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Boy, you Allis guys must not have much fun "strokin'" your "girls"! Actually, I think if the young feller is old enough to be interested in stroking an engine, he can sure handle my "shoptalk". There comes a time in a young man's life when the inevitable happens. It's kinda' like bringing your crank to the machinist for the magic he will perform on your engines torque curve. You tell "Smoky", "I bring you the boy, give me back the man". Enough for the lighter side of gains in torque. This young guy wants to learn about the mysterious performance process called "stroking". Actually all reciprocating engines already have stroke. This is the distance the piston travels during one half revolution of the crankshaft. The stroke is determined by the length of the "crank-arm", which is the measurement from the center of the main bearing journal to the center of the connecting rod bearing journal. Doubling this measurement results in the specified stroke. It is a well known fact that increasing an engine's stroke allows the engine to make more power. This is partly because of the outright increase in cubic inches, but just as important is the extra rotational leverage made possible by the longer "crank-arm". This manifests itself as TORQUE! A major increase in low-end torque is the biggest benefit of "stroking" your crank. The art of "stroking" a crankshaft, in it's most basic form, is simply grinding the rod journals only on the back side and using undersize bearing inserts. A 0.060" undergrind on a 4" bore X 4" stroke V8 engine would yield an increase of slightly over 6 cubic inches. Not bad, for a basic machine operation, huh? The next step might be to undergrind the back side of the rod journals enough to allow the use of connecting rods with a smaller big-end bores than the originals. Now that the ball is rolling, let's just weld a little "crown" on the top side of the rod journals and, along with the undergrind and small, big-end rods, we're startin' to talk some serious stroke increase. The ultimate extent to which one could go is to fabricate a complete "long-arm" crankshaft. Of course the increases in piston travel will eventually cause problems at both the top and bottom of the stroke. The pistons may contact the cylinder head. The pistons may contact the crankshaft. The connecting rods may contact the pistons and bottom cylinder bores at around the 90 and 270 degree crankshaft rotation points. The connecting rods and crankshaft may contact the inside of the crankcase. The connecting rods may contact the camshaft. The wrist pins may need to be moved up in the pistons so far they enter the sealing ring area. Oil lines inside the crankcase may be in peril. It's awful close quarters inside a "stroked" engine's crankcase! Usually some "surgery" has to be performed. The crankcase may need clearance holes cut and covers installed. Connecting rods may need to be cut and "married" to get the right combination of big and small ends. Pistons will need to be special built. The camshaft may need "notching" to clear the connecting rods. In extreme cases, the camshaft may need to be relocated. Is all this expensive? What do you think young man? I would say the costs of increasing an engine's stroke are the highest of all the performance gains you could make. The time involved in getting everything to clear obstructions would cost dearly if you had to pay someone to do it. Most of the "stroke-jobs" I know of were done in the home shop where the time factor isn't so expensive. The last thing is the risk factor. Traditionally, "strokers" are more prone to blow sky high than most other types of engine "hop-ups". This is partly due to the amateur nature of a lot of these build jobs. A 2-cylinder "B", built in a home shop, packin' a 45 HP wallop, may be living on the edge, but the feel of those torque pulses in that small frame make it all worth while!
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