A top-end rebuild is routine maintenance on a two-stroke. Do it on time and the Banshee rewards you with crisp power and reliability. Leave it too long and a worn piston can take the cylinder with it, sometimes the whole engine.
Signs your top end is due
- Compression has dropped, or the two cylinders read noticeably differently.
- The machine is harder to start and has lost bottom-end snap.
- You can hear piston slap, especially when the engine is cold.
- The service interval for your build has passed. Big-bore and high-compression engines need attention sooner.
Measure before you buy parts
Pull the cylinders and measure before ordering. The bore size and condition decide whether you need standard pistons, oversize pistons or cylinder work.
- Bore diameterMeasure at several heights and angles to check for taper and out-of-round.
- Piston-to-wallCompare against the spec for your piston brand.
- Ring end gapCheck new rings in the bore before final assembly.
- Cylinder wallsLook for scoring, plating damage or deep scratches.
Hone, bore or sleeve?
If the bore is within spec and only lightly glazed, a hone and new rings may be enough. If it is worn or scored, a machine shop can bore it to the next oversize. Cylinders that are damaged or already at their largest oversize can be returned to service with a cylinder sleeve kit.
The parts checklist
- Pistons, stock bore or matched oversize, one per cylinder
- Piston rings
- Wrist pins, clips and small-end needle bearings
- Base gaskets and head gaskets or O-rings
- Exhaust gaskets and any worn intake boots
- Cylinder studs and nuts if threads are damaged or you're changing heads
- Fresh premix oil, spark plugs and coolant
A complete top end kit is usually the simplest way to get everything in one order. If you're opening the bottom end too, see our engine rebuild kits.
Tell us your bore size and build and we'll help you pick the right top end kit.
Reassembly tips
- Clean every surface thoroughly and check the cylinders are square to the cases.
- Lubricate the pistons, rings and bearings with two-stroke oil during assembly.
- Torque the cylinder and head nuts in stages, in the sequence and to the values in your service manual or kit instructions.
- Pressure-test the crankcase if you can. It catches air leaks before they cost you an engine.
Break-in
Follow the break-in procedure for your pistons. Most involve several gentle heat cycles, letting the engine cool fully between them, then gradually varying load and RPM rather than holding a constant throttle. Re-check the head nut torque after the first heat cycles if your manual or kit calls for it.
Ready to start? Shop top end parts.
