Our usual recommendation to folks in the hobby is the get themselves a new engine for their helicopter. That said, there are some amongst you, for whom prospects of buying a used engine is not met with trepidation.
Introduction
So to begin, what follows presumes you are mechanically 'ept' (as opposed to inept). Like maybe you're just lacking experience. If this doesn't describe you accurately, consider surfing elsewhere rather than pissin' away your time with this.
What to get
If you're interested in expanding your hobby into other areas, and/or saving some money, then consider shopping for a used engine versus a new one.
Note; don't limit yourself to a 55HZ-H engine, or even the 50SX-H (-H means Hyper). And if it were me and I came across a 'deal', I'd look favorably on an even earlier generation OS MAX engine, their 50SX (the one immediately preceding the Hyper). This, because quite honestly, the non-Hyper has a slightly smaller carburetor bore, and large cast vs large anodized-head, but it's still plenty powerful and runs great.
And in further truth, I wouldn't turn my nose up at a good used OS MAX 46FX-HRING (15470). Especially if it were offered at a great price, but heads up; some early 46FX-H engines are crap! You have to know the difference.
Inside baseball
Some are crap? How do you tell the various 46FX-H engines apart? It's easy, the good ones have a piston ring the ones that are crap don't. Basically, because pistons are made of shiny aluminum and rings are made of soft cast iron, which is quite dark, it's rather easy to determine if you have a ringed engine in your hand . . . just look in the exhaust port at the top of the piston!
This next photo is what you're looking for, a dark ring near the top of the alloy piston.
So here's the backstory; the crappy 46FX-H engines date to early in the days of ABN metallurgy (aluminum piston running in a brass sleeve, which is nickle plated versus ABC, where the plating is chrome). ABN is cheaper than ABC, and these days works well but back then, what made the ABN engines crap is the nickle plating had a tendency to peel if the engine was run lean. That's not good. So OS quickly pivoted to a 2nd generation ringed-engine. And 'these' are good 'uns.
By the way, if you were to stumble upon an ASP brand 46 piston/sleeve assembly, which the Chinese made with true ABC when they cloned the OS 46, then I'd snap it up. Why? Simple, because these parts are a drop-in for the OS and when fitted in place of a ringed engine's components lets the 46 make the horsepower of a 50 on the cheap! But in all honesty, it would be sheer luck to find a new set because they've likely all been hoovered up over the years, but I digress.
Shocking talk
Are you surprised I'm suggesting the possibility of a used engine? Don't be, because as a club pilot who likes my helis to fly like real ones, I also know this about myself; because I'm not flying 3D, then I don't need big horsepower engines. So beginning from the 46FX-H, 'all' the OS small block heli engines have had the stones to let me perform the maneuvers I like to fly. Maybe you're the same. Is this sacrilege coming from the vendor of a helicopter? Nope, I'm as cheap as the next guy and because I've been futzing around with engines since Christ was a corporeal, I figure I can share a few tips and help you along.
That said, the allure of the highest horsepower is real even though it's only needed for certain 3D maneuvers - the video of Kyle performing 3D maneuvers was with a 50SX-H (not even a Hyper). Point being, that should be all the proof you need. That said, if your dream means those are the type maneuvers you want to perform, then by all means buy the most horsepower you can afford. Otherwise, buy smart.
Recapping; the huge benefit of this money saving approach is the existence of a large universe of used engines that will power your model to an acceptable level of performance. Ones, which are generally available very inexpensively.
That, and because it turns out 'any' of their small block engines has ample power to suit me, then I don't rule out any of the ringed OS small block heli-engines as a power source! Point being, in the words of the bard (Shakespeare), to thine own self be true. By this meaning, don't lie to yourself about 'needing' a $700 engine package if you're a duffer like the vast majority of pilots because if you want the big time rush of high acceleration climb outs, then there are better ways to go about it. More later.
Bottom line? If saving money appeals, then keep reading because we're going to detail how to refresh the engine. Best part is it's cheap and easy!
Bargain hunting
This next photo is of an engine I picked up for $50 at a swap meet in hopes it would just need bearings. Seller said it ran good when he stashed it. Told me he'd crashed his model and decided the damage was too extensive for repair, so after stripping it down, he'd bought himself a new model, plus a brand spanking new 55HZ. Exterior looked a bit gnarly and it was locked up solid from congealed oil, but after a week submerged in a sealed quart can full of kerosene, it came free easily enough with a bit of work.
Then once I took it apart, it cleaned up very nicely with just a used toothbrush, WD-40, and a well used green Scotchbrite pad, which I swiped from the kitchen. As for just needing bearings, I was right. They were both rough (notchy) feeling. Otherwise, exhibiting good compression, no additional parts - yippee!
So as deals go, this one was pretty decent . . . and a far cry from $400.
On buying bearings
Engine bearings aren't very expensive. I've seen replacement bearings kits (both bearings) on eBay priced at $13 – yes, for the pair! Point being; everyone values their time differently, but I prefer to do things right the first time.
By this meaning if I have an engine apart, even if the front bearing feels good and only the rear bearing feels rough, I nevertheless do both while I have the engine component parts in my hands. True, if for no other reason than because I'd kick myself if I had to pull the engine out of the heli and tear it down again later in the season.
Note; the classic 'tell' if you don't have the engine in your hands where you can remove the glow plug ad rotate the engine freely by hand is it begins to idle like crap. And the usual reason bearings go south is folk neglect to add a bit of after run oil down the intake at the end of the day.
The actual how-to regarding adding a bit of light machine oil is trivially simple. Assuming your engine is fitted with an open mesh foam air filter element, then use a syringe fitted with a large bore needle and push 1-2cc into the carb throat. Then turn the engine over with the starter for a few seconds to distribute internally, and call it done. And if you're stupid and your engine doesn't have the air filter, then a few drops of 3-in-1 at the carb opening does the same thing.
Anyway, this used engine in the above photo powers one of my models to this day. Until now, because I've never mentioned it to anybody, folks don't realize I'm actually something of a thrifty fellow!
For more info regarding engine repairs and carb troubleshooting, review these brief articles . . . they're free!
https://audacitymodels.com/propulsion/engine-repairs
https://audacitymodels.com/propulsion/carb-troubleshooting
