The Detroit Diesel DD15 engine’s valve covers are prone to warping if over-tightened. This guide outlines the proper installation process, emphasizing the importance of achieving a good seal without excessive torque.
Ensuring a flat sealing surface is crucial. Remove the valve covers and inspect them for any bulges around the bolt holes, a common sign of over-tightening. If bulges are present, gently tap them back down using a small hammer against a flat, hard surface like a heavy piece of steel. Place the cover upside down for this process.
General Motors originally used a high-temperature black silicone sealant for assembling these engines. While composite rubber/cork gaskets can be used, the silicone sealant remains the preferred choice for a reliable seal.
Thorough cleaning is paramount for successful sealing. Before applying any sealant, ensure the surfaces are completely oil-free. Use a quality non-oil-based solvent like brake cleaner to achieve this. Apply a generous amount of silicone to allow for proper compression and a robust seal between the cover and the cylinder head.
When tightening the bolts, use a short 1/4″ drive ratchet to avoid excessive torque. Snug the bolts down evenly around the perimeter. Over-tightening won’t improve the seal and will likely warp the cover. A gentle touch is key.
If opting for a gasket, apply contact cement to adhere it to the cover. Allow sufficient drying time before installation. Apply a layer of silicone sealant to the gasket surface that contacts the cylinder head. Again, cleanliness is critical. Oil on the head surface will prevent a proper seal. With a gasket, avoiding excessive bolt torque is even more important.
In summary, achieving a proper seal on a DD15 valve cover relies on a clean, flat surface and the judicious application of torque. Avoid over-tightening the bolts, as this can lead to warping and leaks. Whether using silicone sealant or a gasket, meticulous preparation and a gentle hand will ensure a long-lasting, leak-free seal.
