When it comes to making a stock block all it can be, one of the long-known hot-rodder tricks is to fill the block’s water passages with concrete. This better supports the cylinders and reinforces the engine block’s structure. However, concrete and Iron don’t always play together very well.
To remedy this, Competition Products developed a material specifically for filling engine blocks called Rokblock. It expands to prevent voids in the fill, cures in 24 hours, is machinable once cured, and actually bonds to the block material, preventing chunks from breaking loose under hard use.
While a simple process, Competition Products does get a lot of calls to their tech line about how to use the product. To help answer those questions, Nick Rinehart, Competition Products’ sales manager, made a video walking viewers through the process of filling a block.
First, Rinehart outlines the tools needed to do the job properly. Besides the Rokblock itself and two funnels, a rubber mallet is to tap on the block with, to help settle the material. A carpenter’s level to lay across the block will ensure a level fill front to back and side to side. A second pail and a heavy-duty paddle mixer that can be chucked into a drill motor and a paint stick round out the tool list.
Rinehart stresses the necessity for block cleanliness. “The block has to be clean. Make sure it’s been hot tanked and is completely free of debris and has no oil or grime on it. The cleaner the block is, the better the material will adhere to the water jackets.”
Another preparatory step Rinehart points out may seem simple, and that’s to make sure all the drain plugs and freeze plugs are installed before you start mixing the compound, whether you’re doing a half-fill or a full fill. “Once you start mixing it, you have 15 minutes to get it into the block.”
Leveling the engine block is critical to ensuring that the material flows into the water passages evenly and thoroughly. This is done one bank at a time and can be as simple as rotating the block slightly on the engine stand and shimming the wheels to achieve a level deck surface in both dimensions.
Once 25-pound pail of Rokblok is enough for the whole engine, but since you are filling it one bank at a time, you’ll need that second pail so you can divide the pail of Rokblock in half. “Follow the instructions for mixing to a ‘T’,” says Rinehart. “Use cold water when mixing this. If you use hot water, it will set up in the pail.”
“Once you start mixing, turn your phone off and don’t get distracted. You have 15 minutes to get the mixture into the block at that point,” Rinehart stresses. “It’s easier to pour with two people, but you can do it with one. You want to pour between the two funnels, back and forth, to make sure there’s even distribution of the product in the block.”
As you’re filling the block, tapping the walls with the rubber mallet will help distribute the mixture internally as well. “In an hour, it will have solidified enough that you can rotate the engine block over and start on the other bank of cylinders,” says Rinehart.
And finally, not a direct tip, but an important procedural step: “Make sure you put the Rokblock in before you bore and hone the cylinders. It will change the shape of the cylinders,” Rinehart says. Following these steps, whether you are doing a half-fill or a full fill, you’ll have a stock engine block capable of holding significantly more power.