1966 Shelby GT350 - How To Rebuild A 289 Hi-Po

In the Dec. '08 issue we knocked down a 289 High Performance V-8 pulled from Rolo Malschafsky's unmolested '66 Shelby GT350. The real news of our effort was the engine's originality. It had never been apart in 42 years.

Why tear down an original, low-mileage, and undisturbed 289 Hi-Po? Because even when mileage is low, engines need to be freshened up if you intend to drive the car. Seals get hard and leak. Piston rings lose tension and bores wear, causing blow-by and loss of power. Corrosion develops between moving parts. Bearings and journals wear. These things happen even when cars don't get driven. More than anything, an engine's oil needs heat in order to stay fresh and free of contaminants. When an engine sits, condensation develops on inside surfaces. With moisture comes acids and other contaminants that create even more problems. A long highway run gets engine temperatures to the point at which moisture evaporates from the oil. What's more, a steady diet of fresh gasoline keeps the fuel system healthy and free from gum deposits.

In last month's issue, JGM Performance Engineering tore down, inspected, and performed all machine work on Rolo's 289 High Performance engine. Now we're ready to put this engine together and see what it does on the dyno.

About Bearing Clearances
Main and rod bearing clearances make the difference between engine building success and failure. When you're running a high-performance engine, clearances need to be looser than with street stockers because journals run hotter. Because they run hotter, they run larger. Everything expands with heat-the crankshaft journal, bearing shell, and oil. You want good oil flow across bearings and journals to carry away heat. At the same time, you don't want sloppy clearances that can lower oil pressure.

Another important issue is crankshaft endplay. When endplay is excessive, it places the engine's moving parts at risk. Move the crankshaft too far fore or aft and you wind up with connecting rods in poor alignment with piston pins and rod journals. This can cause engine failure.

Main Journal Diameter: 2.2482-2.2490"Rod Journal Diameter: 0.1228-2.1236"Crankshaft Endplay: 0.004-0.008"

Why It Is Important To Degree
Blueprinting is something you should do with all engine builds, including stockers, because it ensures that there's no stone left unturned and no detail missed to bite you later. Although degreeing a camshaft and checking for true top-dead-center is believed to be "race only" by many, this is a step you don't want to miss. The first thing we do is check true top-dead-center and how it relates to the block and crankshaft. Not all crankshafts are true to mark, nor are all blocks.

Oil Pump Prep
Oil pumps need blueprinting, too. Rotor side clearances should be checked. The pressure relief valve must also be checked for smooth operation. The piston and spring should move freely without binding. When you are finished checking, fill the pump cavity with engine assembly lube, which will stay there until you fire the engine. Filling this cavity with lube provides a solid shot at lubrication to all major parts when the engine fires for the first time.