Rebuild or Refresh Your Engine?
The cost of rebuilds are not cheap, if your Nailhead is still running well but you are worried about it being dependable because it has never been rebuilt here are some things you can do. The first thing I would do is replace the old plastic covered aluminum cam sprocket used on the 60's Nailheads with a new 3 piece steel timing set. With age, mileage and heat the plastic will start cracking and falling off the sprocket allowing the timing chain to jump. If you think it may have been replaced pull the fuel pump and stick a magnet in the hole, check the cam sprocket, if it sticks it has a steel sprocket already. The Nailhead is an interference engine, what that means is the valves will collide with the pistons if valve timing is off. This does a lot of damage, bent valves and push rods and broken rockers, sometimes even damages pistons. The other thing is sludge in the oil pan for old fuel and oil additives from the past 50 years. Pull the pan and clean it along with the oil pump pick up. We have also seen many original oil pumps where the idler gear shaft and worked it's way up and hitting the crank counter weight so that should be repaired (See "Oiling problems").
IMPORTANT.. ..Put the engine back together and tighten the damper/balancer bolt to 220 lbs! DO NOT skip this step or you will split your damper hub and ruin your crank shaft! This is only on 1957 and later, the earlier Nails had a smaller bolt and torque requirement. FYI the water manifold must be removed to remove the timing cover, slide the water manifold UPWARD not outward or you will break the timing cover or the water manifold, there is a by-pass tube in the bottom of the water manifold that fits into the top of the timing cover. Lastly and very important you DO NOT need hardened seats for todays fuel in the Nailhead but you DO need Zinc in the oil so be sure you are using oils that have it. I would list some brands but they keep changing amounts of zinc so do your own research here..