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Engine Overhaul Manual
Jabiru Aircraft
Pty Ltd
Jabiru 2200 & 3300 Aircraft Engines
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ISSUE
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Dated : 28/10/2014
Issued By: AS
Page: 192 of 201
L:\files\Manuals_For_Products\Engine_Manuals\Overhaul_Manual\JEM0001-7_Overhaul_Manual_DRAFT_(29_10_14).docx
12.3.2 Fretting General Information
Figure 204
– Crankcase Fretting
Cases which have suffered fretting can be identified as shown in Figure 204. There will be
characteristic markings on the crankcase joining face near the main bearing journals which can be felt
by scratching with a fingernail
– the raised portions will be clearly evident.
Suspect cases can also be checked in the field by checking the torque of the bottom crankcase
through-bolts with the torque wrench set at 28lb.ft. These bolts are set at 30lb.ft during assembly so if
the nuts move at 28lb.ft it is a good indicator that the cases have fretted and are no longer seating
together securely.
An engine which operates for an extended period with fretting can lead to unrepairable crankcase
damage, through bolt failure and engine stoppage.
The main causes of crankcase fretting in the Jabiru Engines are:
a. Pre-ignition or detonation due to lean running, incorrect fuel, low octane fuel, contaminated fuels or
combinations.
b. Incorrect through-bolt torque or uneven bolt tensioning.
c. Reduced through-bolt tension due to cylinder base cracking
d. Cracked or broken through-bolts
e. Poorly matched case halves
f. An inadvertent lean run
– for example due to a incorrectly set float level or partially blocked fuel
filter.
g. Running engines with high valve stem-to-guide clearances, promoting oil residue in the intake
system. This has the effect of reducing the octane number (or AKI) of the fuel and can lead to
detonation or pre-ignition.
12.3.3 Fretted Crankcase Repair
Fretting can be repaired
by surfacing (or “decking”) the crankcase, then line-boring the crankshaft and
camshaft tunnels. Surfacing should always take the bare minimum material to remain within the limits
set. Excess surfacing will lead to the sump and backing plate not fitting the cases, rendering them
unserviceable.
WARNING
This process requires specialist equipment, tools and training to be successful. Overhaulers must
not attempt this job without access to these items.
First the crankcases need to be completely stripped. All bolts, studs, dowels, fittings and plugs must be
removed. Heat may be required to extract some items.
“Pulled up” metal
Raised ridge