Tag Archives: karting technical tips

Tech Tuesday: The Crankcase

Combustion in the combustion chamber acts on the piston with a pressure (force when multiplied by the piston head area) which generates a linear movement of the piston. This movement is then transformed into a rotating one since the piston is mounted on a reciprocating mechanism consisting of the crankshaft and conrod. The crankshaft rotates with the support of spherical bearings mounted in the crankcase referred to as the main bearings.

The force acting on the piston is transformed and transmitted through the conrod and crankshaft and must then be absorbed by the crankcase. The crankcase not only has to absorb these forces, it also has many other functions that make it an essential element of the engine. A fundamental role is to act as a pre-compression chamber. When the piston moves downwards in the cylinder, mixture is compressed and pushed into the transfer ducts, through the transfer ports and into the combustion chamber. In addition to this, the crankcase also has the function of being the bond between the engine’s different components such as the cylinder, crankshaft, carburettor, engine-chassis mount, ignition system and coil.

The material used to build the crankcases of modern 2-stroke competition engines, such as those used for karting purposes, is aluminium alloy, which reduces considerably the weight of the engine. Aluminium though has some weaknesses linked to the fact that it heats up more easily than cast iron and consequently deforms more. Its heating up generates a rise in temperature of the crankcase walls which consequently heats up the mixture in the crankcase. A fluid (mixture) that heats up increases in pressure and expands, reducing its density and the volumetric efficiency of the crankcase pump.

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The Crankcasing houses the real guts of the motor

Temperature increases also generate expansion of the aluminium alloy and therefore the walls of the crankcase (they reach around 100°C). This expansion will be different in different areas of the crankcase since the component’s walls vary in thickness and also fresh mixture can act as more of a coolant in some areas than others. Consequently, the crankcase will deform and generate negative effects. For example, alignment between the two main bearings that carry the crankshaft can be lost. Gas sealing between the crankcase and cylinder can also become critical. Another important effect is that the perpendicularity of the cylinder’s axis to the crankshaft is at risk. Finally, main bearings can change the tightness of assembly of the roller balls inside the cages which can produce seizures and breaking of the cages.

The limited mechanical strength of light aluminium alloys from which crankcases are constructed also needs to be taken into account with regard to the threads of the holes for the holding down bolts and the cylinder head studs. To avoid rapid damage to the threads it is advisable for the effective threaded length to be not less than 2.5 times the diameter. Assistance can also be given by the insertion of steel threads that are much more resistant, especially when studs and bolts are frequently screwed and unscrewed. Since the crankcase working as a pump needs reduced internal volume to be effi cient, it is constructed of two halves symmetrical with respect to a vertical plane perpendicular to the axis of the crankshaft. When joined, the two halves must be completely gas tight and to do this a gasket is also positioned between the parts. Mixture loss would reduce the efficiency and performance of the engine.

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The Crankcase houses the Gear box on shifters

To have good matching of the two symmetrical parts, production must be very precise. Cylindrical dowel pins also help couple the two elements. Sealing must also be obtained where the crankcase opens to permit the exit of the ends of the crankshaft. Oil seals are used on both sides and are rubber rings that have one or two ‘lips’ that seal the area around the crankshaft. The aim is to have good sealing but low friction loss generated by the ‘lips’ and the crankshaft that are in contact with one another. As already mentioned, the crankcase also has the role of absorbing all the forces transmitted by the crankshaft. To limit deformation of the crankcase it is built with ribbing all over its external surface. These ribs help both to strengthen the structure and to cool down the surfaces

Tyres: Budget versus Top-End

Competiton tyre versus budget tyre

How does a kart feel when it runs on budget tyres and then competition tyres? We find out. Let’s roll!

You can easily spend £150 on a set of tyres for your kart or you could take the budget option and get a set for £50. But what’s the difference? We pitched a set of LeCont’s top of the range CIK-spec LP11 tyres against entry-level Innova tyres. Fitted to the same kart, driven by the same driver on the same track, it’s just down to the tyres. The lap timer doesn’t lie.

So what is the difference when it comes to lap times? A second, a couple of seconds? Surely it can’t be more than that. Afterall, rubber’s rubber, right? Have a think about what the difference would be over a 60-second lap, remember the number and read on to find out.

What’s the going rate?

We searched the web for kart tyres that cost much less then competition tyres. Web sites selling kart parts actually all deal with professional brands such as Bridgestone, LeCont, Vega, MG, Mojo, Maxxis and Dunlop. Prices are more or less aligned. Using www.kkckartshop.co.uk as a yardstick, you can see that all branded tyres go for a similar amount. YJL Bridgestone tyres can be had for £108, while Maxxis go from £110 to £116. Dunlop are just below £100 for hard tyres and go to over £120 for softer compounds used in the gearbox category. Mojo for Rotax Max are set at £110 and Vega SL6 are just below £110.

For our test, we opted for a set of LeCont medium compound tyres from a web retailer, priced at £120.

Going cheap

With £120 as our benchmark for a set of tyres at the higher end of the spectrum, we aimed to find a set of tyres for a third of the price. On eBay was found a set of medium compound Innova tyres for just £45 a set of new Innova tyres of medium compound, not CIK homologated and for leisure karting, but commented by the seller as excellent!

Our tyres 

LeCont LP11
LeCont are based in France and have come on strong in recent years. Known for offering good performance and excellent durability and stability lap after lap. We used this year’s new LeCont LP 11 (Prime – medium) CIK L/Z. Tyres don’t get much better than this.

Innova IA-2886
Innova tyres are made in China. They produce tyres for many applications, from bicycles and quads to fork lift trucks and lawnmowers. At £10 a tyre, the appear to offer good value.

Start of test: Innova tyres

The Innova tyres looked of reasonably of good quality. Looking at the thread and carcass, it’s hard to see where any corners have been cut. The rubber looked and felt of medium-hard compound and we still had the feeling we could get something good out of our economic set. Mounting on the wheels was easy even through the tyres were new and quite stiff.

We inflated tyres to 0.7 bar at the front and 0.65 bar at the rear, with just 0.05 less on the external rear tyre (left on clockwise circuits), which naturally on our test track, the Viterbo International track, and in most tracks, heats up more and faster, too.

I started slow in my test as I know new tyres must not be run in too fast, since sliding, skidding and correcting too much oversteer or understeer when tyres are cold is extremely counterproductive. This won’t heat up tyres or result in a fast time in the first few laps. Remember, at least with competition tyres, always run them in slowly, following a correct line and avoiding sliding. Your best qualifying lap will almost always come out between lap 3 and 5 and it will be an extremely fast lap compared to all the others.

The Innova tyres seemed to be good at the beginning so I started pushing after a few of laps. I immediately noticed a strange squeaking noise produced by the Innova tyres along each curve, from mid to exit of the bend. Whenever tyres slid this strange noise was produced, as if I was actually running at an lap-record-breaking speed over the outside apex kerb, but, unfortunately, this was not the case. In fact I was actually trying to avoid pushing over the limit of the tyres and having to control over or understeer all the time. There was no solution though: even cornering at a limited speed to avoid the kart sliding too much with a view to getting the power down earlier did not help. To avoid skidding the tyres I had to slow down so much that I could feel I was losing time. It didn’t feel like I was driving a competition kart at all. Lap times were slow, and I had to battle for a terrible 1:03.64 sec lap on lap 4.

I stopped after 8 laps and checked everything was fine, but I was pretty disappointed to be so slow on a track that runs in the Super Rok category with Bridgestone tyres below 55 seconds. Of course this is true during race weekends, where all the rubber laid down provides great grip and all setups are perfectly tuned, but still, I was over 8-seconds off!

The tyre itself looked extremely smooth, which is a very clear indication of insufficient grip. Actually I had never seen such a shiny surface of a used tyre! The centre of the surface of front tyres and two parallel lines on rear tyres, which are the areas of greater contact with the asphalt, were almost polished!

I was back on track for another 15 laps to convince myself there was still margin of improvement… There had to be. I started to push hard, slowing down sufficiently in the braking phase to avoid immense understeer and anticipating the never absent oversteer exiting each corner. It was 15 laps of real torture, struggling with a kart that was much more tiring then when running with competition tyres. All I managed to obtain was a 1:02.84 second lap on lap 11. This result confirmed that the tyres were actually so hard there was no real decay of performance and judging by the lap time, no real performance at all!

At the end of my 15-lap stint, I had an “interesting” experience when braking along the back straight. I was in an extremely fast point of the track where I found myself spinning without really understanding what I did wrong. Sat in the kart, on the grass, I looked around the kart and discovered therear internal (right) tyre had actually come off the wheel even though anti-bead bolts were mounted!

Back in the pits we noticed the tyre was actually not usable anymore. The internal circumference of the shoulder was worn to a point where the tyre was not inflatable anymore. We tried and tried with no luck.

Moving on: LeCont tyres

This year LeCont has homologated new Option (Hard) and Prime (Medium) tyres. We decided to go for the best performing ones: Prime.

We inflated the tyres to 0.6 bar at the front, 0.575 for the rear internal and 0.55 for the rear external tyre. We were ready for our test, hoping for some real fun at last.

I took a couple of slow laps to run in the tyres. After lap 2 the tyres were almost warmed up and I was back to racing again! Although the tyres instantly felt like they offered grip, the lack of rubber on track made it difficult to extract extremely fast laps, but my kart at least was back to racing planet again!!!

It took a couple of laps to get used to hitting apexes again and not locking the wheels under braking. It felt like I was in a brand new kart, one that was twice as fast!

The laptimes moved quickly to low 57 seconds and on lap 9 I ran a 56.68 second lap, which is not bad. During a race weekend, conditions would be different due to the additional rubber on the track and so my fastest lap would have come sooner.

I ran 14 laps in the first session. Looking at the nicely scrubbed-in tyres, you could see the wear on both front and rear tyres was slightly uneven, showing good grip, even though some rubber curls on the internal edge of the surface of the tyres showed that the track was quite slippery and even grippy tyres like these could not compensate completely for these conditions.

I went out for a second session, seeing as there was plenty left in the LeCont tyres. The performance didn’t drop off, despite another 16 hard laps. I shaved a tiny amount off my first-session best time and managed a 56.62 second lap on lap 11, but also 56.66 sec on lap 8 and 56.69 on lap 14!

Our verdict

Save your money!

The difference in lap time between competiton and budget tyres was 6 seconds. Does that surprise you? Before the test we thought it might be between three and five seconds. We were wrong.

More expensive tyres are better than budget tyres is hardly the revelation of the century but it’s not just about lap time. Grip, handling, noise, and also safety, were much better with LeCont compared to the economic and somehow dramatic Innova tyres.

It can be painful shelling out for a set of competition kart tyres, when you can get four tyres fitted to your car at Kwik-fit for not a lot more. While no-one likes to spend more than they need to, the trouble with budget tyres is that the whole karting experience suffers. From missing apexes, to the kart snapping away under braking; a cheap tyre simply can’t hold the chassis, engine and driver input together, making for a frustrating experience.

If your really under a budget, buy a set of competiton scrubbed tyres. Go to any major race weekend and you’ll see teams selling or even throwing out tyres that might not be good enough for that vital extra tenth but would be perfect for the everyday driver.

The characteristics of a good tyre are still good, even when they’re worn.

The next time you’re tempted by budget tyres, think to yourself, are they really worth the money?

CIK-FIA fail to test new front bumper fairing correctly

Bosses of the CIK-FIA have admitted that they failed to test the new front bumper fairing for safety on uneven ground, away from the track.

The use of the fairing, which was introduced at the start of this year, was suspended last month following criticism from drivers and concern at the possibility of the bumper being ripped off and travelling under the kart.

“If the front fairing drops down onto the lower bar, it could, under certain circumstances, pass underneath the kart,” said CIK-FIA executive secretary Kay Oberheide. “This could only happen if the front of the kart is lifted upwards which is possible if a driver leaves the track and the kart crosses the verge or if the driver is off the track on a surface that is not flat, for example on grass. We should reproach ourselves for not having tested this system away from the usual track, on uneven ground. We have conducted a successful test in which we found a solution. I am confident that we will be able to implement this system for all international events at the beginning of May.”

Track Testing: Tony ROK

Why a Tony ROK

After months of organization and setting up of the new “Track Testing” column, me and my photographer managed to visit the great Tony Kart Company and collect our Tony EVR ROK  engine kart. We have chosen this solution as it seems one of the easiest ways to start karting with a very performing chassis (Tony Racer EVR) and a very reliable TAG 125cc two-stroke engine (Vortex-Rok).

From 2003, the year of its establishment, until today the Rok Cup has won the trust of many fans in more than 35 countries all over the World. Rok has been a good novelty since it has been the first real single make solution directly followed by the company.  Start has been in Italy at first, then in Europe. After that it crossed the oceans and has arrived in South Africa, Asia and America. All the national champions, in every category, win the possibility to race in the Rok international Final, which is the CIK-FIA event closing the Rok season every year. The 280 best Rokkers coming from all over the World take part in this race and in the end we discover who the absolute champion in each category is: Rok, Super Rok, Junior Rok and Mini Rok.

Rok engines

Rok engines are a complete family of four different versions for the same number of classes: Mini Rok, Junior Rok, Rok and Super Rok. Mini Rok is the entry level for very young drivers. Vortex has developed two Mini Rok engines:
Mini Rok MINI 60 and Mini Rok BABY 60: the two versions differ from one another in carburettor and exhaust.

MINIROK BABY 60: supplied with carburettor of 14mm diameter and baby exhaust (reduced power), dedicated to the youngest; it is the entry level in the karting world.

MINIROK MINI 60: supplied with carburettor of 18mm diameter and mini exhaust; it is the second step in competitions, usually from 9 to 12 years old drivers.

 Rok range

JUNIOR ROK and ROK

We have decided to go for the ROK for our track testing since it is a good compromise between performance and reliability. To my opinion it probably represents best the aim of Vortex in creating the ROK World.

Junior ROK and ROK are based on the same engine except for the exhaust curve. Engine is a 125cc single-cylinder 2 stroke with reed valve admission in the crankcase. It is mixture lubricated and liquid-cooled with integrated water pump. It is offered with a digital ignition and an integrated electric starter, which uses a dedicated battery. It is provided with a balance shaft which reduces vibrations. A centrifugal dry clutch makes it possible to keep the engine on even when the kart is still.

 

Mini ROK Junior ROK ROK Super ROK
Bore (mm) 42.10 54 54 54
Stroke (mm) 43.00 54 54 54
Displacement (cm3) 60.00 123.95 123.95 123.95
Cooling Free air liquid liquid Liquid
Intake Piston port Reed valve (length 63.5 mm x height 25.5 mm) Reed valve (length 63.5 mm x height 25.5 mm) Reed valve (length 69.5 mm x height 25.5 mm)
Max torque (Nm) 19.6 at 10,000 19.6 at 10,000 20.2 at 11,500
Max power (HP) 10 at 10.300 19 at 11.500 29 at 10,500 36 at 12,500
Max revs 13,800 13,800 16,700
Carburettor 18 mm (14 mm for Baby ROK) Dell’Orto VHSH 30 mm Dell’Orto VHSH 30 mm Dell’Orto VHSH 30 mm
Fuel pump Dell’Orto Dell’Orto Dell’Orto Dell’Orto
Exhaust system With intake sylencer With integrated silencer and depower system With integrated silencer With integrated silencer
Drive Centrifugal Dry clutch Centrifugal Dry clutch Centrifugal Dry clutch Centrifugal Dry clutch
Lubrication 2-3% (Rok Lube or Elf 909 HTX) 3-4% (Rok Lube or Elf 909 HTX) 3-4% (Rok Lube or Elf 909 HTX) 6% (Rok Lube or Elf 909 HTX)
Weight 8kg 17,5kg 17,5kg 15 kg
Ignition system Electronic Selettra or PVL Electronic PVL Electronic PVL Electronic PVL
* Price (in Euro) – with carburettor, fuel pump, exhaust muffler, radiator & supports, thermostatic valve, cooling system pipes, on-off push-button panel, battery, battery support, electric plant, intake silencer. 1,950 + VAT 1,950 + VAT 2,400 + VAT

Prices are only indicative and subject to changes.

SUPER ROK

Super ROK is the ultimate evolution of the ROK engine by Vortex, conserving many of its important characteristics, but featuring an amount of innovations. Not changing the displacement of 125cc and the reed admission in the crankcase, the reed block is now bigger, and the carburettor is still a 30mm diameter VHSH by Dell’Orto. The new cylinder, always with liner, has a 5-transfers scavenging, and the 3-ports exhaust is provided with pneumatic power valve. The digital ignition has a different advance diagram; the exhaust plant is new in design with integrated silencer; the rotor of the centrifugal clutch is now monolithic.

The Chassis

RACER EVR Tony Kart freno BS7

Together with our Rok engine we have chosen one of the most performing and successful chassis from Tony, the RACER EVR. This chassis is available for both KF and KZ categories and represents the natural evolution of the EVXX the chassis that allowed Tony Kart to win all the most noble CIK-FIA competitions, including the World Championship, in these last years. The EVR is composed by a frame realized with Ø 30 mm tubes, which determine the kart to be more “free” when exiting corners. The Racing version is equipped with the new M4 bodywork and the new WTD (Wind Tunnel Design) stickers. The design of the new plastics resulted from several hours spent in the wind tunnel. The plastics have been optimized in order to reach an optimal aerodynamic penetration and to allow the air flow to invest the engine, the radiator and the brake systems in the best way during the races.

Homologation : CIK FIA 56/CH/14
Frame diameter : 30 mm
Wheelbase : 1050 mm
Stub Axles : OTK HST
Braking System : OTK BS5 – BS6 – BS7
Steering wheel : OTK rivestito in alcantara
Wheels : OTK MXP in Magnesio
Side Boxes : OTK M4
Seat : OTK a fondo piatto

 

This top chassis is provided with OTK magnesium accessories. The OTK brake systems BS6 and BS7 are still one of the most important features characterising both the former model and the new one. Front brakes are also included and will be tested to understand if and when these brakes are useful and performing for a driver.

Base setup for Tony EVR is neutral height front and rear and neutral camber and caster. Front torsion bar must be flat and rear bar eliminated. Rear carriage width will be to maximum limit at 140 cm and front carriage width will be adjusted with a small and a large spacer, equal to 2.5 cm additional width. Convergence must be 1 mm “open” at the front, so 0.5 mm per side. Seat will have stiffness bars o both sides, at least one, possibly two per side.

Rear axle stiffness is determined by five different materials indicated on the axles as HH, H, N, Q and U, starting from the stiffest to the softer. Base setup uses the N axle.

Prices of EVR chassis is 4,490 Euros VAT included, including front brakes, magnesium accessories and seat (price only indicative and subject to changes)

Ancient & Modern – Old karts get a second chance

P1010129
It will be worth it. A fully restored 100cc Montesa

Before we continue with our 100cc engine restoration, I would like to introduce a new feature to the readers of this column. Ancient & Modern will now contain race and event reports for the historic, vintage and classic karting clubs. Obviously, 2006 is going to be a busy year with events, races and demonstrations planned up and down the country from April through to November and organisers and club secretaries should simply submit details of their events or results for inclusion. Please telephone the helpline number with the information. We have already had the first round of the Retro Racer series that took place at East Kirkby on April 2nd. The winners were:

Class IV Vintage:
1 Steve Greaves Fastakart/Villiers

Class IV Historic:
1 Tony Keele Keele/Bultaco

Class IV Classic:
1 Bob Phair Deavinsons/Bultaco

Class I Classic:
1 Jeff Gray Barlotti/Parilla

The next Retro Racer round is at Stretton, Leicestershire on May 21st. Visit the Retro Racer website (Weblink 1) for full details. The biggest event of the year is always the Shenington Superprix that will include static displays, on track demonstrations, a kart jumble and a drivers’ reunion. The event takes place on the 16- 18th June and is one not to be missed. Visit the Historic and Classic Kart Club for Great Britain’s website (Weblink 2) for full details. The winner of the Ancient & Modern photo competition was G. Rosenegk who correctly identified the kart as a Please Kart as well as naming several of the west country drivers. Well done.

The CIK have produced an excellent leaflet on karting to celebrate the sport’s 50th birthday. A copy can be downloaded from www.cikfia.com

100cc Engine Restoration (Part 4)
The final job to do is to remove the main bearings and oil seals from the crankcases. A heat source will be required to expand the aluminium cases and allow the bearings to drop from their housings. Every engine builder has his or her own preferred method but the easiest thing to use is a domestic, electric hotplate. The job is made easier if you have some suitable metal weights made for you so that the bearings will drop from their housings via gravity, without the need for any external force. Once heated, set the cases aside to cool. We can now start to examine the components previously removed from the engine so brace yourselves.

Barrel and Piston
I would strongly advise you to take your barrel and piston to a specialist kart engine builder and request that they carry out the required measuring and corrective machining work for you. The tight tolerances involved require measuring and cutting equipment capable of producing results to less than 0.01mm. Your chosen engine builder should have no problems working to this type of accuracy. As an example, piston to bore clearance on an old 100cc rotary valve engine will usually be set in the region of 0.09 to 0.10mm and the entire bore life of an old 100cc engine will be in the region of 0.5mm before it is scrap! I hope this helps put things in perspective.

Crankshaft and Connecting Rod
Things don’t get much better with the crank and rod assembly. For reliable performance, the crankshaft must be assembled and trued to within 0.01mm. Only your trusted engine builder has the tools and expertise to part your crankshaft, fit a new rod and big end bearing and then reassemble and true the crank. The work on the barrel and crank assemblies won’t be cheap but a failure of the piston, crank or rod under racing conditions will usually result in a scrapped engine. Make your choice. Next month we will continue with inspection and replacement of the component parts and, hopefully, we can do some of the work ourselves and save some money.

Jon Pearce

Track Testing: LeCont tyre compounds

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We were at the international track of Viterbo. Asphalt temperature was 37°C

LeCont tire compounds
After our studies on weights last month, as promised we finally managed to put up an interesting track test on tire compounds. Tires, as we know, are one of the major parameters that act on kart performance. LeCont is an important company that works 100% on performance tires. Racing tires for cars, karts and mini motorbikes are studied and offered by the Italian firm.

Which tires to test

LeCont kindly and quickly sent us a set of three different tires named LH01, LH03 and LH02, together with a set of rain tires. These last ones have not been part of our test. The three LH tires go from the ones with the softer compounds (LH01) to the hardest (LH02). Such hardness is measured in IRHD grades. So LH01 tires have 48 IRHD, LH03 have 54 IRHD and finally LH02 have 60 IRHD, shifting in steps of 6 IRHD grades. The three types of tires are also recognisable from the coloured line that runs along the entire diameter of the thread. Yellow for LH02, green for LH03 and blue for LH01. Dimensions are 11×7.10-5 for rear tires and 10×4.50-5 for front ones. The LH tires in general are made to be simple to use and have good lasting performance. They are made with polyester and have quite a soft structure that works quite well with low grip track, but maybe is not as performing as other racing tires with high grip tracks and rubber on the asphalt and with high temperatures. Also prices as indicated on the Internet (www.lecont.com) site are pretty interesting with cost of a set of LH02 equal to 125€, LH03 139€ and LH01 145€.

Start of testing – LH02

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Rear LH02 tyres indicating practically no wear except for some diagonal lines in the internal area of the tread just toward the axle hub. The very smooth surface indicates low grip

Considering that all three sets of tires had the same structure, differing only in tire compound, the idea was to understand how a difference in tire compound hardness can act on tire performance and on lap times. We mounted the first set of tires starting from the hardest ones, the LH02, the yellow lined. Inflating pressure set at 0.65 bar. We know that for LH tires LeCont indicates a 0.84 – 0.87 bar working pressure.

We were at the International track of Viterbo. Asphalt temperature measured equal to 37°C.

The were no karts on the track except us, so very low grip. This was the reason to have 0.65 bar instead of a more traditional 0.6. First laps I needed to find the right pace, also trying to get the feeling both with the tires and the track. Grip was not particularly high and performance was acceptable, but not astonishing. Balance of the kart was good and no particular defect was shown by the tires, with grip quite constant from the first laps and no sudden loss of grip at any time. Good performance entering the curves, but some limits in traction and generally on rear tires having limited grip especially along fast curves. Lap times started from high values both for my need to warm up and for the need of the tires to warm up!

1° lap 1.04”68

2° lap 1.04”25

3° lap 1.03”16

4° lap 1.03”10

5° lap 1.02”57

6° lap 1.02”15

7° lap 1.02”01 (best lap with LH02)

After the 7th lap, times were more or less constant. The hardness of the compound was evident all the way. Good overall performance by the LH02 tires, but the need to have long lasting tires with harder compound had on the other hand some limits on a low grip track and especially when lateral acceleration on fast curves asked for high lateral grip. Braking performance anyway was also pretty good. After around fifteen laps tire thread showed very good resistance to wear, which is the main aim of the LH02 tires.

LH03

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Rear LH03 tyre with grainy tread surface indicating much greater grip compared to the LH02. Still just a little wear in the internal area of the tread indicated by small diagonal lines

We then quickly changed to softer tires, the green LH03 tires. 6 IRHD degrees less of compound hardness compared to the LH02. Starting pressure at 0.6 bar. Already in the first laps I felt performance was extremely higher. Grip was greater with the tires doing all the job to obtain grip even with a track asphalt still almost completely without rubber cover. Traction and lateral grip were greatly improved and lap times quickly confirmed my feelings.

1° lap 1.02”03

2° lap 1.01”70

3° lap 1.01”18

4° lap 1.01”39

5° lap 1.01”00 (best lap with LH03)

6° lap 1.01”09

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Front LH03 tyres with slightly grainy surface and no real wear

Laps times went on constantly after lap 6. Great difference was evident especially at the end of the great straight of the start, where the very fast right turn needs great grip, especially on rear tires, so that speed can be kept high without releasing the accelerator for too long. Rear tires with good grip slide just slightly towards the external part of the curve permitting the kart to turn following the right trajectory. With the yellow LH02 tires such curve was pretty hard and speed had to be reduced too much.

LH01

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Rear LH01 tyres with grainy tread surface indicating good grip but also visible wear effect in the internal area of the tread with greater diagonal lines formed. The balance between performance and wear (20 laps) is still very good

Final testing was done with the blue LH01 tires. Another 6 IRHD degrees reduction for the softer tires of the lot. As said IRHD intervals from LH02 to LH03 to LH01 are equal to 6 degrees. Starting pressure set again to 0.6 bar. The feeling in the first laps was of great easiness in driving the kart. High grip, just slightly, as driving sensation, greater then the LH03 tires. But the astonishing performance came from the fact that high grip left the kart free to smoothly run along curves and exit them. Pushing harder and harder lap times decreased constantly. Braking and entering curves was great and also traction and lateral grip given by the tires was excellent. When the limit entering corners was somehow passed, the front tires slid laterally, but performance was not impacted too much and control of the kart was always possible.

1° lap 1.01”02

2° lap 1.01”00

3° lap 1.00”80

4° lap 1.00”41

5° lap 1.00”72

6° lap 1.00”70

7° lap 1.00”20

8° lap 59”90 (best lap with LH01)

9° lap 1.00”01

So finally the blue tires gave, as predictable, the best performance. And incredibly enough lap time difference was very similar, around 1 second (1”), between LH02 and LH03 and between LH03 and LH01. So it is as if 6 degrees of IRHD are equal, at least on Viterbo track and with Rok kart, to 1 second. Wear of the blue and green tires was also very low and so performance seems to be very good and combined with longevity of the tires. Only front tires showed some wear of the thread because of lateral sliding when pushing really hard entering the curves. This aspect could though most probably be solved acting on chassis setup. We will surely see that in future issues.

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The front LH01 tyre with good grip indicated by the tyre surface but also rubber being ripped by excessive sliding when pushing hard for performance. Lines both diagonal and longitudinal are present in a wider area of the tread. Set-up should be improved

Ancient & Modern – Old karts get a second chance

Before we continue with 100cc engine restoration , I would like to briefly share with you some karting photographs that were given to me recently. It was not the technical content of the photographs that impressed me but the sense of fun and friendship that they depict. How many modern day karters will have photographs like these to look back on in forty years time? If any of you older karters can identify the kart or any of the karters shown, I am offering the prize of a drive in an historic kart at one of the upcoming 50th anniversary events. The only clue I will give you is that they are all west country drivers, the date is 1960 and the circuit is Crisbett Mendip. Answers to the address at the foot of the page please and best of luck. 100cc Engine Restoration (Part 2) Having established that your barrel still has some bore life left in it and that you are going to bite the bullet and restore your cherished engine, proceed as follows.

Comp Pic 1
Happiness is a sport called karting

Carefully remove the barrel while supporting the piston and connecting rod with your other hand. Put the barrel to one side for now, we will need to measure it up at a later date. Next, remove the piston circlips and slide out the gudgeon pin, having packed the mouth of the crankcase with rag to avoid any loose rollers falling into the engine. Note the arrangement of any small end spacers that may be fitted. Have a quick look at the small end eye in the connecting rod. Any signs of scoring or bluing will mean that a replacement rod is probably going to be required. Some of the very early connecting rods have a plain bush fitted to the small end eye. Again, inspect for damage or excessive wear.

Check that the piston rings are not trapped in their grooves and that the ring pegs are still in position. Most early pistons will be of the boost port type and will have a rectangular window cut in the side of the piston. Check carefully for cracks in the piston skirt, especially around the boost port window and the transfer passage cut-outs. Depending on the state of tune of your engine, you may have additional holes drilled in the piston that connect to additional transfer ports. Five or seven port arrangements were not uncommon. Some later engines will be of the TT type and may not have the window in the piston. Carefully remove the barrel base gasket or gaskets without tearing them. You will probably have to make new gaskets using the old ones as templates so take care. That’s the top end of the engine removed, now for the bottom end. Before you can proceed too far with dismantling the bottom end of the engine you are going to need one or two basic but essential tools.

Comp Pic 2
Identify the kart or some of the karters and you could win a prize

The first of these is a sprocket puller, still available from most good kart shops. This will enable you to remove the engine sprocket when used in conjunction with a home made chain wrench. The chain wrench can be made from an old chain and will enable you to lock the drive sprocket prior to undoing the crankshaft nut. The next tools you will require are an ignition locking tool and an ignition extractor. Again, the locking tool can be manufactured at home and is used to lock the ignition rotor to allow the crankshaft nut to be undone. The extractor can then be used to remove the rotor from its taper on the crankshaft. If you have Motoplat ignition, the tools are still available from good kart shops. Should you have the original CEV flywheel magneto ignition you will require an extractor with a different thread form on it. These extractors are no longer commonly available but I can probably source one for you if you want to persevere with the original CEV ignition. That’s all for this month, next month we will separate the crankcase and inspect the parts removed from the engine. Jon Pearce Helpline: 01380 730585 (Evenings only) Competition Address: J. Pearce, 4 Gaisford Chase, Worton, Devizes, Wiltshire SN10 5RX.