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Class Legality

UIM · Engine

Aftermarket cylinder head (2-stroke), UIM

UIM answers this part for 11 of its classes, and publishes no rule for it in 8 more. 2 of those answers permit the part outright and 0 permit it with stated conditions, leaving 9 that do not. 5 of the ones that do not are classes we read as open rather than as refusing it. 9 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 page is UIM only, and the bodies do not agree. The same part under IHRA and IJSBA. Which one applies to you is decided by whoever sanctions the race you enter.

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

Not permitted, not listed in the rules
Treat it as coming off. The class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list, so this is our reading rather than a rule we can quote at you.
Legal
Keep it. The rules permit this part in this class.
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.

Not permitted, not listed in the rules 3 classes

Ski GP3 lists replacement gaskets and interchangeable cylinders but no cylinder head allowance, and bars internal work on any engine component, so the original head stays. · 501.02.03.02, 501.02.03.06

Not permitted, not listed in the rules 1 class

Not listed in this class. Illegal under the class's own stock clause.

Aftermarket cylinder head (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.

Engine · two stroke · legal in 2 of 11 answered

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