By Malc Pinnock

Although I am new to published engine testing, I have had a very great interest in the model engine for the last 35 years. From the very early “vintage” sparkers and diesels, through glows, to what’s on the market today. And how they have developed.

I have always enjoyed taking them apart to see what makes them tick, buzz or scream. So, when Graham Ashby, RCME Editor, asked me if I would like to try some testing, I readily agreed.

I will try and explain to the average modeller what he would like to know e.g. cost power output; quality of construction; noise, which is very important nowadays; is it easy to start; set up; run and does it hold its tune etc.

All engines will be hand started when possible or if the makers recommend the electric boot e.g. engines with very small props or some 4 strokes. Right, enough blurb, let’s get testing.

Leo Engines

Leo, a new name to the U.K., imported by the good folk at Just Engines, Paul and Jenny Landels. Made in Taiwan, R.O. China, and sold as budget engines but with a good design heritage, the Leo factory is owned by the nephew of the owner of Thunder Tiger – who employ a designer who used to work for O.S. This can be seen just by looking at the engines, before even taking them apart. Some O.S. parts are usable straight swops for Leo parts.

Leos come in good quality boxes with a tool kit comprising 2 double-ended spanners and 2 allen keys. A standard silencer but options are available, from duel cone to tuned pipes etc. You get a fireball plug but this may vary and very comprehensive instructions written by Just Engines which, if followed, will make life easier and your engine life longer. There is also an excellent colour brochure on further products in the Leo range, from pull starts, mufflers, carbs to electric ignitions. Engines in aero, marine, car and petrol from 12 to 61 in size. Right, nitty, gritty over, let’s have a look at the engine and see what we found.

The Crankcase and Backplate

The crankcase and backplate are both die cast from good quality aluminium alloy. The castings are of very good quality, much higher than the words ‘budget engine’ suggests. Overall the appearance is O.S. 46 SF. but with the maker’s name, Leo, on the transfer side of the case and the size 46 cast in just below the exhaust. The machining is also to a high standard, good and crisp with no tearing to the surfaces. There is a small location peg pressed into the top of the case for liner position, which is a good detail and makes for easy and correct positioning of the liner.

The case has been cast and drilled for two through bolts for silencer mounting, same spacing as O.S. so a large range of pipe silencer options are readily available off the shelf. Carb mounting to case is by the cinch bar method which I prefer to the twin or single grub screw type. The case is fitted with twin ball races which feel very smooth and of good quality. The front one is of the single sealed type, the seal being to the front external part of the case.

The backplate is a good fit to the case and of the four bolt fixing type and is sealed with a plastic gasket. it also has a cast in tower which could be drilled and tapped to fit a crankcase pressure nipple.

Cylinder Head & Crankshaft

Once again, good quality die casting is apparent in the head with machine finished sides and tapered finning, held down to the crankcase by 6 M3 allen bolts. It is fitted with an alloy gasket and has a squish band of some 4mm with a deep bowl combustion chamber and is tapped for the usual long reach plug.

The crankshaft is machined from one piece of steel, hardened and finished by grinding. Side by side, nearly identical to O.S. 46 SF: 10.6mm gas passage, 15mm mainshaft, stepping down to 9.5mm for the front bearing, then down again for the prop shaft which has a UNF ¼-28 thread. Overall, once again to a high quality standard and finish.

Liner, Piston & Conrod

The liner is of machined brass and plated internally with hard chrome. It has a good sliding fit into the crankcase and is located in position by a slot cut into the lip of the liner and the pressed in pin in the crankcase, for easy and correct positioning of the liner. The liner is of the Schneurle port type, two large slotted boost ports, one each side of the large bridged exhaust port and a large angled transfer port at the rear of the liner.

The piston is of high content silicon alloy which is cast. it has a large web each side to support the fully floating hollow steel gudgeon pin which is located with wire circlips at both ends. it is machined at the bottom to clear the transfer ports and to reduce friction. It also has an oil retention groove 1.5mm below the flat piston crown. Even after 5 hours running, it has a very tight fit in the liner which was a 0.52mm taper.

The connecting rod is again of high quality alloy, machine finished and bushed at both ends with twin oil ingress holes for the big end.

Prop driver is machined from alloy barstock with a dirt shroud for the front bearing and well cut prop driver teeth. It is held onto the crankshaft with a split brass tapered collet once the UNF ¼-28 is tightened. It also has a machined chromed prop washer.

Carb & Silencers

Die cast alloy body with 8.5mm choke. Ground steel barrel, twin needle type. All fixtures and fittings, including extended throttle arm, are steel. The carb is fully sealed with ether. ‘O’ rings and fibre washers and a very good fuel needle with tight fine ratchet adjustment. Easy to tune in and once tuned, held its settings.

Two types of silencer were supplied with the engine. One standard duel cone which in the test proved quieter than the extended duel cone but also limited the RPM output by some 200RPM across the prop range. Both die cast alloy with a central through bolt and internal steel cone. Both types have offset exhaust outlets which you can adjust to your liking.

The Running Test

Firmly mounted in the test stand, tank filled with Flair yellow Spot 5% Nitro and following the Just Engines running in guide. The engine felt too tight for hand starting on a 10x6 so I put on an 11x6 ram. Primed as per instructions, glow clip on ¼ throttle, six flicks and engine was running. After the first tank (6 oz), the engine was allowed to cool. 10x6 ram prop now fitted, engine primed, second flick running. Third, fourth, fifth and sixth tanks of fuel, gradually leaning out and opening throttle. First and second flick starting all the time. Hot or cold, no problem.

The tests were carried out after 1½ hours running in. All in, the testing and running period period took 5 hours and the liner piston fit was still a little tight suggesting there is still an improvement over the published report to come.

Summary

The Leo 46 EP ABC is of good all round quality. Had I not been told it was a budget engine, I would not have known. On strip down, there was no wear whatsoever, even after 6 hours running. The honing marks were still evident in the bore and the usual black ring around the piston was not evident. It offered excellent throttle response on all props with a very good reliable tick over. My opinion: money well spent.

Test Results

Engine: Leo 46 EP ABC
Configuration: Aluminium Piston, Chrome Plated Brass Liner. Front Induction, Side Exhaust
Capacity: 7.45cc
Bore: 22.00mm
Stroke: 19.60mm
Weight: 342 grams
Stated Power: 1.43 BHP @ 16000 RPM
Shaft Thread: UNF ¼-28
Fuel Recommended: Good Quality 2½% to 5% Nitro

PROP PERFORMANCE QUIET SILENCER
10x6 Radio Active Ram 13900 RPM Idle 2400 RPM
10x7 Ram 13600 RPM
11x6 Ram 12600 RPM
11x7 Ram 11600 RPM
12x6 Ram 10700 RPM
13x6 Black Master 8200 RPM

PROP PERFORMANCE EXTENDED DUEL CONE
10x6 Radio Active Ram 14200 RPM Idle 2400 RPM
10x7 Ram 13900 RPM
11x6 Ram 13100 RPM
11x7 Ram 12300 RPM
12x6 Ram 10900 RPM
13x6 Black Master 8400 RPM

Fuel used in tests: Flair Yellow Spot 5% Nitro.

Decibel range, STD Silencer 79 to 82 at 7 meters
Decibel range, Duel Cone Extended 76 to 83 at 7 meters

Extreme RPM test, open exhaust 8x6 Ram, 17400 RPM

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