This vintage Chevrolet inline-six cylinder engine rear main crankshaft seal. Part Breakdown ENGINE REAR MAIN SEAL ROPE: A rope-style rear main seal used to prevent oil leaks at the back of the crankshaft.40-53 216: Fits the 216 cubic-inch Master Deluxe / Thriftmaster engine built from 1940 to 1953.41-62 235: Fits the 235 cubic-inch Blue Flame engine built from 1941 to 1962.54-62 261: Fits the 261 cubic-inch truck engine built from 1954 to 1962.Critical Installation TipsSoak the seal: Always soak the new rope seal in clean engine oil for at least 30 minutes before installation.Roll it in: Use a smooth mandrel, pipe, or specialized tool to roll and pack the rope tightly into the block and cap grooves.Trim carefully: Cut the ends flush with the parting line using a razor blade, leaving about 1/32" of extra material on each side for a tight crush fit.Do not use silicone: Avoid modern RTV silicone on the rope material itself, as it prevents the rope from absorbing oil and sealing correctly.