Tip & How-To about Garden
Nobody likes to be told there chainsaw has seized up, the very nature of the word seized implies the the machine is solid and will not turn over, the reality is the piston has lost the oil film between it and the cylinder wall, it now has metal to metal contact, material from the piston skirt now transfers to the cylinder wall, the cylinder fins are very effective and the piston cools very quickly, and the engine will now rotate,so technically it is not seized up, unfortunatly the damage is done, the material from the piston has scuffed up over the piston ring, which is now stuck in, compression is lost , and the machine now refuses to start.
Stock answer from the dealer is usually a simple one line answer, no oil in the fuel, but this is not always the case, most engine seizures come under the heading of a lubrication breakdown, the reasons for this are as follows.
Insufficent two stroke oil in the fuel.
Poor quaility two stroke oil in the fuel.
Incorrect grade of oil in the fuel.
Incorrect carb settings, causing over speeding.
Poor chain maintenace, causing over loading.
Fuel system blockages, causing lean mixture.
Blocked cooling finns.
Operator miss use.
Engine air leaks, causing lean mixture.
Stale fuel, water contaminated fuel.
As you can see there are many reasons for a lubrication failure, you must remember this small engine is reving at anything up to 14000 rpm probably three times the rpm of your motor car engine flat out,and in a very hostile environment, the machine is air cooled, and basically a stationary engine, so all the cooling air is supplied by the vanes on the flywheel via the starter cover grill, if you allow dirt and debris to collect in the starter cover vents,you have now effectivley cut off the cooling air to the cylinder. Poor chain sharpening can and will cause over loading, and in turn increased cylinder temperature. Clogged fuel filters, dirt in the carb, dirty fuel, incorrect carb settings ,all increase engine revs, increased revs and lean fuel oil mix to the cylinder results in engine over heating and possible seizure. Engine air leaks, either through leaking gaskets or crank seals will also increase engine speeds and possible cylinder failures.
If you suspect an engine seizure, or your saw will unexplainably not start, remove the muffler, this is normally only held with a couple of screws, check the condition of the pistons exhaust skirt ( this is the hottest part of the engine, betwwen the centre of the piston and the opposite side to the flywheel, as the flywheel side runs a little cooler ) any signs of piston scuffing,and the engine has seized, and will require further investigation.
Other possible reasons for cylinder seizures are main bearing failures, or foriegn objects entering the saw through the inlet port. When removing clutches, or flywheel nuts, you should never enter anything into the cylinder to lock the piston, piston stops, bits of starter rope etc, these items can damage the piston, or get caught between the cylinder and the piston.
A final thought on two stroke oil, there are many different makes and colours of oils out there, what you need to ask youself is, how many of these oil suppliers actually produce a chainsaw engine? how do they know the lubrication requirements of the engine? why would anybody spend there hard earned money on a good saw, and then buy the cheapest oil they can find, always buy the best two stroke oil you can, preferably from a chainsaw manufacturer, and to be mixed at 50-1 ( remember the environment, if not that remeber you are breathing an amount of the exhaust gas in )
And finally a piece of trivia, an engine running for two hours a day, five days a week, running a 9500rpm the crank has rotated 1.7 million times in the first day, the diaphrams have cycled 3.42 million times, an engine running at 13500 rpm the spark plug sparks 225 times a second.
I hope you find this interesting and informative.
Posted by Andrew... on
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