Gobler-Hirthmotoren KG 3503 User manual

Operator's Manual
Engine
3503
Göbler Hirthmotoren KG
Max-Eyth-Str. 10
71726 Benningen
Deutschland Germany
Tel.: [phone]; Fax: [phone] Phone:[phone]; Fax:
0049-7144-5415
e-mail: [e-mail] , Internet: www.hirth-engines.de

Operator's Manual
Engine
Model 3503
Read this operator's manual thoroughly before putting the engine into operation for the first time and comply
strictly with the instructions given here.
In the interests of continual development of our engines we must reserve the right to change conditions of
delivery for design, engineering and fixtures. We also request your understanding that no claims can be made
against statements and Figures from this manual.
THIS ENGINE DOES NOT COMPLY WITH FEDERAL SAFETY REGULATIONS FOR
STANDARD AIRCRAFT. THIS ENGINE CAN BE USED IN EXPERIMENTAL AND ULTRA-
LIGHT UNCERTIFIED AIRCRAFT ONLY IN CIRCUMSTANCES WHICH AN ENGINE FAILURE
WILL NOT COMPROMISE SAFETY. BEFORE OPERATING THE ENGINE READ OPERATOR'S
MANUAL INFORMATION AVAILABLE FROM YOUR AUTHORISED HIRTH DISTRIBUTOR.

Table of Contents
Germany.........................................................................................................1
Phone:[phone]; Fax: [phone]..............................................................1
1. Description of the Engine, Mounting Instructions and Technical Data...............5
1.1. Overview.....................................................................................................5
1.2. Description of the carburation system.........................................................5
1.3. Description of the Ignition System...............................................................6
1.4. Description of the cooling system ...............................................................7
2. Model Identification plate................................................................................... 7
3. Installation instructions....................................................................................... 8
3.1. Mounting and securing the engine..............................................................8
3.2. The engine’s air supply...............................................................................8
3.3. The engine’s fuel system and fuel supply...................................................8
3.4. The operation of dual carburettors .............................................................9
4. Monitoring Apparatus.......................................................................................10
4.1. Exhaust gas temperature .........................................................................10
4.2. Fuel Pressure............................................................................................ 11
4.3. Coolant Temperature Gauge.................................................................... 11
5. Instructions for assembling the coolant system ...............................................12
5.1. Operation..................................................................................................12
6. Specifications – 3503 engine...........................................................................14
Operation of the Engine......................................................................................14
6.1. General.....................................................................................................14
6.2. Running in - Recommendation ................................................................. 14
6.3. Initial Inspection........................................................................................15
6.4. Starting Procedure.................................................................................... 15
6.5. Operating condition of the engine............................................................. 15
6.6. Powering down the engine........................................................................ 16
Maintenance .......................................................................................................16
6.7. General.....................................................................................................16
6.8. Tools, special tools and torques ...............................................................16
7. Maintenance rate - Daily inspections...............................................................17
Replacement of Parts .........................................................................................17
7.1. Maintenance instructions - Carburettors...................................................18
7.2. Synchronisation of dual Dellorto carburettors...........................................18
7.3. The basic setting of the mixture regulating screw.....................................18
7.4. Cleaning of the carburettors......................................................................18
7.5. Inspecting the air filters.............................................................................18
7.6. Inspecting the fuel lines ............................................................................18
7.7. Inspecting pulsation lines..........................................................................18
7.8. Spark plugs and sparkplug leads..............................................................19
7.9. Inspecting the condition of the sparkplug leads........................................19
7.10. Installing and removing sparkplugs.........................................................19
7.11. Condition of the sparkplug......................................................................19
8. Coolant Pump..................................................................................................19
8.1. Changing the coolant pump V belt............................................................20
9. Trouble Shooting.............................................................................................. 21
9.1. Engine does not start or is difficult to start................................................ 21
9.2. Engine will not Idle.................................................................................... 21
9.3. Engine Runs Rough, Uneven, and with Insufficient Power.......................21
9.4. Engine does not develop full power.......................................................... 22

9.5. Excessive Liquid Temperature..................................................................22
10. Exhaust System.............................................................................................23
10.1. Exhaust parts and measurements .......................................................... 24
11. Wiring Diagrams ............................................................................................25
11.1. Single PVL Ignition system - 3503.......................................................... 26
11.2. Dual PVL ignition system – 3503............................................................ 27

Page 5 of 27
1. Description of the Engine, Mounting Instructions and Technical Data
1.1. Overview
The 3503 engine (Figure 1.1.1-1) of Göbler-Hirthmotoren KG is a two cylinder in-line two-stroke liquid
cooled engine.
The cylinders consist of an aluminium alloy with a Nikasil coated running surface that is highly resistant to
wear. The cylinders are mounted onto the crankcase by stud bolts, discs and hexagon nuts. The cylinder
heads consist of a special hypereutectic aluminium alloy that resists high temperatures while maintaining
constant hardness. They are secured onto the cylinder by means of cylinder screws and washer using ‘O’ ring
seals between the head and the cylinder.
The pistons consist of an aluminium alloy and are sealed off from the cylinder running surface by two piston
rings. The piston is connected to the con-rod by the gudgeon pin and a needle bearing.
The crankshaft is made of chrome-molybdenum steel (42 Cr Mo 4) and is mounted in five deep groove ball
bearings. It‘s an assembled crankshaft and the individual parts are pressed together to form a complete unit.
Two deep groove ball bearings are installed on the PTO drive side, two between the con-rods and one on the
ignition side. The drive shaft is tapered and has a centred thread in order to secure to the PTO shaft. The
con-rods are connected to the crankshaft by crank pins and needle bearings.
The crankcase consists of an aluminium alloy and constructed as a case in two halves. It is secured together
by eight fastening studs and nuts which secure the cylinders to the case. Opposite the PTO end of the
crankcase, there is an ignition stator unit. This is fixed to the crankcase and is concealed by the flywheel and
the fan housing..
Figure 1.1.1-1 (Engine 3503)
1.2. Description of the carburation system
The carburation system (Figure 1.1.2-1) of the 3503 engine consists of two Dellorto carburettors. Each
carburettor is connected to the inlet aperture of the crankcase by a rubber flange and is secured to the inlet
aperture by means of a clamp held in a rubber flange. The carburettors have a dry air filters installed.

Page 6 of 27
Figure 1.1.2-1 (Dual Dellorto Carburation System)
1.3. Description of the Ignition System
The ignition system (Figure 1.3-1, 1.3-2) consists of an armature plate, a magneto, E-Box(s), ignition coils
and the ignition cables with the required number of spark plug leads. The ignition system is completely
electronic and possesses an E-PROM for a freely programmable ignition curve however, this can only be
carried out by the manufacturer. Alternating Current (AC) power for electrical components during running
and charging of the battery is provided. The engine is available with a single or dual ignition system
installed.
An electronic stator plate is secured on the ignition side with the crankcase. A magneto is fixed on the
crankshaft and encloses the armature plate. The fan housing covers the ignition system’s magnetic wheel.
The electronic E-box and ignition coils are mounted on a fixture plate secured to the crankcase as shown in
figure 1.3.3.
Figure 1.3-1 (Single PVL ignition)
Figure 1.1.3-2 (Dual PVL ignition)

Page 7 of 27
Figure 1.3-3 (View of ignition side with installed ignition system)
1.4. Description of the cooling system
The 3503 engine has a mechanically operated liquid cooling system. (Figure 1.4-1).
The liquid pump is installed above the flywheel housing. It is driven by a V belt pulley that is fixed to the
ignition system’s magnetic flywheel. Coolant is pumped from the radiator system into the cylinder water
jackets then to the cylinder heads. The hot coolant then exits the outlet of the cylinder returning back to the
radiator system. The temperature of the cooled liquid is controlled by a thermostat located between the
radiator and the inlet of the liquid pump.
Figure 1.4-1 (View of the fan housing and the liquid coolant pump)
2. Model Identification plate
The model plate is attached to the intake side on the upper part of the crankcase. This also includes the serial
number of the engine and must be quoted should a warranty claim be required.
Figure 3.5-1 (Position of the Model Plate)

Page 8 of 27
3. Installation instructions
3.1. Mounting and securing the engine
The six screw threads (M10) located on the underside of the 3503 engine crankcase is for fastening the
engine to a suitable engine mount.
Figure 2.1-1 (Fastening thread points)
The engine should be mounted so that the moment from the engine to the mounts can be absorbed as widely
as possible. The absorbing of the mounts should also be made as hard as possible, since the engine can
become unstable if these mounts are too soft. This also leads to problems within the carburettors fuel bowl as
well as uncontrolled vibration of the fuel pump diaphragm, intimating to an unsafe operation of the engine.
- Suggestion for securing the engine:
The engine is secured to a fastening plate that is about twice the width of the engine (the wider the better).
On the two outer surfaces of the fastening plate six (or more) hard rubber absorber elements (three on each
side) are attached in an axial direction. This complete substructure is secured by the rubber absorber
elements on to a corresponding base plate.
3.2. The engine’s air supply
The engine must be installed so the cooling air stream fed to the engine radiator is sufficient to ensure the
engine is cooled and that air is also supplied to the carburettors.
3.3. The engine’s fuel system and fuel supply
The engine’s fuel supply is provided by a Mikuni diaphragm pump (Figure 2.3-1) that is driven by pressure
pulsation from the crankcase.
This diaphragm pump is positioned in the fuel line between the fuel tank and Dellorto carburettor(s). A fuel
filter should always be installed between the fuel pump and fuel tank.
The Mikuni fuel pump should be secured to a location with the least influence of vibration or heat. It is
important that it is installed upright with the fuel outlet at the top. The assignment of the fuel connection
direction can be identified on the housing by arrows.
The central connection of the Mikuni pump is connected to the vacuum impulse line from the crankcase and
should be as short and straight as possible. When choosing the impulse line and the fuel line it is important to
ensure that rigid lines are used and do not expand under pressure. The impulse line should not exceed a
maximum length of 150mm with a minimum inner diameter of 6 mm.

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Figure 2.3-1 (Fuel-diaphragm pump with impulse connection)
The positioning of the fuel tank over the engine is advantageous as would ensure a reasonable fuel supply
pressure. It is recommended to maintain a consistent fuel pressure under all conditions. Additional
monitoring of fuel pressure by means of a fuel pressure gauge may also be considered.
When installing the fuel tank beneath the engine, the maximum fuel line length between the fuel tank and
diaphragm pump should not exceed 2,000mm. The maximum suction head should not exceed 1,000m with a
minimum inner diameter of 6mm.
Be aware of the possible gradient of the vehicle the engine is installed in during operation i.e. ascent-/descent
with aircraft, uphill-/downhill with ground vehicles.
The maximum length of the fuel outlet pressure line should not exceed 500 mm with a minimum inner
diameter of 6 mm. A maximum pressure head between the centre of the diaphragm pump and centre of the
carburettor float chamber may not be exceeded.
If a Mikuni pump is installed on the engine, it is recommended the diaphragm of the pump stands vertical to
the crankshaft axis (drive or ignition side ). This will ensure that resonance produced by the crankshaft axis
from the engine does not impair the action and function of the fuel pump.
3.4. The operation of dual carburettors
The throttle valves of the Dellorto carburettors are operated via two Bowden type cables. It is advantageous
to run both cables from the throttle into a single cable by means of a Y-shunt or cable splitter.
If at all possible, both throttle cables between the Y-shunt and the carburettors should be the same length.
In idling position (both throttle valves sit on the idle – adjusting screw) there should still be enough play in
the throttle cable to ensure that the throttle valves can reach the idle position stop.
It is essential to ensure that both throttle valves in the Dellorto carburettors are completely synchronised.
The idling position of the throttle valves must be equal in both carburettors. To do this, use the idle adjusting
screw to bring the throttle valves to the same level in idle position.
Measure and match the size of the aperture of both slide valves.
When the slide valves are drawn upwards they should lift simultaneously from the idle-adjusting screws and
open the outlet together.
Securing the spark plug leads in a hanging (inverted) installation
If the engine is installed in a hanging or inverted position, the sparkplug leads should be secured so that any
breaking or interruption of contact by engine vibrations is prevented (support or secure by wires).

Page 10 of 27
Switching off the Ignition System (dual ignition)
It is essential that both ignition circuit breakers are located on separate grounding switches. It is important
each earthing wire is installed separately to avoid circuit failure. This method also aids the operator to check
each ignition side when the engine is operating.
4. Monitoring Apparatus
It is recommended that the coolant temperatures, the exhaust gas temperature and the fuel pressure be
monitored.
The basic setting of the engine guarantees a problem-free engine function under the general installation
conditions. It is very important for safe running of the engine that the cylinder head, exhaust gas temperature
and the fuel pressure are monitored.
The equipment listed in Table 3-1 can be purchased from Göbler-Hirthmotoren KG.
Table 3-1
Description Part No.
Westach Exhaust gas temperature measuring device (2x, as a set) 029.30
Westach Coolant temperature devise 029.36
Westach Fuel pressure measuring device 029.20
Westach Tachometer 029.14
4.1. Exhaust gas temperature
A gauge that we recommend on all Hirth two stroke engines is the Westach Exhaust Gas Temperature gauge
(EGT) as in figure 3.2.1. This gauge is a reliable measurement tool that measures the exhaust gases as they
exit the engine. A rich fuel/air mixture which can be caused by improper jetting, clogged air filter, improper
prop setting, will generally show up as a cooler temperature. A too lean mixture can be caused by an air leak
or fuel blockage, can result in overheating and engine seizure.
Figure 3.2.1 Westach Dual EGT 029.30
The proper location of the EGT probe on the exhaust manifold is extremely important. Mounting the probe
too close or too far from the piston will result in an incorrect reading.
If the engine is installed with one carburettor, the probe needs to be located in the centre of one of the
exhaust manifold ports 85mm from the exhaust outlet of the engine cylinder exhaust port. If the engine is
installed with two carburettors, each probe needs to be located in the centre of each of the exhaust manifold
port, 85mm from the exhaust outlet of the engine cylinder exhaust port. Install the probe before reinstalling
the manifold and make sure the probe will not touch the other side of the manifold wall.
The 50mm round EGT the gauge will mount from the front of the panel and will require a 52.388mm round
hole, a U bracket holds it in place from the rear.