The Stovebolt Site Forums The Shop Area Engine Shop 235 smoking, blow by, low oil pressure low power

The old Sun Electric Co. slogan that they put on all their diagnostic equipment definitely applies here- - - - - -"We test- - - -not guess!" Before you start throwing parts at the problem, some precision measurements need to be involved. The cylinders wear tapered, with the majority of the wear happening in the first 1 to 1 1/2 inches of the piston travel. If you can hang a fingernail on the ridge at the top of the cylinders where the rings don't travel, chances are a re-ring job won't last long. The ring ridge can be machined away with a tool made specifically for that job, but if the taper wear is much over .005", the rings will flex constantly trying to maintain contact with the cylinder walls and they will lose their tension quickly. You'll be back to burning oil when that happens. A ring running in a taper-worn cylinder is flexing 66 times a second at 2000 RPM. A quick and fairly accurate measurement of cylinder taper can be made with nothing but a used piston ring, a feeler gauge, and a calculator. Position the ring up against the top of the cylinder where the ridge begins, stack up feeler gauge blades to measure the ring gap, and write the measurement down. Use a piston to push the ring to near the bottom of the cylinder and measure the gap again. Subtract the bottom measurement from the top, and divide by 3. (Actually Pi- - - -3.14) The result will be the cylinder taper in thousandths of an inch.

Example:
Top measurement: .045"
Bottom measurement: .020"
Difference: .025"
Divide by 3.14 = .008"- - - - -time to rebore and install oversize pistons.

Also measure the crankshaft rod journals with a micrometer (not a dial caliper!) They should be round within about .001", and the taper wear from front to back should be .0005" or less. Egg shaped or taper worn crankshaft journals will wear out bearings in a hurry, and will also drop oil pressure.

Good luck with your rebuild!
Jerry