Carrera McLaren M20 - initial set up for non magnet racing

Squeezing out those last few tenths

Carrera McLaren M20 - initial set up for non magnet racing

Postby wixwacing » Sun 11 Jul, 2010 2:06 pm

It’s always a disappointment when a long awaited model arrives from a manufacturer you don’t have full confidence in, based on their previous track record. Bracing yourself for the worst, you open the box and things look fine, but, in my case, being a competitive racer without a home track, I have to wait until I can get it on a friends track or steel a few laps between races at the next meeting. In this case the model was tried out at a ‘happy hour’ at a local friend’s track

I won’t go into detail, you can see all that for yourself in the Carrera review section, but the M20, obviously built solely for magnetic track racing, was not going to behave competitively on the painted blacktop! A few laps at speed confirmed that and it was then a case of noting the foibles, then in the comfort of my garage the next day, carry out as many ‘fixes’ as I could before the next race night.



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Front tyres radiused and scored lightly


First up was the models tyres, these were hard to sand and were of the old type compound we got on models five or six years ago. Firm and a bit irregular in profile. Sanding at the track didn’t work and eventually, when I was home, I removed the tyres and mounted them on blank hubs in a drill press and using some 120 grit emery paper and a flat edge I sanded the outer edges away till the tyre centre section was at the same level as the tyre edges. The edges too had a radius sanded on them to minimise any unwanted track antics. The front tyres had a similar treatment and besides sanding a radius across the tread area, I cut five small grooves into the tread face. This was to minimise front tyre grip when they were side slipping in corners. I have also glued the front bearings in place. These were held forward and down while the glue set, giving them a bit of ‘toe-in’. This was to reduce the amount of toe out generated by the sloppy fit from the factory.


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An original braid


Next was the braids. In a non magnet set up the front tyres didn’t touch the track. The braid material was harder than most and the braids had jacked the model clear of the track at the front. The solution here was to carefully open the braid holders with the pointy end of a modellers knife and substitute the braid material with some softer compound tinned competition braid. The braid holder was then pressed back together again with a small pair of pliers. While I was at it, I fitted the smaller guide keel which I had hollow ground with a dremel to improve its tight corner capabilities.


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The trimmed guide with new braids


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The new braid material in place


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The new braid


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New braid along side old


A couple of other things I wanted to deal with while it was apart was reducing the model weight at the front. I removed the front bar magnet. The screw to the polarity switch is removed and the switch and magnet will fall out. The switch was removed from the power input line by the two miniature plugs. The remaining plugs can then be pushed back together to restore continuity. The model was then set up on the scales again and I had saved about eight grams in all and shifted the C of G back a little way. Because the motor is able to move in its cradle if provoked, I decided to add a little weight either side of the motor. The hot glue was heated well and a small spot was placed to one side of the motor. Some pre cut lead ballast was then pushed into the hot glue. This was repeated on the other side. Once in place, the remaining gap down the side of the motor was filled with hot glue. Hopefully this will hold the motor in place also.


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Ballast in place

This has brought the model up to ninety five grams! Is this too heavy for local racing? Only time will tell. If the model had been running on urethane tyres I might have been inclined to make it a little lighter, but, as the wheels are unusually wide for an RTR model I will be running on the original tyres for a while no doubt, and the extra weight should do the trick.

I’ve left the guide spring in for now but it is on the ‘to watch’ list at its next outing. Everything else might need some minor adjustments but I am fairly confident I have got it closer to what I’m looking for. This coming Friday and Saturday should be educational and maybe not too much else will need to be done. In the meantime, who will be first with the urethanes??
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Re: Carrera McLaren M20 - initial set up for non magnet raci

Postby holty » Thu 22 Jul, 2010 12:49 pm

Given it may be a while for urethane tyres to come onto the market, have you considered swapping the rear axel and wheels to Slot.it or Ninco to accommodate existing urethane sizes.
I like the look of this car, but I am wary of buying one if I can't make it manageable on my tight timber 2 lane track. I'll be very interested in the progress you make with the tyre sanding and weight distribution.

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Re: Carrera McLaren M20 - initial set up for non magnet raci

Postby wixwacing » Sun 01 Aug, 2010 10:58 pm

I've managed to get the rear tyres round on this model and like a lot of other tyres, it responds well to a drop of CRC/WD40 on the rear tyres, rubbing it in a bit then wiping it off again before running.
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Re: Carrera McLaren M20 - initial set up for non magnet raci

Postby wixwacing » Sun 08 Aug, 2010 7:43 pm

I had a chance to run the model on a board track this week and was still perplexed as to some of its habits. Juddering in corners and rattling noises to say the least. A further 'in depth' look was required. The juddering I attributed to the very poor rear wheel hubs. At first I thought it was poor tyres, (they are still poor!) but eventually I removed the body and checked the hubs. Sure enough they date back to the bad old days of plastic wheels and needed attention. This time I have run the model to half speed, and using the edge of a sharp modellers knife, I have scraped at the hub circumference. The illustration shows that while half the hub isn't being touched, the other half has lost quite a bit of material!!. I eventually scraped them ‘til the hub was concentric.



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'Before and after' hubs



Another problem was the rear axle bearings. These had become loose in the chassis and was probably the cause of a bit of judder on acceleration. The axle was removed and I cleaned the bearing outer and the seat in the chassis. The axle was refitted and with the point of a modeller's knife I put a couple of spots of superglue on the axle bushes and watched it soak in to the seat. Even running an unloaded axle it sounded better.



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Left : The original rubber tyre inverted. Right : the MJK after treatment.




Next, tyres!! I've been itching to get some urethanes on this but there is nothing 'off the shelf'!! Eventually I succumbed and got my last pair of Vanquish MG MJK's! These are a little narrower than what is wanted but that would only be the appearance and not the performance. I reversed the tyre and checked the centre ridge dimensions. As it happens, the Carrera tyres have a wider recess in them than they need (another QA problem??) and the Vanquish tyres are actually a closer fit than expected. So, what to do?? The inverted tyre was fitted over a 'dremel' sanding drum and put in a vertical drill press. This was set running at about 1,000 rpm and the tyre was trued on the drum whilst spinning. Using a pointed and a flat ended hobby knife blade, I widened the centre recess to Carrera dimensions and then, as the depth isn't enough, I took the tyre recess a little deeper. Testing every couple of cuts, to see I hadn’t gone too far. Eventually, the tyre was as I was hoping for and all I needed was to do the second tyre.



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The chassis with the finished MJK's and a little extra ballast at the front.



Once both were done, I mounted the tyres on a sanding hub mounted in the drill and sanded the tread area down a little and more importantly, flat. I am loathe to spend too much time sanding tyres on the model as in the past I have had some terminal incidents when things have gone on for too long. All I need to do now is refit the tyres to the hubs and carry out a minor dressing in place, saving gears and motors from unnecessary stress.

Once the tyres were ok, I ran the chassis at half speed and radiused the outer edges of the tyres. I also added a couple of grooves towards the outside edge. I am finding this minimises a models tendency to judder and to lift a wheel in some fast corner entry situations. Hopefully, it will do the same for this model. All that's left now is to try it!!

Another annoying problem were the body rattles. These were reminiscent of the original SCX LMP cars from several years back. I inverted the body and before reassembling, I put a spot of superglue on all the heat welded areas. This made a noticeable difference but if the body was tapped with the finger, there was still one more annoying one. This turned out to be the windscreen. Now! the windscreen is fixed in first and the driver's tray sits over its heat welds!! I wasn't going to remove the tray but the fix hopefully was simple. I got some clear enamel paint and using the tip of the modellers knife, I applied a quantity to the back edge of the windscreen. Capillary action caused the enamel to run along the air gap between the screen and the body. When this had dried ten minutes later, the rattle was gone!!

So, will the mods work out, have I wasted my time? Unfortunately, I won't know at least until next Friday when the Red Team are on the move.

Stay tuned..............
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Re: Carrera McLaren M20 - initial set up for non magnet raci

Postby holty » Tue 10 Aug, 2010 2:34 pm

This appears to be turning into quite a saga. The longer you have to spend tweaking this car, the more reluctant some of us will be to buy one. Hopefully your efforts will have shaved valuable tenths off your lap times. Who knows, may be the Can Am Porsche won't have so many foibles.
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Re: Carrera McLaren M20 - initial set up for non magnet raci

Postby wixwacing » Wed 11 Aug, 2010 4:08 pm

Hi Holty

The main cause of the protracted review is that I don't have a home circuit and rely on good friends for their time, which means fix a bit, run a bit, fix a bit over the weeks. The model's performance is improving dramatically. But you are right, it might put some off, but hopefully, for those who have already bought them, it might remove some of the frustration. Lets hope the Porsche is better! :grin:
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When I'm not racing slotcars,
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When I win, it's because of my talent, not my car or my controller!
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Re: Carrera McLaren M20 - initial set up for non magnet raci

Postby wixwacing » Sat 02 Apr, 2011 1:03 pm

Finally the Can Am series is finished, and after racing on at least six diverse tracks (see the features section) the results were announced. Out of a total of almost twenty participants I came second, three points behind Paul, at least twenty years my junior (coming second to Paul is as good as winning anyway!!). The model had very little adjustments after the initial setup and I was very pleased with its performance , even the one appearance on Ninco track!!
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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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