JohnB. wrote:Have you tried simply unscrewing the piston to back off the spring pressure as opposed to compressing the spring? That's how the spring is typically removed on the single spring versions. If the larger spring is the same length as the spring in the single spring groups the pressure should be relieved well before the piston fully unscrews from the shaft.

Bosco uses a single 9 bar spring which gives a peak pressure of just over 8 bar, tapering down to 6 bar during the shot.

I first tried unscrewing the piston but it would not budge. I used a brake caliper unwind tool.

One of the adapters has two studs that match the two holes in the end of the piston. I was able to apply considerable torque, but the piston would not turn. I thought the spring pressure on the piston was holding it tight, so I built a jig to hold the complete group head so that I could compress the springs with the lever. Once compressed, I secured the outer spring using some stainless steel cable ties. After releasing the lever, the piston still would not turn. My next attempt will be to heat the piston, trying to expand it to help loosen it.

Any other thoughts on how to remove the inner spring would be appreciated

William, looks Like I need to stop by...SOON! Enjoyed the coffee my last stop in. Beautiful machinery.

Sure. This is set up at the house. Have the k30 and Pharos here as well on the weekends.

chappcc wrote: My next attempt will be to heat the piston, trying to expand it to help loosen it.
Any other thoughts on how to remove the inner spring would be appreciated

The piston should easily unscrew either by hand or using a tool similar to the one you used unless there is thread lock sealer/corrosion on the shaft threads or the threads were messed up at some point. If there is thread lock on the threads heating the piston should free it up.

I think it must be thread lock. The piston and the shaft all look very clean - I am the original owner and the machine is only two years old.
When I next change the gasket set (in a few weeks), I will try heating the piston.

EDIT: I finally got the inner spring removed. I did not need to heat the piston. I first compressed the outer spring and held it in a compressed state using stainless steel cable ties. With this tool:

I was able to get the piston loosened and removed. It unscrewed from the lever end. The inner spring was still compressed when the piston shaft was totally unscrewed.
Installing the shaft into the lever head was easy with the outer spring compressed. With a single spring, the required grind is now not as fine as with the two spring setup. The measured pressure with one spring is 7.8 bar, while I measured 11.5 bar with two springs.

This may be coming from a place of ignorance. If headspace is an issue, couldn't you just dose the same amount into a larger basket. I have paul's gaskets and modified ims screen and it still gets dirty. I tried dosing in a deeper basket, now less gets on the screen. I'm sure i'm missing something basic here though.

Or less coffee into the same basket. I routinely dose 14g into a 15g VST basket, to compensate for the reduced headspace in my Londinium group. Before that, I had issues with the wet puck sticking to the shower screen.

Matt

Yes that would work. Lately I've been dosing 20g in a 22g Decent basket (rebranded VST, I think?) I was thinking about getting the 25g VST, just to play with.

I've been using the clip on style screens since I got my new lever groups and I've been dosing 17 grams in an 18 gram VST basket. With the stock screen I'd be lucky to be able to fit 16 in the same basket.