Product Info


Cut-away of 454 cu. in. Chevy, bored 0.125" oversize shows HARD BLOK Water Jacket Filler and cylinder walls in perfect condition after four years of winning drag racing.

Cut-away of 454 cu. in. Chevy, bored 0.125" oversize shows HARD BLOK Water Jacket Filler and cylinder walls in perfect condition after four years of winning drag racing.


HARD BLOK WATER JACKET FILLER is a specially formulated, cement-based product with refined, size-graded iron particles combined at an optimum ratio to provide maximum strength, vibration dampening, and heat dissipation required in high performance race engines. Its coefficient of thermal expansion is identical to cast iron engine blocks. Product has been tested and proven effective in aluminum blocks.

  • Remains stable at all operating temperatures. Does not soften when exposed to high heat, nor erode under water.
  • Fills the smallest spaces in the water jacket. Does not shrink or pull away from the cylinder walls. Does not expand.
  • Extends cylinder wall life both by preventing cracked walls and by causing the walls to wear truer. Honing is minimized during rebuilds.
  • A race-proven advantage used by winners in all types of racing since 1986.
  • Non-hazardous and non-corrosive. Contains no toxic material. Once hard, it cannot be removed from the block.

NOTES: Block castings are not precise. One side may vary from the other. Variance between blocks can be considerable. H & H is not responsible for this variance. One TALL FILL Unit will fill most big blocks to the bottom of the water pump connection. In certain tall deck blocks, the fill level may be an inch or so lower. This level is adequate to stiffen the cylinder walls.


Order the TALL FILL Unit for 350 cubic inch and larger blocks. Order the SHORT FILL Unit for circle track and street rod applications. Detailed instructions and contingency decals are shipped in each unit. To avoid coolant flow restrictions, check flow requirements and the pattern of your particular block before filling. HARD BLOK becomes permanent and cannot be removed after hardening. H & H Specialties, Inc. cannot be responsible for any coolant flow blockage or overheating problems caused by installation of water jacket filler.


WARRANTY: No warranty is stated nor implied due to operating extremes in race engines and manufacturer's inability to control installation. Manufacturer is not responsible for any cooling problems that may result from filling water jackets. User is responsible for determining suitability of product for intended use. All risk and liability connected with use of the product is assumed by user.




HARDBLOK Premium Filler

  • Easy to mix and pour. Dual, pre-measured packaging is convenient for typical V-8 installations. Detailed instructions included.
  • Ample working time to pour and install torque plates.
  • No high heat build up during setting to cause distortion.
  • Rapid strength gain. Can hone and assemble 24 hours after completion.
  • Does not shrink, does not expand.
  • Optimum ratio of graded iron for strength, vibration dampening, and thermal expansion.
  • Stable under water. Will not erode.
  • Non-hazardous.
  • Track-tested since 1984 with perfect success.

OTHER Brands

  • Packaging requires user to guess at amount needed.
  • Proper mix ratio of water-to-powder not specified. Results in improper mix.
  • Quick-set materials do not allow time to properly fill and install torque plates.
  • Quick-set cements and epoxies can generate high heat that distorts thin or unsupported engine sections.
  • Some gain strength too slowly for quick assembly. Some require 28 days!
  • Some shrink when mixed wet enough to pour into blocks. Some expand 0.3% and will distort walls and critical engine sections.
  • No iron content. Addition of “shop iron”may actually weaken a mix due to poor sizing and impurities.
  • Gypsum-based materials erode under water. Potential water pump damage.
  • Epoxy hardener component is usually corrosive and hazardous.
  • None have the record of HARDBLOK!