Hello new here maybe you guy's have already dealt with this issue on the hk500 models
I have both the hk t500 and the hk500gt classs helis and have come across numerouse problems to over come .
Remember both these helis say trex compatible

Well not so the hkt500 main shaft is not but the gt is how strange is that ?
I have changed on the hkt500 main gear tail drive gear the rotor head the tail gear box
the only thing left on this heli that is hk is the main frame every thing else is either Align or copterx finnaly flys decent sport only so far

Well ok now for the hk500gt it also is a basket case so far in needing replacement
just a list, main bearings, oneway bearing, canopy bolts knight head bars, or tail support bars as each bar is in three peaces but did some checking and the heli is actualy interchangeble with align I am currently building the hk500gt thought I would share in the build

Also ran into similar problems with the hk250gt and it has been changed to all align parts

Sorry dont have a hk 450 but do have numerouse other brands of 450's

hope this info helps

ps I know this string was about 450s but there is someone building a 500 so thought would share