MJK Bob Jane J2

MJK Bob Jane J2

Postby wixwacing » Sat 03 Apr, 2010 12:19 pm

The Bob Jane J2



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It’s not often one gets to see a ‘first’ up close and serious but this time, not only do I have the pleasure of seeing a pre release model, albeit a local model, but I also get to paint it, build it, and do the art work for the box. Well that can’t be bad can it! And what’s more it isn’t half bad as a slotcar either.



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I became friends with Ian and Daniel Goodland a little while back now. They were down at the Gold Coast on holiday and were visiting another associate who was a mutual friend. A few phone calls and Ian and Daniel eventually appeared at the home of the Red Team and there we struck up a friendship based on the sharing of a hobby.



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Ian is one of the three guys who make and distribute MJK slotcar kits, spare parts, chassis and of course, their burgeoning range of slotcar tyres. The miracle here is that they still have their own daytime jobs and hectic family lives too. The hobby must be crammed into every spare minute and vacant evening they can find. One things for sure, they do it because they have a passion for the hobby and derive great satisfaction from sharing it with others.



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Just before Xmas I received a call from Ian saying there was something ‘special’ coming in the post. Not having a clue what, the parcel eventually arrived, packed with all sorts of MJK goodies, one being the J2 subject matter. I will refer to it as the J2 for certain reasons but I’m sure you know exactly what I’m talking about. Any way the request was simple, if I built the model up and took some photos for him, I could keep the model!! Well, you don’t get an offer like that everyday, so being in agreement, I started the project.



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The first delay was the fact that I already had one or two projects on the go and apart from some precursory probes into the box, not a lot happened for a few weeks. Eventually it was time to start and the bench was cleared of the remnant slotcar pieces left over from previous builds. First up was the body / chassis mating. The body seemed very wide at the sills, probably a result of sitting for some time , maybe in the heat, so the body needed to be reset to realistic dimensions.



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This I did by running it under the hot tap at the kitchen sink. Once hot, the sides of the body were coaxed into a more realistic width. This involved applying pressure to the body sides until they aligned and stayed in line with the front and rear guards (wings). Next up and before anything else I needed to fit the chassis mounts to the insides of the body.


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The new body width was measured and the internal depth of the mounts were measured. This allowed me to trim the side tongues on the chassis to the width required. These were offered up several times and the chassis wheelbase was adjusted until the wheels were approximately in line with the wheel arches. Chassis fine tuning could be done at a later stage! Once I was happy with this, the wheelbase was set precisely and some extra strength, slow curing epoxy resin was mixed.



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The epoxy was placed on the back of the body mounts and on the premarked area inside the body, and without making a mess, the chassis and mounts were offered up inside the body. As part of the chassis tuning I had made some short MDF blocks, approximately six millimetres thick. These were placed under the sills of the J2 body and supported it over the chassis on the test block. Here it stayed for a good twenty four hours.



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With the chassis mounts in place I prepared the body for painting. Once again the body was mounted on a ‘lolly stick’ so I could handle it without all the stress of touching wet paint. The body got it’s traditional coat of flat grey acrylic. This shows up a host of blemishes and time can be spent either eliminating them or minimising their impact.



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A couple of jobs I did do at this stage, more from a pernickety point of view rather than an essential, was to reprofile one of the rear wheel arches and to build up some of the side window frames which had suffered a bit of enthusiastic trimming somewhere after the moulding stage. Once done, minor blemishes were sanded down or filled and other body features enhanced a little with a sharp modeller’s knife.



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Another dusting of primer in the repaired spots saw the model ready for its next adventure. The top coat and finish colour! Mmmmmm? Ian had left me instructions to build the model faithfully to the kit as he wanted the art work to represent what the model could and should be built into, but I wasn’t tied down to a colour scheme. As it happens, the model comes with a set of Bob Jane stripes and various other sponsor decals, so I went in search of the real thing on the internet and found a few examples of the Jane J2 in track mode. One thing that confused me was the colour. In some photos the original was white and in others, it came across as a pale primrose. Eventually I was looking at some illustrations of 1/43 Bob Jane J2 diecasts and the model was definitely white, but by now I was being more and more attracted to the pale primrose!! So a hybrid it was to be.



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The colour was going to be Acrylic and I had a jar of flat yellow. I poured some gloss white into a spare spray gun bottle and tinted it with the yellow until a discernable pale yellow was achieved. I then thinned it a little to improve its spray characteristics and after a couple of dummy runs on an old Ferrari 250 GTO body I was ready for the first coat. The first coat went on and as always, the few blemishes which appeared were sorted and the second coat was then applied. At this stage I decided to leave the body for a couple of days to cure. The reason for this was that I was to apply a coat of clear enamel. I know from experience that if you put enamel on to fresh acrylic you might very well cause it to react and blister. I have experimented many times before and I now know that if the acrylic is allowed to dry thoroughly you can apply one and more coats of clear enamel with relative impunity, providing it is sprayed on. It’s a different and horrible story if you try to brush it though!!!



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So, the first coat of clear enamel was applied. Again, once set and cured for a couple of days it is OK to handle the model in moderation without leaving finger prints in the clear coat (one of the problems with fresh clear acrylic). The next job was to paint the silver parts. The silver I used was a decanted quantity of ‘Chrome’ silver from a local auto store. A lot more effective if sprayed on but not too bad if brushed either. The grille and headlights were brush painted and after the wheel inserts were fettled and fitted to the alloy wheels, they were sprays painted. Yet again, after a period of a couple of days I decided to do the chrome body and window mouldings.



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The body trims were masked using Tamiya flat sheet masking strips. In a packet you get a sheet of one millimetre and a sheet of two millimetre strips. Ideal when you want to achieve some tight curves on the body and a lot more manageable than their rolled masking tape. The tape was applied, the edges of the tape were pressed down with a flat wooden tool and the areas to be painted had a sparing coat of clear applied.



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This would eliminate the ‘bleed’ you sometimes get under the edge of masking tape (check out the waist trims on this model). A couple of hours later I brush applied the silver to the masked areas. Harder, but not too much of a challenge were the window trims and mouldings. These were brush painted too using a steady hand. Once dry, the masking tape was removed leaving a crisp line along the model.



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The minimal decals were cut and applied. Where the stripe puckered a bit around the curved areas I applied Mr Hobby ‘Softer’ decal flattener with great success. I also picked out the front and rear flasher lenses in amber and red respectively. Lastly after yet another curing period, the second coat of Tamiya clear enamel was applied at a distance of three hundred millimetres or so after being stood in some warm water for fifteen minutes or so, and yet again, the model was left to dry far a day.



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While all this was going on there was still stuff to be done in other parts of the model. I had to decide how I would approach the clear window challenge! And there was the driver’s tray to paint along with the drivers head. But that was the easiest bit.



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The vacuum formed clear piece is a relatively good fit in the body and to fit it is not a massive effort, but I was looking for a little better fit than a one piece clear would give me. I decided to trim the piece into separate constituents and apply them one at a time. I had already trimmed the body window openings prior to body painting. This allowed me to get an extra close fit from the clear parts.



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Each separated and trimmed part was put in place, one piece at a time, and held strategically in place with blue tack. Doing the front and rear screens first I blue tacked them in at the ends and then painted some extra strength epoxy around the clear edges and on to the body. Next day the side windows were fitted in a similar manner. The blue tack was removed from the front and rear screen and the exposed unglued edges were glued.



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With all this in place, the drivers tray was offered up and in order to get it to fit inside the cab area I needed something a little stronger than blue tack. The solution was to drill a sixteenth hole in each end of the drivers tray at a centre point were it touches the inside of the body. Making sure the drivers tray was in its final position I applied a spot of superglue to the front drilled hole. This bled through and after a period of twenty seconds or so, the front of the tray was anchored.



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The same method was repeated at the rear and the result was a well fitted drivers tray, but, it wasn’t enough to rely on superglue alone! Because the sides of the body have to be flexed to remove and refit the chassis I decided to anchor the drivers tray by the front and back edges only. With the superglue holding the tray in place I proceeded to mix and paint some epoxy resin along the front and rear joint edges the width of their contact area. Again, once dry, the drivers tray was firmly in place, fixed front and rear. Leaving the sides to flex harmlessly when moving the chassis.



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Had I bought the model off the shelf I might have made a few alterations, simply for no other reason that I would liked to have a bit more detail in the light lenses etc and possibly spent days making a separate grille!! Prior to window fitting the body eventually had its last coat of clear enamel and the wheels and inserts also had their clear coat and once all had dried it was time for some pictures.



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The chassis is the MJK laser cut adjustable type and was easy to assemble and this was done early on to allow chassis mounting brackets to be positioned early in the build. The motor appears to be an 18,000 rpm ‘S’ can type motor and drives very much like one. The axles will need to be cut to size and I took the liberty of grinding out the inside of the wheel arches to a minimum thickness, especially at the top, to allow the widest axle possible.



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Wheels are grub screwed alloy and the kit comes with some very effective pressed steel wheel inserts. These I fixed simply by applying some thick double sided tape. This ensured the inserts sat near the outer edge of the rims for greater effect. The guide is a healthy size too and is reminiscent of the Ninco board track guides and is a massive 23 mm long.



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So what does it drive like? Well, not bad really. The model was created to compliment other models from the MJK range based on the sixties Hardy Ferodo races. It fits in nicely with the EH and FJ and a couple of others which are soon to be available. The body is robust and was designed to be so. You won’t be loosing antenna, lights and door mirrors on these models and things like the bumpers and grilles are well modelled and going no where. They were conceived to be raced against each other and as such will supply plenty of Aussies with a good reason to disappear down the shed for a few hours. Priced at the higher end of mainstream RTR models these are almost unique at this moment. There are already racing series for this era of model on both the east and the west coasts.
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When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
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wixwacing
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Re: MJK Bob Jane J2

Postby wixwacing » Wed 21 Apr, 2010 12:45 pm

I had an opportunity to take the Jag out on a local board track last week. The track in question was a lot more technical than the previous one it had been on. Cornering ability ranked high on the agenda and on the first track, when pressed hard, the Jag showed a tendency to 'cock a leg' under pressure. Between tests I decided to apply a recently learnt preparation to the tyres to improve its corner performance.

The problem was that in a race situation with the model pushed hard, there was a tendency for it to tip up and eventually deslot, sometimes roll over style. I identified the problem as too much grip in the tyres when cornering. The tyre edges were radiused and the model run again. Slight improvement, but still a 'knife edge' situation under pressure. The model has an inherent high centre of gravity and the first solution might be to add some low down ballast to keep the model upright. The downside is that extra weight will affect acceleration and extend the braking zone. Both undesirables as for as body tuning is concerned.

The next solution is to reduce the effective grip of the tyre in a corner to allow the model to 'wash off' a little bit of corner speed and allow it to navigate bends more like a non magnet racer should. So, how do we go about it? The solution has been at hand for a long time but it was a case of spotting it which has taken me time.

When racing some of those highly raceable Ninco NC1 touring cars, it became apparent to me that you could get some models, like the Audi A4, to tip in corners when running extra sticky tyres. Once the standard ribbed tyres were refitted good cornering behaviour was restored, but at the expense of some good straightline acceleration. What was needed was something between the two, Mmmmmmmm? Once again, whilst trying to tame a problem model, the Autoart Lamborghini Murcielago, with the massively wide MJK tyres on the rear of that model, cornering was also a bit of a lottery. In desperation I decided to reduce the grip of the tyres by cutting some slots in the tread area. The first attempt was the complete width of the tyre and it soon became evident that this was too much, allowing the rear of the model to flail viciously on corner exit. Obviously there were too many grooves in the tread.



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With the next pair of tyres I approached the problem from the opposite direction! I cut one groove in the outer edge of the tyres and tested. A minor but significant improvement was experienced. I then cut an extra groove besides the first and retested. The solution was at hand and along with radiusing the outer edge of the tyre, I had achieved a tyre which gave good straight line grip. So could I apply this to the Jag?

Back to the Jag tyres and not a lot to play with here, the tyres are barely 7.0 m.m. wide so there wasn't going to be too many groove. I settled for four grooves to start with and the tyre was mounted on a spare hub fixed to a dummy axle and installed in my drill press. The tyre /axle was spun up at about 1200 rpm and the point of a modeller's file was carefully applied to the tread area of the spinning tyre. Being careful not to overdo it I lightly pressed the file into the tyre which it cut quite easily. This created a rough groove slightly deeper than it was wide. Happy with that I cut another three grooves into the tread surface, repeating this process on all four tyres. The tyres were refitted to the model and it was packed up for the next race outing for a test.



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Once on the track it was blatantly obvious the tyre grooving had been a success. The grooves had allowed the model to brake away controllably in the corner and still retain almost all its straight line speed. Problem solved. Being unconvinced by the many exponents regarding the 'tripod' theory of chassis setup, I have the Jag running on all four wheels. This contributes greatly to its corner stability too. But when tyres touch the track and unless the model has steering and independently rotating front wheels, there is an inherent risk that too much tyre contact will cause the model to 'snow plough' in corners. It is for this reason I have ribbed the front tyres too. This reduces the front end drag of the model and increases the model's front end ability to 'side slip' in corners. Minimising any unusual behaviour patterns caused by front end drag.

So, I am very pleased with the results and I would dare say that the Jag handling is greatly improved, not that it was that bad to start with! So if you have any model which is causing you cornering grief, before you start adding weight, address the items which are more important firstly.

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When I'm not racing slotcars,
I'm out in the back yard, burning food!!

When I win, it's because of my talent, not my car or my controller!
User avatar
wixwacing
Marshal!!!
 
Posts: 1889
Joined: Thu 10 Jul, 2008 8:22 pm


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