peacecup wrote:Over my head, or a least within the allotted time.

One thing you're failing to account for is that much of the force of the lever is being applied to the top of the group at the fulcrum. This, in addition to the roller cam, absorb the force.

The simple question is does the roller cam on the lever fulcrum reduce the force that would be exerted (in reverse) in the figure A above? I suppose it does, otherwise the machine would tip over. In reverse, if you tried to insert the piston by pushing it upwards without applying counter-force (i.e. holding the machine) the machine would tip over. Yet it does not do so when you pull the lever down. So.. that force is going somewhere.

On your machine, peacecup, it is going into the crema.

peacecup wrote:...if you tried to insert the piston by pushing it upwards without applying counter-force (i.e. holding the machine) the machine would tip over. Yet it does not do so when you pull the lever down.

...but it would if the group were not connected to the base, which is the equivalent of not holding the machine when pushing the piston upwards.

Bob, thanks for sharing your concept and tool design. Life just became a bit easier.

I am still convinced that the piston-replacement tool should be supported by the top of the group.

I have gotten lost in the physics of this whole thing, but it is a pretty simple thing to take off the group and just service the piston, using a clamp. I think the OP had a pretty goot gizmo designed to release the small amount of force exerted by the spring. From my experience one can simply pull the pin and let the entire thing uncoil on its own....the spring is so close to its relaxed state that there is not that much force at that point. I can see the use for a piston jack as was described by the OP.

I once took a tech course and the professor's main theme was that there are 1000 solutions to every problem and it seems that this is just one of the 1000.

DOUG IS WRONG ABOUT PULLING THE PIN AND LETTING THE PISTON DROP. DO NOT DO THIS WITH A NEW PONTE VECCHIO. THE SPRING WILL EJECT THE PISTON WITH CONSIDERABLE FORCE. Doug, if you can do this with your sama you need a new spring.

It is also simple to use a c-clamp to remove the piston while the group is attached, but it needs to be the proper shape. I do think Bob's idea is a very good one, but I maintain that it should be supported by the group, not the base.

I soon will post a photo of the small damage I did to the Export trying to replace the piston by supporting it from the base.

PC

I have to disagree with remarks that suggest piston reinsertion is easy. I found it quite difficult because there's little room on the top of the group for a clamp to get a firm purchase, and the rubber shoe of the clamp tends to slip off as the clamp is tightened if the clamp is not perfectly aligned.

mousetail's device makes things much easier .... the question is whether upward forces place too much strain on the machine -- on the screws, the tubing, whatever -- because the shell cannot distribute the forces down onto the chassis when the force is in an upward direction.

You'll see from the above photo that I, at least, found the force enough to bend the aluminum base. I used my Subaru jack to accomplish this little feat. The piston was very nearly re-inserted when I noticed the extreme flexing of the base, but too late.

The force of the lever being pulled down is largely counter-acted by the top of the group, and the roller bushing. That's why the machine doesn't tip, or flex too much.

I found the right shape of c-clamp, and it was easy to re-insert the piston. BUT, BOB's device, if simply modified to be supported by the top of the group, would be great!

PC

peacecup wrote:You'll see from the above photo that I, at least, found the force enough to bend the aluminum base.

Aluminum, really? The Lusso's frame and base are made of heavy gauge steel.

Yes, the Export base is cast aluminum (or some softish alloy -not magnetic). Nothing wrong with that, unless someone is foolish. The body is heavy-gauge steel.

The point is, there is really no point in using the base to support piston re-insertion, since it definitely applies some additional force on the group-body bolts. This force is not applied when the top of the group supports the force.

I'll now bow out of this thread,

PC