Engine Overhaul Manual
Jabiru Aircraft
Pty Ltd
Jabiru 2200 & 3300 Aircraft Engines
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Dated : 28/10/2014
Issued By: AS
Page: 80 of 201
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After cutting the seal of the valves must be checked using a vacuum tester. This can be done without
fitting the valve springs as the vacuum which is applied in this test holds the valve against the seat.
Figure 92
shows a vacuum test rig. This system connects to the workshop’s compressed air supply
and uses a venturi effect within the silver box (right) to generate a partial vacuum. A fitting must be
made to connect the vacuum tube to the cylinder head
– we use a layer of insertion rubber to seal
between the metal fitting and the cylinder head. Once operating the vacuum is assessed via a gauge.
If the valve achieves 25inhg or less then the valve must be cut against the seat to improve the seal.
Again, remember that the seats and valves must be cut as little as possible.
Alternatively the seal can be checked using bearing blue, assessment of the lapping marks or by using
liquids to look for leaks. Vacuum is the preferred method as it is fast, clean and accurate. The unit
pictured below used compressed air to generate a vacuum and is manufactured by SMC, P/No. ZH13B.
Figure 92
– Vacuum Test Rig
If the valve seats are badly worn or recessed into the cylinder head then a new cylinder head must be
fitted or new seats must be fitted to the old head. However, replacing the valve seats is a specialist
task which we recommend that overhaulers do not attempt as it requires special tools and extreme
temperature differences.
Note that the hydraulic valve lifters have an internal piston with approximately 4.0mm of total travel -
±2.0mm from the original set position. This allows these engines to automatically adjust for up to this
amount of variation in the valve train. Variations larger than this can lead to incorrect valve actuation
and engine damage. Valve recession, cylinder head recession and similar factors all affect this
measurement and must be monitored carefully during overhaul. Shorter length pushrods are available
for hydraulic lifter engines to address this, however they are normally not required if the engine is
overhauled using the guidelines given within this manual. Note that fitting shims to the engine will have
the same effect on the lifter as using a shorter pushrod
– i.e. the piston in the lifter will run higher in the
bore. Accordingly the effect of using shorter pushrods can also be gained by fitting longer cylinders or
cylinder shims. Normal valve tip to rocker clearance with lifter fully bled is around 1.8 / 1.9mm. With
later shortened pushrods of 215mm, add 1.0mm to above dimensions.
