Last month in Driving Old Cars, we completed engine disassembly on our '49 Buick Roadmaster Sedanet 320 Straight 8. Even though the engine ran "okay", there was excessive blue smoke coming from the tail pipe at idle that increased upon acceleration. The car had a rebuilt carburetor and had been timed out, so we felt that the smoke problem was internal. It was time to run a compression test. This revealed a more than 15% variance in one of the cylinders (later this cylinder would produce a collapsed piston). With this test, we decided to take the engine apart.
Everything outside the engine had already been rebuilt and repainted. Our job would be strictly internal. All parts were out on a shelved rollaround cart, with all bolts put into plastic bags labeled with their contents. It is easy to mis-match bolts, and sometimes this can be disastrous. The '48 70-Series cars had two head bolts that attached the air cleaner, which were 1/8" longer than the other head bolts. These two had an "X" on their heads. If these were used in holes other than those to attach the air cleaner to the head, the threads might strip, or worse, they could bottom out and distort the cylinder bores.
There are a few points of comparison between the Buick Straight 8 and the Packard Straight 8:
1. The Buick engine does not have to be raised to remove the oil pan.
2. Like Packard, there are holes in the frame for easy access to bolts.
3. Buick utilized locks on their rod nuts to keep them from backing off.
One unusual thing about the 320 Buick Straight 8 is in the location of the timing mark. It is on the flywheel on the passenger side, neatly covered by a snap-in cover in the bell housing, just over the starter.
With out parts laid out for inspection, we found signs of a blown head gasket. There was severe corrosion in several places, although not all the way through. All of the pistons were fine except one. It was slightly scored and collapsed .005", probably due to a previous vacuum leak, as the engine had been apart before. The cylinders were inspected for wear. There was some water damage on one cylinder that we could hone out later. We checked the cylinder wear: Using an inside micrometer, we took that measurement, then used an outside micrometer and measured the piston. Subtracting the piston measurement from the cylinder bore measurement, this gave us our clearance. Ours was within tolerance. Since we wanted to keep our original Fireball domed pistons, we decided to have our collapsed piston knurled. Knurling is a process piston is made larger by putting it in a knurling machine, making short indentations, pushing in the aluminum wall of the piston, then pushing out the other spots in between the indentations. This saved our piston and was done by Reggie Tideman of Austral Engine Rebuilders of Davie, Florida, 954-587-2476.
We replaced the rings with a new "standard" set from Hastings. There is a specification for ring thickness clearance. This is found by checking the end gap before putting the rings on the pistons. On this engine, there is a ring width specification measuring the ring lands (where the ring goes). Ours were within specs. Our block-to-head surface had been checked with a straight edge and looked good, so we now honed the cylinders, and the pistons were installed with the rod oiler holes and piston slots facing the cam shaft. The nipples on the rods face the rear of the engine. The crank required no work. The surface looked great, and the rods and mains showed almost no wear. The oil pan was cleaned along with the oil pick up tube assembly. The pan easily went on with a new gasket held in place with a little Permatex 2-B on the pan side. The head was disassembled and the valve springs tested. These are two per valve (an inner and an outer). Ours tested well at the correct 52 @ 1 5/16" on the inner and 119 @ 1 19/32" on the outer. The valves and seats were ground, head resurfaced, new valve guides installed, and the rocker assembly was rebuilt. We used a NOS copper head gasket and installed and torqued the head bolts. The head torque pattern is unusual, starting in the middle and going down one side and then down the other (see illustration). The Roadmaster with Dynaflow transmission was equipped with hydraulic valve lifters with zero clearance. These were cleaned and reinstalled, along with the push rods. Care must be used when tightening down the rocker arm assembly. It fits into alignment pins and can break if not properly aligned.
The biggest problem we had was with our intake and exhaust manifold. They were warped--a common problem on these engines. Ours was warped .100". Motorvation Engine Builders carefully resurfaced the manifolds, keeping them together for a uniform surfacing. But there was a problem: So much material had to be removed that one end's line-up rings did not fit. This problem was solved by using a die grinder with a carbide burr to re-cut the correct depth of the line-up ring at the low end of the manifold. Using new manifold and exhaust gaskets, the manifold was put into place and tightened down.
We set our timing at 6 degrees BTDC, our points at .016, and gapped our plugs at .025. We changed the oil filter then filled the crankcase with 7 quarts of 30-weight detergent oil. All of the hoses, clamps and thermostat were new. We filled the radiator with coolant: 40% antifreeze and 60% water for summer (water allows the engine to run cooler than antifreeze). The carburetor was primed with gas, then we hit the remote starter button. The engine started right up. Smoke came out of the tail pipe from engine assembly but quickly cleared as the engine reached its running temperature of 180 degrees. A manual remote gauge showed our oil pressure to be about 40 pounds at fast idle. The book calls for 35 pounds. It revved nice, sounded good and all the numbers were right! We ran it for about 20 minutes and the temperature stayed right at 180 degrees. After shutting it off, we checked the compression, finding all cylinders uniform. See you next month. Keep 'em driving!