Motocross, Off-Road, Enduro Bikes Scheduled Maintenance Engine High-Performance Parts
Piston & Rings Maintenance:
Most modern two stroke / four stroke Motocross/Enduro motorcycles recommend piston and ring replacement at 15 hour or 5-6 race intervals. Just because the kick starter feels firm or it starts easy, it still may be time for maintenance.
Why do they suggest so often?
|50-125 CC 2-Stroke||15 Hours (Single Ring Piston)||7 Hour (Single Ring Piston)|
|175- 250 CC 2-Stroke (4-Stroke Piston||40 hours (Dual Ring Piston)||15 Hours (Dual Ring Pistons)|
|150F-250F cc 4-Stroke||40 Hours (Multi-Ring Piston)||15 Hours (Multi-ring Piston)|
|350F-450F cc 4-Stroke||60 hours (Multi-ring Piston)||20 Hours (Multi-Ring Piston)|
What will go wrong if you do not follow manufacturer's scheduled service intervals, to maintain your motor?
- Piston ring failure (score the cylinder)
- Damage the exhaust port area
- Damage power valves
- Damage cylinder plating
- Piston skirt can break and damage lower end of motor (crank Casse)
- Damage cylinder head
The rings edge start out with a slight bevel edge, it may look square, but it's not. See images below
Okay, a second reason why I piston wears out. Is the piston skirts collapse, what does that mean. The piston skirt starts out larger than the top of the Piston by a few thousand, and with the constant and up and down and the piston and rocking back and forth in the cylinder bore the skirts will eventually to collapse. If you allow this to go on for an excess time, the piston skirts will crack or break, and then you’ve got a big mess on your hands. The other thing that can happen on a 2-stroke the piston can damage the exhaust port and power valves. Now, what maybe a crankshaft, cylinder, and crankcases who knows what else will get destroyed. That all because you let the put off maintenance, replacing the piston, and rings.
Just Remember you piston travels up and down at about 200 per second..... WOW, I can't see that it's just a blur. Remember it's called maintenance, it should be to keep the motorcycle running at top performance. When you have a problem, like hard starting it's too late. The rule is to replace the piston when you're supposed too. It cost less to do a top end than repair the whole motor.
When it comes to the crankshaft the most important thing is to perform an inspection every time you do a top end. Now a crankshaft won’t last forever but many times on a well-maintained engine where the air filters are kept real clean. You can sometimes see a hundred and fifty to two hundred hours on a crankshaft. Now 200 hours will not happen on an 85cc crankshaft probably isn’t going to happen. So keep in mind the smaller the engine, the higher the RPMs, the more wear and tear the top & bottom.
Inspect the crankshaft with every top end replaced. Two Strokes you should also remove the ignition side cover, to look at crankshaft oil seal and check the crank for play at the bearing. Make sure there’s no sign of leakage behind that cover, it should stay dry. No play at the bearing. If you see oil that’s a sign you have a seal leaking or bearing play, that should be taken care of immediately. That seal can create an air leak and damage the motor. If the bearing has played, it will also damage the seal and cause an air leak.