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http://www.ultralightnews.ca/hirth-engines.htm Page 24 of 31
The Ultralight News
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.
9.11Fan
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.
9.12Remove 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.
9.13Remove 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.
9.14Changing 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
wheels, insert the part of the belt that is outside into the other slit in the fan housing and then remount the
metal guard.
9.15Cylinder 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
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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.
9.16Cylinder 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.
9.17Checking the condition of the cylinder head
Check the seal of cylinder heads and cylinders for places on which exhaust gas has blown through. These
places can be recognized by black lines over the seal and burned residue on the cooling fins. If this is the
case, the cylinder head must be immediately replaced. Check the indentation on the cylinder head for the
black residue. If present, remove it and eventually change the type of oil used.
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