The piston shows yellow spots on the dome and
seizure marks on the skirt but there is no sign of metal aluminum.
If you inspect an engine and find yellow or yellow-orange deposits on the piston
dome, that engine has experienced an abnormal combustion condition known as detonation. In
this situation, combustion begins normally with ignition from the spark plug but as the
flame front moves across the combustion chamber, rather than burning smoothly, the
unburned portion of the charge spontaneously ignites. This results in extremely high
temperatures and a shock wave heard as "pinging." What has happened is
combustion has been completed in about 29 degrees or crankshaft rotation instead of the
normal 50.
The oxide of calcium, an element found in 2 - stroke oil additives, is normally near
white in colour. At temperature very near that of the melting point of the piston, the
oxide will change colour from white to yellow-orange and is an indicator that the engine
was overheated. The excessive heat results in rapid piston expansion and possible failure
of the lubrication film.
Possible
causes:
too low an octane fuel used or fuel with too much alcohol used
jetting too lean or failure of the fuel system, i.e., clogged fuel line or filter, fuel
tank not venting, problem with fuel pump, carburetor,m air leak into crankcase
spark plug heat range too hot
ignition timing too far advanced, possible failure of the c.d. amplifier box
restricted exhaust system: back pressure too high
overheated, loosely-installed spark plug
Ultralight
Aircraft News Magazine
Ultralight Aircraft News Web Magazine -
You may link to these pages or print
them out for your own personal use, but no part of this
publication may be copied or distributed, transmitted, transcribed,
stored in a retrieval system, or translated into any human or computer
language, in any form or by any means, electronic, mechanical,
manual, or otherwise, without the written permission of Ultralight News.
By copying or paraphrasing the intellectual
property on this site, you're automatically signing a binding contract
and agreeing to be billed $10,000 payable immediately. Copyright Ultralight News.
.