Whenever I checked the oil on my boat, the oil on the dipstick appeared to be composed of a brown milkshake type substance. This meant that water was mixing with the oil in the engine. A likely symptom of the oil mixing with water on a Chevy 350 engine is that the head gasket is blown. The next likely cause would be a cracked head, and the final cause could be a cracked block, so we changed the head gasket......
The next summer, we figured out that the reason that the oil had condensation in it was because we were running the engine without a thermostat. Marine engines are cooled by water that is circulated from the lake, which flows through the engine and then through the exhaust manifold. Running the engine without a thermostat doesn't allow it to get to a hot enough temperature to keep the exhaust manifolds from sweating, allowing condensation in the oil.
Special head gaskets must be used on a 350 marine engine.
Items Needed:
Take pictures of the engine before the work begins.
If you don't remember where a certain wire or hose goes, the pictures will remind you.
Remove the exhaust risers and thru-hull pipes.
Remove the spark plug wires (No need to remember where they go until later)
Since the drive cable is attached to the starboard riser, there is no need to disconnect the cable. Just lay the riser and pipe behind the engine.
Remove the valve covers (4 bolts on each)
Remove the intake manifold and carbuerator (8 hex head bolts).
The carbuerator does not need to be removed from the intake manifold. We removed the carbuerator from the intake manifold in order to clean the intake manifold more thoroughly while it was off of the engine (why not?).
Notice the brown milky-like oil near the bottom of the push rods.
Loosen the nuts on the lifter enough to remove the push rods
Remove the bolts which hold the heads on (4 on the top, 5 in the middle and 8 on the bottom). The heads should then come off. Be careful of the edges, they are sharp and can cut you.
After the heads are off, remove the remnants of the old head gasket. The old gasket and any carbon deposits in the combustion chamber can be removed with a razor scraper. When using the razor scraper, keep the blade as parallel as possible to the surface. Remove the gasket, not pieces of metal from the heads.
Clean up the bottom end of the engine while the heads are off. Inspect the pistons and cylinders for any cracks or rust. DO NOT use anything to clean the inside of the cylinders.
Be sure that the cylinders are not completely smooth, the cylinder walls should appear to have a cross-hatching type pattern (very smooth cylinders and old rings may not allow the engine to have a good compression ratio causing the engine to run inefficiently or not at all).
Re-install the heads and tighten the head bolts to 65 lbs-ft.
Use the diagram below to properly tighten the head bolts.
Use this diagram to install the head bolts.
Tighten the head bolts according to the diagram. Tighten the bolts snug with a regular socket wrench, then tighten the rest of the way with a torque wrench to 65 lbs.-ft. After all of the bolts are tightened to 65 lbs.-ft., go through the sequence again to make sure all of the bolts are set to 65 lbs.-ft.
Time to adjust the valves.
Re-install the push rods and center the lifters over the push rods. Just make the lifter nut snug for now.
Use a socket wrench and socket on the center nut of the crankshaft to turn the engine over. Looking at the front of the engine towards the rear, turn the crank clock-wise.
Each cylinders' valves need to be adjusted seperately. After the intake valve closes, both of lifters corresponding to that cylinder can be set.
Start at cylinder 1. Rotate the crankshaft until the intake valve for cylinder 1 completely closes. After the intake valve is closed, tighten the lifter nut until there is some resistance when trying to rotate the push rod. Turn the nut another 1/2 turn. Move on to cylinder 8
Reinstall the intake manifold, the valve covers, and the distributor.
If the engine is at top dead center (TDC), the rotor on the distributor should be pointing at the point that corresponds to cylinder 1.
To find TDC: with the valve cover off, rotate the crankshaft until the intake valve closes. Rotate the crankshaft as you have another person put their finger over the spark plug hole of cylinder 1. When air stops coming out of cylinder 1 and it begins to suck air in, STOP....the engine is now set to top dead center.
After TDC is set, the distributor can only be inserted one of two ways....the right way, and the wrong way. With the cap of the distributor off, slide the distributor into the engine. If it goes all the way down flush with the intake manifold and the rotor is pointing towards the cylinder 1 point, it is in the right way. If the rotor is pointed towards the 6 or 5 cylinder point, it is in the wrong way. A keyway in the gear inside of the engine only allows the distributor to be inserted 1 of 2 ways (dead on and 180 off)
Remove the old gaskets from the exhaust manifolds and risers. Sand paper and the razor scraper can be used. Remove only the gasket and not the metal
To be continued...