Technical guide
Group gasket: sizes, how to identify yours and when to replace it
The group gasket is the rubber ring that seals the portafilter against the brew group. It is identified by its outer diameter, inner diameter and thickness, and by its profile, flat or conical. Replace it when the portafilter leaks at the rim, when the handle locks further round than before, or when the rubber has gone hard.
What does the group gasket do?
It seals the joint between the rim of the filter basket and the brew group, so that water under pressure (around 9 bar on most machines) can only leave through the coffee. It sits in a groove in the group, around the shower screen, and is compressed every time the portafilter is locked in.
Pressed against hot metal, the rubber eventually dries out, hardens and stops sealing. Coffee grounds left on the basket rim speed up that wear.
How do I identify which group gasket my machine takes?
Start with the manufacturer's parts list for the exact model; without it, measure the outer diameter, the inner diameter and the thickness, and note the profile.
- Measuring: use calipers. A used gasket is compressed, so its thickness reads below nominal; measure the groove in the group as well.
- Profile: flat gaskets have a rectangular section; conical ones have a sloped face (bevel).
- Cuts: the 3 or 4 cuts on the edge of some gaskets do not change the nominal dimensions.
- Thickness of conical gaskets: some lists quote the height of the flat part, others the overall height. The standard La Marzocco gasket appears as 6 mm in many lists and as 8 mm in the manufacturer's own maintenance checklist.
What are the most common group gasket sizes?
On most 58 mm groups the gasket measures roughly 71–74 mm outside, 55–58 mm inside and 6–9 mm thick; some brand-specific groups use rings of around 64 mm.
| Group type | Outer × inner Ø | Thickness | Notes |
|---|---|---|---|
| E61 pattern (Faema E61 and E61 groups from other makers) | 73 × 57 mm | 8 or 8.5 mm; 9 mm for worn groups | Flat |
| Rancilio | 73–73.5 × 57–57.5 mm | 8 mm | Edge with cuts |
| La Marzocco | 72 × 55 mm | 6 mm at the flat part (8 mm overall) | Conical; a version 1 mm thicker exists |
| Nuova Simonelli, Victoria Arduino, La Cimbali | 71 × 56 mm | 9 mm at the top of the bevel | Conical |
| La Spaziale (53 mm portafilter) | 64 × 52 mm | 6.3 mm; 6.7 mm for worn groups | Brand-specific size |
| La San Marco | 64.6 × 53 mm | 5.5 mm | Flat |
These are nominal figures: models and production years differ, so confirm against the parts list before ordering. The gaskets are in Gaskets & O-rings.
When should a group gasket be replaced?
As soon as it leaks or the rubber hardens; on a commercial machine it is best treated as scheduled maintenance. The La Marzocco Linea PB maintenance plan, for example, lists new group gaskets and shower screens every three to four months.
- Water or coffee escaping around the portafilter rim during extraction.
- The handle has to turn further to the right than before until it feels tight.
- The rubber is hard, cracked or comes out in pieces.
The real interval depends on cups per day and on the hours the machine stays on.
How is a group gasket replaced?
With the machine off, isolated from the mains and cold: remove the shower screen, pull out the old gasket, clean the groove and fit the new one the right way up.
- Switch the machine off, isolate it from the mains (plug or circuit breaker) and let the group cool down completely (La Marzocco allows about two hours).
- Remove the shower screen. On groups with a centre screw, undo it; on E61-pattern groups the screen is held by the gasket and the two are levered out together, carefully.
- Hook out the old gasket with a pick, remove every fragment and clean the groove.
- Fit the new gasket in the right orientation. On La Marzocco-type conical gaskets the flat face goes into the group and the bevel faces down; on E61-pattern groups, the ECM manual has the rounded edge facing up and the screen pressed into the gasket first, so both go in together.
- On groups with a screw, refit the screen; seat the gasket by locking the portafilter in a few times and, with the machine hot, check for leaks.
What if the handle still turns too far with a new gasket?
If the gasket is the right one, the wear is in the group or in the portafilter lugs, and the lock position is recovered with a thicker gasket or with a thin shim behind the gasket.
Group gasket shims of 0.5 and 0.8 mm sit at the bottom of the groove. Go up in small steps. Other group parts are in Group & Portafilter.
FAQ
- Is a silicone group gasket better than a rubber one?
- Both seal properly if the size and profile are right. Nitrile rubber (NBR) is the most common and silicone versions exist for the same groups. La Marzocco's instructions accept either and recommend a film of food-safe silicone grease on the flat face when the gasket is rubber.
- Should the shower screen be changed together with the gasket?
- It makes sense, because the screen has to come off anyway to reach the gasket. The La Marzocco Linea PB plan lists both parts at the same interval and the ECM manual has them changed together.
- Does a leaking portafilter always mean a worn gasket?
- Not always. First check that the basket rim is clean and free of dents and that the portafilter is locked in properly, the first cause the ECM manual lists. If the leak continues, replace the gasket.
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