Neotec Gas Chainsaw Piston Cylinder Carburetor Fails Analysis Guide for All Types Including Stihl and Husquvarna Some chainsaw owners have no idea if or to what extent the machine is damaged. One and quite useful way which is available for all our types of chainsaw including Neo-tec NS892 and NH872) to find the causes of the damage is by analyzing the piston after an engine failure. So what is a piston? The pistion is called to be “the heart” of the engine, reciprocating pumps, gas compressors, hydraulic cylinders, and pneumatic cylinders, among other similar mechanisms. Common symptoms are as follows and we hope this guide will help you analyze and confirm the cause to piston failures. NEW PISTON First of all, let us see the new piston for comparisons with the damaged. 1.CARBONSEIZURE Piston damage from excessive carbon build up can at first appear to be a lean seizure. The piston will be scored on the exhaust side and the piston ring will most likely be stunk in the ring groove. Furthermore, carbon deposits will be present on top of the piston and in the combustion chamber of the cylinder. Heavy carbon deposits are usually present in the exhaust port. Main Causes: ①Wrong type of engine lubricant or fuel ②Incorrect fuel:oil mixture ③Incorrect carburetor adjustment ④low rotational speed may due to the cold weather so that it cannot to burn completely. 2.LEAN (INSUFFICIENT LUBRICATION) SEIZURE A damage piston due to insufficient lubrication is commonly referred to as a lean seizure. Lean seizures are always caused by a lubrication failure such as a lack of lubrication. And lack of lubrication can be caused by the wrong fuel: oil mixing ratio, the wrong type of oil or no oil. Main Causes: ①Improper fuel:oil mixing ratio ②The carburetor is set to lean oil. ③Air leaks in fuel system including fuel house, intake gaskets and cracked intake manifold or split intake boot ④Air leaks in engine system such as crankshaft seals,cylinder or crankcase gaskets⑤ Improper maintenace: dirty cylinder cooling fins; plugged air intake openings in starter housing; plugged spark arrestor screen ⑥Gasoline with a lower then recommended ocatne rating ⑦Engine speed higher than factory recommended maximum no-load rpm ⑧The selection of engine models that did not correspond to the work led to overload. 3.EXCESSIVE ENGINE SPEED DAMAGE (OVER SPEEDING) Piston Ring retaining clips breakage Piston ring breakage Psiton ring locating pin breakage Bearing failure Piston damage may occur if the ring breaks apart. Piston ring breakage is commonly due to the result of engine overspeeding. The engine may not be running lean enough to cause a lean seizure but the above normal operating temperature causes the ring to tighten up in the ring groove which prevents the piston ring from fully entering the ring groove thus exposing the sharp side edge of the ring.This edge can then catch on or clip the cylinder port breaking the ring and sometimes destrorying the piston. Main Causes: ①Excessive engine rpm(over speeding) ②Piston ring worn out ③Piston ring groove worn ④Excessive engine speed can cause the piston pin retaining clips to vibrate. ⑤The crankshaft or connecting rod bearings fail. Bearing failure is usually caused by engine over speeding which overloads or overheats the bearing. 4.FOREIGN OBJECT DAMAGE Fine Dust particles Larger dust and dirt particles Large soft particles Large hard particles Clean air and fuel entering the engine through the intake port will cause some kinds of abnormal wear and threaten the piston. One of them is the intake side of the piston starting at the lower section of the piston skirt where it passes the intake port. Furthermore, damaged piston wear is the result of improperly filtered air passing through the carburetor into the engine. It is obvious that if the engine is operated with a damaged air filter or without an air filter, rapid piston wear or damage is a certainty. Main Causes: ①Wrong air filter. A finer mesh air filter is needed. ②worn out air filter, including air filter is cleaned to many times which causes samll holes in filter material. ③Improper air filter maintenace: flock type air filter cleaned improperly. ④Air filter improperly installed ⑤Air filter damaged or missiong ⑥Parts from carburetor or intake stystem came loose and entered engine. 5.DEFLAGRATION Piston top with holes (non-combustible). The piston ring groove is damaged. The cylinder block flange is damaged. The connecting rod is bent. The bearing frame is flat or broken. Main Causes: ①Due to the low octane fuel, the air/fuel mixture automatically ignites, with a delay of one millisecond compared to the normal wire transfer interval. ②carbon deposit. ③The air/oil mixture ratio is small ④the engine is over-loaded ⑤Engine components are subjected to 2-3 times normal pressure 6.EARLY INGITION There are deep scratches on the intake side of the piston. The top of the exhaust piston is shattered. Small pieces of molten aluminum are deposited on top of the piston. The spark plug electrodes may melt. The piston ring may be trapped in the ring groove. Main Causes: ①Due to excessive carbon accumulation, the ignition of the air/fuel mixture is one millisecond earlier than the normal ignition interval. ②The wear of the piston and cylinder block wear lead hot spots to detonate on top of the piston ③The spark plug calorific value range is incorrect ④The carburetor is set to lean oil.
