Precision Meets Passion – Restoring a 1985 Lancia Delta S4 Stradale Water Pump

Every now and then, a project rolls in that takes us right back to the golden era of engineering.

This week: a Lancia Delta S4 Stradale — a true Group B rally legend, now worth between £500,000 – £750,000 with fewer than 70 surviving worldwide.

The issue? Its water pump.
The spring-loaded carbon seal and impeller seating face had a 0.030–0.040 mm flatness error, creating a leak path between the two surfaces. With parts like this, replacements simply don’t exist.

We lapped both components on our Speedfam 32” open-face machine using F500 silicon carbide, achieving:
✅ ≤ 0.010 mm flatness on both faces
✅ 0.1 Ra surface finish – critical for sealing performance and eliminating micro leak paths
✅ A perfect carbon-to-impeller seal – no more leaks

From high-end motorsport to everyday precision components, our goal is the same: engineered accuracy you can measure in microns.

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