The valve stem seals seal the exhaust port from leaking exhaust gasses when on exhaust stroke and intake charge on intake stroke.
They are pressed into the head with the valve then pushed through.
The valve is then held via springs and retainers.
To replace them, generally it is best to remove the head as you will have to retain the valve without dropping it into the cylinder. Also the seals are tight and sometimes damage can occur trying to rove/replace them with removing valve.
To retain the valve some people use a compression test fitting on an air compressor and charge the cylinder to hold the valve. Other makes a, "Hook" type tool to hold it.
Then picking the seals out is tough and usually requires and dental pick type of tool. If the valve get scratched, it won't seal.
It is best to have them out so you can clean and prep surfaces so the seals last longer.
I hope this information helps.
Wednesday, August 24th, 2011 AT 9:44 PM