Powerhead Break-In Recommendations
Break In Your Motor Right!
Before starting your overhauled engine please
do the following:
- Test/replace the thermostat(s).
Pressure relief bypass valves should be serviced for correct operation.
- Examine or
Replace the water pump.
the timing 2-4 degrees. This can be done on most engines by turning
in the timing screw towards the timer base 2-4 turns.
to be certain you have the correct heat range spark plugs.
sure you have fresh, clear 89 octane premium fuel and TCW-III
oil -- I strongly recommend using oil supplied by one of the major
engine manufacturers. e Even better are the newly available synthetic
blend oils as they will prevent carbon accumulation. Cheap oil
and gas are a false economy on modern engines. I recommend extra
oil for the first 10 hours -- double oil seems to foul the plugs
and 1½ oil seems to work.
the high speed jet sizes in the carburetor. Check for the latest
factory recommendations and use them or one size larger.
Start your engine at home base using flush
muffies to see that it actually does start and doesn't have any
obvious problems i.e. - water leaks, etc... Once it is obvious the
engine will start and run I suggest the engine be put in the lake
and run for 20 minutes at high idle RPM (750 - 850) unloaded or
out of gear. Check the plugs and carefully feel the engine to make
sure it is not overheating. Restart the engine and then move it
up to around 1500 RPM loaded in gear and vary the speed from idle
until you have two hours on the engine. All the foregoing may be
accomplished on the trailer. It is time consuming and tedious but
it is the basis for long and happy engine life. If everything seems
to be okay check the timing on #1 & #2 cylinders on a V-4 or V-6.
Use the cylinder with the highest reading and set the timing 2-4
degrees less than the factory specs. If the spec is 24 degrees BTDC
set the engine at 22 degrees. Leave the engine at this setting for
the break-in period. If later you want more power the timing can
be advanced to the factory spec but the engine will live longer
if you leave the timing retarded. Don't guess. Use a timing light
and set the timing UNDER LOAD, at FULL ADVANCE! Don't run it there
other than to check the timing.
At this point you can run the boat, cruise at
3000-3500 RPM, periodically giving it short runs up to full throttle.
This should continue until there are ten hours on the engine, then
your powerhead should be broken in. If you follow the outlined procedures
you will get better service from your engine. Be sure that at maximum
throttle the engine will turn up to 5500 RPM, the top operating
RPM for most 2 strokes. If it doesn't the propeller should be changed
until the engine runs at or slightly over the rated operating range
with a light load. The wrong prop can cause the motor to lug, overheat
or at the other extreme over rev and destroy all your good work.
Be sure to check and retorque the cylinder head gaskets.
Rebuilt Motor DO's and Don'ts
You must determine the reason the original
powerhead failed. If the problem is not identified and corrected
it is almost certain the newly rebuilt powerhead will fail. If a
restricted (lean) carburetion problem caused the original powerhead
to fail, the new one will also fail unless the problem is corrected.
The most common causes of engine failure
are detonation, pre-ignition, and overheating or any combination
thereof. The result of these problems is that the temperature in
the combustion chamber gets too high. As soon as the temperature
in the chamber gets higher than normal the engine begins to run
poorly and the damage to the engine begins. Detonation is usually
caused by the air/fuel mixture being lean and the erosion of the
piston starts at the edge or outer diameter of the piston. If the
erosion starts in the center of the piston it is probably an ignition
problem. An engine running hot due to deteriorated water pump or
cooling system blockage compounds the problem.
The other common failure mode I see is scuffing
and/or cold seizure which occurs mostly in new or rebuilt engines.
When the engine is started, the piston heats up and expands quicker
than the cylinder walls which are liquid cooled. When the engine
is broken in and running at the correct operating temperature it
runs with around .002 clearance. Normal human hair is about .003
inches. Once the rings are seated and a glaze forms on the cylinder
walls this problem is not likely to occur. This makes the break
in period very critical. The proper break in of a new or rebuilt
powerhead will help insure that you get good value from your investment.
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