Devcon Block Fill: Reinforcing a Honda B-Series Open-Deck Block for Boost

Strip the block down to a bare casting and mount it on an engine stand or set it on a solid bench. Shim or adjust until the deck reads dead level in both directions, front-to-back and side-to-side. Epoxy that cures on a tilt will pool unevenly around the cylinders and leave an inconsistent fill.

Rough up the exposed water-jacket walls and the outer sleeve surfaces with 80-grit sandpaper so the epoxy has tooth to grip. Blow out the abrasive dust, then spray everything down with contact cleaner to strip oil and grit. A clean, keyed surface is what lets the Devcon bond permanently to the jacket.

Use a hacksaw blade as a simple depth gauge. Stand it against the outside of a sleeve with its end aligned to the top of the water-pump passage, then mark the deck where the blade crosses it. That mark sets how high to build the salt, which corresponds to a fill of roughly 1.5 inches. Keep the layer no thicker than about 1.25 inches on a street engine to avoid choking off heat rejection.

Pour table salt into the water jacket, distributing it evenly around every sleeve up to the line you marked. Pack it down firmly and prod it with the blade to collapse any voids so it sits level and dense. Fine table salt is preferred over coarse rock salt because it compacts tighter. This packed salt is a sacrificial dam: it stops the thick epoxy short and preserves the coolant passages beneath.

Combine the two Devcon components and stir continuously for at least 4 minutes, until the mix turns an even grey with no streaks. Pour it through a funnel into the jacket on top of the salt. To minimize trapped air, transfer the mixed epoxy into a zip-top bag, snip off one corner, and pipe it down into the cavity like a pastry bag. One pound of Devcon yields about a 1 inch layer on an F- or H-series block.

Run a gloved finger around the top of each sleeve to level and smooth the fresh pour. Keep the epoxy below the gasket surface, leaving about 1/16 inch of the sleeve top exposed. Nothing should stand proud of the deck. The material shrinks slightly as it cures, so a pour that sits a hair high usually settles flush.

Allow the poured fill to set at room temperature for 4 hours. Next, hold it at 200 degrees for 4 hours; the writeup improvised an oven from a space heater inside a large box. Finally, let the block rest a further 18 hours before handling. Devcon Liquid Aluminum F-2 is rated to 120 degrees F while still wet and 250 degrees F once cured, so it must be fully cured before it ever sees coolant temperature.

Once the fill is hard, set an old head gasket over the deck and trace each coolant port onto the cured epoxy with a marker. Drill each passage back open through the fill, using a bit one size smaller than the gasket opening so a clean shoulder of material remains around every hole.

Back out the freeze/drain plug with a 19mm wrench and run a hose through the block. Keep flushing until the water runs clear and streams evenly from every coolant hole you drilled, which confirms the salt has fully dissolved and washed out. Reinstall the plug once the passages run clean.

Wipe the cylinder walls with light oil to prevent flash rust. Give the bores a final hone, or have the block bored oversize at a machine shop, then assemble the short block as normal. Because the epoxy exerts no clamping pressure on the sleeves, the bores keep their shape; a light hone is usually all that is needed if they were already finished.