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ADVISORY ENGINE BULLETIN #19

 

– June 2011

 

To all Dealers and Maintenance Persons

 

CONTENTS

 

1 HYDRAULIC ENGINES (PUSHRODS)

 

·

 

Inside a hydraulic valve lifter there is a piston which “floats” on oil with its position

 

regulated by springs, valves and oil pressure. The way it moves relative to the

 

lifter body is what allows the hydraulic lifter to automatically adjust for valve train

 

variation and maintain the correct valve seating parameters. The piston has a

 

limited range of movement however – and if it reaches the limit of its travel valve

 

control issues will result.

 

·

 

A number of factors such as a recessed head/cylinder spigot, a very deeply cut

 

valve seat and a crankcase which has been surfaced/line bored (reduced width)

 

can affect the position of the piston within the hydraulic valve lifters – bringing it

 

to the limit of its travel.

 

·

 

In cases where the lifter travel has all been used there are a number of different

 

solutions –

 

i. The standard pushrod length is currently 216mm. A 215mm rod is available

 

as a spare part to allow for the effects noted above.

 

ii. If the engine is currently equipped with 107.0mm long cylinders fitting a

 

0.5mm shim (recommended to improve the engine’s tolerance of various

 

fuels) will also help counteract the valve lifter issues. Note that due to the

 

gear ratio of the valve rocker increasing the length of the cylinder has the

 

effect of moving the piston within the lifter by about 0.6 – 0.7mm.

 

iii. Replacing worn valves and rocker bushes can also help.

 

2 NEW PLENIUM CHAMBER (INTAKE)

 

·

 

The shape of the induction chamber for 3300 engines was changed from S/N

 

2331. The new chamber has a different shape, different internal diffusers and

 

uses some new-shape induction pipes. The effect of this chamber is to create a

 

more even mixture distribution between the cylinders. The result is that the

 

difference between the hottest and the coldest EGTs are reduced.

 

3 CYLINDER BASE NUTS

 

·

 

Jabiru Service Bulletin JSB031 was recently released to address issues with

 

cracking of the through-bolts which hold the engine halves together. This

 

bulletin affects the majority of the engine fleet and operators & maintainers are

 

urged to familiarise themselves with its content as soon as possible.

 

·

 

With regard to this issue, engines overhauled must now use the new 3/8” nuts

 

(shaped in 12 points) instead of the previous MS21042-type nuts.

 

·

 

The torque of the cylinder base nuts remains set at 30lb.ft and through bolts

 

have been lengthened to take advantage of the increased number of threads on

 

the nut. Because they have no “deformity” for locking they must be locked with

 

620 Loctite on installation. Our website has the 3 documents available which are

 

relevant to this issue: the Service Bulletin, Bulletin Procedure for carrying out the

 

work called for in the bulletin and a procedure for chamfering the base of the

 

nuts to ensure they do not bind on the base radius of the cylinder.

 

·

 

New production engines are now using either the 12-point 3/8” nuts or a custommade

 

stainless steel 7/16” nut. Note that the use of the 7/16” hardware has

 

forced changes to cylinders, crankcases and crankcase dowels meaning that

 

7/16” bolts cannot be easily used in an older engine.

 

4 FLYWHEELS

 

·

 

In 3300 engines the inner part of the flywheel “starfish” has been altered to give

 

a reduced advance on spark timing (not cam timing). Spark advance is now set

 

at 20° BTDC. This has been introduced on 3300 engines from S/N 2391.

 

·

 

This change has had negligible effect on power output but makes the engine

 

significantly more tolerant of poor fuels and other factors which can lead to

 

detonation.

 

5 CRANKCASE DOWELS

 

·

 

The fit of the dowels which locate the two halves of the crankcase has been

 

identified as a significant contributor to structural issues with the crankcase

 

– be

 

it fretting or damage to the case hardware. Accordingly new “oversize”

 

crankcase joining dowels have been produced and must be used at overhaul to

 

maintain a “snug” fit of case halves.

 

·

 

These dowels now come as:

 

- standard @ 12.501 – 12.512

 

- 1 dot @ 12.512 – 12.523

 

- 2 dot @ 12.523 – 12.534

 

- 3 dot @ 12.534 – 12.545

 

·

 

The identifier “dot” is on the mid section of the dowel. This means careful

 

measurement of case when overhauling to fit all “snug” dowels.

 

·

 

When overhauling it is necessary to assemble the case (potentially several

 

times) to check bearing clearances. During this process it is recommended that

 

older dowels are used to simplify repeated assembly and disassembly. These

 

must then be replaced with tight new dowels at final assembly.

 

·

 

The fit of these dowels is critical to the structure of the engine and must be

 

checked carefully whenever cases are split.

 

6 THROUGH BOLTS

 

·

 

See Service Bulletin JSB031-1 on through bolts requirements, depending on

 

engine lift nuts changed and or through bolts at nominated time in service or time

 

since overhaul. Also refer to the companion documents for workshop

 

procedures for carrying out the required work.

 

7 OVERHAUL MANUAL

 

·

 

This document is available on the Jabiru web page. It will be regularly updated –

 

several of the points discussed in this bulletin will be detailed in the next revision

 

of the manual.

 

8 ENGINE MANUALS

 

·

 

Because now a detailed overhaul manual is available it was decided that

 

duplication of much information on engine disassembly and assembly could be

 

therefore omitted from these manuals (4 and 6 cylinder).

 

·

 

The 8 cylinder manual remains the name. All the necessary information could be

 

sought from the one overhaul manual.

 

9 SERVICE BULLETIN - FLYWHEEL

 

·

 

All owners and service persons should be aware that all Jabiru Engines are

 

currently subject to periodic checks of the flywheel installation. JSB012-2 refers

 

– please read it carefully and it will clarify what the requirements are for each

 

given engine configuration.

 

10 CLIMB OUT SPEEDS

 

·

 

There appears confusion on best climb out speeds. Manual specifications for

 

best rate of climb for J160 and J230 is 68 and 75 knots respectively.

 

·

 

This means this air speed will give the best chance of clearing obstacles if the

 

need arises. However the rate of climb for best engine management has been

 

largely left to operators.

 

·

 

The quickest way between two sets of traffic lights is to floor the accelerator and

 

race the engine

 

– but it’s not the way most of us do things because we

 

understand that driving that way will use more fuel and wear the engine out

 

faster. Similar arguments apply to climb speeds with a Jabiru Engine.

 

·

 

The 4 cylinder engine will look after you better with better air/oil cooling if

 

climbed around 80 knots while the 6 cylinder will think highly of you at a 90 knot

 

climb or above. If flying a J430/J450, climb speeds for load will differ especially

 

according to load. Once heading to that cross country destination cruise climb at

 

elevated speeds (shallow angle of climb) contributes to good engine

 

management.

 

·

 

At these higher speeds not only is there more air available to cool the engine but

 

the RPM is higher, allowing the engine to rev more instead of “lugging”. This

 

significantly reduces the stress on the engine and makes it less likely to suffer

 

detonation or other long-term maintenance issues.

 

·

 

Also see JSB031-1 at Section 3.3 on climb out speeds.

 

·

 

Training organisations with limited runway distances will need to use best rate of

 

climb initially but then can accept a higher air speed / lower rate of climb when

 

safely into the circuit. When operated this way engines with the fine finned heads

 

are difficult to elevate the heat range.

 

·

 

There also appears much debate on static or rolling RPM. Manuals state around

 

2800 RPM static. This was written mainly with the 2200 engine in mind – 3300

 

figures are slightly different (and limits will be adjusted in the next manual

 

revisions). To clarify, a new engine (6 cyl) driving a 60x53 Jabiru prop in a J230,

 

rolling in take off mode will show 2700 or there abouts. Once clear of ground

 

and in clean configuration, 90 knots will give a good 2800 RPM or better.

 

Manuals recommend RPM area guide especially for non Jabiru prop fit ups.

 

Secondly, if static or rolling RPM is in the 2700-2800 range this is relevant to

 

carby tuning and directly related to cruise power at 75% power.

 

11 OPERATING RPM

 

·

 

Historically we have always recommended that operators allow their engine to

 

rev rather than lug. Done properly this approach works very well, however in

 

certain cases it can also be damaging as it has been over-simplified and does

 

not necessarily consider percentage power.

 

·

 

For example, consider a Jabiru J200 with a Jabiru engine, propeller and cowls.

 

In a full power, straight and level run at sea level this aircraft should reach

 

speeds in the 130 – 140 KIAS range and the engine will be revving to around

 

3100 – 3200RPM. In this aircraft – which is fairly sleek and fitted with a wellmatched

 

propeller – cruising at 2900 rpm is fine because it will be at a relatively

 

low power setting.

 

·

 

In comparison, the same engine and propeller could be fitted to a bush plane

 

with slats, flaperons, tundra tyres and the aerodynamics of a brick. In this case

 

the static RPM and RPM on take-off would be similar to the J200 – but flat out

 

straight and level at sea level the aircraft won’t do much more than 100 knots

 

and the engine will be stuck at about 2900 – 3000 RPM or less. In this case

 

trying to cruise the engine at 2900 RPM would be disastrous as it would be a

 

very high percentage power setting.

 

·

 

The above examples are deliberately extreme but their message can be applied

 

across all airframes and engine models.

 

·

 

In the near future we plan to publish limits for manifold pressure at given RPMs

 

–

 

the combination of MAP and RPM allowing the pilot to accurately know how what

 

percentage of their engine power they are using at any given time. However,

 

until that information becomes available operators must avoid over-simplifying

 

the “more RPM is better” rule.

 

12 RECENT CHANGES BY SERIAL NUMBER

 

3300 2200

 

Cylinder length increased to 107.50mm 2290 - 3443 -

 

Hollow pushrods/rockers 2210 - 3358 -

 

* Thicker walled crank gear 2310 - 3443 -

 

** 3300 engines only with 7/16” thickness through bolts 2391 -

 

Spark tuning change to 20

 

o

 

BTDC 2391 -

 

Longer through bolts and 12 point nuts 2371 - 2390 3483 - 3498

 

“Starfish” inner (steel) for flywheel attachment 1522 - 2732 -

 

New induction body (parallel sides) 2331 -

 

·

 

Note:

 

Thicker walled crank gear uses a narrower rear seal. O.D. of seal is the

 

same as original seals.

 

·

 

These engines have larger holes in cylinder bases to fit larger diameter though

 

bolts. 7/16” stainless nuts manufactured for Jabiru engine used on cylinder base.

 

Leith McLennan

 

JABIRU ENGINE DIVISION