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"A 2-stroke is more vulnarable to piston/cyl dammage than a 4-stroke due to thinner oil film and higher heat. -I found some light scoring all around the piston and cylinder wall as well as a few deeper grooves on the piston and through the piston rings, and deeper scoring, through the chrome, on the cylinder wall. I took it into the shop from where I bought it and they showed me the scored cylinder wall ... (91 or higher) mixed with the Stihl 2-stroke oil. As the piston expanded from the heat load, they scored cylinder walls in two cylinders. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day. An oversized sealing ring may cause improper positioning of the liner. If they don't end up being good well then atleast you can weigh the costs of having a machine shop rebuild it, or possibly find a used short/long block in good condition. The 2-Stroke High Speed Diesel engine concept was investigated in 1999 also by Yamaha, who built a 1000 cm 3, 2-Cylinder engine, with crank-case loop scavenging . I have a two cylinder with one burnt piston and cylinder wall. I have fine gray scotch brite and some very fine emery cloth that I cannott feel any abrasive on. Seems simple just … Trusted got a bad rap on that deal, but there is alot of behind the scenes crap that doesn't get aired too, keep in mind there are 3 sides to every story. ... because there is really only one cylinder with obvious 'scuffing,' cylinder 2. Cylinder 4 has a bit of imperfection if you look really, really close, but cylinders 1 and 3 look like the first picture I posted. ... but as a general rule, for a large bore engine a wear rate of 0.05mm/1000 hours is acceptable. Use a .020 or .030 feeler guage and see how it feels compared to your score in the cylinder. A piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine.. The walls don't have any scoring that can be detected with a finger nail. You should see the dial move from "zero" as you cross the score. When the oil film on a cylinder is momentarily burned or brushed away, the metal surfaces of the piston and the cylinder wall will actually touch. We measured the tops of all 6 cylinder walls with a set of calipers. The same goes for when you find your intake boot and airbox was not sealed properly. The damage you see was caused in the moments before the piston "stuck," which seized the engine. It happens becuase of two things: 1) too tight piston to cylinder clearance and b) too much heat too soon causes the piston to expand too fast into the cylinder wall. ... fine. With ever-tightening global engine emissions regulations, creating a cleaner-burning engine that doesn’t lose out on power is a motorcycle designer's most important quest. The lack of lubrication on the piston has caused it to seize to the cylinder wall. The problem is that if you have a cylinder, glazed and tapered .005” and you use a rigid hone, by the time you have the wall de-glazed you have probably had to remove so much metal so as to make the cylinder unusable. If it's still within a few thousandths there, get some file fit rings and go to town. I had 1/2" of spark from both and plenty of fuel. For the uninitiated, in lieu of a four-stroke engine’s valvetrain, two-strokes use ports in the cylinder walls to transfer the air-fuel mixture into and the exhaust out of the combustion chamber. However, unlike most later two-stroke engines, his had a separate charging cylinder. Anytime you find leaks, you’ll want to tear down and inspect for damage. That is why it is called a cold stick. I am being told to replace one piston with an oversize after Boring the one cylinder wall to .020 over (Hopefully that is all that will be required). If your cylinder walls turn out to be good, you could just rering it and throw it together with new bearings and gaskets. The main functions of piston rings in engines are: Sealing the combustion chamber so that there is minimal loss of gases to the crank case. Seizure and scoring are two different stages of the same problem. A damaged cylinder may need reconditioning or replating. History. Above are just my thoughts. When over-boring, the piston for that cylinder should be given to the machinist. The tension of the piston rings could be lost because of overheating, and so the problem of … This gauge reads .0002-inches (two ten-thousandths of an inch), which is commonly referred to as “two-tenths.” That is 15-times thinner than the average human hair! When this happens, there is a sort of scraping that takes place between them. ; Improving heat transfer from the piston to the cylinder wall. I have read about deglazing cylinder walls with green scotch brite. It’s recognised as a championship-winning formula and is delivering success in most forms of high-performance motorsport including F1 … improper fillet, grind it down until the lower surface of the flange seats properly on the mating surface of the cylinder deck.