UIM · Engine

Aftermarket cylinder (2-stroke), UIM

UIM answers this part for 11 of its classes, and publishes no rule for it in 8 more. 0 of those answers permit the part outright and 6 permit it with stated conditions, leaving 5 that do not. 5 of the ones that do not are classes we read as open rather than as refusing it. 5 are inferred from how the class is written rather than quoted from a rule naming this part. 5 are inherited from a parent class the rulebook points at.

---

This is one body's answer, not the sport's. You are bound by whichever body sanctions the event you enter. If you race more than one series, build to the stricter answer. The differences are set out in the rulebook comparison.

Where it stands, class by class

19 classes, grouped where the same rule gives the same answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules. 5 of them borrow another class’s rules and are marked below; for those, the link to the parent class is read from the categories table rather than stated in the rulebook. 8 publish no rule for this part and name no parent to borrow one from, and are grouped together at the end.

What each answer below means

Legal, with conditions

Keep it, but measure it: the rules permit this part only inside stated limits.

No rule, this is an open class

Probably keep it. The class carries no stock clause at all, so anything unlisted appears to be open. The rulebook does not say so in terms, and this is our reading rather than a permission anybody wrote down.

No rule published for this class

Unanswerable here. This class publishes no rule for the part and names no parent class to borrow one from, which is an absence in the rulebook and not a permission.

Legal, with conditions 3 classes

Cylinders may be interchanged between homologated watercraft of the SAME MANUFACTURER. Engines may be bored. No internal modification of any kind. · 501.02.03

• Ski Division GP3
• Ski Juniors GP3.2 · borrows another class
• Ski Juniors GP3.3 · borrows another class

Legal, with conditions 1 class

Bored; cylinders interchanged between homologated craft of the same manufacturer. · 502.02.03

• Runabout GP3

Legal, with conditions 1 class

Plus machining to accept girdle system cylinder heads. · 502.03.03

• Runabout GP2

Legal, with conditions 1 class

Cylinders may be machined to accept girdle-system cylinder heads. If OEM cylinders do not give displacement within 10% of the maximum allowable, an aftermarket cylinder SLEEVE may be used, keeping the same port sizes and specifications as the original OEM sleeve. · 501.03.03.14

• Ski Division GP2

No rule, this is an open class 5 classes

No article covering this part. Free under the open-list reading of GP1.

• Ski Division GP1 · 501.04
• Runabout GP1 · 502.04
• Runabout Veterans GP1 · 302.01.05 · borrows another class
• Ski Ladies GP1 · 314 · borrows another class
• Ski Veterans GP1 · 302.01.05 · borrows another class

No rule published for this class 8 classes

No component rules are published for this class and no single parent class is named, so this part cannot be answered for it. That is an absence in the rulebook, not a permission.

• Endurance · 317.03
• Freestyle Amateur · 312
• Freestyle Free · 312
• Jet Raid · 317.01
• Offshore · 317.02
• Parallel Slalom · 313
• Ski Future Electric (SFE) · 302.01
• UIM Hydro-Fly · 900

---

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 UIM class · where the rulebooks differ · checks on parts the shop sells · how this site reads a rulebook.