01/06/2026
A Volvo rolled into our Welshpool workshop this week still leaking from the front of the engine — and the front crank seal had just been replaced elsewhere the week before.
When we pulled the cover, the seal was fine. The silicone job was the problem.
The previous workshop had left the silicone as a thick, lumpy bead and bolted the cover on top of it.
Three things went wrong as a result.
1. No flat sealing surface — the silicone bunched up unevenly, leaving thin spots with no seal at all.
2. A thick bead takes much longer to cure. By the time the cover went back on, the silicone was already skinning over and couldn't bond properly to both sides.
3. Excessive squeeze-out, both outside (the visible mess) and inside (where it can break off into places it shouldn't be).
The right way: lay an even bead, then smear it flat with a finger or small tool into one thin smooth film.
That fills the small pores in the casting, eliminates the squeeze-out, and gives both edges a clean wet surface to adhere to. Then the cover goes on, the bolts get torqued in sequence, and the joint sets up properly with no leak path.
Two workshops can fit the same part and walk away with completely different results. The trade is in the bits that don't have a part number.
Webbie's Mechanical, Welshpool WA. Heavy diesel specialists.