SUPERTECH exhaust valve stem seals BMW MINI B46 B48

BMW and MINI engines concerned

This set goes on the exhaust side of the transverse 2.0-litre modular B46 and B48 four-cylinders, whose exhaust valves have 6 mm stems: BMW 1 Series (F40, F70), 2 Series Active Tourer, Gran Tourer and Gran Coupé, X1 and X2, and MINI Cooper S, John Cooper Works, Clubman and Countryman, since 2013, codes B46A20A, B46A20B and B48A20A, B, E, F, H, P and S.

Eight exhaust valves per engine, two per cylinder. BMW fits seal 11 34 0 035 853 from the factory; it caps each guide and leaves the stem only its lubricating oil.

SUPERTECH exhaust valve stem seals

On the B48, the manifold built into the head and the closely mounted turbo make the exhaust the hottest area of the engine, and the stem seal feels it directly. When its lip hardens and cracks, oil works its way past the stem to the chamber: the engine needs top-ups, puffs blue smoke and loads valves and ports with carbon. A fine trace of oil must still remain on the stem to protect the guide.

This exhaust seal is made by SUPERTECH from Viton (FKM), a heat-resistant elastomer picked to age well beside hard-working exhaust valves: the maker says the compound accepts higher temperatures and holds 204 °C (400 °F) continuous. It fits a 6 mm stem. The 8 pieces equip the full exhaust of the B46 or B48; on the inlet, the 5 mm stem takes another Viton seal, sold separately.

Stem seal technical specifications

Stem seal installation

Technical guide

The brand offered

For more than 30 years, valvetrain parts by SUPERTECH have come from a San Jose, California workshop devoted entirely to racing. Each new part is first modelled by finite elements, then validated by tuners well known in drag, rally and circuit racing.

Inlet or exhaust?

Both seals on these modular engines are Viton (FKM); only size separates them: VSI-BM60-E for the 6 mm exhaust stem, VSI-BM50-I for the 5 mm inlet stem, so they cannot be swapped. SUPERTECH rates the Viton at 204 °C (400 °F) continuous. Eight seals per side.

When valve stem seals must be replaced

• Oil top-ups, blue smoke on the B48
• Head rebuilt or valves removed
• Valve guides changed
• Uprated springs or valves fitted

Vehicle compatibility

BMW

MINI

OEM part number (BMW exhaust stem seal): 11 34 0 035 853 (B48)

Remember the inlet valve stem seals

With the head open, also change the inlet seals, which age in exactly the same way. For the B46 and B48, SUPERTECH offers: