let me start by saying I was going to post here first but I couldn't figure out how to post pictures without using a 3rd party and photobucket crashed I am hesitant to use another sight.

I have a thread on the HAMB that is a longer verson of below with pictures, but I wanted you guys to be included and offer opinions if you want. Hope the link is OK to add. https://www.jalopyjournal.com/forum/threads/old-school-cool-248-gmc.1178420/

As early as I can remember I have loved by grandpas old 55.1 GMC and after learning the racing history of GMCs there could be no other power plant. The original 248 had cracked the head on top under the rockers and filled the crank case with antifreeze. My plan always was to find a 302 but though we should be tripping over them here in farm country the larger 302-270s are pretty elusive. I recently bought a military 6X6 302 and wouldn't you know a week later a hopped but GMC shows up on facebook market place. The only thing I knew for sure was it was a 248 block, a 302 983 head, a small gmc Nicson Dual with 2 Rochester Bs, Fenton exhaust, mallory dual point, a pan modified for a car and it was stuck.

Long story short it had been assembled but never started. The internal surprises were a ISKY LDB cam, 3.960" cast Jahns open chamber pistons (55cc), 302 head combustion chamber ground open like a 270H, tubular pushrods, aluminum retainers, double springs and the bad, 2 pinned sleeves and 4 gallons of water in the pan that rusted off the oil pump pickup, oil pump pressure line and corroded the pump but everything else looked good.

After finding the pinned studs the block was scrapped but I wanted to use as much as I could of the old engine.

I found a horribly stuck 270 (1941?) short block in a snow drift that my awesome machinist and I spent a Saturday beating the pistons out of. We saved its crank and block. I bored the block an additional .120 to 3.960 on 5 cylinders and have to sleeve number one (broke the cylinder removing the pistons). The block sonic checked with an average of .220 before the bore with the thinnest cylinder of .198. The block will be short filled to reinforce the lower end of the cylinders. Then we will mock it up with the 248 rods and the Jahns pistons to determine the amount the deck needs to be removed to get it to 9-9.5 to one compression.

The Isky LBD has a lot less duration and lift than would be common now so I need to pull the forged steel cam from my spare 248 at the farm for a core to regrind at Bullet racing cams. I also bought a Nicson Dual Large GMC, 2 Stromberg 1bbl 99-25 (duals off an American Lefrance fire truck) and dual Chrysler air cleaners from an inliners member. Carbking doesn't like the Strombergs or the 11475 Zeniths I have for a dual application but I may try them because it is what I have. Should be a 295 when I am done. The plan is just a hot street engine.

Thanks,

John