Thread: Building a Flathead for the very first time

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If you're going the full tear down route I would suggest you not spend a dime on parts until you've had the block cleaned, magnafluxed, AND pressure tested. A sonic check of the bores would be in order too if it needs more than just the hone. These blocks are notorious for cracks. The most common are from valve seat area to the bore edge........and many times down the bore. BUT, they can often crack IN the intake and exhaust runners (not easy to see, thus the pressure check). The deck cracks can sometimes be stitched, the cracks down the bore are often fatal, but might be saved with a sleeve. After all that these also need greater attention paid to cleaning out the coolant passages, particularly near the base of the cylinders. It's not unusual to find original core sand, and of course scale build up from years of water. Poking with rods, dropping repeatedly on a piece of plywood, whatever it takes to get in the nooks and crannies. You'll never work so hard to make (with some speed parts and good tuning) around 150 hp.

Originally Posted by Bob Parmenter

If you're going the full tear down route I would suggest you not spend a dime on parts until you've had the block cleaned, magnafluxed, AND pressure tested. A sonic check of the bores would be in order too if it needs more than just the hone. These blocks are notorious for cracks. The most common are from valve seat area to the bore edge........and many times down the bore. BUT, they can often crack IN the intake and exhaust runners (not easy to see, thus the pressure check). The deck cracks can sometimes be stitched, the cracks down the bore are often fatal, but might be saved with a sleeve. After all that these also need greater attention paid to cleaning out the coolant passages, particularly near the base of the cylinders. It's not unusual to find original core sand, and of course scale build up from years of water. Poking with rods, dropping repeatedly on a piece of plywood, whatever it takes to get in the nooks and crannies. You'll never work so hard to make (with some speed parts and good tuning) around 150 hp.

yes been there )