. The seat could have become worn or cracked or it might not have had the right seats for the type of fuel; this can happen if you use natural gas, for instance. If the seat can’t be ground any more, you’ll need to replace it.
Step 2 - Removing the Valve Seat
You need to strip the engine all the way down and remove the cylinder head, including the rocker arms. This is an involved procedure, and you shouldn’t rush it. Take the time to do everything properly. The way you take off the valve seat in going to depend on the type of vehicle you have, and the method that suits you best. You can punch up through the valve ports, although you have to be especially careful not to damage the counterbore.
If you choose you can even use a pry bar. This will only work, though, if you can get a grip. Again, with this it’s very easy to damage the counterbore.
Step 3 - Machining
Once you’ve removed the cylinder head valve seat you need to see whether the couterbore will need machining to accept a new head. Where it’s necessary it should be minimal, and it’s work that needs to be done by a professional, who will have the tools to be it with absolute precision.
Step 4 - Replacement Valve Seat
When deciding on a replacement cylinder head valve seat, always buy the very best you can afford. Make sure the valve seat matches the head. A hard valve requires a hard valve seat in order to perform well. If you’re not sure what’s best, ask at a garage or auto parts store where you trust people. They’ll be able to offer unbiased advice and have the experience to give a good opinion.
Step 5 - Installation
After you’ve selected the new cylinder head valve seat and had the counterbore machined (if necessary), you’ll finally be ready to install the new valve seat. It’s vital that the valve is absolutely clean and the surface smooth. Lubricate the valve seat and put in on the valve with the camfer side facing downward. To drive it into the valve you’ll need to use a special piloted driver that’s made for the job. Prior to installing inspect the valve seat. If you find any sharp edges, remove them so it won’t affect the head later.
You’ll find it much easier to install the cylinder head valve seat if you both heat the head and use dry ice to chill the seat. Do this and use the piloted driver and you’ll have no problem. From there, reverse the procedure you used to disassemble the engine.