4/7/2023 0 Comments Flowstate muscle club![]() The size difference isn’t much, but if the piston heats up too quickly, it will expand faster and get too big to properly fit in the cylinder bore, thus creating scoring, and possibly a “cold seizure”. This clearance is for “growth”, because it will get bigger as it heats up. A lot of top-end damage is done if you start your bike and immediately ride it hard or rev it without giving it enough time to warm up.Ī piston has a certain amount of clearance between it and the cylinder wall. It makes me cringe when people try to warm up their dirt bike too quickly, and I see it quite often. Scoring is caused by metal to metal contact, which is common on 2-strokes when they aren’t warmed up properly. A lack of lubrication from not enough 2-stroke oil in the gas or lean jetting can damage the piston and cylinder, as well as the crank assembly and bearings. The cylinder was used again because it was surprisingly still in good shape! Here’s some more causes of a fouled plug.Ī scored piston or cylinder can be caused by multiple things. It turned out that the piston was cracked and it eventually just lost compression. I have personally seen a CR80 that fouled plugs because of a bad top-end. This definitely indicates a new top-end is required, as well as a new spark plug. If the jetting is right, a fouled spark plug can also be caused by a bad top-end or blow-by from the worn piston/ring/cylinder. How often are you replacing the spark plug? If you have to put a new one in every ride, stop and inspect before riding again. A 2-stroke piston can last over a hundred hours if the bike was casually ridden and properly maintained, but an aggressive motocross racer can wear out a top-end in less than 20 hours of ride time. This often happens after a top-end has so many hours on it, and will get worse/less powerful over time. Noticeable loss of powerĭoes your dirt bike feel like it lost its power-band(sarcasm)? A worn piston/ring will make the engine feel weak and low on power even when WOT (wide open throttle). For more info on a ‘no-start’, read this article on Diagnosing A No-Start. On the flip side, just because your bike takes forever to start doesn’t always indicate a worn top-end. ![]() Certain bikes require more muscle and/or technique to get started, but a solid running engine will only take 1-3 kicks to start, hot or cold. Unless you are riding in extreme climate, your bike shouldn’t take more than a few kicks to get started. This is a common symptom for both two and four stroke dirt bikes. Although, if none of the symptoms relate to your bike, there’s a good chance it won’t need a rebuild yet… It Takes 50 Kicks To Start My Bike… If you have most or all of the symptoms listed below, you can count on replacing at least the piston and ring, and possibly a cylinder and head. However, before tearing your engine apart, there’s several signs that can tell you it has a worn top-end. A top-end rebuild is pretty easy to do on a two stroke engine, and the only special tool you’ll need is a torque wrench for most dirt bikes. If you buy or put a lot of hours on a 2-stroke motocross bike, chances are it will need the top-end replaced. J5 Signs Your 2-Stroke Dirtbike or ATV Needs A New Top-end Rebuild
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