Help on rebuilding a 73 340

If you want to get an idea of the Scr of your 340, now is the best time to do it.
You need to roll the engine over and get any one cylinder to have its spark plug be the highest point of the chamber. Then you put the piston for that cylinder at TDC/compression stroke. Next measure out 100cc 0f oil into a graduated container. Could be a measuring cup from the wifes kitchen, or my favorite is a veterinarians syringe. Then start filling up that chamber, to the bottom of the plughole. I usually shuttle the piston back and forth a few degrees to prove its at TDC. Then figure out how much oil went in there. Which should be 100cc less whats left in the container.After that its simple math: ( Swept + cv)/cv : where swept is( bore sz/2) squared,x Pi x stroke, x16.387. and cv is chamber volume. Heres an example for a stock bore 340.
Swept = (4.04/2) x (4.04/2) x 3.1416 x 3.31 x 16.387 = 695.3cc
So (swept+cv)/cv =(695.3swept +90.5cv)/90.5cv = 8.68Scr. Badaboom!

Well I suppose theres a slim chance that more than 100 ccs goes into that chamber! Just suck up another 50cc into the syringe and carry on.
This method is only as accurate as the tools you use and the care you take in the set-up, and the ring/valve seal. If you spill some oil,stop.Set up a new chamber.Use a thick single viscosity oil, like 50 wt.If the oil is too thin it will run down the piston and through the ring gaps. If the oil level in the chamber does not remain stable try a different cylinder. Do not use any cylinder more than once.Just one cc of oil remaining in the chamber will skew the results.I like this method and have used it many times, to help estimate what to expect from a loose motor.
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This method can be dead accurate.