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Your Reviewer

My Credentials
So who's doing this reviewing then?

Well I've been building and flying or driving radio controlled models for over 40 years and during that time I like to think I've built up a reasonable amount of knowledge.

I'm also a qualified electronics engineer who has worked in radio frequency, analog, digital systems and software for more than three decades. In fact I designed and built my first RC set back in 1969.

For the past nine years I've also been involved in the design and manufacture of some rather sophisticated engine technology and UAV flight control systems.

So, chances are I've been there, done that and have a huge pile of tee shirts to prove it.

Right now I'm heavily into 3D flying and enjoy all aspects of the RC hobby. I may be old but I don't feel it.

In the Pipeline

Here's just a little bit of what's to come on this site...

RC explained: Demystifying terms such as PCM, PPM dual conversion, single conversion, full-range etc., this feature will explain it all.

Cheap Chinese Engines: Just how good are those cheap Chinese glow and gas engines that sell for half the price of their "brand-name" equivalent? I put several to the test.

Build your own radio gear?: Back in the old days, building your own RC gear was not uncommon and now the arrival of 2.4GHz has made it practical again.


Review: ASP52 glow/nitro engine


ASP 52 aka Magnum 52 engine

Dated: 20 May 2010

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 hand 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.

Update (17 July 2010): I have tried the new OS#7 plug in this engine and it makes a world of difference. Although still not as smooth as an OS or Thunder-Tiger, the ASP52 with a #7 plug has a much improved mid-range and transition. It looks as if OS's claims in respect to this plug are true.

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.

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