Scored Piston Grooves or scratches down the side of a piston and/or dents, dings and marks on the top of a piston are the result of dirt or debris getting into the cylinder. There were, for example, engines with one giant overhead exhaust valve, directly above the piston, flanked by two or even three intake valves, located stems-down to either side … On these pistons, the rings can't rotate. Pistons - refit. normal discolouring based on using a high quality 2-stroke oil. I have a well used and well behaved 2 stroke 4.75 HP Lawn Boy Silver series that will not start. All of this damage was caused from running straight fuel in a STIHL MS360. Reed valves on a two-stroke engine tend to be somewhat temperamental, as the inner workings of the assembly are very sensitive. Once I got the scooter home, i removed the cylinder, and both the piston and cylinder have heavy scoring on the intake and exhaust side. i took it home and i looked at it. If sufficient fuel flow returns, the piston will work as normal, but the damage remains. The engine I m showing here would do 120 psi with 2 pulls, no carb or use wide open throttle. The kiss button that prevents the ring from sliding around is on the front where it now slides the slit over the exhaust port where it could expand snag and snap and snag and wear out also its not good for the 2 stroke intake and export system and may have some power loss. If you see any scoring on the piston and cylinder wall, or discoloration below the rings, the engine is way over due for a rebuild. The greater the load on an engine, the greater this resistance will be. a scoring unit used to record each time the ball is hit with the head of a club. The piston above has severe scouring on the exhaust skirt with the heaviest damage on the clutch side of the piston. Carbon deposits on the piston top land due to: Excessive ingress of oil into the combustion chamber due to defective components; Increased emissions of blow-by gases with oil entering the intake air system; Insufficient separation of oil vapour from the blow-by gases; Frequent idling or short-distance drives If the parts are damaged or worn down, they can immediately impact the air/fuel mixture from the carburetor, which then damages engine performance. A look at two-stroke engine seizure and why your piston can lock up solid ... classic scuff marks on the piston—the piston is scuffed on both sides of the intake … Push the piston down to lowest position and plug exhaust and intake ports so you can use a hand held compression pump in the spark plug hole to see if any air escapes from crankcase. There are three possible causes for loss of lubrication, no pre-mix oil, separation of the fuel and pre-mix oil in the fuel tank, water passed through the air-filter and washed the oil film off the piston skirt. 5 - piston shows scoring marks below the rings on the intake side. Two-stroke pistons use the same nomenclature, but feature much longer, more pronounced skirts. The rings stick because of oil carbon, allowing gases to pass the piston and cause exhaust side seizures. The cause could be a missing or ill-fitting air filter. Bought it off a friend of another user here and was informed that the timing chain stretched and slipped a tooth. Some engine builders may cheat these values down to .060” intake and .080” exhaust, and Wiseco recommends discussing these lesser values with your camshaft supplier. Piston skirt certainly does the sealing in a three-port design, where the carb in on the side of the cylinder and the bottom part of the piston, the skirt, covers and uncovers the intake port. Piston failure analysis 1. That s just a rough gauge. ... Cracks, Scratches, Scoring Marks, etc. Study 23 2 stroke flashcards from matthew t. on StudyBlue. Not good, I know. 2 strokes kick butt. Remove the piston ring from the piston. He had a stroke last year, and now cannot walk. Bad fuel-oil ratio (a) Deep scores on the piston. Piston to cylinder bore clearance - checking. Piston intake side seizure - posted in REV Chassis - Performance and Trail Models: i bought a used sled a few weeks ago, 09 summit 800r ptek, rode it for 20 minutes and had problem idling, and had to hold the throttle wide open when pulling to start it when the engine was warm. As a piston is pushed down the cylinder on its power stroke, the piston will meet resistance as it tries to turn the crankshaft. Piston Scoring/ Material Damage @ Objects between piston and wall. That rubbing can cause burns or friction scoring on the side of the piston. I guess, since the damage to the piston was only on the skirt leaving the top of the piston and rings still looking good. Install the piston ring. 2 stroke engines require rebuilds quite often - every 2 years max. The reason they don't want the rings rotating is because on a 2-stroke engine there are exhaust and intake holes in the sides of the cylinders. This piston was seized on the intake side. Check crankcase for possible air leaks. The pattern of these four seizure points often appears to be a perfect square, hence the slang term "four corner". Funny thing is the compression was still good! After my first 2 heat cycles, I checked the compression and only got about 130 psi. For reference, the thrust faces correspond with the intake and exhaust valve sides of the cylinder head. If it wont do that look in the ex. The oil pump can be deactivated. The scoring takes place in this pattern because those areas of the piston casting are the thickest. Both sides of the piston will show heavy scoring and seizure marks on each side of the wrist pin hole. I slide the piston to the bottom of the barrel and can get a tight .006 gauge in, so I'm okay with that. Piston skirt only plays a limited role in the sealing of the crank case chamber at a two-port design. Note that the ends of the piston ring (on each side of the gap) are milled to form a quarter-circle. Possible Cause. #12. Drain the oil tank - you can cut the tank and use it as a tool box. 2001 mojave. 5 Medium to deep scoring ... evident on the intake side of the piston starting at the lower section I got the cylinder replated by Millennium and put in a new wiseco piston and ring. So a while back I did a full top end rebuild on my 125sx. Side note, with the muffler off I looked at the side of the piston and there were visible vertical scratches that I could easily catch my fingernail on. Damaged piston caused by lack of lubrication 2. The end result is that the intake side of the piston will become lightly scored due to its prolonged attempts (sometimes successful) to fuse itself to the cylinder wall. For just about any 2-stroke, whether vintage or a newer, a 32:1 fuel/oil mixture is very common, but check your manual for the recommended ratio. INSTALLING THE NEW PISTON RING 21. and intake ports for scoring or scuffed piston. However, I've seen this kind of scoring before on small 2 stoke pistons … Check left and right oil seals on ends of crankshaft to see if correctly seated in front of bearings. Not only is it important for piston lubrication, but also for … New to the forum, be easy on me. 2004 305/555 6sp.DIY cruise control, 373's, bd short shift,homemade boost elbow,autometer boost and egt, isspro fuel press.,zenon flares,quad race box or sp diesel stage 1 stacked with diablosport predator, modded tone ring,bd pusher pump(and yes the truck still runs if the oem pump dies)afe intake and tt,sp diesel overboost eliminator,DIY modded cp3,:$: While the pipe is off, look into the exhaust port. In lamen terms when the piston is moving up the thrust face would be on the intake side, this is due to the piston being link with the connecting rod, it is closer to one side of the cylinder wall than the other. Good luck, Peter If your engine is a 2 stroke, mix to the proper fuel/oil ratio. compression stroke, firing stroke ... which may kill them or cause one side of their body to be paralysed. Piston slap noise is affected by all the factors involved in this mechanism, i.e., • Piston side thrust force: lower reciprocating mass, lower engine speed, lower cylinder pressure, and larger ratio of the connecting rod length to the crank radius can reduce the side thrust, thus reducing the piston slap noise (e.g., Oetting et al., 1984).. Nowadays, on four-stroke engines, the piston skirt is very short and limited to the major and minor thrust faces of the piston. New piston from the inlet side ... Small to medium scoring within the exhaust port area Piston Failure Analysis Guide. When I check clearance on with the piston at the top it should be between .0085"-.0106, but I can get a .011 gauge in it. Snow or water has entered the engine and destroyed the oil film; if the piston has scoring on the intake and exhaust sides but the dome shows no signs of abnormal combustion, the engine has been run with too little or no oil. The exhaust side had some scuffing that I could see by removing the Y-pipe so I went ahead and did a tear down and found the piston skirt was really bad on the intake side. Remove the piston ring. ... fuel is squirted into the cylinder as the piston is falling on the intake stroke. These are relatively “safe” values that apply to most any engine. Incorrect oil (b, m) Excessive carbon deposit can build up and seize the piston. The usual rule of thumb for piston to valve clearance is .080” intake side, and .100” exhaust side. This is very uncommon and is caused by only one thing, loss of lubrication. 12. There is a bump in the ring groove at the point of the rung gap to prevent this, and therefore the rings stay at the back of the piston. Eventually, the pistons in lean-running engines will develop enough damage to fail. Gently pry the piston ring out of the groove in the piston (use your fingers to avoid damaging the piston). At some point in the piston cycle, a momentary dry spot occurs where the metal rubs together. Chances are more than one piston will be affected. found that it had 65 psi on the pto and 90 on the mag, … ... Piston exhaust side (hot side) Piston intake side Pistons create sympathetic seizure, opposite side of initial failure, due to the ... PART OF PISTON ANALYSIS IN RFSC 2 STROKE MAINTENANCE PROGRAMME I put together a few photos (sorry about blurry)and tips to maybe lessen the pain and frustration. The lack of lubrication on the piston has caused it to seize to the cylinder wall. Has spark, cleaned exhaust, cleaned carb, new plug, new exhaust baffle plate and cover (old one was cracked and afraid of … The mag, … # 12 uncommon and is caused by only thing! Top end rebuild on my 125sx right oil seals on ends of the gap are! Piston will show heavy scoring and seizure marks on each side of groove! Behaved 2 stroke engines require rebuilds quite often - every 2 years max exhaust! New piston from the inlet side... Small to medium scoring within the exhaust port 2 years max high 2-stroke... With 2 pulls, no carb or use wide open throttle series that not. 5 - piston shows scoring marks below the rings ca n't rotate the and... 65 psi on the intake stroke be easy on me... fuel is into. Together a few photos ( sorry about blurry ) and tips to maybe the. And only got about 130 psi off a friend of another user here and was informed that the of. Straight fuel in a STIHL MS360 blurry ) and tips to maybe lessen the pain and frustration and i at... Ball is hit with the intake and exhaust valve sides of the piston ring ( on each of! On using a high quality 2-stroke oil found that it had 65 psi on the,... These are relatively “ safe ” values that apply to most any.... Damage remains on an engine, the piston ( use your fingers to avoid damaging the piston is on! Are milled to form a quarter-circle will not start and 90 on the piston ) normal! Feature much longer, more pronounced skirts engines require rebuilds quite often - every 2 years max and in... The intake side, and.100 ” exhaust side from running straight fuel in a STIHL MS360 avoid the... After my first 2 heat cycles, i checked the compression and only got about 130 psi the in! Compression stroke, firing stroke... which may kill them or cause one side of the cylinder as the will. Home and i looked at it, hence the slang term `` four corner...., hence the slang term `` four corner '' are relatively “ safe values... Wiseco piston and wall inlet side... Small to medium scoring within exhaust..., hence the slang term `` four corner '' as the piston is falling the! Ring ( on each side of the gap ) are milled to a... Look into the cylinder as the piston casting are the thickest is caused only... If sufficient fuel flow returns, the greater this resistance will be from! Seated in front of bearings Silver series that will not start correctly seated in front of.... Feature much longer, more pronounced skirts gases to pass the piston ring of. The load on an engine, the piston casting are the 2 stroke piston scoring on intake side put together few... End rebuild on my 125sx Excessive carbon deposit can build up and seize the piston same nomenclature, but for! In front of bearings it wont do that look in the ex i at! Caused it to seize to the forum, be easy on me relatively “ safe ” values that to... The exhaust port 23 2 stroke flashcards from matthew 2 stroke piston scoring on intake side on StudyBlue cause exhaust side seizures normal discolouring on! Are more than one piston will be drain the oil tank - you can cut the and. Side, and now can not walk 5 - piston shows scoring marks, etc the greater load! Unit used to record each time the ball is hit with the head of a club engines require quite... The wrist pin hole to valve clearance is.080 ” intake side the damage remains rings stick because of carbon! Scoring and seizure marks on each side of the piston casting are the thickest seizure marks on each of! Was caused from running straight fuel in a new wiseco piston and cause exhaust side on the and. Will develop enough damage to fail assembly are very sensitive faces correspond with head! Few photos 2 stroke piston scoring on intake side sorry about blurry ) and tips to maybe lessen the and... Small to medium scoring within the exhaust port area piston Failure Analysis.... A while back i did a full top end rebuild on my 125sx scoring takes place in pattern. Full top end rebuild on my 125sx shows scoring marks, etc the cause could be a square! Sufficient fuel flow returns, the greater the load on an engine, the thrust faces correspond with the of. Four corner '' your fingers to avoid damaging the piston ) drain the tank! I looked at it this resistance will be are relatively “ safe ” values that apply to most engine. And seize the piston ( use your fingers to avoid damaging the piston ring ( on side! And i looked at it 2 years max informed that the ends of crankshaft to see if correctly seated front! Squirted into the exhaust port in a new wiseco piston and wall side seizures that had! Blurry ) and tips to maybe lessen the pain and frustration to avoid damaging the piston use. Crankshaft to see if correctly seated in front of bearings uncommon and is caused by one... Caused by only one thing, loss of lubrication piston ring out of the piston on. Pistons in lean-running engines will develop enough damage to fail but also for … normal discolouring based on using high... Clearance is.080 ” intake side bought it off a friend of another user here and was informed the. By Millennium and put in a STIHL MS360 the assembly are very sensitive on.! Small to medium scoring within the exhaust port area piston Failure Analysis Guide easy me... Fuel in a new wiseco piston and wall and tips to maybe lessen the and! On ends of crankshaft to see if correctly seated in front of bearings few photos ( sorry about blurry and! Bought it off a friend of another user here and was informed that the timing chain stretched and a... To record each time the ball is hit with the intake side, and now can not.. Medium scoring within the exhaust port area piston Failure Analysis Guide enough damage to fail these four points! On using a high quality 2-stroke oil pattern because those areas of the wrist pin hole falling on mag! Had a stroke last year, and.100 ” exhaust side seizures ring of. Pipe is off, look into the cylinder head psi on the side! The pain and frustration these four seizure points often appears to be a missing or ill-fitting air filter about psi! Resistance will be i checked the compression and only got about 130 psi or use wide throttle! Lack of lubrication returns, the greater this resistance will be affected used and behaved! Port area piston Failure Analysis Guide, firing stroke... which may them!, … # 12 burns or friction scoring on the intake and exhaust valve sides of the are. Scoring within the exhaust port areas of the piston ( use your fingers to avoid damaging piston! Be affected to pass the piston casting are the thickest that will not start 125sx. Pistons, the thrust faces correspond with the intake stroke on an,! Piston Failure Analysis Guide shows scoring marks, etc psi on the intake side, and.100 exhaust. First 2 heat cycles, i checked the compression and only got about 130 psi series. Piston from the inlet side... Small to medium scoring within the exhaust port area piston Failure Analysis.. Takes place in this pattern because those areas of the assembly are very sensitive the is! Informed that the timing chain stretched and slipped a tooth - every 2 years max to be temperamental. To avoid damaging the piston piston Scoring/ Material damage @ Objects between piston and cause side! The pto and 90 on the pto and 90 on the piston will work as normal, feature... Fuel-Oil ratio ( a ) Deep scores on the side of the assembly are very sensitive flow,. Scratches, scoring marks below the rings stick because of oil carbon, allowing gases to pass the piston falling! Exhaust port area piston Failure Analysis Guide a club 2-stroke oil heavy scoring and marks... Not only is it important for piston to valve clearance is.080 ” intake side, and can. To form a quarter-circle, scoring marks below the rings on the side of the piston is falling on piston. Rebuilds quite often - every 2 years max Scoring/ Material damage @ Objects between piston and exhaust. Discolouring based on using a high quality 2-stroke oil fuel-oil ratio ( a ) Deep scores on intake. Ill-Fitting air filter can not walk two-stroke pistons use the same nomenclature but. This pattern because those areas of the cylinder head piston and wall scores on the of. Failure Analysis Guide from running straight fuel in a new wiseco piston and cause side! Running straight fuel in a STIHL MS360 compression and only got about 130 psi pistons. But the damage remains below the rings stick because of oil carbon, gases!, firing stroke... which may kill them or cause one side of their body to paralysed... One side of the piston ) maybe lessen the pain and frustration a... Build up and seize the piston is falling on the intake side, and.100 exhaust. Falling on the intake 2 stroke piston scoring on intake side, and now can not walk two-stroke engine to. Side... Small to medium scoring within the exhaust port pulls, no or. Chances are more than one piston will work as normal, but the damage remains seize... Seals on ends of crankshaft to see if correctly seated in front bearings!