1971 Olds Cutlass 350c.i.d. build
Technical Article part 2
Our second part of this article will now focus on the engine build itself starting with the steps taken at the machine shop to prepare Frank’s engine components for re-assembly. This process starts with a trip to Dougan’s Machine shop here in Riverside Ca. to have the block, heads, replacement crank, and rods all cleaned and magnafluxed to insure there are no cracks and they are sound pieces for machining.
Once all the components were confirmed to be serviceable, we blueprinted the block by having the cranks main bore housing align honed to insure the crank will be perfectly straight in the block. Then we had the deck surface machined flat and parallel with the crank centerline, then finished up with boring the blocks cylinders to an overbore of .030 to establish a straight cylinder as well as being perfectly perpendicular to the crank centerline. The cylinders are treated to a final hone to achieve the proper finish for ring seal as well as build in the proper clearance for ring gap and the new pistons. The final hone is performed with a torque plate to insure the bore will be perfectly round when under load from the torqued head bolts. Other block prep included pressing in new cam bearings, deburring all casting irregularities inside the block that may hinder oil drain back, running a bottom tap through all bolt holes, and a thorough final cleaning prior to assembly with hot soapy water and bore brushes to remove any machining residue.
The crankshaft, a used replacement salvaged from my daughter Melissa’s crashed 71 Cutlass was an interesting piece as it still had the ink date stamping on the front throw when I removed it from her salvaged engine. This crankshaft was treated to a crank grind on both the main and rod journals to establish a fresh and perfectly round surface, followed by a micro polish and heat treat ( nitriding ) to insure the bearing surfaces are as smooth and hard as possible.
The original forged steel rods were treated to a re-sizing with new high strength rod bolts to insure the housing bore ( big end ) is perfectly round and clearanced to match the crank journal size. Then the new hypereutectic ( high strength cast ) pistons were pressed back onto the rods with new tool steel wrist pins. These pistons are dish pistons of the same cc rating as the originals so we could keep the compression rating of this new motor close to the original rating to deal with todays lower octane fuels.
The final machine shop process for the bottom end was a complete digital spin balancing of the rotating assembly, using the new harmonic balancer, flexplate, pistons, rods, rings, and crankshaft to insure this motor runs as smoothly as possible to eliminate dangerous harmonics which can cause breakage as well as abnormal wear of the rotating components.
Finally we come to the rebuilding of the heads. We decided to build the original 7a casting heads to W-31 specs using the larger diameter valves along with a stiffer valve spring recommended for the cam being used and intended rpm range. The use of larger valves required some minor pocket work in the ports to properly blend the port into the wider seat area. The heads were also surfaced to insure the gasket surface is perfectly flat and parrallel to the combustion chambers to insure all cylinders are of equal volume. New stainless steel valves, chrome silicone valve springs, and chrome moly steel retainers were incorporated for durability as well as lighter weight to improve valvetrain stability. The valves were all finish surfaced on the tips to insure the installed valve height was to spec and the rocker arms were upgraded to individual adjustable units with roller tips, screw in studs, and pushrod guideplates. This design upgrade allows for more valvetrain stability as well as adjustability and reduced wear.
Now that all the freshly machined components have arrived back at my assembly facility ( ok, my garage..lol ) a final cleaning and inspection of all these parts is performed and all the other new components inspected / staged for re-assembly.
In part III of this tech article, we will go through the engine assembly process as well as discuss the choice of components used for this build. Enjoy the accompanying photos and feel free to call or email me if you have any questions.
Grant Warner