Introduction
The best introduction was already written by some of this site's most knowledgeable posters in the Possible to install group-mounted pressure gauge on La Marzocco GS/3 MP? thread. Fair warning - that full thread is six screen-pages long and rambles a little, but it's a good read, playing out the genesis of GS/3 pressure profiling and how we managed to get here (and also how some people's assumptions - especially mine - can be happily mistaken: large helpings of crow were baked, dished out and eaten with gusto).

On Page 6 of that thread, you'll find a long post detailing my own experiences with the upgrade with some notes and considerations. I'd promised to document the conversion method for others who might be similarly inclined - and especially for those who acquire their courage from text as opposed to strong drink - and H-B suggested this information be provided via a fresh thread.

The decision to add pressure control to the GS/3 would appear to fall into the "no-brainer" category for most MP owners. It may be called an "upgrade" or "conversion" here - which it is - but in truth you're really only (a) adding the manometer/pressure gauge to the grouphead for real-time feedback and (b) reversing the pump microswitch so that its timing cooperates. It may not sound like much, but believe me, the result is like having a whole new machine. This converts/upgrades your standard GS/3-MP grouphead into a Strada-MP grouphead.



Conversion Benefits
The upgrade itself is neither difficult nor risky and doesn't require any more mechanical capability than needed to do your annual O-ring maintenance. You don't need to get deep into the machine or into complex areas where an amateur could really mess things up. Further, the conversion is easily reversible: if you don't like the way it's going or turned out, just return your GS/3 to its former state using the original parts.

If tinkering is just not your forte, your local service person can do the conversion, and the cost should be reasonable. An experienced LM technician will rip through this in less than an hour, and half of that will be spent warming the machine up for a final check. Remember, this upgrade just makes a standard GS/3-MP grouphead into a standard Strada-MP grouphead, so an LM tech will not be dealing with anything new or unfamiliar.

Benefits of pressure control (or a virtual "GS/3 a Leva"):

• Pressure-controlled pre-infusion - it's widely assumed that plumbed-in machines will have about 3 bars of pre-infusion line pressure, but measurements at the grouphead show that you may be getting only 1½ or 2 bars. The new manometer will now show you exactly what you're getting and you can manage it in real time to use whatever pressure you like.
• Pre-infusion for reservoir users - this upgrade finally enables real PI for those who don't have line pressure available from a plumbed-in machine. If you have granite counters, the GS/3-MP upgrade may prove easier than drilling through your counter and a lot less costly in terms of domestic tranquility. It's also cheaper than most plumbers.
• Ramp-down ("post-infusion") - near the end of the shot, lever users often lighten up on the pressure to extract some additional flavor and body from the puck when faster flow would compromise the body and concentration of the shot and quickly blonde. Jim Schulman gives a fine demonstration of this in one of his excellent Bezzera Strega videos - now you can do it too.
• Low-pressure shots - I've discovered that some coffees taste better to me when pulled at, say, six bars instead of the default eight or nine bars. Also, the normal fix for too-fast shots (when the grind is already perfect for flavor) is to up-dose, but you may find that down-pressuring works as well or better, plus you can make this change on the fly (I've always found it difficult to change the grind once the shot starts pouring). So now you'll have another option in your arsenal.
• High-pressure shots - the default GS/3 factory pressure setting is about nine bars, a long-accepted mid-point that works for most coffees, but others may pull better using even finer grinds or higher doses. The upgrade enables you to set your machine's pressure higher for those occasions, while still pulling "normal" coffees at eight or nine bars. One size need no longer fit all.
• Optimizing (or saving) a shot - once you've ground the coffee and locked in the prepped basket, your dice are cast upon the table. Your final task as a barista is now to make the best possible shot from that basket. By watching the flow and adjusting the paddle pressure, you can now fine tune the pull in real time to make it the very best it can be. Even if you really screwed up the grind, you might may be able to rescue a drinkable beverage instead of wearing out the sink. The main point is that you're not condemned to suffer push-button pass/fail shots.
• Satisfaction - pressure control adds another dimension to your espresso-making, and using it well is another skill to develop and enjoy. Lever-heads justifiably love the hands-on feel of a manual process and the on-the-fly finesse; this conversion will not only upgrade your machine - it will raise the bar on your own capabilities and give you a new challenge. For me at least, it's been a lot of fun.

...Where Credit is Due
Let the record show that other people did all the heavy lifting on this development. Credits - and a lot of thanks - need to go first to Marshall Fuss for showing us (with a real experiment instead of the "thought" variety) that the stock GS/3-MP flow/pressure could realistically be controlled from the paddle. Pat Campbell ("Danetrainer") was the first (that I know of) to convert his own GS/3 and he posted this utterly convincing video showing how it worked in actual practice. Pat gave me a ton of great advice and enabled me to replicate his successful upgrade, plus he contributed hugely to this post. Chris Scott from LM freely dispensed indispensable advice and operating analysis, and verified the critical materials information to create the upgrade itself. And special thanks to Mark and Ken from Portland's Clive Coffee for their great GS/3 expertise and support.

The next installment provides some key resources for the upgrade and describes the parts you'll need.

This post continues the above by covering the resources and the parts you'll need for the GS/3-MP pressure profiling upgrade. Please forgive the immense quantity of pixels (in some previous life I must have been paid by the word). It's important to start with those subjects, however, since the upgrade requires some new parts, and while you wait (im)patiently for that box to appear on your doorstep, it'll buy me the time to take a few pictures and scrawl out the rest of this tome.

Resources to Give You Some Context
Unless you're already an expert, you should definitely check out these items before you begin. These give you a good overall understanding of how the La Marzocco grouphead works, and you'll feel much more confident - or if not, at least you'll now know to get yourself some help. (Spoiler alert: there are sure to be many other useful videos, documents and guides, some better than these - and I'm sure the H-B community will write in and tell us all about them any minute now.)

First, watch this brief animated video that explains how the GS/3-MP's paddle and valve work. It's a nice little piece that shows the operations very clearly.

Second, download this La Marzocco catalog with clear exploded diagrams that are indexed to parts lists. This is a primary document showing how the Strada-MP grouphead fits together. The only relevant pages for this project are 32-35 - the rest of this catalog is about other parts of the Strada, which you likely don't own anyway given you're reading this. (Note: you received - and then promptly lost - a similar manual along with your GS/3, and it's useful to explain what you already have, but not useful to show you the Strada-MP grouphead parts you don't have.)

Third, watch this short video from La Marzocco that shows how to service the grouphead. This video goes much further than this upgrade project requires you to know or do, but you'll quickly understand how straightforward the limited disassembly and re-assembly will be to complete this upgrade. On the other hand, if after watching this video you don't think swapping the shaft and replacing the O-rings is a happy part of your future, at least now you'll know that your upgrade project will need a little outsourcing.

Fourth, DO read - through to the very end - all the additional and very helpful posts provided by other members in this thread. You'll find many good ideas, techniques and tweaks on the basic methodology, not to mention a better overall sense of the project and some useful alternatives to some of the steps. Plus you'll pick up some confidence from others' successful results and how to overcome unforeseen questions, hitches, or random unauthorized H2O discharges.

What Parts do you Need?
This upgrade is essentially a conversion of the stock La Marzocco GS/3-MP grouphead to a stock La Marzocco Strada-MP grouphead. The new parts you'll need simply constitute the difference between the two parts lists. Three of the required parts are substitutions or modifications of your existing native GS/3-MP parts; these being the slightly different Strada-MP versions of those same basic pieces. The balance of the parts you'll need are the items specific to the manometer assembly - and you don't have any of those yet. So here we go, with the La Marzocco part numbers and descriptions, plus a little information and the approximate list prices as of this writing (which will change with the Euro, the timing, management whim and so forth):

E.3.009 Vertical Gauge for Paddle (manometer)
This is the manometer gauge that is mounted just above the group cover and which shows you the pressure as measured right at the valve as the pressurized water enters the distribution screen block. You'll need to purchase this part. (List price: ~$50)

H.1.021 EPDM O-ring 103
This is a tiny O-ring that seals the gauge assembly connection to the vertical manometer fitting immediately below. You'll need to purchase this part since it is unique to the Strada-MP. (List price: ~$2)

A.2.019 Vertical Manometer Fitting
The bottom (male) threads of this fitting screw directly into the valve shaft, and the top (female) threads receive the manometer. This part also needs to be purchased. (List price: ~$47)

A.2.018 Vertical Manometer Nut
This is essentially a nicely machined cylindrical lock-nut that holds the viewing angle of the manometer steady so the gauge doesn't rotate. There's a small hole in the side to insert a stud (or the chuck end of a drill bit) to tighten. This part is also unique to the Strada-MP and needs to be purchased. (List price: ~$38)

H.1.020 EPDM O-Ring 3024
This is a small o-ring that seals the joint of the manometer fitting to the valve shaft. You'll need to purchase this part. (List price: ~$2)

A.5.010 Ryton Valve Shaft MP
This is the Strada-MP's group-head valve shaft that rises and falls to open and close the flow as you move the paddle. It's made of Ryton, a high-performance polymer that's resistant to heat, abrasion, acids, wear, aging and so forth, and it's the bright blue item you see in photos of the La Marzocco saturated groups. The original GS/3-MP uses a different model of this shaft, but this Strada-MP version is hollow through the center core and threaded at the top for connection to the manometer fitting and gauge. The hollow core permits the gauge to read the pressure at the valve opening at the bottom of this shaft (where four tiny ports in the shaft move upward into position to enable the coffee boiler water to pass through them and into the dispersion block.

At LM's current list price of about $225, this is by far the most expensive item in this bill-of-materials. If you have good machining skills and tools, you can save a bundle by converting your original GS/3-MP shaft to the Strada-MP version. You will need to drill out the shaft's core and then tap the top with a 7mm fine thread (at this writing, I'm not sure of the pitch specs for this thread, but obviously they match those of the manometer fitting above. I will edit them in when I locate that information.)

F.1.020.MP Group Cover, X Paddle
This is the familiar shiny black group cover that fits over the paddle workings. Your stock GS/3-MP's cover (F.1.020) is flat on top with no opening for the manometer gauge. The Strada-MP cover provides a hexagonal opening for the manometer fittings to come through. Here again, you can order yourself a brand new group cover (about $75 LM list price) or you can remanufacture your stock F.1.020 into a close approximation of the F.1.020.MP. The prettiest conversion results will come from a skilled lathe or drill-press operator, but all manner of drills, Moto-Tools and sandpaper can get you there too. But note that the cover is made from a hard Bakelite-type material that can chip if you're not careful or smooth in your drilling technique. Those Who Know recommend a Forstner bit, carefully centered. But don't worry about the difference between your round hole and the LM hex hole though - the round one looks great, and in fact is slightly easier to install since the home-made round version doesn't require you to line up the hex shaft/bolt with the hex opening in the cover.

NOTE: if you spring for a new Strada-MP cover from LM (F.1.020.MP) it will not come with the two Allen-head cap bolts (I.1.028) that fasten the cover to the grouphead. You simply transfer them over from your original group cover - you'll need to take off the capture rings to free them from the cap, but that's an easy step in the instructions below.

C.1.067 MP Microswitch Holder
One of the important steps in the upgrade is reversing the orientation of the grouphead micro-switch that controls the pump. Why? Because you need the pump to engage at a different point in the paddle travel than with the stock GS/3, and that requires re-mounting the microswitch with it orienting it in the opposite direction, with the wires exiting to the right instead of the left. This revised mounting requires a holder/bracket with mounting slots that enable that reversed position. You can save about $25 at list price by modifying your current bracket - this involves a simple lengthening of the existing mounting slots with a Moto-Tool, Roto-Zip, drill, file, hacksaw or a really determined Maine Coon Cat. If you choose to remanufacture the bracket though, make sure that whatever tools you use were designed to match wits with stainless steel: LM doesn't use pot metal.

• EDIT - additional information: all versions of this microswitch holder apparently use the same LM part number (C.1.067). This is why your GS/3-MP parts catalog uses this part number and so does the Strada-MP catalog. Sometime in mid-2012 however, LM updated the way this part is machined (without updating its part number) and GS/3s started shipping with the new version. So if your GS/3 was delivered around mid-2012, it may already have the new/updated bracket version. Even LM in the US isn't aware exactly when or with which serial number the change occurred, so the only way to be sure is to take off the group cap and check for yourself. The new version is pictured below - the telltale feature is that both slots are positioned the same distance from the top of the bracket: that's what you need to mount the switch in the reversed position:
  
  

SA600/K Mechanical paddle valve rebuild kit
This isn't strictly part of the upgrade, but as long as you have the grouphead open, you may as well replace the gaskets unless they are very fresh. It's particularly important with pressure profiling that the
O-rings that seal the valve shaft are firm and smooth: the control of the pressure requires almost microscopic adjustment as the tiny shaft ports rise progressively over the rings, and frayed, worn, flattened or otherwise compromised O-rings can't provide predictable or smooth pressure control. Just do it. (List price: ~$37)

Bullet Connector, Female, 10-12 Gauge Why do you need this? (If you guessed that the LM switch is equipped with a Bullet Connector, Male, 10-12 Gauge, you win a prize.) Assuming you reverse the switch, you'll also need to reverse the ON/OFF default operation on the microswitch. Although the switch provides a perfectly good third wire to connect to the incoming line, that wire is just capped off. So, for a really nice job, you need to crimp a corresponding female connector onto that wire. Warning: it can be surprisingly difficult to find this size in your local hardware store, but they are available on Amazon if you don't mind having lots of left-overs from the 20- or 40-count packages. Or you can substitute in a new Male/Female bullet connector pair in an easier-to-locate 14-16 gauge set (no fireman will call...). Or, you can improvise a temporary connection using your choice of paper clips, electrical tape, the ever-popular Bazooka Joe or the ruthless application of tin snips to a tomato can.

Silicon Based Lubrication for O-Rings If you're a guy, you never cracked LM's nice "Mechanical Paddle Manual & Parts Catalog" that came with your new GS/3. Instead, when your machine was finally delivered, you put it on the counter, filled it up, plugged it in, made one sink shot followed by six amazingly delicious ones and never looked back. Meanwhile, the manual bounced from drawer to drawer until it disappeared forever along with your favorite blue shirt. If you're not a guy but you are reading this anyway, then your attitude is just like a guy's, and your manual bounced from a notebook to a shelf to a box and then it went the way of the fourteen jars of freezer jam you made with your then-boyfriend in 1992 but no one ever ate but you couldn't stand to throw out until one of those jars cracked and then all those ants showed up.

But I digress - the point is, the manual says use "silicon based lubrication for the O-rings," and you don't want your grouphead parts spread all over the counter before you realize the closest thing you've got is an ancient tub of Crisco. So get some SBL. Orphan Espresso, for example, will sell you some NSF-certified Dow Corning 111 for three bucks. Granted, it's a tiny, tiny package containing only six grams, which is barely enough to last you through the year 2086.

What's All This Going To Cost?
Including the gasket rebuild kit, if you buy every part here, the list price will be just about $500 at LM's current pricing. However, if you can modify the microswitch mounting bracket and the grouphead cap, you can save yourself almost $100 right there, and if you can also modify the valve shaft (granted, that's probably unlikely unless you have some pretty good tools) you'll save another $225.

So it's possible to keep your out-of-pocket cost down to as little as $175. Yes, that counts as real money, no doubt, but it's a very small cost increment considering how much value this adds to your original GS/3-MP investment.

Next up: The Recipe...

• While I was taking my machine apart again to get all the steps and write them up, Danetrainer and others added some great information in several posts below. The "recipe" for the actual upgrade/conversion has finally been completed, and these instructions continue on the following page of this thread. Thanks for your patience and the many encouraging PMs while I finished up the job.

Anvan; thanks for all the great info. I plan to mod my GS/3 in the near future when it needs o-rings. I have had it for 6 months and really enjoy it, but realize this will add a whole new dimension.
I do have a small metal lathe and plan to drill/tap the shaft to save the exorbitant price of a new shaft. Did you do this also?

Good luck, Derek - as nice as the stock GS/3-MP may be, your "new dimension" is a good description.

Unfortunately, my tools - and limited skills to match - were not up to the task of re-machining the valve shaft. I know it can be done, however, and Danetrainer mentioned it in the previous thread that led to this one. And unlike, say, cast iron or styrofoam, Ryton appears to be an excellent material for machining.

Excellent write up Antony!

Nice job documenting the conversion, Tony. The tap size needed for the gauge adapter is 7mm x .75 pitch. Here in the US I ordered it from Victor.

The hole that needs to be drilled through the shaft is 2mm.

Two notes on machining the shaft to accept the adapter, I recommend a 15/64 drill bit, rather than a 1/4" for the tap process due to the soft material. Second, I take a face cut off the top (approximately .005") after the tapping process to give a larger area for the o-ring seal due to the amount of radius the original shaft has at the outer edge.

Pat; can you clarify a couple of things on the shaft machining?
Do you drill a hole all the way through the shaft? Did this affect the small holes perpendicular to the new hole?
What do you mean about "The hole that needs to be drilled through the shaft is 2mm"?
Do you cover the shaft with any protective material or just put it right in the lathe chuck?
Thanks.

Derek, Yes the hole goes all the way through from top to bottom (as the shaft would sit in the group head), and intersects the perpendicular holes, but does not alter them. I used a 2mm sized drill bit (this is the measured size LM used on the Strada) although you could certainly use a 1/16" bit, it would not make any difference. Standard jobber length drill bits are only long enough to go a little over half way through, then you need to turn the shaft around and finish from the other side. I used two wraps of 3M electrical tape on the Ryton shaft where I insert it in the metal jaws of the lathe. I would recommend tapping the hole on the lathe to keep the threaded section of the hole true.

Awesome write up Anvan! I completed the pressure gauge install a few weeks, the main reason i did it was so i could pre-infuse/pre-brew as i couldn't get 3bar of pressure when pre infusing. When installing the gauge and playing around with the microswitch position I found out that i couldn't originally get 3 bar due to the pump kicking in to early when it was set up in factory. Anyway that issue is irrelevant now. It also has the added benefit of playing with different pressures, the Ethiopian Harrar i have in the grinder at the moment tastes a lot more sweeter and fruiter when pre-brewing at 4 bar then heading up to 8 bar. I also think it looks pretty sweet too! Thanks "danetrainer" Pat for all the information i needed to clarify, your a champion! Also Chris at LM USA was a great help in the parts area if you need the parts required.

Welcome to HB Mick!!! Quite a sweet setup you have!