Rotec AEROSPORT R2800, Operation Manual, Page: 63 / 87

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All cylinders can experience hydraulic lock but the most likely are the lowest
two, namely: cylinder #4 & #5 on the R2800 and cylinder #5 & #6 on the
R3600. Out of the two cylinders, R2800’s cylinder #4 and R3600 cylinder
#5 are the most likely to experience a lock due to the relative position of the
intake pipe and the mechanics of the engine.
Example Situation:
If on shutdown, the intake valve is partly open and the exhaust valve ful-
ly closed on cylinder #4, then any oil that penetrates into the combustion
chamber will flow through the open inlet valve and fill up the intake pipe. On
restart, this stored oil is sucked into the engine resulting in a hydraulic lock.
This accumulation of oil presents the greatest danger as hand cranking does
not detect or remove it. Nor will cranking using the starter motor with the
ignition off. In both instances the speed of the piston action is not sufficient
enough to develop a vacuum strong enough to remove any accumulated oil.
However once the engine is started under power (ignition on) the piston
speed does become sufficient to create a vacuum strong enough to suck
the oil back into the chamber and cause an instance of hydraulic lock along
with associated damage.
1. The amount of oil required to do damage is very small. The combustion chamber’s volume is only 55cc (on both
the R2800 & the R3600). If the amount of oil exceeds 30cc, it is unlikely the engine will survive serious damage.
2. Hand cranking cannot remove this oil - the speed of the cranking process is not fast enough to create a vacuum of
sufficient strength to suck the oil back into the chamber.
3. Using the starter motor with ignition off does not remove this oil. Like hand cranking the speed is not high enough
to move the oil.
4. Once the engine is started, the speed is high enough to suck the oil back into the chamber.
5. It is imperative that the fitted drain cocks be employed.
CYLINDERS MOST SUBJECT TO HYDRAULIC LOCK
KEY POINTS
Drain
Oil
Cock
Fig #. Accumulation of oil in the
intake pipe of the 2 lower cylinders
INTAKE PIPE DRAIN COCKS
(Fig #. R2800 Drain Cocks example)