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. Piston to cylinder bore clearance - checking. Piston failure analysis 1. 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. These are relatively “safe” values that apply to most any engine. 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 Check left and right oil seals on ends of crankshaft to see if correctly seated in front of bearings. Chances are more than one piston will be affected. Study 23 2 stroke flashcards from matthew t. on StudyBlue. The pattern of these four seizure points often appears to be a perfect square, hence the slang term "four corner". 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. I have a well used and well behaved 2 stroke 4.75 HP Lawn Boy Silver series that will not start. This is very uncommon and is caused by only one thing, loss of lubrication. 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).. 12. 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. Not good, I know. INSTALLING THE NEW PISTON RING 21. Remove the piston ring from the piston. The lack of lubrication on the piston has caused it to seize to the cylinder wall. 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. The oil pump can be deactivated. 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. If sufficient fuel flow returns, the piston will work as normal, but the damage remains. 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. 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,:$: The greater the load on an engine, the greater this resistance will be. Bad fuel-oil ratio (a) Deep scores on the piston. 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. 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. I slide the piston to the bottom of the barrel and can get a tight .006 gauge in, so I'm okay with that. The scoring takes place in this pattern because those areas of the piston casting are the thickest. 2 stroke engines require rebuilds quite often - every 2 years max. 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. a scoring unit used to record each time the ball is hit with the head of a club. At some point in the piston cycle, a momentary dry spot occurs where the metal rubs together. Has spark, cleaned exhaust, cleaned carb, new plug, new exhaust baffle plate and cover (old one was cracked and afraid of … 2001 mojave. As a piston is pushed down the cylinder on its power stroke, the piston will meet resistance as it tries to turn the crankshaft. normal discolouring based on using a high quality 2-stroke oil. 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. 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. New piston from the inlet side ... Small to medium scoring within the exhaust port area Piston Failure Analysis Guide. 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. 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. 5 - piston shows scoring marks below the rings on the intake side. That rubbing can cause burns or friction scoring on the side of the piston. 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 … ... fuel is squirted into the cylinder as the piston is falling on the intake stroke. Note that the ends of the piston ring (on each side of the gap) are milled to form a quarter-circle. On these pistons, the rings can't rotate. Two-stroke pistons use the same nomenclature, but feature much longer, more pronounced skirts. i took it home and i looked at it. Bought it off a friend of another user here and was informed that the timing chain stretched and slipped a tooth. Reed valves on a two-stroke engine tend to be somewhat temperamental, as the inner workings of the assembly are very sensitive. Install the piston ring. If your engine is a 2 stroke, mix to the proper fuel/oil ratio. The cause could be a missing or ill-fitting air filter. Piston skirt only plays a limited role in the sealing of the crank case chamber at a two-port design. 2 strokes kick butt. 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. compression stroke, firing stroke ... which may kill them or cause one side of their body to be paralysed. Incorrect oil (b, m) Excessive carbon deposit can build up and seize the piston. ... Cracks, Scratches, Scoring Marks, etc. However, I've seen this kind of scoring before on small 2 stoke pistons … #12. Possible Cause. found that it had 65 psi on the pto and 90 on the mag, … Piston Scoring/ Material Damage @ Objects between piston and wall. The usual rule of thumb for piston to valve clearance is .080” intake side, and .100” exhaust side. I put together a few photos (sorry about blurry)and tips to maybe lessen the pain and frustration. He had a stroke last year, and now cannot walk. Good luck, Peter If the parts are damaged or worn down, they can immediately impact the air/fuel mixture from the carburetor, which then damages engine performance. Gently pry the piston ring out of the groove in the piston (use your fingers to avoid damaging the piston). The piston above has severe scouring on the exhaust skirt with the heaviest damage on the clutch side of the piston. The engine I m showing here would do 120 psi with 2 pulls, no carb or use wide open throttle. After my first 2 heat cycles, I checked the compression and only got about 130 psi. Funny thing is the compression was still good! New to the forum, be easy on me. 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. If it wont do that look in the ex. 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. 5 Medium to deep scoring ... evident on the intake side of the piston starting at the lower section 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. This piston was seized on the intake side. Drain the oil tank - you can cut the tank and use it as a tool box. ... 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 Remove the piston ring. For reference, the thrust faces correspond with the intake and exhaust valve sides of the cylinder head. Damaged piston caused by lack of lubrication 2. Pistons - refit. All of this damage was caused from running straight fuel in a STIHL MS360. and intake ports for scoring or scuffed piston. While the pipe is off, look into the exhaust port. The rings stick because of oil carbon, allowing gases to pass the piston and cause exhaust side seizures. Nowadays, on four-stroke engines, the piston skirt is very short and limited to the major and minor thrust faces 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. 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