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http://www.ultralightnews.ca/ Page 23 of 31
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7.6Inspecting the condition of the sparkplug leads
Remove the sparkplug leads and check the contact socket inside for corrosion. Check the SAE-contact (the
screwed on contact hood) of the sparkplug for corrosion or "deposits". If there is corrosion or "deposits",
replace the sparkplug lead and SAE- contact of the sparkplug (usually here the sparkplug would be
completely exchanged - see next paragraph).
7.7Installing 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.
7.8Condition 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.
8Fan
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.
8.1Remove 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 entire muffler after the elbow in the exhaust manifold (see later chapter. Remove
both screws to the crankshaft housing underneath the elbow of the exhaust manifold. Then remove the screws
to the fan housing on the side of the cool air exit. Pull off the shroud over the elbow of the exhaust manifold.
To install the shroud, reverse the process used for removal. Should there be any damage to the shroud, it has
to be replaced immediately.
To install the air cowl, assemble in the reverse order. If there is any damage to the air cowl, it is to be
replaced.
8.2Remove and assembling the fan housing
To remove the fan housing, take out the screws of the shroud on the side of the cool air exit. Turn the
adjustable cam centre of the fan wheel so that the flat belt of the 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 flat belt off the belt disk. To install
the fan housing, reverse this process in logical order. Turn the adjustable cam centre of the fan wheel and set
to maximum tension.
8.3Changing the fan belt
To change the fan belt, take out the fan housing (see previous section). Cut up frayed fan belt and remove
from fan housing. Remove the shroud with a screw driver and wrench. Put a new flat fan belt into one of two
slits of the fan housing and hang it into one of the wings of the fan blades and slowly turn the fan blade. The
other fan blades of the fan wheel have to always run between the belts. After three quarter turns of the fan
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