The Stovebolt Site Forums The Shop Area Engine Shop More info on bad rebuild

HrL, You are correct in that the first engine failure sounds like it was due primarily to the piston having insufficient clearance. There are many reasons for scuffing and scoring, I will try to list a few that I have encountered over the years.

Scuffing and scoring are caused by

1. The lubrication system

a. worn oil pump
b. clogged oil screen or passage
c. oil pressure relief vavle stuck open
d. incorrect bearing clearance
e. contaminated oil
f. low oil level

The cooling system

a. external leaks
b. internal leaks
c. clogged radiator
d. deposits in block (this is one I think may be where your problem is at)
e. defective thermostat
f. defective radiator cap
g. worn or broken fan belt or corroded water pump impeller

3. carburation

a. too rich, to lean, or stuck automatic choke

4. Incorrect ignition timing

a. wrong ignition advancement
b. worn distributor altering spark advance

5. Combustion knock, detonation or pre ignition

6. Improperly fitted parts

a. insufficient piston clearance in the cylinder (this was the one I thought for the first tear down)
b. tight piston pin fit (or this one also)
c. rings with insufficient gap
d.improper cylinder liner fit

7. Improper break-in

a. slow idle
b. coolant not being allowed to reach operating temperature

8. Lugging or overloading

There are probably many other reasons that I haven't encountered but this may help others also. Use a welding rod or coat hanger and see if you have heavy deposits around the number one cylinder. Since it is "out of sight" it is easy to overlook. Good luck and let me know what you find out.