Stories from the bone yard:
For what it's worth, I replaced a crank shaft that passed all the (Shade
Tree) tests that are thought to give a good indication of the rods on the
crank shaft. It turned out that the Left (drivers side) center bearing was
bad and made the same sound as the rod.
Then there was an engine that I pulled the crank shaft on and it was missing
the bearing cage and rollers to the outer bearing also on the left side,
however it sounded more like the wrist pin than a rod knock. And the engine
ran like that for 6 years. I knew the owner that put the engine together.
And, because I pulled the crankshaft, I checked the end for runout to see if
it was bad (which there was none) put in a new bearing cage and rollers and
the engine is running today with no sound coming from that area.
So, you do have to check them out, and maybe Miles or Mike have a few tests
I haven't used. But here are a few of them:
- With the crank shaft out, use carb cleaner and clean all the oil out of
the bearings you can't remove. Check for metal coming out, aluminum will
cause just as much damage as steel. If you find metal, the crankshaft is
most likely bad. If none go to the next step.
- set the crankshaft up between two end blocks under the center bearings
and check out the end play with a dial gauge.
- All rods will move from side to side so this is not an indication of a
problem.
- Use a squeeze bottle with a pointed end, (I find the plastic bottle my
wife uses for her hair die works well - but she didn't believe me when I
said I can rinse it out and she can use it again.) Anyway, it works really
well to get oil into the bearings of the crankshaft. Then with the center
bearings and rod bearings full of oil, try moving them up and down - the
indication here is if they move. If they move up and down then they are
bad. If not go to the next test.
- Lay out some news paper to catch the oil and make sure the bearings are
full of oil and using a "SMALL" hammer give the back side (opposite of the
long end of the rod) a good rap while holding the long end and listen/feel
if the bearing moves or there is a metal sticking metal sound (the rod is
hitting the bearing that is loose which is hitting the crankshaft), which is
bad. If it sounds like one "thud" with no movement, the sound is like
hitting one part vice several, then the rod bearings are not loose and the
rod will not knock.
However, there could still be foreign matter in the bearing which will
cause a roller to lock up, wear and cause a problem after only a few miles.
This is why many crankshafts are just changed out.
Bill