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Before you disassemble
your engine, clean the engine and the rest of the paramotor. That will
reduce the risk of dirt and debris falling into the engine. Once you remove
the cylinder, stuff a clean rag down into the crankcases.
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The cylinder and head
use alignment pins to hold them straight in position from the crankcases on
up. The pins make it difficult to remove the cylinder from the cases and the
head from the cylinder. Sometimes the steel alignment pins corrode into the
aluminum engine components. Try spraying penetrating-oil down the mounting
studs before attempting to remove the cylinder and head. Never use a
flat-blade screwdriver, chisel, or metal hammer to remove the cylinder.
Instead use this technique; buy a lead-shot plastic mallet, swing it at a
45-degree angle upwards against the sides of the cylinder. Alternate from
left to right, hitting the sides of the cylinder to separate it from the
cases evenly. Clean the steel alignment pins with steel wool and
penetrating-oil. Examine the pins closely. If they are deformed in shape,
they won't allow the engine parts to bolt together tightly. This can cause a
dangerous air leak or a coolant leak. The pins are cheap at about $2/£1
each. Replace them if they're rusty or deformed.
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Never re-use old
gaskets. Remove them with a razor blade or gasket scraper. Don't use a
drill-driven steel wool type pad to remove old gaskets because they can
remove aluminium from the cylinder and head. That will cause a gasket to
leak.
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Always check the ring
end gap on a new ring by placing it in the cylinder between the head gasket
surface and the exhaust port. The gap should be between .012 to .024 inches.
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Always install the
circlips with the opening facing straight up or down, that way inertia will
hold it tight into the clip groove. Place one clip in the groove before
installing the piston on the connecting rod. Its easier to install a clip
with the piston in your hand rather than on the rod. There also less chance
that you'll drop the circlip in the crankcases.
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Always install the
rings on the piston with the markings facing up. Coat the rings with pre-mix
oil so they can slide in the groove when trying to install the piston in the
cylinder.
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Always install the
piston on the connecting rod with the arrow on the piston crown facing
towards the exhaust port.
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The traditional way to
assemble the top end is to install the piston assembly on the connecting
rod, compress the rings, and slide the cylinder over the piston. That can be
difficult with larger bore cylinders, or if you're working by yourself. Try
this method instead. Install one circlip in the piston, install the piston
into the cylinder with the pin hole exposed, install the piston pin through
one side of the piston, position the cylinder over the connecting rod and
push the piston pin through until it bottoms against the circlip, install
the other circlip. It only takes two hands to install the top end using this
manor and there is less chance that you,ll damage the rings by twisting the
cylinder upon installation.
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On cylinders with reed
valves and large oval intake ports, take care when installing the piston
assembly in the cylinder because the rings are likely to squeeze out of the
ring grooves. Use a flat-blade screwdriver to gently push the rings back in
the grooves so the piston assembly can pass by the intake port.
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For steel head
gaskets, place the round side of the "bump" facing up. Don't use liquid
gasket sealer, use aerosol spray adhesive types instead. For hybrid
fibre/steel ring head gaskets, place the wide side of the steel rings facing
down.
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When you initially
start the engine after a rebuild, manipulate the choke to keep the engine
rpm relatively low. Once the engine is warm enough to take it off choke.
Keep it under 2/3 throttle for the first 30 minutes. Two common myths for
proper engine break-in are:
