Video: Rebuilding A Pontiac Tri-Power 389 In Time-Lapse

There is no denying the Pontiac Tri-Power 389, which powered the GTO through 1966, is an engine that is worth saving. Known for its winning history and sheer historical value as the engine of the mighty GTO, the tri-power variant was the most powerful in the 389s varied lineup at 356 horsepower.

So it comes as no surprise that someone would go through all the effort of rebuilding one which has without a doubt seen better days. This particular project, documentd by Hagerty’s Redline Rebuild team, started its rebuild with a golf ball-sized hole in one of the cylinder walls. While to most people, that would be an automatic trip to the scrap heap, thankfully someone had the drive to pack everything into Rubbermaid containers and store it.

The rebuild started off with a new cylinder sleeve to replace the walls of the damaged cylinder. After boring the engine block just enough that the liner would be a press-fit, it was pounded into place and machined flush with the deck of the block. Once the block was properly decked, they heads received some love in the form of new valve seats, guides, and a fresh surfacing of the decks.

Usually, something like this would mean a trip to the recycler. Luckily someone had the foresight to hang on to the block and devote the time, money, and effort into repairing it.

The original connecting rods were able to be salvaged and the machine shop set about pressing out the old pins, trashing the original pistons, and honing and polishing all the rods’ journals. The original crankshaft required some significant work, but it, too. was able to be saved.

Fortunately companies like JE pistons can whip up custom pistons at the drop of a hat, and were able to recreate some factory-ish pistons and wrist pins for the project. One of the cool features of going with a modern piston is the upgrade to a floating pin setup, as opposed to the pressed-in pin.

Along with the new pistons and wrist pins, a new camshaft and timing set were utilized in the rebuild of the 55-year old engine’s short-block. Up top, the heads were rebuilt with and all new valvetrain, as the OEM pieces had all seen better days. Howard’s lifters and Trend pushrods, coupled with aluminum roller rockers, provide a some modern aftermarket flair to the otherwise as-stock-as-possible rebuild.

Topping off the combo with a set of chrome rocker covers, the freshly painted intake manifold and rehabbed tri-power carbs are set in place, a MSD distributor is dropped in, the shop door cracked, and the engine fired up. The engine eventually purrs like a kitten, but not without a nice fireball out of the carbs, first, bringing this 55-year old 389 back to life for another half-decade or more of faithful service.

Gotta make sure the timing is right! A quick adjustment to the distributor ended the fireballs and had the Pontiac purring like a kitten.

About the author

Greg Acosta

Greg has spent over a decade in automotive publishing as Senior Editor of Race Pages magazine. In his free time, he is a firearms instructor and volunteer in the police armory.
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