spend $30 for a valve spring compressor, thread a piece of airhose into the sparkplug hole for the cylinder you want to work on , pressurize, then remove spring ,install new seal, reinstall spring, then move to next cylinder,
yes it needs to be on the compression stroke,
that's all fine and dandy, the only problem is that the rocker arms can take a bit of maneuvering to do the job with the head on the motor
