on line source: mk-2 hp piston seat

[Couv]

As @rsingler pointed out, the generic seat is too short which will bring the IP too high out of range. Adding a shim to the spring would raise the IP even further. Basically, anything that tends to compress the spring raises the IP. E.g. Shim on the spring or short seat that requires further piston travel.

Additionally, if the seat is so short that it is recessed in the piston end, that could cause mating issues with the orifice.

 

[rsingler]

With a shorter seat (4) embedded in the tip of the piston, the piston has to travel further to reach the volcano orifice to seal.

That additional travel compresses the spring more, raising IP. As @couv points out, shimming the spring will compress it even more, further raising IP.

However, your intuition is correct. We need to shim something.
In this case, to reduce spring compression, we need to "lengthen the piston". The way to do that is to tuck a shim under part #4 to lift it higher, so it hits the orifice and seals before the spring is so compressed.

 

[herman]

Found an OEM MK-2 kit
The seat measures 0.1373in / 3.478mm tall .18275 in /4.631mm diameter

 

[Couv]

With a shorter seat (4) embedded in the tip of the piston, the piston has to travel further to reach the volcano orifice to seal.
View attachment 669937
That additional travel compresses the spring more, raising IP. As @couv points out, shimming the spring will compress it even more, further raising IP.

However, your intuition is correct. We just need to shim something.
In this case, to reduce spring travel, we need to "lengthen the piston". The way to do that is to tuck a shim under part #4 to lift it higher, so it hits the orifice and seals before the spring is so compressed.

"They took twenty seven eight-by-ten colour glossy photographs with circles
And arrows and a paragraph on the back of each one explaining what each
One was to be used..." A. Guthrie

 

[rsingler]

You can get anything you want, at Alice's Restaurant!
I miss Arlo. I miss innocence.

 

[halocline]

Herman if you end up making seats I'd like to buy a few.

 

[johndiver999]

yeah i bet he could sell a few. I would buy some

 

[herman]

I won't make them for sale, liability is the first issue and they take a good bit of time since they are all "cut by hand" so not worth my time unless I am restoring a reg for which seats are unobtainium.

 

[SlugLife]

Thanks, not sure if I want to pay $15 plus shipping when I need just a seat. How do you remove the seat, with a needlle - without destroying it?

Take compressed air & a blow-gun, and use pressure to push it out. Just make sure to cup it with your hand so the HP seat doesn't go flying off.