Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 13

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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ANeat

#121: Post by ANeat »

Gary if its not a decal it looks like a simple enough design that could be applied with a stencil and some heat resistant paint.

Ive seen some of those engine turned applications where they applied a clear coat for some added protection. Especially if its on aluminum.

On stainless it should be pretty durable and help hide any slight imperfections
LMWDP #332

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RayJohns

#122: Post by RayJohns »

ANeat wrote:You could always do a turned finish, I grabbed this image off the web

<image>
That turned / circular burnished look is always very cool. It sort of reminds me of the nice frosted look of a hand scraped lathe bed way.

Here's a site I pulled up via a quick google search:

http://www.woods-metal-shaping.com/mach ... e-turning/

The only draw back (to me) is that it sort of makes your espresso machine look like a juke box in a car hop or something. I still like it though :)

Ray

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RayJohns

#123: Post by RayJohns »

If you wanna get real pimp... send it off to Otto Carter and have him etch / engrave the whole darn machine! :-)

http://www.ottocarter.com/

Ray

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drgary
Team HB

#124: Post by drgary »

But before I pimp this beauty, it's time to deal with the beast!

Today Jay (aka Jaycan) came to the rescue and we made great progress removing most of the stuck bolts. The remaining bolts were cut off on one end so they can be drilled out and the holes rethreaded. He coached me on that and I will start on it soon.

Before Jay arrived, I started to disassemble the steam and water taps and got part way there. Following is lots of photo documentation for anyone taking on a Prestina or similar project.

Here are the valves before disassembly.

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First I had to remove the spring clips. The orange sheet is gasket material I'll custom cut for the boiler.

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Then unscrew the valve stem.

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Here's the valve stem, still lubricated, with gaskets that I'll replace.

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Next I remove the valve body.

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Here's the valve stem and body.

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There's still a nut on the valve body with a gasket baked in. At first I tried to turn it off with no success.

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Then I realized I at least need to remove the Teflon tape.

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Which comes off quite stringy, using a picking tool.

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I then repositioned the valve body in the vise and tried to turn it out, hoping the part sticking out would provide needed resistance, but no luck. I've padded the vise to avoid damaging the work piece. I think I'll need to apply heat to this.

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So I used the propane torch and heated it for about 30 seconds, not wanting to overheat. The propane torch isn't actually burning here, since I only have two hands! Still no luck.

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And these gaskets should go. Here's the other valve body with the same gasket, showing scale that also shows up blue white (but not in the picture).

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Next, Jay arrived, and we got to work on those stuck bolts.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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drgary
Team HB

#125: Post by drgary »

To the Rescue!

Jay backed his truck up to our garage and set up shop. He's shy about being photographed, so I focus on the work (actually, Elvis may have left the building, but he's retired to Northern California).

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He started by using a Makita grinder with cutting wheel to cut the bolts that were keeping the boiler plate and rear bowl stuck together.

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He removed a valve stem.

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Then applied a pry bar to the boiler halves.

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Finally the boiler face was freed from the back. Hallelujah!

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Now we finally got a look at the heating element and siphon tube from the hot water tap. And we can see residue to the fill line.

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Here's the back bowl with some bolts still stuck.

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So it was time to apply some heat. This vintage torch obtained from an old Ford plant has a special fitting that preserves the gas/oxygen setting.

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The idea was to paint the area surrounding the bolt with heat. He did this for about 20 seconds with the goal of not going over about 400 degrees F so he wouldn't change the metal and would heat it only a little more than it was with hot water and steam inside.

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Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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drgary
Team HB

#126: Post by drgary »

He was able to knock out a few heated bolts with a hammer.

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Now all bolts were removed from the back, where the holes aren't threaded.

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The siphon tube came right off after the nut was removed from the inside. All it took was a hard turn of the wrench.

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Here's removal of the steam valve base.

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Next he applied heat to the area around another bolt, this time on the face plate. What we hadn't yet figured out was all the bolts with a raised surface on the face plate were threaded. Adding some water and using vise grip pliers, each bolt would make a bit over a quarter turn, but that was it. We eventually resolved that those would have to be drilled out and rethreaded.

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Next he turned to the group head bolt mounts, heating the back.

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I've very lucky these all turned out of their threading using vise grips.

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Here's one of those bolts removed.

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Now it was time to cut off the threaded bolts.

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The studs were trimmed to create a smooth surface for drilling out.

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Next Jay coached me in using an automatic center punch to create a divot in the middle of the stud that would guide the drill bit. The advantage of a spring-loaded punch is it can be centered carefully and then pressed down to create its mark much more precisely than one that needs to be hammered. He recommends Starret or Proto brand tools for extraction because they're made of high-quality, hardened steel needed for this work. He then advised me to start with a very small drill bit, so if it breaks off, I can have a rescue strategy of drilling a small adjacent hole. He also taught me to use a thumb as a guide on the body of my power drill to make sure I'm not torquing the bit, since I don't have a drill press, and to lubricate the hole frequently with oil or WD40. By gradually applying larger bits, I'll approach the rim of the hole and can then tap new threads. I'll post that stage next and will now stock up on some citric acid and possibly muriatic acid for immersing the parts for cleaning if citric acid isn't sufficient.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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drgary
Team HB

#127: Post by drgary »

Drilling out a bolt

This is my first time trying this and I found it more like playing jazz than following a simple procedure. So here are pictures captioned to show how I was able to arrive at a fully drilled out hole where a bolt once lodged itself.

Here's where I started. Notice the polished off stud at the bottom, which has a hole center punched to guide the drill bit. I've started to drill the bolt to the right with a small, carbide steel bit and have centered it as much as possible without a drill press. I'm using a Black and Decker hand drill and using both hands to steady it and apply "about a 30 lb. tamp" of moderate pressure.

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So much for centering! The bit started coming through the other side of the bolt, which caused a bit of a shudder but no more. I've been using WD40 to lubricate and cool the drill bit.

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Next I applied a larger bit, and the hole is more obviously off center.

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Soon part of the rim of the old bolt came off.

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Next I used the cutting wheel attachment of a Craftsman rotary tool to remove the rest of the bolt edge so it's now flush with the surface.

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I then changed to a filing bit in the rotary tool to try and re-center at least the top of the hole to guide the next drill bit.

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Seeing that the other end of the bolt would come off anyway, I wanted to control that process and tried cutting it off with the rotary tool cutting wheel. That thin, tiny disk flew apart. So I clamped the work piece into the bench,

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and I used a hacksaw to quickly dispatch that bolt end.

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The other side of the hole still showed an uncentered remnant of the old bolt, and it was a little raised. So I attached a new cutting wheel to the rotary tool and made it flush. I also angled a drill bit toward the bolt wall remnant. Then I started drilling through the other side with the largest drill bit, one that's sized for the tapping tool I'll use to re-thread the hole.

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There were some stops and starts throughout as I carefully and gently drilled, starting with the smallest bit. The bit would occasionally catch, but my trusty old drill has a safety feature where it disengages traction when approaching a bit-breaking load. Then I would back it out and start again. For my last pass with a bit, I drilled from the side where I started. The shaft of the hole steadied the bit until the last remnants of the bolt came out.

Here we see the final result before tapping. The hole (the one at about 2 o'clock) now looks clean. When I fit the tapping tool into the hole, it fits snug. Now I've got to get to the store and get the wrench that holds that tap. This all took a little over an hour, and I feel fortunate that I didn't break any drill bits or lodge them in the hole.

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Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

phillip canuck

#128: Post by phillip canuck »

Epic. Citric acid will work wonders. I've removed far more gunk than what I see in your photos. Keep on chugging.

-phillip

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drgary
Team HB

#129: Post by drgary »

Just ordered citric acid and powder coated parts should return soon. So as I think ahead I thought I would float a few questions. Doug Garrott suggested upgrading to Sirai PSTAT. Others have written these can be noisy. Should I consider PID - not as much for temperature control of 4 liters of water as for quiet switching? Also, these can build false pressure and I'm thinking of connecting my Prestina to an appliance timer to save energy. I think a PID would eliminate the failure to heat issue because it would measure temperature with a thermocouple that I'm thinking of strapping to the boiler to not create new holes. Does that seem feasible? There's a related discussion on CoffeeGeek here: http://coffeegeek.com/forums/espresso/l ... 485?Page=1. Also Jaycan suggested installing a vibe pump inside the case for filling with water. Alternatively should I stick with a Flo-Jet pulling water from a large bottle?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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orphanespresso

#130: Post by orphanespresso »

Nice progress there! Yes the breakers on the Sirai can be on the clacky side....never saw it as a big issue, but a PID could be interesting. I think a lot of people think the tight temp control on a lever is overkill but I don't think a lot of commercial machines have been done with PID to get a good sample of performance, as in better worse or the same performance. You could solve the false pressure idea with a vac breaker somewhere (likely a new triple fitting around the pressure safety valve area with the safety horizontal and the vac valve vertical). I tried a surface mount PID on the FAEMA wall machine and found it to be annoying since it turned on and off about every 10 seconds and the element makes its own unique sound each time. Without the PID the thermostat cycles about every 5 minutes or so and I don't hear it until it sounds funny or different which means it is time to descale.
I would think that you will be pretty good at drilling and tapping holes so a properly installed probe should not be an issue to install in the boiler plate!