Many common problems can be remedied without going into the deep dark
recesses of the engine. However, some will require either a partial or
total overhaul. Eliminate all other possibilities from consideration
before considering an overhaul - it will not be a fun afternoon (or
weekend, or week, or month,....).
|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Do you need an overhaul?
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The following are indications that at least a partial overhaul may be needed:
- Mechanical damage - broken, damaged, or bent parts resulting in inability
to start or even turn the crankshaft for starting or excessive vibration
while running. In most cases, this will be obvious - the mower died very
suddenly - possibly with a loud clunk or p-ting and now the crankshaft hits
something really really solid inside when attempting to pull the starter.
- Low compression - this is due to wear or abuse (lack of oil) of parts like
the rings or valves or due to a blown head gasket. Perform the compression
test described in the section: Compression testing.
Symptoms would be difficulty in starting and unusually little resistance when
pulling the starter cord, and perhaps, loss of power once you get it started.
If rings are bad, there may be excessive oil consumption and blue exhaust
smoke. If only the valves are involved, only the cylinder head may need to be
- Excessive oil leaks - a failure of the oil seals (the lower one on mowers
at the PTO/blade end, most likely) will result in oil dripping or pouring
from under the mower deck. The blade will be coated with oil and there
will be a puddle where the mower is stored. Of course, if this is severe
enough or neglected, you may end up with much more serious problems when
the internal parts fail due to lack of lubrication. Replacing an oil seal
is not difficult. The old seal is removed by piercing its thin metal shell
with an awl or ice pick and carefully prying it out. Take extreme care not
to scratch or dent the mounting surface or crankshaft. This may be possible
without extensive disassembly. The new one is then pressed on. In fact,
installing the new seal is best done with the crankshaft in place as there
will be less likelihood of damage to the new seal and it can then be driven
in straight. There is a special tool for this but a piece of pipe that just
fits over the crankshaft cut off square will work just as well. Remove any
burrs on the crankshaft to prevent damage to the new seal and take care that
any rubber lip on the seal does not get folded over.
- Excessive noise - knocking, banging - while an engine powered piece of
machinery is not exactly quiet, there should not be unusual or excessive
mechanical noises. Such noise can be an indication of an excessively worn
engine or of some part that is about to fail. Should you strip the engine
based on this? I cannot say - it is a judgement call. It something about
the sound suddenly changed, then investigating the cause is certainly
In some cases, multiple problems may be present and/or there may just be
excessive wear of parts like the cylinder, rings, and piston. Under these
circumstances, the cylinder may need to be rebored to accept a replacement
oversize piston and ring set. The cost of the parts and labor (you really
don't want to rebore a cylinder) will likely be more than you want to spend.
This is when a new engine or mower is the best option.
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