Moki 1.80 review; Brian WinchBack 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. Tony Farnan, the father figure behind Model Engines (Aust), imports the Moki range into Australia, and when he told me he was sending one for testing he also offered a new workshop. His reasoning was that the power of the engine would blow the walls down of that which I had, and I would be in need of a new shelter. To save a lot of rebuilding hassles I did the testing out of doors, but the prop blast still blew the mortgage off the farm.
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.
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 eader 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)
| 18 x 8 Zinger wood | 7,300 rpm | 1,500 idle | | 18 x l0 Classic | 7,500 rpm | 1,300 idle | | 18 x 10 Zinger wood | 7,200 rpm | | | 20 x 10 Bolly | 5,700 rpm | | | 20 x 10 C!assic | 6,400 rpm | 750 idle |
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.
Engine for test supplied by Model Engines (Aust), Richmond, Victoria (wholesale only), and available from model shops where good stuff is sold.
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
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