We learned the hard way about sealing small- and big-block Chevys when a friend built a 454ci big-block that found its way into a pleasure boat. The owner bolted the engine in the boat and hooked up a water outlet at his house to test-fire the engine. At first, the engine ran fine. But, soon suffered from hydraulic lifter clatter so the owner shut the engine down. That’s when he discovered water in the oil.
The initial diagnosis was that the head gaskets had failed, but that seemed doubtful because the engine builder had used Fel-Pro quality composition head gaskets and the engine was fitted with a new set of TFS aluminum heads. We were asked to diagnose the problem, so the engine ended up in our shop. We drained the milkshake oil from the pan and replaced the filter and then decided to pull the heads. After only the third or fourth head bolt, we noticed that the threads had no sealant, and there was a substantial amount of water still clinging to the unthreaded portion of the bolts. We found the smoking gun.
All Gen-I and Gen-II small-block and Mk IV big-block Chevy engines are machined with the head bolt holes in the block drilled straight through to the water jackets. This demands a sealer on the head bolt threads to prevent pressure in the water jackets from pushing coolant past the threads in the block and entering the crankcase area.
We decided to remove the heads anyway and replace the head gaskets just in case. This also allowed us to more closely inspect the combustion chamber and tops of the pistons. There appeared to be very light valve witness marks on the pistons, so we checked the valvetrain and discovered the “engine builder” had placed the cam gear one tooth off from the crank. We also removed the oil pan so that we could clean the remaining water out of the corners which required a new pan gasket.
We moved the cam to its proper position, re-assembled the engine, and carefully re-torqued the head bolts after using ARP thread sealer on all the head bolts and ARP Ultra-Torque between the head bolt washers and the bolt heads. We refilled the engine with oil and ran it on our test stand to ensure no more leaks. To completely eliminate the last vestiges of water required a third change of oil and filter but now the engine is healthy and running well. All this required at least 8-10 hours of work to fix the problems stemming from a hasty assembly. The original engine builder was lucky that the damage was really confined to water in the oil. It could have been much worse if the valves had hit the pistons.