Not legal 1 class
Two-stroke internal modification of any kind is prohibited.
IJSBA · Engine
Aftermarket cylinder (2-stroke)
IJSBA answers this part for 12 of its classes. 9 of those answers are permissions, with or without limits attached, and 3 are not.
Where it stands, class by class
12 classes, grouped by the answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules.
Not legal 1 class
RAS.4.4
- Runabout Stock · RAS
OEM part required 1 class
CYLINDER MUST REMAIN OEM with original port timing. No internal modification of any kind. · VSKL.3.1, VSKL.3.5
Legal, within limits 1 class
Aftermarket cylinder SLEEVE only, retaining the same port sizes and specifications as OEM, and permitted only where displacement is more than 10% below the 850cc maximum. Cylinder interchange between homologated craft of the same manufacturer is allowed subject to IJSBA restrictions. · SKL.3.12
Legal, within limits 1 class
Yamaha Waveblaster may upgrade to 701 62T-style cylinders; Yamaha 760 cylinders allowed subject to ignition restrictions; pre-1996 Yamaha may update to 1996+ components. Max 1mm overbore across the board.
- Sport Spec · none - this document uses ALL-CAPS section headings, not numbered rules
Legal, within limits 1 class
Machining cylinders for girdle-system heads allowed. · RAL.4.1
Legal, within limits 1 class
Cylinders may be interchanged between same-manufacturer homologated craft; ports may be added, deleted or reshaped; BUT two-stroke cylinder or crankcase MODIFICATIONS require written IJSBA approval. · SPGP.5.5
Legal 2 classes
Explicitly permitted by this class document.
- Vintage SC · VSC
- Vintage X2 · VX2
Legal 1 class
VSK.3.3
- Vintage Ski · VSK
Legal 1 class
FREST.3.3
- Freestyle · FREST
Legal 1 class
Modified or aftermarket cylinder and cylinder head - effectively unrestricted. · SKGP.3.3
Aftermarket cylinder (2-stroke): if the rule your class applies reads differently to you, or the rulebook has changed since this was read, ask. We answer with the section we read it from, or that we have not read it. Ask a rules question.
Every IJSBA class · where the rulebooks differ · signed checks on parts the shop sells.
Engine · two stroke · legal outright in 9 of 12