there seem to be 4 versions of that engine
18TZ SERIES INSTRUCTIONS
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This manual handles the following four versions.
18TZ-T with 11L carburetor
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18TZ(S)-T with 11L carburetor
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18TZ-TX with 11L carburetor
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18TZ(P)-T with 11K carburetor
exploded diagrams with part numbers are here...
Nope, never done that
I did see cranks on eBay. I think you have to change the backplate too.
I am no expert on nitro engine workings though. I just run them.