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312 Y-Block Build-up  Part 1
by Larry D'Argis



Owning some of the great Fords from the '50s means you're likely to run into the Y-Block V8 that powered a good many of them.  From the introduction of the 239 in 1954, to the 312 that made its debut late in 1956, the engines are basically the same, with some rather important differences in carburetion, distributors, cylinder heads and rocker arms.  With my '57 Fairlane 500 almost ready to come out of the paint shop, it was time to get working on assembling the 312 that was going to make its home between the front fenders.  With the machine work done on the block and most of the new parts on hand, I asked our Club President Albert Lannoo to help me with this task.  If you've ever taken a look under the hood of Albert's '56 Merc you'll know why.  One peak at the glittering chrome accessories and Offenhauser tri-power intake setup is almost enough to make you weak in the knees.  This is what Hot Rod magazines used to write about and it's right here in our own river city.  Having rebuilt and hot rodded many of these engines over the years, Albert's got some pretty unique tricks he uses in assembling them that ensure a very reliable motor.

First, we're staring with a 312 engine from a '56 Monarch.  The motor ran before it was dismantled, but had developed a knock due to a turned connecting rod bearing.  The motor was completely dismantled and the block and crankshaft sent out for machining.  The crank was turned .010  on the mains and .020  on the rod surfaces and the block bored .040  over to accept the new Sealed Power pistons.  Piston Ring Service supplied a set of moly rings for us and after replacing a twisted connecting rod, new ARP rod bolts were installed, the rods resized and the entire rotating assembly balanced.

One problem area on the Y-Block is the rear main seal.  Originally an asbestos rope seal was installed and it would usually develop a leak after a few thousand miles.  On a rebuild, if you didn't know how to install the new one properly it would generally allow quarts of oil to leak under your car.  New engine rebuild kits now have both a rope seal, now made out of synthetic material because they can no longer use asbestos, and a more common rubber seal.  The rubber seal is the way to go, it's easier to install and it won't leak.  Problem is, there wasn't a rubber seal for the 312.  The 239 through 292 Y-Block have main bearings that are .125  smaller in diameter than the 312 so the new rubber seal won't work.  Recently Best Gasket started manufacturing a silicone rubber main seal for the 312 and Albert was anxious to try installing it and testing it.

The crankshaft was returned to the machine shop to have the seal area polished to ensure a good sealing surface for the rubber seal.  With the engine on a stand, the top half of the seal was installed and the main bearings and crankshaft laid in the block.  Normally the main bearing caps are then installed and torqued to specifications followed by the top half of the seal in its retainer.  Albert thought that if you could install the seal retainer and Permatex seal it from the inside, your chances of a leak would be nil.  The only problem was with the retainer installed the forward lip on it wouldn't allow you to install the bolts into the rear main cap.  His solution was to grind two reliefs in the retainer lip that would allow the grade 8 main bolts to pass into the main cap, but there still wasn't enough room for a socket to torque the bolts.  The ultimate solution was the use of two grade 8 cap screw bolts with a recessed hex head.  The head on the cap screw is smaller than the standard bolt head so less material has to be removed from the seal retainer and with the correct hex head socket, torquing the bolt is easily done.

With the seal retainer installed and sealed from the inside of the block with Permatex, Albert laid the engine stand back so the rear of the block was level with the floor.  He then put approximately three ounces of oil on top of the seal retainer and left it there for more than a week.  Even rotating the crank periodically to try and disturb the seal had no affect and not one drop passed through the seal.  Mission accomplished!  Albert says, "The Permatex sealer dries like concrete and is impervious to heat so there isn't any issue with it ever flaking off inside the engine.   The cap screw bolts are also much stronger than the factory bolts, so you could replace all of them if additional main cap retention strength was required, for supercharging or nitrous oxide use.  This little trick should work on any Y-Block V8 and give that little extra insurance against any rear main seal leak.  Next issue we'll let you know how the rest of the shortblock rebuild went and some of the trick parts that were using to ensure it will make some real horsepower.

On To 312 Y-Block Build-up - Part 2