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http://www.ultralightnews.ca/ Page 30 of 39
The Ultralight Store - your one stop ultralight store.
8.6Installing and removing sparkplugs
To uninstall the sparkplug, remove the sparkplug lead. Loosen the sparkplug with the sparkplug wrench and
unscrew it.
Before installing the new or still serviceable sparkplug, the air gap (0.8 mm) is to be checked with a feeler
gauge and adjusted as required.
Screw the sparkplug into the cylinder head with a sparkplug wrench and torque to the correct setting.
8.7Condition of the sparkplug
The spark plug should have a dry bright brown colour tone on the central electrode, the insulator of the
central electrode and the earth side of the case. If the colour tone changes to a bright very dry grey, the
engine is running very hot and the mixture is too lean. Where there is a wet dark brown to black colouring,
the engine is running with too thick a mixture. In both cases, AATI Pty Ltd or your Hirth distributor should
be contacted.
Check the sparkplug central electrode and earth strap for corrosion (burning). If signs of burning are
detected, the sparkplug should be replaced. For more information on how to read sparkplugs, go to the
maintenance pages on the http://www.ultralightnews.ca/web site.
9Fans
It is necessary that the opening for the fan remain unobstructed. Only sufficient flow of fresh air and
satisfactory operation of the fan can guarantee proper cooling of the engine.
9.1Remove and assembling the air cowl
To remove the air cowl, remove the sparkplug leads and unscrew the sparkplugs. Mark the position of the
sparkplug leads. Remove both screws which secure the cowl to the cylinder heads. These are directly below
the spark plug access holes in the cowling. Remove the two screw which attach the air cowl clamp to the fan
housing. You should be able to leave the clamp attached to the air cowing by the M6 bolt. Remove the
housing from the engine To install the air cowl, reverse the process used for removal. Should there be any
damage to the air cowl should be replaced immediately.
9.2Remove and assembling the fan housing
To remove the fan housing, unscrew the nylex nut of the adjustable cam centre of the fan wheel so that the
polyflex belt of each fan is without tension. Remove the four front screws of the fan housing and pull the
shroud off along the axis of the adapter sleeve. After the fan housing slips off the adapter sleeves, push the
fan housing downward and take the polyflex belts off the pulley. Replace any suspect or damaged belts. To
install the fan housing, reverse this process in logical order. Turn the adjustable cam centre of each fan to a
suitable tension.
10Cylinder head
The cylinder heads are manufactured from a special aluminium alloy which permits a maximum temperatures
of 280C. If the metal is overheated (ca. 300° C), the material looses hardness. This loss in hardness leads to
0
leakages in the seal surface between the cylinder head and the cylinder. Tightening the cylinder head screws
will have no effect. The cylinder head must be replaced.
10.1Cylinder head removal and installation
To remove the cylinder head, remove the spark plug caps, the spark plugs, and the fan housing, as described
above. Loosen and unscrew the eight cylinder head screws with a hexagonal socket wrench. Mark the
position and placement of the cylinder heads, then remove cylinder heads. To install the cylinder heads,
reverse the process, tightening the cylinder head screws lightly and first, then applying the prescribed torque
values using crossway technique.
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