J'EN (Just Engines) .56 By Malc Pinnock, RCM&E September 2004 Summers finally arrived and here I am sat in front of the computer, typing an engine test. Not only of a brand new product but the production 1st off brand new JEN .56 ABC R/C, in fact so new the case had not had been painted black, Just so you guys reading RCM&E could see it first, it was flown Air Mail from China for special delivery into my eagerly awaiting grubby little hands.
Paul from Just Engines, phoned just before the engine arrived, and told me he had a .56 for me to play with and to explain that this engine took 2 years of R&D to develop [on and off] with time permitting, whilst still running the business.
The idea for the .56 came after listening to feed back from a questionnaire sent out and talking to you guys. It was clear that what you wanted was a small in size powerful engine, reliable and quiet and of course one that is easy to operate and at an affordable price. Easy task EH?
So to celebrate the 10th birthday of Just Engines they are launching the first in hopefully a small range of JEN Engines starting with the .56. The idea was to see how far you could go with a 40 sized crankcase by boring and stroking, before it becomes too fragile or just doesn't work any more. So starting with a .52 they tried every piston / liner crankshaft and crank-case combination possible and came up with a
.56 in fact no bigger than a .40. So is this the .40 that thinks it's a .60 with 1.85 bhp on tap and bags of torque it could well be, read on and we will endeavour to tear it to bits, bolt it back together again and go test it.
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 JEN 56 StripOverall the JEN 56 appearance is quite striking, from its purple anodised cylinder head to its purple prop driver and black lacquered crank case this engine has a super finish, although my preference is for bare metal cases [sorry Paul and Jenny] As I think painting cases is a way of hiding an inferior quality casting. This is not the case with the JEN 56 as both bare and painted cases are of super quality, as you will see from the photos. Lets start the strip by removing the back plate.
The back plate is retained in the crank case by 4x M3 cap head bolts, and is die cast from alloy with a flat at the top for liner and piston clearance, sealing is taken care of by a plastic gasket and casting quality is super with no blow holes or pock marks.
CYLINDER HEAD
Next part to come under the microscope is the head, resplendent in its purple anodised coating. The head is retained by 6xM3 cap head bolts and it has been bored and tapped centrally for a std long reach plug. Pressure die cast from alloy, and deeply finned on top with 2 deep cooling fins at the side. Sealing is by 2x alloy gaskets that sit in a machined in recess in the underside of the head, surrounding the
wide flat squish band and shallow hemi type combustion chamber. Machining casting and anodising are to a high std so let's see if the next parts are up to scratch.
LINER / PISTON AND CON ROD ASSEMBLY
The liner fitted to the JEN.56 is a very tight fit in the crankcase so some heat was required to remove it. Once removed close inspection reveals that the wall thickness of the liner has not been thinned to fit .56 into a .40 casing, 1.75mm wall thickness for the brass liner and a good coating of ?real? hard chrome should give a long life. Porting is of the Schneurle type with a large bridged exhaust port that has a single angled transfer port at each side with a single angled boost at the rear opposite the exhaust. The liner is retained in the case by a 2mm thick flange at the top, this has a
width of 3.10mm for head gasket seating and rounds up the liner, so lets have a look at the piston con rod assembly. CNC machined from high tensile alloy the substantial con- rod has bronze bushings for both big and small ends with 2 oiling holes for
the big end bearing and a single hole for the small end bearing. Over to the piston, this is a die casting from high content silicon alloy and is finished by machining and lapping. Looking inside the piston we notice the 2 large supporting webs for the hardened steel hollow gudgeon pin and recessing of the lower piston skirt for lightness, the lower piston skirt has also been machined front and rear to clear
both the flywheel and back-plate. Back to the gudgeon pin this is a very firm push fit in the piston, it is retained at the rear of the piston by a semi blind or smaller diameter hole than the gudgeon pin. The pin is inserted from the front of the piston and once inserted it is fitted with a PTFE wear pad. All that remains to say is all these parts
have very good fits and finished to a very high quality so a little care when running in and they will last a very long time.
CRANKSHAFT AND FITTINGS
First components to come off are the black finished steel prop nut and blackened steel prop washer, then we come to the sexy purple anodised prop driver. This has been machined from alloy bar stock and has been wasted around it?s centre, the driving face has been helically cut for good prop grip and moving round to the rear the driver has been machined to form a dirt shield for the front bearing. A puller was used to remove the driver from the shaft to avoid damage and once removed we notice the small steel thrust washer and very positive double ?D? drive cut in the prop driver. Now for the crankshaft this was a very tight fit in the bearings and took a very firm push to remove it, a tight bearing to shaft fit will make the bearings do the job they were fitted for and prevent skidding on the shaft.
Now the shaft has been removed lets take a close look, Turned from a single billet of chrome steel case hardened then finished by fine grinding on its working surfaces. The substantial big end has a diameter of 6mm and is supported by a fully counterbalanced flywheel of some 10.25mm thickness, moving forward to the
main-shaft, this has a dia of 15mm and has been cut with a large timed, angled intake port that leads into the 9.50mm gas passage. The next part of the shaft is for the front bearing and prop driver it has a dia of 8mm and has been machined with 2 opposing flats for retaining the prop driver, and finally the output portion of the shaft with a dia of 6.50mm and length of 285mm of which the last 18mm is threaded for the prop nut, and rounds up the very substantial crankshaft.
CRANKCASE
As mentioned earlier the test engine was the first production version of the JEN.56 and came to me without its black lacquored finish, The quality of the pressure die cast crankcase is excellent, with all details being very crisp and no signs of pock marks or blow holes, any machining carried out is also to the same high standard, so lets have
a good look and see if it measures up. Lets start with its OS sized exhaust port 37mm between centres and bored for the 2x3mm silencer or manifold 'through' mounting bolts this will give you lots of options over the standard silencers if you require pipes or in cowl pits type or dustbins etc.. Below the exhaust port, on a vertical stiffening web lies the size plate .56 and below this the first of the 2 very substantial mounting lugs, that have been reinforced around the 2 mounting bolt holes. The front end of the case has 2 very thick stiffening webs one per side running axially between the engine lugs and front bearing housing, with a single stiffening lug at the bottom of the case running axially between the main-case and front bearing housing. Further stiffening comes from a single web sitting between the cylinder front transfer passage and massive square carb mounting boss that has been bored at the rear for the steel carb retention pinch bolt, lock washer and retaining nut, all in all a very stiff strong front end.
Moving round to the other side, that contains the second of the very strong mounting lugs from which runs vertically the boost port transfer passage, and contains for the first time the 'JEN' logo and above this the substantial cylinder cooling fins.
Now its round to the back door for a look inside. The first thing we see is the rear bearing, this and the front bearing are of a good quality and very smooth running, just short of the main bearing we notice the machined in groove for the con-rods big end clearance. Looking up inside the cylinder we can see the two angled transfer passages and single angled boost passage. Quite often when over boring an engine the size of the ports diminishes, not so with the JEN.56 they cast in bigger gas transfer passages so no power restrictions here, or no case strength lost by over cutting the passages. And that rounds up the basic engine lets have a look at the fittings.
JEN TN2 CARBURETTOR
The JEN TN carb has been in use for quite a few years, is quite a proven carb and is usually sold as an after market or replacement fitment for other engines as 'a carb that works'. The carb body is from pressure die cast alloy, and is finished by machining. Sealed to the engine with a rubber O ring and fitted with a very smooth finely ground steel throttle barrel that has a choke bore of 8mm and contains the fully sealed brass slow running jet and adjustable chrome finished steel throttle lever. The main jet assembly is turned from brass and is fitted with a very positive chromed steel ratchet device that clips on and a chrome finished steel fuel needle that is sealed by a rubber O ring, the end of the fuel needle has been bored for a needle extension the can be locked in place by a capped grub screw. Last parts of the carb are the sealed by fibre washer, brass fuel nipple and steel capped throttle barrel retention bolt.
Over the years I have found these carbs very easy to operate, and if the excellent instructions are read and not fiddling with a screw driver, they are very reliable and once the engine has been run in all that has been necessary is the odd click to the main needle, so please read the instructions before fiddling.
SILENCERS AND OPTIONS
Two silencers came supplied with the test engine the standard large volume one for those of you with less sensitive rules on noise and a super quiet type baffled silencer, first off lets take a peek at the large volume type, but as mentioned earlier the manifold spacing is 37mm the same as OS so the options available are endless.
LARGE VOLUME (STD) SILENCER
This is made up from three parts the front and rear parts being pressure die cast from alloy, with the front containing a sealed brass pressure nipple and finned and tapped flange for its cap head mounting bolts. The rear part contains the out-let pipe that is adjustable for position. The centre is turned from alloy bar stock and contains no baffle all three parts are bolted together by a central rod with a lock washer and ny-lock nut at both ends, a simple device and does not reach the recommended 82dba at 7mtrs recommended by the BMFA unless the engine is swinging a large prop at low RPM.
SUPER QUIET SILENCER
This is my choice and well worth the extra couple of quid, and will help save our flying sites. Once again a three part item, slightly smaller in dia but made up in the same way but with the front part being heavily finned and containing a baffle between it and the turned centre section. The assembly bolt differs here in having a cheese head bolt inserted through the front portion, that screws into the tapped rear part, then locked up with a ny-lock nut, this has to be removed first before trying to dismantle or adjust the tail pipe or you will strip the threads in the tail part of the silencer. That rounds up the engine and its fittings but lets have a look at pricing at this stage as prices vary with silencing options.
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TestThe original non painted JEN.56 had some 5 hours running under its belt when I received it so running in was not required. This made life easy for me, no laborious slow running and waiting for it to cool, just bolt it on the bench and go for it. But before I did this I decided to strip it and do the write up. On dismantling the engine for the first time, it was obvious the engine had been run in correctly by the method used in the instructions and by the same method as I use. At this stage there were no signs of wear so when the writing was done the parts were reassembled using some light oil so as to not damage the engine with a dry start. Then the engine was bolted to the bench with an 11x6 prop fitted to it. The plug used was a Fireball Medium but any long reach medium plug will suffice. My fuel choice was Flair Yellow/Gold 10% Synthetic oil <Actinic:Variable Name = 'ML70'/> 5% Castor oil, 5% Nitro, 80% Methanol.
5% Nitro is all the engine requires, using more is likely to cause damage due to detonation, so stick to what the engine was designed for and you won't go wrong.
The carb was not touched from the settings it came with, and once the engine was primed it started second flick and settled down to a steady tick over. The .56 was allowed to bed down for a short period as it had been dismantled, once this was done I was rewarded with a smooth and instant throttle response to high RPM with only a couple of clicks on the main needle being required. Testing was carried out over a 5 hour period including replacing my old 52 in a model. The engine performed faultlessly, and proved easy to start and operate it was hand started at all times, requiring no more than a couple of flicks hot or cold. It was not quite as rev happy as my old .52 due to the longer stroke, but with bags more torque available it was able to out perform it by throwing a higher pitched larger diameter prop.
On stripping the now abused JEN.56 no further wear was found and that's after over 10 hours hard use, and to show this the stripped unpainted abused engine is the one in the photos. I now have one with the black painted cases and the Performance figures are just the same with the handling being just as good, This engine I ran in carefully using Flair Yellow Spot fuel containing 5% Nitro, 20% Castor Oil as per Instructions.
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SummaryThe Jen 56 is highly recommended. It offers superb value for money, with the starting price of £63 for the basic engine, carb and silencer. Word has obviously got round, as the first batch was sold before the shipment arrived in the U.K..
Just Engines offer manifolds of various bends, so if you have a specific requirement in that area then give them a call. Actually it's worth noting that the excellent instructions supplied with the engine also offer some useful tips on pipe use.
As a footnote, I've recently tested a full production, black painted case .56 and the performance figures and handling are just the same as the pre-run review example. By the way, I ran the engine in using Flair Yellow Spot fuel containing 5% nitro and 20% castor oil as per the instructions.
Last word; the JEN56 is indeed a .40 size package that thinks it's a 60.
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Technical DataPROP PERFORMANCE
| SIZE | MAKE | IDLE | MAX | | 11 X 6 | A P C | 2,800 | 13,000 | | 11 X 6 | RADIO ACTIVE [R A M] | 2,800 | 13,200 | | 11 X 7 | R A M | 2,800 | 12,800 | | 12 X 6 | R A M | 2,600 | 11,800 | | 12 X 6 | MASTER AIRSCREW | 2,600 | 11,400 | | 12 X 8 | A P C | 2,600 | 9,400 | | 13 X 6 | MASTER | 2,600 | 10,100 | | 13 X 6 | R A M | 2,600 | 10,400 | | 13 X 6 | A P C | 2,600 | 10,200 | |
Average Noise Test at 7 meters. 82dba. On Super Quiet Silencer.
DATA FILE
ENGINE JEN .56 ABC R/C
CONFIGURATION Single cylinder 2stroke, ABC liner
Assembly with Schneurle porting,
Twin ball raced crankshaft.
DISPLACEMENT .56 or 9.14cc
BORE 23.0mm
STROKE 22.0mm
POWER OUTPUT 1.8 BHP
WEIGHT 480grms. Including super quiet silencer
SUPPLIED WITH 2 x Allen Keys, 2 Year Warranty,
Excellent written English Instructions
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