Ultralight Aircraft Engine Problems

Ultralight Aircraft Engines:

In the early days of ultralight aviation we would strap just about anything that would turn a propeller onto the front or back of our craft. A rule of thumb was not "if the engine quits" but "when the engine quits," be prepared for a forced landing!

 When buying, try to buy a craft powered by an engine that parts or a replacement engine, are readily available. You will find that replacing an engine, with another make and model, will usually mean that you will also have to buy a new prop and redrive as well. 

A good way of judging the condition of the engine is to remove the exhaust/ intake manifolds, and the cylinder heads. You can do this for the cost of replacement gaskets and about 30 minutes worth of work. This allows you to view the pistons, both front and back, as well as the top.

Any kind of scoring means the engine has had a seizure requiring in most cases an engine overhaul. If carbon deposits are visible below the rings it means ring seizure, or piston/cylinder wear. This also means engine rebuilding. If the top of the piston shows signs of foreign material embedded in the head it usually means, the engine has ingested something or an internal engine component has failed!

A damaged piston dome could indicate; a problem with ignition timing, spark plug heat range, lean fuel mixture, low octane fuels.

For better understanding read Troubleshooting the Cuyuna Engine, Trouble shooting the Rotax Engines Volume 1, 2 and 3  as well as our  Ultralight Advisory Bulletins.

Other areas to look at are; the cowls surrounding the engine , the fan tower , intake manifold(s) recoil housing ignition wiring especially on Kawasaki, Cuyuna engines using CDI ignition, failure of the wiring occurs where wires engine CDI box. If engine is equipped with Rotax electric start look to see that spacer between magneto and flywheel has been update from that shown on left to that on right.

​Check the magneto for damage, caused by improper propeller balance, loose magneto nut, substandard motor engine installation. Also check to make sure wiring has not been pinched or burnt . A poor ground on electric start, will result in severe damage to electrical system.

Look at the physical appearance of the engine! It should be clean! Any sign of leakage from gaskets, or seals means the engine requires disassembly, replacement of parts and reassembly. A leaking seal or gasket can result in, erratic engine performance, overheating, lack of performance and or engine failure!
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Gasket sets $ 100. - $150.
Labour rates for engine tear down $ 40. - $ 60. per hr.
Pistons $ 150.
Rings $ 30. (each)
Wrist pin bearings $ 25. (each)
Engine rebuilding videos and manual $ 69.
CDI box for Cuyuna/Kawasaki $ 200. (if you can find one)
Ignition coil $ 50.
277 Rotax engine
447 Rotax engine
503 Rotax engine
582 Rotax engine
340 Kawasaki engine
Zenoah engines
Hirth engines