Hello Gentlemen! I see lots of you are from Australia, im making an assumption here but i can only imagine there arent lots of snowmobiling opportunities for many of you where you live.
anyway, I have been around sledding quite a bit in my life and have owned a number of them. From a Canadians perspective (who sleds regularly) the Yamaha 4 strokes are considered to be the most reliable sleds a guy can get. They arent popular in the rockies because of the sleds weight compared to the Skidoo etec/ arctic cat/ or polaris 2 strokes that are available- this is a sled weight issue not an engine issue. Anyway, out east where they dont do much powder riding and stick to trails the Yamys are super popular. It is not rare to see these sleds with over 30,000k on them. Hours wise this is 2000hrs + (the sidewinders and Apex's have hr meters in the gauge cluster for maintenance). The YG4 Apex is the NA 4cyl, the Yg3 NA is in the Nytro 3 cyl, and the Yg3 turbo (998t) is the sidewinder which yamaha is still producing in 2024. Notably the sidewinder (998t) is a fn beast. the internals are good to 400hp, aftermarket tunes bring the sleds to 300hp just on tuning but with injectors/turbo and fuel rail guys are pushing stock rotating assemblies beyond 300hp regularly.
For what its worth, from my perspective anyway, i wouldnt think twice about flying behind one at all, lots of guys in the states have been flying Gyros and LSA's for over a decade with the raven adapters when only the old RX1 bike motors (same as YG4 apex engine) were available and logged many hundreds of hours.
Some interesting resources for anyone interested in powering aircraft with the Yamaha, you should check out some of the following:
BD Turnkey engines
Steve Henry and Wild West Aircraft
Edge performance engines (Epex line)
Project Kitfox (youtube)
Eddie Sanches highlander (devil girl)
Skytrax gear boxes
GT gyro Raven PSRU's and adapters
Anyways gents take care, hope all is well in the land of Aus.
Mike.