SUPERTECH exhaust valve stem seals BMW M3 E30 S14B23 S14B25

BMW engines concerned

These seals fit the 7 mm stem exhaust valves of the BMW Motorsport S14 four-cylinder of the M3 E30: 2.3 litre S14B23 (195 to 220 hp, M3, Convertible and Evolution) and 2.5 litre S14B25 of the M3 Sport Evolution (238 hp), from 1986 to 1993.

The S14 carries 8 exhaust valves, two per cylinder. The original seal surrounds the guide and meters the oil that lubricates the stem; BMW supplies it in seal set 11 34 9 059 171.

SUPERTECH exhaust valve stem seals

On the S14 exhaust, the 8 seals sit next to the hottest valves of an engine that loves high revs. Hardened or split after years of M3 E30 use, they let oil flow down the 7 mm stems toward the chambers, which burn it: the level falls, blue smoke leaves the system, carbon invades valves and ports. Each seal must still leave a trickle of oil for stem and guide.

For this side, SUPERTECH relies on Viton (FKM), an elastomer made to last against the 8 exhaust valves of the S14; according to the maker, this material lets the seal hold elevated temperatures, namely 204 °C (400 °F) continuous. It sits on a 9.8 mm guide (outside diameter) around the 7 mm stem. The set of 8 covers the whole exhaust of an S14B23 or S14B25; the inlet uses a polyacrylate (ACM) seal under its own part number.

Stem seal technical specifications

Stem seal installation

Technical guide

The brand offered

Operating in San Jose, California, for more than 30 years, SUPERTECH produces racing valves and springs, along with its own guides and stem seals. New designs are first computed with finite element analysis, then signed off by well-known engine tuners.

Why two different materials?

On the S14, the 8 seals on each side share dimensions; it is the M3 E30 exhaust valve that bears the greatest heat. SUPERTECH therefore puts its tougher Viton (FKM) VS-VW7-E on the exhaust, while polyacrylate (ACM) VS-VW7-I remains the choice for the inlet.

When valve stem seals must be replaced

• Oil receding, blue smoke at the exit
• S14 cylinder head off for repair
• Valve guides changed
• Uprated springs or valves planned

Vehicle compatibility

OEM part number (BMW stem seal set): 11 34 9 059 171 (S14B23, S14B25)

Remember the inlet valve stem seals

The S14 inlet wears just the same: use the removed head to renew its 8 seals as well. For the M3 E30, SUPERTECH offers: