I am wondering what a good way to descale chrome parts (such as a group head) would be without damaging the chrome plating.

Citric acid in my experience has messed up the chrome finish and turned it a rather pink color such as seen in the la marzocco rebuild from timothy blue's site: http://www.timothyblue.com/linea.php

You can see it in the upper part of the image

I was thinking of possibly covering the outside of the groups in some sort of grease to prevent the citric acid to getting through? OR maybe gluing plastic around the inlet holes and only soaking the inside?

Anyone have any better ideas?


Thanks!

Anyone have any better ideas?

This is what I recall from my automotive bumper plating days (as a customer, not a doer):

When someone talks about chrome plating, they are really "talking about" having a part nickel plated, followed by a chrome plating. The chrome evidently polishes much better (easier?) than nickel. The major cost contributor to having a part plated and then polished is in the polishing. So, if you can do without the polishing on the part or a portion of the part (as in these LM groups), the cost may be minimal and may override the pitfalls of a citric acid bath.

A visit to a plater might reveal a lot.

It is true that most chrome plating has a pre-coat of nickel, my understanding is that it serves to both improve adhesion and build up material, with a cheaper material than chrome, to fill up pores and scratches. I'm pretty confident that chrome plating doesn't typically involve polishing (except the base material if necessary). There will be limited cost savings by re plating rather than avoiding it to begin with.

I would try to cover the chrome in wax or grease as you mentioned or maybe others have better ideas.

godlyone wrote: Citric acid in my experience has messed up the chrome finish and turned it a rather pink color such as seen in the la marzocco rebuild from timothy blue's site: http://www.timothyblue.com/linea.php

You can see it in the upper part of the image

Ilya: What you are seeing, I believe from my own experience, is some of the copper that was removed from off of the copper tubing chemically and deposited onto the chromed brass and brass. I noticed that all of the brass connectors on my copper tubing were pink when they came out of the citric as well. When I polished the connectors, the fine copper plating came off of the brass and the group heads.

Edit: If you are specifically speaking about LM group heads they don't require as much time in the acid bath as some of the other items. Again, in my experience, I found that the head was not as covered with scale as other parts.

Ilya: What you are seeing, I believe from my own experience, is some of the copper that was removed from off of the copper tubing chemically and deposited onto the chromed brass and brass.

so what you are saying is that it isn't actually messing up the chrome finish but just putting the copper from other pieces onto the chrome -- which can then be buffed/polished off?

Can anyone confirm this? I just want to make sure I don't turn my groups pink!

The picture I posted above shows two of the copper water tubes with brass fittings. The one on top is pink before buffing and the lower one is after buffing.

For the group head, I think I left it in hot acid for 20 minutes two times to get the little scale out. I was afraid of damaging it.

Before Polishing:

After Polishing:

wow that looks great! what did you use to polish the parts?

I bought an 8" bench grinder and replaced the grinding wheels with buffing wheels. I found most of the instructions on HB for polishing. You'll need a wheel for each color of buffing compound. I think I used only two for the brass and copper: red first and then white. The stainless takes much more work and using the 8" grinder isn't the most efficient. I ended up taking the stainless to a metal shop to polish although just about everyone on HB who's rebuilt a machine did their own stainless steel polishing. I found a good resource was YouTube for videos about polishing. I just checked inside the Linea and I can see the copper has oxidized rather quickly, the brass connectors are pretty shiny.