need a MKV piston - shouldered one

[halocline]

I'm trying to imagine what would make the piston dig into the seat in the first place. If the spring failed, IP would go way down, not up. I guess if everything was locked up and spring suddenly broke (hard to believe that happening, but...) then the pressure in the IP chamber would no longer be working against the spring and you'd have much higher force on the piston knife edge. As soon as anything happened to open the system, like a breath, that force would disappear and not come back. You'd have IP essentially equal to seating force on the piston, maybe 25-30 PSI? (that's a wild guess)

You'd need super fine tolerances to prevent seat damage in the event of this mythical impalement, my guess is that a small fraction of a millimeter would do it. This would mean there'd be no way you could use varying height seats to adjust IP; the piston would simply not be able to reach the lower seat.

 

[chile7236]

when I went through the reg tech course, rene said they hadn't had any problems but the minute chance of it occurring was enough to make the litigators concerned....or something to that effect. edit: and, if you don't service your own gear, no shop will service it w/out the stepped/shouldered piston.

 

[halocline]

Sounds like total B.S. to me, I'd be very surprised if the engineers that designed it even had anything like that in mind.