Engine Test

Moki M 135 RC by Ian Bell, courtesy R/C Scale Aircraft magazine (Vol 14 Issue 7) :

UK Ian Bell checks out this latest 23cc 2-stroke from Hungary. If you are lucky enough to own a Moki 1.80 then you will already be aware at a glance of the quality and workmanship that hits you in the face when you open the box. The exception with this NEW engine is in that there is a little extra. You will immediately notice that the outer edges of the cylinder cooling fins have been machined and polished to a very high standard indeed.

Being easily identifiable as a Moki by the round slow running needle, instead of the normal 'screw' type often seen on other engines and all original 'Moki' engines have the same type of carb.

The main components;

The crankshaft is 102mm long running on two ball-bearing races. The machining on the crank is superb and the prop driver is held on by a tapered collar. The Moki 135 has a stroke of 30mm, just under 1 1/4" in real money with the transfer tunnel measuring 14mm down the centre of the crank. The cylinder head is made from aluminium and machined with a quality of excellence. The piston is also ali and ringed and the conrod is ali with a phosphure bronze Big End and Small End bearings, and the gugeon pin is held in with tiny circlips. The crankcase is an excellent piece of engineering and looks like a beautiful piece of sand-cast aluminium. The transfer ports are quite big for a 1.35 size engine, but again Moki seem to have got it right. The balance of power and reliability is just right.

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Running In;

It is suggested that 30 minutes running-in time is ample to let the parts bed-in properly. The running-in procedure should be for just 2-3 minutes at a time, being sure to let the engine cool down between runs. A 'ringed' engine should always be run-in ' slightly rich which gives the engine a good lubrication and helps in cooling the engine.

Starting and running;

Again I decided to run the engine on our special engine stand with props ranging from 16" x 8" - 18" x 10". The silencer used on the engine was a BCM Pitts exhaust, again supplied by the same importer as the engine. The fuel used for testing was a 17% Morgans Cool Power Synthetic - 80% Methanol mix . With ease, the engine was primed and started after just a couple of flicks. Take care with large props and they can 'bite' if over primed.

The figures show the results of the static running test.

17% Cool Power - 80% Methanol

Prop Size Safe Idle RPM Max RPM APC 16x8 1,900 9,500 APC 16x12 1,900 8,300 Airflow 17x10 1,800 8,300 Dynathrust 18x6 1,800 8,100 Premier 18x8 1,500 7,800 Smart 18x12 1,400 7,000 Smart 19x10 1,400 6,800 Menz 19x10 1,300 7,000

Silencer and Engine Mount;

A Radial Mount is optional, and screws straight on to the back of the engine in place of the backplate. The wide selection of silencers is also optional from this importer. The quality of the whole engine appearance, including the material quality, is always first class and of course being supplied by the UK Moki importers, Just Engines will give a full back-up service. Supplied with the Moki 1.35 is a manual/instruction booklet that tells you everything you will need to know about your new engine.

inexpensive with the option of mounts and silencers for your installation.

Back in the early 1970s I looked at a 25 cc Moki engine in a model shop.

The general consensus was 'Who would ever need an engine that big?'. I remember the engine being large, but I also remember that the high quality was apparent. These days it would be classed as a small, big model, engine considering the monsters used by the large wing fraternity.

For the modellers who like a large model but not a heavyweight monster, 30 cc is a happy limit for most. This engine is spot on the mark for that category and, as we shall see, it is an engine worthy of calculated consideration if you want quality, reliability and all-round performance.

Recently a modeller suffered a terrible accident in my presence when he misjudged and put his hand into the propeller of a large engine. The thought of that was with me when I thought of running this engine. However, after a couple of careful runs I realised that this engine was not going to jump at me. In fact, it was a pussy cat to handle, but I kept well behind it when it was roaring. Let us look into this monster.

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Moki 1.80 review; Brian Winch

CASTWORK To survive as long as this in engine manufacture you have to present a good product. The Moki castwork is the equal of anything on the market, and better than some. Well designed, sturdy yet lightweight, with a bead blast finish and high grade machining. Cast components comprise the maincase, backplate, front housing, throttle body and piston. The head is machined from bar stock, is deeply finned, hemispherical in the combustion chamber with a slant surface squish band, and is sealed at the top of the liner with an aluminium gasket.

THE PISTON ASSOCIATION The piston is a casting fitted with one ring which is pegged to a particular position, so be aware if you strip the engine. The 8 mm diameter gudgeon pin is blind one end and secured by wire circlips. The conrod is an awesome piece, fully machined and fitted with bronze bushes both ends. it is a fine example of engineering, and gives me confidence that it would take all the reasonable punishment encountered in an engine.

The liner has an overall chrome plating. This is a bit unusual, as it is common to leave the outer surface unplated. Possibly the cost of masking lost out to the little extra chrome used. There are two side ports each side of the liner in the Schnuerle configuration, but the usual rear boost has been left out. Obviously the engine performance has been carefully calculated and the rear boost was found to be not needed.

CRANKSHAFT The main journal diameter is 25 mm (possibly to suit available bearings) and this steps down to 23 mm for the fuel port area, then steps down to 12 mm for the front shaft section, then down to 8mm for the thread portion. The crankweb is 48 mm diameter and 12.75 mm thick. The crankpin is 9 mm diameter. The fuel passage up the shaft is 16 mm, and the port is 23 x 14 mm. Even with an extension eyeball (loupe) I could not detect the surface finish on the shaft. It is truly superb bit of engineering that give you confidence in that you have a quality product. The thread is clean and well formed, and the fine 1 mm pitch gives bit of insurance against props coming loose.

The aluminium prop driver is secure by the tightest taper collet I have yet fought with, and the knurling is in the form of straight V cuts across the 31mm diameter. The prop nut is shouldered and fits into the aluminium prop washer.

THROTTLE Something a bit different here. The needle and nipple unit is off at an angle to the rear of the throttle body, which keeps fingers well clear of the prop. The idle mixture control is a knurled disc in the same end of the body as the main mixture. It is sealed with two 0 rings. The hardened steel rotor has a spigot end that fits into the idle disc, and a crescent slit is the fuel supply governor for the low range RPM.

All in all a very simple, precise design that works extremely smoothly with excellent transition and an amazing idle. Tuning is very broad on the main needle, and the centre mark of the idle disc was perfect for this engine on the fuel used.

BLAST OFF I used straight 4:1 fuel for all tests as I accumulated a total of about 50 minute running. I would consider the engine needs about 3 hours running-in before switching to the lower oil fuel. I use heavy leather glove for starting engines but, even with this, due to being still bit prop shy as mentioned, I considered using a chicken

stick. I felt the engine over compression for the first start, and it gave a little bump on the first turn. A careful, tentative flick and it was away and idling like it had been running for hours. This engine is very easy to start, hot or cold. Bring the prop to compression and give it a mild flick for first hit starts 9 out of 10. I don't know what the plug is, but I would like a few more. Checked with a tacho, the engine didn't drop one rpm when the power was disonnected. The plug body is brass and it has an idle bar machined in. (Note from Paul, Just Engines; - the plug is a Moki plug)

I used a Cairns Engineering flexible header feeding into a 1/2 scale, 1959 style BMW motorcycle muffler I made. The muffler looks just like a tuned pipe and is only 38 cm long. From a 1/4 throttle up you could not hear any exhaust noise as it was drowned out by prop noise. I was very pleased with this exhaust combo. I double checked everything for this next bit of information, and can vouch that it is true. On an 18 x 10 classic prop with the engine locked to 6,500 rpm, it ran for 16 minutes on 14 ounces of fuel. That is less than one ounce per minute! Hard to believe, but I guarantee that it is correct.

PROP FIGURES (see Notes)

Even from the amazingly low 750 RPM idle, the engine could be accelerated without hesitation or coughing. It was a pleasure to run, and I am looking forward to fitting one in a large seaplane in the near future. I need reliability for float flying, and I am confident that Moki and I will enjoy many happy hours.

Notes (by Paul, Just Engines).

I really rate Brian as an engine reviewer - but I'm not sure what that home made silencer did for engine performance!! Our tests (and customer feedback) shows that on a standard (or in-cowl) silencer we would expect a Moki 1.80 to do between 7800-8500 on 18x10 props. Any 1.80 we run in for customers or test following servicing, we only release after testing with our Master 18x10 prop. If it doesn't do 8300 rpm - we worry about it. And as they say in Australia........so far - "no worries"!! Performance will also depend on type of prop and blade section, which varies between prop manufacturers. Jim Gerard (US Moki distributor) quotes the following performance figures; Zinger 18x8 @ 8200, Zinger 18x10 @ 7800

18 x 8 Zinger wood 7,300 rpm1,500 idle

18 x l0 Classic 7,500 rpm1,300 idle

18 x 10 Zinger wood 7,200 rpm20 x 10 Bolly 5,700 rpm20 x 10 C!assic 6,400 rpm

750 idle

The MOKI 180 by Clarence Lee

Now that the political barriers around the old Soviet Union and the Eastern block countries have began to fall and stringent exportation rules relaxed, quite a few of the engines popular in Europe but produced behind the "Iron Curtain" are now being imported into the U.S. Such is the case with the Moki engine line.

Produced in Budapest, Hungary, the Moki engines have been in production now for over 30 years with only a few making their way into the U.S., having more or less being smuggled in by visiting friends or relatives.

The Moki engines have always been noted for their excellent quality, especially for a former Iron Curtain country, their high power output, and a long life expectancy if given the proper care and treatment. The Moki engines were first brought into the U.S. in quantity by Davis Diesel Development/Model Products and first gained major recognition when Bill Hempel, Jr. took the lst place Gold Trophy at the Ist Giant Scale "Reno" style Unlimited Air Races held at Madera, CA in 1991 using two Moki 180s in his A-26 pylon racer.

In 1993, Jim Gerard of Gerard Enterprises, was appointed the new exclusive U.S. importer. The first Moki engine we reviewed was the Moki 150 in the March '92 issue and we were quite surprised at the overall quality of the engine and the power it developed, in some cases actually surpassing some of the larger displacement size engines in its class such as the Super Tigre 3000 and OPS Maxi-30, both with 1.8 cu. in. displacement and even the O.S. Max BGX- I with 2.1 cu. in. displacement. Even so, the Moki people quickly followed the 150 with a larger bore 180 (1.8 cu. in.) engine, giving them a definite edge power-wise over the competition.

Basically, what we have with the Moki 180 is an increased bore 150 with the 150's bore having been increased 3mm from 32mm to 35mm or 0.118" with both engines sharing the same crankshaft, bearings, connecting rod, front housing, backplate, carburetor, and related prop drive parts. If a person happened to have the machining facilities, a 150 could be easily converted to a 180 by boring out the crankcase to accept the 180 piston/sleeve assembly. The only other parts required would be the 180 wrist pin and head. Those who may have read our review of the Moki 150 a little over four years ago will find our present review of the Moki 180 a little repetitious, so bear in mind that there are only so many ways of describing the various engine parts, especially when they are identical.

Crankcase:

The crankcase would appear to be an investment casting composed of a one piece center block with removable front housing and back cover. The machine work is well above average and some of the best I have seen coming from a former Iron Curtain country. Due to the quality of the machined surfaces, no gaskets are used between the crankcase. the front housing. and back cover, depending on the fit of the machined surfaces for crankcase sealing Some of our older readers may remember that the post WWII Dooling and McCoys had this feature. i.e., depending on the machined surfaces for crankcase sealing without the use of paper gaskets.

Crankshaft And Bearings:

The monstrous crankshaft has been machined in one piece from bar stock steel, hardened, and finish ground on all bearing surfaces including the crank pin - always a desirable feature. The finish grinding has been performed by the "old world" on centers technique which means the crankshaft is supported at both the front and back ends during the grinding operation which results in both bearing surfaces and the main journal being dead true with each other. Most modem day grinding shops use "centerless" grinding where the crankshaft is free to float, and although still quite accurate, is still not up tothe precision of "on centers" grinding. Most model engine manufacturers use the centerless grinding process, due to being both faster and less expensive.

The counterbalance is of the constant thickness design, cut away on either side of the crank pin for counterbalance action. The counterbalance would balance out the full weight of the con rod and wrist pin but no part of the piston's weight. This would seem a little on the light side, but the engine was very smooth vibration-wise, one of the smoothest if not the smoothest engine in this displacement size we have tested.

The crankshaft is supported by a giant 42mm (1.654") o.d. x 25mm (.984") i.d. steel caged ball bearing at the rear and a 28mm (I. 102") o.d. x 12mm (.472") i.d. steel caged, unshielded bearing at the front. Unusual is a 2mm (.079") reduction in the main journal diameter directly ahead of the rear bearing seat. Normally, the main journal is reduced only a few thousandths smaller than the rear bearing i.d. in order to facilitate installation of the bearing, i.e., it does not have to be pressed the full length of the crankshaft journal. Why Moki has used such a large journal reduction could only be answered by those who designed the engine.

The crankshaft intake port was timed to open 42o after BDC and close 61' after TDC for an open duration of 199'. The closing timing was actually 2' earlier than the 150 we reviewed, but even so, could be considered rather late for the engine's intended operating range, however, this would also account for the engine developing its maximum horsepower at higher rpm with smaller prop sizes if one should want to go that route as did Bill Hempel, Jr.

Normally, with later closing timing, you can expect a tendencv for an engine to kick back and fire up backwards during starting and some fuel blow-back out the carburetor at idle, but we found the engine to be very easily hand started and no particular problem with carburetor blow-back that could affect the idle and acceleration as will be seen in the performance section.

Piston, Sleeve, And Rod:

The piston has been machined from an aluminum casting and is used in conjunction with a single .042" wide expansion type ring that has been pinned to prevent rotation and runs in a steel sleeve that has been hard chrome plated. Whereas the 150 we reviewed had a slightly "domed" piston head. the 180 has been machined flat. A full floating 8mm (.315") diameter. hardened steel, tubular wrist pin is retained in the piston by wire snap rings at either end.

Due to the high silicon content of the aluminum piston, no bronze bushings are used for the wrist pin holes. A modified version of Schnuerle porting is utilized with two transfer ports on either side of the divided exhaust port. The two transfer ports closest to the exhaust are aimed slightly upwards and to the rear. The rear two ports are aimed steeply upward and to the rear with no boost port opposite the exhaust. All four transfer ports were timed to open 58o before BDC and close 58' after BDC for an open duration of 116'. This was actually 4' less than the 150's 120' duration. The exhaust was timed to open 75' before BDC and close 75' after BDC for an open duration of 150' - 2' longer than the previously tested 150. This was obviously intentional and not just a variance in tolerance as the exhaust ports were also .006" taller, i.e., .358" versus .352".

The really hefty con rod has been machined from bar stock aluminum and bronze bushed at both the crank pin and wrist pin ends; another very desirable feature we like to see. A slot cut in the bottom of the crank pin end and a hole drilled in the top of the wrist pin end provides lubrication.

Cylinder Head:

The deeply finned one-piece head has been machined from bar stock aluminum and utilizes a.340" deep x .980" wide semi-hemispherical combustion chamber surrounded by a. 198" wide squish band angled at approximately 8'. The combustion chamber bowl has actually the same dimensions as the 150, but the squish band width has been increased to accommodate the increase in bore size. The measured combustion chamber volume was 3.25cc which computes to a compression ratio of 7.48:1 measured with the closing of the .358" high exhaust ports. Right in the ball park for a sport type engine and somewhat higher than the 150's 6.72:1 which could be considered a little on the low side.

Carburetor:

The Moki carburetor is a completely original design and not a clone of the 2-needle, rotating barrel type originated by Super Tigre that many of the model engine manufacturers are using nowadays. The carburetor is of the rotating barrel, fuel metering type utilizing a 10mm (.394") intake. The principle of operation is similar to that of the Perry carburetor in that a tapering slot in the stepped down shoulder of the rotating barrel aligns with a hole in the aluminum reservoir disc. Rotation of the barrel increases or decreases the length and width of the tapering slot, in turn, regulating the fuel flow to the venturi spraybar. A modification has been made to the positioning of the needle valve assembly in that it is now mounted horizontally and to the rear rather than vertically and to the rear as was the 150 carburetor. A positive barrel stop screw is used for setting the idle speed which we always like to see. Due to many fellows backing out the idle speed screw and setting the idle speed with the transmitter stick position and then using the idle trim to kill the engine after a flight, many engine manufacturers are now omitting the positive idle adjustment screw. Using the transmitter to set the idle speed can often result in servo "over- shoot" if the throttle is closed rapidly killing the engine, trying to idle the engine too slowly, etc. A lot of idle problems, especially unexplained dying of the engine at idle in the air can be attributed to using the transmitter rather than the carburetor to set the idle speed. In operation, the carburetor performed flawlessly with a beautiful tick-over idle and almost instant acceleration.

Performance:

Our review engine was supplied with a "Bisson" sport muffler; however, this muffler is optional equipment and not included with the engine. The Bisson sport mufflers, one of many models made, are manufactured in Canada, with Gerard Enterprises handling distribution in the U.S. A complete line of different types for all of the more popular makes of engines are available from Gerard Enterprises. These are well constructed mufflers that effectively lower the sound level with a minimum of power loss. Jim also has Mac's Products headers and tuned pipes available for the Moki engines as well as J'TEC "in cowl" manifolds. The Bisson muffler was installed on the engine for our testing. Something that always wins points was the inclusion of a Moki idle bar glow plug with the engine. It is my opinion that all engines should come equipped with a glow plug although many do not.

The recommended break-in fuel is 80% methanol and 20% castor oil (FAI) and the instructions specify that at no time should straight synthetic oil be used in the engine.

After the break-in, a mixture of castor/synthetic may be used as well as 5%-10% nitromethane, although the engine will run fine on no nitro fuel. At no time should less than 15% lubrication be used, which should be part castor, and then, only after the engine is completely broken in. We gave the engine our standard 30 minute break-in period with the FAI fuel and then switched to 10% castor, IO% Cool Power, 5% nitromethane, and balance methanol for the testing - the same fuel used when testing the Moki 150. The Temperature of the day was a little cool at 65'F, the Humidity a little high at 50%, and the Barometric Pressure 29.98 inches of Mercury. All propellers were Zingers. For comparison purposes we are also including the power figures for the Moki I50.

Moki 180 Moki 150 16 x 8 10,000 16 x 8 9,350 18 x 6 9,100 18 x 6 8,400 18 x 8 8,650 18 x 8 7,950 18 x 10 7,800 18 x 10 7,700 20 x 8 7,700 20 x 8 7,600

20 x 10 6,400 20x 10 -------

As can be seen by the preceding figures. the Moki 180 was only 100 rpm stronger with the 18 x 10 and 20 x 8 than the Moki 150. However. with the more practical prop sizes that would normally be used, the engine really showed the displacement increase turning as much as 700 rpm stronger with the 18 x 8 which is the recommended prop size for the engine. We were a little surprised at the small low end gain, but several factors enter the picture here. First, as you raise the exhaust port height and lengthen the exhaust duration, you also raise the engine's peaking speed where it develops its maximum horse- power at the expense of low end grunt.

Although the 180's exhaust duration increase was quite small, it obviously had an effect. Second, the 150 was tested with a Davis Soundmaster muffler and the I 80 with the Bisson muffler. Possibly the Davis muffler had a slight turning effect at lower rpm, and the Bisson at higher rpm. Whatever the case. the Moki 180 is a strong running engine. 'Me overall handling was beautiful with easy hand starts and no nasty tendencies. At no time did we use an electric starter, with the engine always fifing up in one or two flips of the prop following prop changes, idle check- ing. etc. The engine would hold a remarkable 1,450 rpm idle with the 18" prop sizes and we had it ticking over at 1,350 rpm with the 20 x 10 with almost instant acceleration. We were particularly impressed with the engine's smoothness - smoother than many 60/61 displacement size engines we have tested.

By Clarence Lee

Over the years Moki engines have proven to be top quality, powerful and dependable - one reason that many of the top scale flyers such as Jeff Foley (four time Top Gun champ and three times National winner in the designer scale class) choose the Moki engines to power their scale aircraft

The 2.10 is the 5th engine we have reviewed and like the previous versions the Moki 210 turned out to be a beautifully handling engine with above average power - topping its major competitors - the2mm longer stroke accounting for its advantage when it comes to big prop lugging ability

We were particularly impressed with the carb.

After 30min break in on a BCM sport muffler the following prop figures were recorded. All props were wooden Zingers

18x8 8900 18x10 7600 20x8 7800 20x10 6800 22x8 6600

As can be seen - real stump pulling power (21Lbs thrust on 20x10 - and 25Lb claimed by importer on APC 20x10)

Even with the power it develops, the engine had very docile handling characteristics, being easily hand started and low vibration.

Even more impressive was the low idle speed of 1600 on 18" props and we even had it down to 1350 on the 22x8!!.

If you're looking for a top quality engine in the 2cu in range with above average power and proven reliability, you would do well to consider the Moki 2.10

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