DSP stands for "DeStroking Port". That was McCulloch's trade name for their compression release system. Opened a small port from the side of the cylinder to the muffler. Effectively raised the exhaust port and shortened the compression stroke to reduce compression during starting. Works very well. Newer McCulloch designs used the now common replaceable 'poppet' type comp release valves in the DSP systems. The first versions were like this one with the integral valve seat (in the steeel cylinder liner itself) and tapered valve pin.
The stem has staking on the end to retain the spring seat (which is broken off here). Between the staking and the mung that's still on the valve in the pic (shot right after removing the spring, bracket, and broken valve spring seat) it looks boogered. Other than the broken off spring seat (which has the center of it broken out), the valve pin itself has no visible damage. If I wasn't able to get a good used replacement valve pin from a friend, I would have probably made my own spring seat and staked it onto this stem.
I'm really hoping that the old valve pin comes out, and the cylinder's valve bore cleans up and allows the 'new' valve pin to seat and seal in it. The Shop Manual mentions lapping a replacement valve pin in the cylinder using valve grinding compound............so if I have to do that I'll be tearing most of the saw down. I hope to have this saw back up and running to take with me to the NorCal GTG in November. Got a few more saws to sort out still before then.
