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Dated: 20 May 2010

There was a time when the only engines anyone would really consider for their .40-class glow-powered models was an OS.

There were a long line of popular and reliable OS engines including the FP series, the FSR, the SF and so on.

There was a bit of a hiccup when the OS46FX first appeared, with many engines suffering from peeled liners and a lot of unhappy customers swearing never to buy another OS engine as a result -- but today's OS engines are as reliable and powerful as ever.

But this isn't a review of an OS engine, it's a review of the current .52 cubic inch (8.5cc) 2-stroke engine from Sanye.

A lot of people reading this review will never have heard of Sanye, but chances are you've seen their products many times before. The engines made by Sanye are sold under a growing number of names, including ASP, Magnum, Super Custom and others.

The engine I'm reviewing here is the ASP.52 2-stroke but, for all intents and purposes, it's the same as the Magnum.52.


First Look

The test engine was purchased from Hobby King and cost little more than $50 which is an absolute steal when compared to the price that you'll pay for an OS or even a Thunder Tiger .40-class ball-raced engine these days.

Like most other brands, it comes in a cardboard box containing plenty of padding and various parts of the engine (muffler, carburetor, engine) in separate bags.

Although an instruction sheet is supplied, it makes no mention of how to assemble these parts, which is a shame because there are some traps novices that really ought to be covered (I'll tell you about those later).

The instruction sheet that is included is a generic one that seems to be designed to cover the entire range of Sanye engines, right from their 1cc 2-stroke through to the monster 64cc 5-cylinder radial.

For a Chinese-made document it contains pretty good English, although I noted with a grin this extract: "NEVER ALTER, REPAIR, BENO, OR SHAVE A PROPELLER." How on earth do you BENO a propeller I wonder?


Design and quality of construction


Like most modern glowplug engines, the ASP has nicely finished pressure die-castings which show no signs of porosity or other flaws. Likewise, the machining appears to be done to a high standard and finish.

The crankcase, cylinder head, backplate, carburetor body and two parts of the muffler are all cast from aluminum.

The cylinder sleeve is chrome-plated brass, meaning this is a true ABC engine, a design choice that is technically superior to the nickel-over-brass used by OS, Thunder Tiger and some other manufacturers. Because of the overbored nature of this engine, the liner itself is quite thin, which leaves little potential for quick hop-ups by way of some port-grinding. However, as you'll see, it's more than powerful enough without the need for such modifications.

The crankshaft is steel with the usual diameter (for a .40-class engine) and appears to be well made. It is supported on two industry-standard sized bearings (6902 and R8) but the bearings provided seem to be of relatively low quality. I find it strange that these days, even "quality" brands such as Saito and OS tend to skimp on the quality of bearings used in their engines -- ASP is not alone in their cost-cutting here.

The connecting rod is machined aluminum with a phosphor-bronze bushing on the crankpin journal. I don't know if the wrist-pin is also bushed, it didn't seem worth dismantling the engine to that extent to find out. I've never heard of any modern 2-stroke engines suffering wrist-pin failure and this is (after all) just a $50 engine.

The carburetor is the biggest disappointment of this engine. It is a two-needle type with the conventional rotating barrel and auto-mixture control. However, the main needlevalve is a very sloppy fit and despite having two O-rings to try and maintain a good seal, it is prone to air-leaks. What's more, the small spring-loaded arm designed to stop the needle from rotating with vibration is not always strong enough.

The carburetor is attached to the engine by way of two cap-head screws that are threaded into the carb spigot. Personally I dislike this method of carb attachment as it is also prone to allowing air-leaks and requires *very* careful tightening of the retaining bolts. Too loose and they'll vibrate right out. Too tight and the threads in the cast aluminum carby will strip -- whereupon the bolts will still fall out. Two tiny spring washers are provided to assist -- but, given the lack of suitable instructions, I fear that some owners will mistakenly use these on the muffler bolts instead.

I really recommend a little blue (low-strength) thread-locker on the carby retaining bolts and a "gentle but firm" hand when tightening them.


I presently have three ASP52 engines, the oldest of which has already clocked up about 50 hours of running and the newest of which is the subject of this review.

The ASP52 comes with a lot of ABC pinch, which is good.

For those unfamiliar with the term "ABC pinch", it refers to the fact that the engine can be almost impossible to turn over when brand new -- the piston appears to stick in the bore as if it's too big. That's because it is too big!

ABC engines are designed with a taper to the bore which means, when they're new and cold, the piston will tend to stick as it moves towards top-dead-center (TDC). This is particularly noticeable if you try to turn the engine over slowly -- which is something I don't advise.

A brand-new ABC engine should not be turned over slowly by and unnecessarily, that's because as the piston/bore clearance reduces near the top of the stroke, the protective oil film can be displaced and the result may be a squeaking noise caused by metal-to-metal contact. The amount of force required to turn the engine slowly like this can also place undue strain on the connecting rod, crankpin and wrist pin.


Some tips for running the ASP 52


Tip 1: ASP engines don't come with a glowplug so you'll have to provide your own with the .52 and here's a useful tip... Don't use a brand new glowplug to break in a brand new engine.

During the break-in process, very fine particles of metal are often polished-off the various moving parts and those bits of metal will tend to stick to the glowplug coil, effectively contaminating it and making it "colder". If you use a brand new plug, for the first few runs, you'll significantly shorten its life and be wasting money. It's much more sensible to use an old plug for the first few runs, then put a new plug in once the engine has got a few minutes running on it.

Tip 2: is to leave out the blue paper gasket that is designed to fit between the muffler and the engine's exhaust stack. The machine-finish of these two surfaces is more than good enough to prevent leakage and because the gaskets tend to compress over time they can often result in loose muffler screws and even a lost muffler if you're not careful.

Tip 3: the 3-part muffler provided with the ASP 52 is notorious for leaking where the various sections join. To avoid this, and the rotation of the rear section with where the exhaust and oil actually exit the muffler, pull the muffler apart and apply a thin layer of red-silicon along the mating edges of the three parts before reassembling. This will stop the various sections from rotating with vibration and eliminate any leakage of oil or exhaust from between those sections.

Tip 4: if you are attempting to run the engine for the first time in a very cold climate you may find the ABC pinch is simply too tight for the engine to be turned over properly. In such cases you can pre-heat the cylinder/head of the engine using either an electric heat-gun or (cautiously) with a propane torch, until it can be flipped more freely by hand or spun with your electric starter.


Starting and Tuning


The test engine was assembled (as per the tips above) and started easily, both by hand and with the electric starter.

The main needle was (as earlier noted) a rather sloppy fit in the carburetor but adjustment was easy. The low-end needle was very sensitive and required adjustment just 1/32 of a turn at a time to get a good idle setting.

The engine was run on my standard fuel, containing 5% nitromethane and 15% Aerosave oil and, after just a few minutes running, had freed up nicely -- holding a slightly rich-of-peak needle setting without any signs of overheating.


Power and Performance


There can be no doubt that this is one of the most powerful engines in its class.

As seen at the top of this page, it happily turns a 10x7 prop at almost 14,500 RPM using fuel with just 5% nitro and it spins an APC 12x4 prop at only a few hundred RPMs less.

During flight testing when used on a low-wing World Models Skyraider, a 10x7 prop provided best performance -- offering excellent speed as well as unlimited vertical. The ASP52 was noticeably more powerful than a Thunder Tiger 46Pro or OS46AX in the same airframe.

Perhaps the weakest aspect of this engine is its throttling characteristics.

Although it responds well to throttle most of the time, it still has a tendency to load-up if idled for more than 20-30 seconds or held at a mid-range throttle setting for too long. No amount of tuning would completely eliminate this behavior, although switching to a hotter OS-F plug from the OS#8 normally used did help a lot.

This sometimes stuttering mid-range/transition means that I wouldn't recommend the ASP52 for 3D flying, it's more of a "pedal to the metal" engine that likes to be given its head with slippery airframe and a small prop.

And here's a tip for those who want maximum performance from their ASP52 (or just about any .40-class motor actually). Throw the stock muffler away and fit a Tower muffler. This will give you an instant improvement of up to 1,000 RPMs for a one-time investment of about $15. I now run the Tower mufflers on all my .40-class engines and really notice the performance boost they give


Reliability and durability


During the 50 or so hours that my oldest ASP52 has been run, it has not been without problems -- although I should add that I fly my engines very hard.

The original bearings only lasted about 10 hours of running but the replacements show no signs of wear. It's not uncommon for a hi-reving engine to chew through bearings but the original bearings do seem to be of dubious quality right from the start.

The needle-valve on all my ASP52s continues to be an annoyance. It is such a loose fit that sometimes it vibrates open while in flight and causes the engine to go rich.

Bending the small ratchet arm can help but that can apply so much side-pressure to the needle that even the two O-rings can't stop the engine from then sucking air past the needle and causing erratic running. In the end I've had to put heatshrink tubing over the whole thing -- which seems to have sorted it. I did try using silicon fuel tubing but that wasn't a complete cure.

Before I started using thread-locker I did lose one carb mounting bolt which vibrated out in the air and resulted in a dead-stick landing. After replacing that bolt, the other one actually broke about 3/16 from the end and part of it screwed its way right into the engine's intake -- badly scoring the crankcase and creating a nasty burr on the crankshaft.

I figured that this engine would be toast but, after stripping it down, getting rid of the burr and tidying up (as best I could) the crankcase, I fired it up and it continues to run to this day -- albeit it's a few hundred RPMs down on the newer ones.

The ABC pinch has quickly disappeared on all my ASP52s, which may indicate a slightly soft piston alloy or perhaps that the liner is so think it has stretched slightly. By comparison, my Thunder Tiger 61GP (also ABC) never did lose its ABC pinch -- thanks to a thicker liner and harder piston. From this I would suggest that the ASP52 will last a reasonable time if treated properly but won't have anywhere near the longevity of some more expensive engines -- but hey, you can buy three ASP52s for the price of just one OS46 so who cares?




It's hard to knock a $50 engine that delivers almost as much power as OS's 55AX but costs barely a third as much.

This is a powerhouse of an engine, yet it's also very mild-mannered -- starting first-flip by hand or with the lightest touch of the electric starter if that's your preference.

If it weren't for the needle-valve issues and the problems I've had keeping the carby attached without losing or breaking bolts, this would be a five-star engine.

Unless you fly 3D - in which case it's just a 2-star engine, let down by its occasionally unpredictable response to the throttle. If ASP could fix that damned carburetor they'd really have a winner and I'd pay an extra $20 for the resulting engine because it would be "near perfect".

If you want an engine with lots of power, don't need a precise throttle response and are willing to take a few extra steps to sort out the "issues" then the ASP52 represents killer value for money.

If you're a novice, just looking for a good, reliable .40-class motor for your trainer, then I really do think that a Thunder Tiger Pro 46 or OS46AX might be a better choice -- simply because they will work with 100% reliability straight out of the box.


Permission to reproduce this article has been obtained from RC Model Reviews. 

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