Malc Pinnock
(RCM&E December 2004)

At long last an engine with a bit of muscle and one that I am very familiar with, the Fuji BT 50 petrol engine.

Not a new engine on the market but one that has been available from Just Engines for about three years. Fuji offer a range of easy to use petrol engines in sizes of 32cc, 50cc and 64cc in single cylinder format, and a very nice 86cc twin and all are at very affordable prices.

Standard versions of these engines come equipped with a magneto for supplying the sparks, and Seiji Tanabe's ATM [automatic timing module] that makes starting easier and safer as it advances and retards the ignition for optimum timing throughout the RPM range, unlike most magneto equipped engines that have fixed timing and require a hard belt of the prop to avoid being bitten.

With the BT50 came a pack of Fuji's new electronic ignition for me to try out and evaluate, Complete with Japanese style English instructions and full engine fitting kit, except the ignition switch/wiring harness and battery that you have to supply. Is it worth it, does it improve the engine, is it easy to fit, [and most important can I fit it] read on as we strip the engine and run both versions magneto with ATM and the fully electronic version, and then all will be revealed.

Where to Start

First off lets remove the machined alloy prop driving shaft, steel prop retention bolt and alloy prop washer. Just Engines can supply various lengths of prop driving shaft to suit your models requirements. The prop driver is fastened to the magneto with 3xM5 allen capped bolts and lock washers, now the prop driver has been removed its time to remove the ATM and its alloy mounting bracket. The ATM is retained on its alloy mounting bracket by 2xM4 allen bolts and is fitted with tubular alloy spacers, and once these are removed the 3xM4 bolts that retain the alloy bracket to the engine can then be removed.

When reassembling the Fuji care must be taken to set the air gap between the ATM sensor points and the Mag, these are set at 0.010-0.015thou. If these gaps are set to tight, damage will be caused to the Mag so please use the correct feeler gauge [not a fag packet] as the gap will not be correct.

Now the ATMs on the bench its time to remove the Mag, How's this carried out? Read on.
Fuji suggest the use of a special holding tool for the Mag. As the retaining 12mm crank shaft nut is torqued to 300kg.cm, once the nut has been removed I suggest the use of a puller to remove the Mag as it is a very tight fit on its woodruff keyed tapered shaft, and this now leads us on to the silencer.

Silencer

Next part for removal is the simple pressed steel box type silencer, this is a simple device made from 2 steel pressings for the box and a single steel pipe outlet, the silencer is retained to the cylinder by 2xM6 allen bolts that pass through steel tubes inside the silencer box. Sealing of the silencer to the cylinder is by a composite heat proof gasket.

Just Engines also offer a whole range of after market silencers pipes and manifolds for Fuji Engines, including the very popular Pitts type in its various different guises.

Carburettor and Fittings

Lets remove the Walbro carb next, this is retained to a heat proof bakelite type manifold by 2xM5 allen bolts and lock washers that pass through the carb body, the carb is sealed to the manifold by a paper gasket. But before we do this the rubber tube that provides the carb pumping pressure from the crankcase has to be removed this is retained a each end by a wire C clip, once these are removed simply pull off the pipe.

Now we come to the heat proof plastic spacer / carb adapter, once again retained be 2xM5 allen bolts and lock washers and sealed to the cylinder by a paper gasket. Carb and fittings now removed its round to the rear of the engine, to remove the 2 alloy engine mounting plates that are retained on the crankcase by 2xM5 counter sunk allen bolts, for each mounting plate.

We now have a bare engine, so its time for the proper strip.

Cylinder and Piston

When first viewing a Fuji the light blue finished cylinder is quite striking to the eye, very heavily finned with its Champion RCJ6Y spark plug canted over at a an angle at the top. Looking at it from the front the Walbro carb protrudes from the left hand side, with the silencer mounted on the right. OK, lets remove it.

A long shafted 5mm allen key will be required here for ease of removal, as the Fuji has had its cooling fins bored from the top to insert the key down through for access to the 4 retaining bolts. Once the bolts have been removed gently ease the one piece cylinder from the crank case taking care not to damage the paper sealing gasket and twin ringed alloy piston.

Now the cylinder has been removed lets see how it measures up.

A one piece alloy casting with piston porting, It has a single shaped induction port, with a large opposing rectangular exhaust port. Looking inside the liner it has two very large shaped and gas flowed transfer ports that lie to the front and rear of the engine, when assembled. Deep down inside the liner lies the cast in shaped combustion chamber, with its short reach spark plug protruding into the chamber. The cylinder bore or working surface is from hard chrome plated directly onto the alloy barrel, and even after some 2 years very hard use and a lot of experimenting with oils and mixes, my engine is showing no signs of wear.

That's the Barrel sorted, now lets have a look at the piston, this is from a permanent die cast in alloy, with machining to its outer wall and for the 2 steel pegged piston rings, at the top of the piston is a cast in arrow for directional fitting, this is important for port alignment as the piston has been machined at the bottom of its skirt at both sides, with the 2 [piston ports] so when fitting the arrow points towards the exhaust port.

The piston has been bored for its finely ground hollow steel gudgeon pin, caged roller small end bearing and spacers. The pin is a firm fit in the piston, so once the 2 retaining circlips were removed from their grooves a small amount of heat was applied to the piston, to enable easy removal of the gudgeon pin and not damage the piston.

Looking inside the piston there are two large webs that support the piston with an oil hole bored in each webb to lubricate the gudgeon pin, and that rounds up the liner / piston assembly, now lets split the crank case.

Crank case assembly

The 2 halves of the vertically split crankcase are fastened together by 4xM5 capped bolts and locking washers inserted from the front case. Once removed you will have to use a piece of wood and light mallet to split the cases [against the proper lugs cast on the cases please and no metal chisels or screwdrivers inserted between the case joints]. It is very important not to damage the crank case joints on a 2 stroke so take care when dismantling. The cases are sealed by a paper gasket and aligned by 2 steel pegs pressed onto the rear case half if dismantling its advisable to use new gaskets all round as leaks will cause a serious lack of performance or refusal of the engine to start.

Once the cases have been separated care must once again be taken so as not to damage the 2 rubber seals fitted to the crank cases, on reassembly please grease the seals before inserting the crankshaft.

Rear case first, this contains the 2 steel alignment pins mentioned earlier, and is fitted internally with a quality main ball race bearing. Externally at the rear we can see the caged rubber crankshaft seal and 4xM5 tapings for the 2 alloy engine mounting plates. Moving to the front case this also contains a similar ball race and seal to the rear case, and has 3xM4 tapings for the ATM mounting bracket. It has been bored tapped and fitted with a brass carb pressure nipple on its left hand side.

When both cases are put together and looking from above we can see the bottoms of the twin transfer passages cast into the cases that align with the porting in the cylinder barrel and just about rounds up the 2 very nicely cast crank case halves.

Crankshaft

Built like a brick out house best describes the BT50 crankshaft.

A 3 piece shaft comprising of, A front shaft and rear shaft from forged steel that has been finished by machining, and a hardened steel hollow crankpin, that has a very strong heavy duty forged steel conrod with caged roller main bearing, and caged roller small end bearing fitted to it, with all three parts of the shaft being carefully aligned and pressed together.

The rear part has a large heavy counter balanced flywheel that has been machined on its rear face, this supports a finely ground 15mm dia portion for the rear bearing and seal. The final part of 10mm dia. is for the Lilly livered amongst us who don't like hand starting, and would like to show off by fitting an optional on board electric or spring starter.

Moving forward we have the pressed in hardened steel 15mm big end pin, with its finely ground bearing surface and forward again a similar flywheel and first part of shaft as the rear this contains a steel spacing shim / thrust washer. In front of this the shaft steps down to 12mm and has been tapered and cut for the woodruff key, that either drives the magneto or electronic EIS ignition rotor.

The remaining portion of the shaft has been threaded for the M8 mag retaining nut and lock washer, and completes the shaft.

Walbro Carburettor

The Walbro carb fitted to the Fuji is the same diaphragm type as fitted to nearly every chainsaw, strimmer and small 2 stroke petrol mower so its well proven and reliable, Its also the choice for just about every model petrol engine on the market.

Fitted with twin needles that are clearly marked with an H for high speed and L for low speed running, very easy to operate and once the engine has been run in can be left untouched.
The carb is fitted with a manual choke that is only required until the engine fires when first starting from cold, once the engine has fired the choke is switched off and with the next couple of flicks the engine should be up and running, yes its that easy.

Needle adjustment is also easy, the engine comes factory set for running in on a 25:1 petrol / oil mixture and is best left alone until running in has been carried out. Once the engine is run in and the correct mixture of 40:1 is being used then the carb will require leaning out this is usually no more than an 1/8 of a turn 'in' of each needle. If any problems occur please read Just Engines excellent instructions as they will explain all you need to know, having said that they should have been read first before you attempt to operate your Fuji.

Prop Performance with Magneto

Prop Size, Prop Make, Idle RPM, Max RPM
18x10, Grupner Profi, 1800, 7600
18x10, Smart Wood, 1800, 7600
20x8, Master Classic, 1800, 7400
20x10, Master Classic, 1800, 6800

Summary

Having decided to try petrol powered models some 3 years ago, I did some personal market research and decided to try a Fugi BT50 armed with the Graham Whitby plans for his 8ft span High Voltige I thought it could be a good combination, a large forgiving 3D style model with a simple petrol engine to power it.

The Fuji proved an excellent choice, easy to start, economical, maintenance free and most important to me no fiddling required, just assemble the model, tank up and fly. And having said all that if you go flying on Saturday and use all your fuel after a good days flying, with the model shop now closed, no problem just pop down your local garage for a gallon of unleaded. And mix it with some quality synthetic 2stroke oil, a Litre of oil will probably last most flyers about a year. With a gallon of petrol lasting a good couple of weeks flying, if used on both a Saturday and Sunday and the occasional weeknight like I do.

Over the 2 year period I have been using my Fuji it has proved to be very reliable easy to start and operate in its Magneto format, in fact its just been put in the model and taken for granted that it will start within a few flicks hot or cold and operate reliably, how many engines can you say that about? Most will require a tweak now and again but not a case with my Fuji, it just works.

So to sum up the BT50, I highly recommend it for newcomers to petrol engines or even hardened users who require something different from what they are already using.

Data

Engine Fuji BT-50S-A
Configuration
Single Cylinder 2 Stroke Petrol
Piston Ported, 2 ringed piston
Running in chrome bore.
Ignition, Magneto with ATM or
Electronic EIS

Displacement 3.0cu.in 50cc
Stated Power 5.2 bhp@ 10000rpm
Weight 4.2lb 1.9kg w/o silencer

Fuel used in test 40/1 petrol oil mix using Motul 800 racing Synthetic 2t premix oil. 25/1 mix for running in period

Supplied With
Champion RCJ6Y plug,
Very comprehensive instructions
Covering all aspects of operation
Plug Spanner, Engine mount,
Standard steel box silencer,

Just Engines 2 Year Limited Warranty.

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