One step forward, two steps back.

It would be difficult to try and silver solder in the confines of the cylinder, and the gouges are not that deep.

The hone showed up yesterday, so I honed out one of the groups and smoothed with 600 grit paper and polished with bronze wool. The bore was smooth and the gouges gone.

Unfortunately it still leaked. I pulled the group one more time thinking to do the teflon tape trick, just to out of determination. This has become personal...

After removing the shower screen I noticed that the piston was not centered in the bore, which would affect the performance of the seals. There was no slop in the piston, so it would not self center.

Upon pulling the piston it became apparent that someone had got to the piston shaft with a grinding wheel. This not only impacted alignment of the piston, in the process of tightening it the interface with the piston was damaged. The top of the group also has damage where the shaft is inserted.

My guess is all this is the reason for the poor fitment of the piston in the bore, and leaves replacing the groups as the only solution.

Nuts

David,

Thanks for this latest update. I don't easily see where a grinding wheel was used on the group or shaft. I do see wear marks where the piston may have been inserted and the lever pins were out of line, creating wear. I'm also surprised that the piston won't self-center when seals are installed unless the piston shaft itself is bent. Scratching my head on this one.

The piston is centered sans the shaft. With the shaft installed, the piston goes off center immediately and the shaft does seem to be slightly out of plumb on the piston. Replacement shafts are available but look different, so I'd have to contact Zacconi to verify if they would work in this machine. The shaft on their site looks to be a slightly larger diameter, and if so would not fit the pistons and the shaft port in the groups. The only info I could get from them about the 2 group was it was made in '80 and few were produced. It seems this was about the time the company was transitioning from Riviera to Zacconi. Why they would go through having to redo the molds and machining tools for a slight difference in piston diameter doesn't make much sense. It makes sourcing parts and seals difficult and half the time the replies I get from Zacconi it sounds like they're winging it.

I would have to take the piston shafts to a machinist, not having access to a lathe. And there would be no guarantee it would solve the problem.

I wonder if you could have a machinist true up one shaft and piston so you can test it? Or, have Zacconi provide measurements and thread pitch? Ira's suggestion makes this look do-able.

The thread tolerances are a bit sloppy and when you tighten it onto the piston it throws the rod out of alignment. My guess is it's due to the butchery, which removed the flat at the top of the threads.

I've got a donor machine and remembered it had the piston assembly, so used the rod from that. Unfortunately the assembly was now too long. So pulled it again and went over everything. Although the pistons were the same diameter, the original was taller than the donor. My guess is that's why the original shaft was ground down. Someone may have replaced the piston and ground the rod to bring it to a workable height. All things considered, I need to find out if the owner had actually used it at any time, don't see how. The electrics had been worked on and it had a dead short to ground when I got it, so could not test before replacing all wiring.The way forward seems to be to replace the piston and rod, after confirming with Zacconi they will work with these groups. I still don't know what the situation is with the other group, not hopeful.

It's a contract job, so need to have the owner contacted to see if they want me to continue throwing parts and labor at it. It's a mess and I'm ready to toss in the towel. It's the first machine that's got the best of me.

found a spare piston:
https://www.ebay.com/itm/333626500568
though that doesnt help if the same thing is going on with the other group.