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Driving on slicks in the wet

A situation that really puts the cat amongst the pigeons. Observation and confidence are the two characteristics that will enable a driver to capitalise on such a situation.

Firstly you need to understand just how wet the track is and whether or not it will dry quickly. You may find yourself with a lack of grip for a few corners and then be able to attack again after that, if a driver is slow to pick up on this fact they can lose a huge amount of time and potentially places. For this reason drivers need to be looking as far in front of them as possible to give them the best chance of staying on the track.

Watching other competitors will show just how much grip is available on that bit of track, this may allow the following driver to avoid the same mistakes, brake earlier or simply react differently to the grip levels.

The confidence part comes from being able to ‘throw’ the kart around, using an opposite lock braking technique and big, certain steering movements will produce a bigger weight transfer and in turn greater turning forces. By driving too tentatively the kart will simply understeer off the track or have to be matched with a pace almost equivalent to stopping, just to get around a corner.

Without confidence in both the capabilities of the kart and the drivers own skill levels, this aggressive style can lead to driving to simply spinning off the track.

Trent Valley KC Club Championship

Alternative Tips 

Other pointers can include braking off line, using the driver’s body weight and using the kerbs. Braking off of the normal racing line is quite often less slippery which allows the driver to slow the kart down much quicker, without locking up and without sliding off the track.

By leaning to the outside of the kart when cornering, the driver can maximise the weight transfer and grip to the outside wheels, increasing the cornering ability of the kart. Kerb use can be advantageous in that they can increase weight transfer if used correctly, if they are hit too hard or at the wrong angle the kart may simply spin off the track, they should be used at the discretion of the driver.

This article was originally published in Karting magazine in October 2015

 

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Tech Tuesday: Engine cleaning

This week we’re going through the process of cleaning and checking your X30 engine after a race meeting.

Remove the chain guard, the earth cable and the carb and plug up the holes so degreaser doesn’t get inside the engine.

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Remove the clutch, using a tool to hold the ring gear so you can undo the nut that holds the clutch on. It’s better to use that than a piston stop tool which will put the crank out of balance costing valuable power!

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Check the clutch for wear on the teeth – the one taken off our engine was good, but the 10-tooth shown here for comparison has some “shark-fin” wear on it which will get worse.

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The old style clutch drum shown here on the right has holes which can let grease and track crud in which can make your clutch illegal if checked by the scrutineer, so check your clutch for grease (you should do this throughout the weekend anyway).

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The washer and the o-ring that sits inside the clutch helps prevent ingress of grease from the needle roller bearing that the clutch drum rotates on. Make a note of the order – bearing, o ring then washer – as you take them off the clutch.

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The clutches shoes are very robust, but you need to watch closely for wear and cracks on them in the area indicated by the screw driver and for wear and possible corrosion on all the parts you took off.

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Finally take the cover off the Bendix to clean it

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Spray the engine with elbow grease and give it a good scrub with a paint brush, leave the elbow grease on for a few minutes and keep brushing. You can get parts cleaners from Machine Mart which use kerosene or even old mixed petrol as a cleaning agent but we prefer to use Elbow Grease which is a cheap and gentle degreaser. Engines can be filthy after a wet weekend, covered in oil and mud. The aluminium cases and barrel are naturally porous which holds on to dirt so when you give them a good clean you have the chance to get a close look at everything. The engine looks much better after a good scrub too!

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Once you’ve given it a good wash and scrub with degreaser then rinse it off with brake cleaner and to dry it blow it off with a compressor.

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The Bendix cover and the chain guard are damaged from a chain which snapped at the last race so we’re going to replace them.

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Next take the reed block out and check the reeds for chips and cracks, it will usually be at the corners and edges.

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Check the condition of the two reed block gaskets.

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Check the big end of the con rod for discolouration which will indicate a serious problem, although it’s rare.

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Check the oil level – this needs to be done when the engine is level and due to the engine mount it isn’t. You can either take the engine mount off or prop it up with something.

Take the 14mm gold bolt out. The oil is just starting to drop out here so the level is OK. The amount of oil required in the gear case is specified in the owners manual. Although the owners manual specifies a relatively thick SAE30 engine oil it’s best to use a thin oil like light gear oil or Automatic transmission fluid. Thin oil in the gear case saps the least amount of power. If you need to put more oil in take the cap for the breather out and use a syringe to fill it up again.

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Take the head off to check the general condition of the piston and the o-rings inside the head.

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If you’re going to take the barrel off make sure the o-rings don’t fall down inside the engine! It’s easily done and a pain to get them out again. Worst case scenario is you would have to split the cases to find the O ring although washing the bottom end out using petrol and turning the engine upside down would probably get the lost O ring out.
In good light, have a look at the condition of the barrel, looking for scoring of the bore and any unusual wear marks. Check for carbon deposits around the exhaust port and scrape off the carbon if there is any.

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Check the general condition of the piston, looking for bad score or wear marks and check that the ring is free around the piston. The piston has ‘rings’ present on the skirt from the manufacturing process. These rings help retain oil on the piston. If there are any polished areas on the piston where you cannot see the rings then this is a likely place where a seizure could occur. The older a piston gets the larger the polished areas get and the less oil being retained on the piston. The coating on the IAME pistons is very good and the engine is not prone to seizure unless by human error on the carburation but the longer a piston is left in the engine, the higher the chance of damage to the bore by normal wear or by a seizure!

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Check the crankshaft for cracks.

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Reassemble, paying special attention to the o-rings and the gaskets and when you go to put the nuts back on the head you need to do them up to the torque specified in the owner’s manual.

 

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Carbs

Tech Tuesday – Axles

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Tech Tuesday: Seat Basics

The seat and its supports are often underestimated by chassis tuners and drivers, but the seat is a fundamental part of the chassis and determines a lot of the handling characteristics of your kart.1900_IZ1

Various seats and supports

The structure of the seat and its connections to the chassis generate a system which will change the chassis stiffness. The material of the seat: glass fibre, Kevlar, carbon or mixtures of these elements, with different thicknesses will generate variations in the torsional flexibility of the chassis, since the seat itself can vary in stiffness.

For example a carbon fibre seat is, with the same thickness, three times as stiff compared to a glass fibre one. A Kevlar seat is on the other hand much more elastic if compared to a glass fibre one. Costs are also to be considered and, as usual, carbon fibre seats cost at least double a glass fibre ones.

MLT5KG

 

Costs

Seats vary in costs, depending on the materials used. The cheapest seats, start from £30 for a very basic OMP junior seat, up to around £200 for a seat like the Tillett T11. Seat fitting kits cost around £10 and additional padding can cost up to £30.

Seat fitting tool

Serious karters would be wise to invest in a Tillett T Board seat fitting tool which enables the user to log the sit fitting position, making it easy to return to successful setups when revisiting circuits. The Tillett seat fitting tool not only provides a consistent seating position but saves time in getting to that position. The tool ensures accuracy and can be used to position seats in relation to axles on other kart chassis. The tool isn’t cheap at £290, however your local club or kart shop may well have one you can use.

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‘Tillett T-board will aid your setup’

 

Seat position

Three distances need to be addressed to fit a kart seat:
» Front to back in the chassis, » Angle or tilt of the seat
» Height

Most kart manufacturers tell you their recommended height – measure from top edge of the seat down to rear axle surface and the distance between the extreme edge of the seat to the front (often two measures are used starting from left and then right), and the front tubing of the chassis (where the heels usually hit)

Effects of supports on chassis behaviour 

As the seat is part of the chassis, it determines the overall rigidity, especially of the rear of the kart. Generally speaking, so seats work better for low power karts, as these free up the chassis, stopping the inside rear wheel from dragging on the track and absorbing power (rear internal wheel lift earlier and at lower speeds). As the power of the engine increases the additional weight transfer of a slightly stiffer seat may prove advantageous (rear wheel not lifting too early and going back into position quickly for early acceleration).

However on some track surfaces or track conditions it may be better to achieve grip by putting as much of the tyre surface as possible in contact with the track, on others it may be that the only way to get grip is to increase the downward forces that act on the outside tyres. So there seems to be no absolute solution.

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Tech Tuesday: Welding Part

Karts are made of steel tubes with different compositions of Carbon, Nickel, Chrome and Vanadium. Such tubes have particular characteristics that determine the functioning of the chassis. Elasticity of the material, diameter of the tubes and thickness of tube walls determine the capacity of the chassis to bend, absorb bumps in the track and generate vertical forces on tyres as to create downward forces that are the base for grip generation between tyre tread and asphalt. All these situations are possible only because steel tubes are linked together in a certain way. This “way” is welding of the tubes one to the other.

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A welder doing his thing

What is a welding?

A welding is a volume of material that has been fused and solidified by the heating with different systems of a volume of material. This volume usually is composed by the sum of parts of two different elements that have to be joined one to the other and some additional material added and mixed with the two parts. In karting weldings are used for unifying together the tubes of the chassis and positioning parts such as rear axle bearing mounts. The way the weldings are realized determines much of the quality of the chassis in terms of resistance, flexibility and deformation.

Kart chassis are welded using a welding machine that creates a high tension between a cathode and an anode and, through the passage of energy between the two, generates very high temperatures. This high temperature melts the metal of an electrode and of the tubes of the chassis. These metals mix and solidify together creating a unique metallic element that links the tubes together.

These electrodes are made of iron or, for better quality, of steel. Finally the welded parts will show an area of melted and solidified material that, in ideal conditions and perfect welding procedure, will have almost the same strength and characteristics of the tubes themselves. In reality though, air and high temperature determine oxidation of melted metals and change in the microscopical structure of metals. This can bring to weakness of the welding.

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An example of where you may need to welf your chassis, though this one might be a write off!

Welding machine and process

A welding machine has the capacity of generating a tension between two electric lines that end one with a clamp, that has to be positioned on the chassis, and one with a changeable electrode that is mounted on a second clamp held by the welder. The welding machine has a scale that regulates the tension between the clamp, and the chassis to which the clamp is linked, and the electrode. When this element is positioned close to the clamp and/or the chassis the high tension between the two elements creates a passage of electricity and the creation of great heat between the parts even though they are not touching each other. The greater the tension regulated on the machine and the earlier and with greater distance between the two elements we will have a passage of electricity and the melting of both the electrode and the area of contact between the electrode and the chassis. This will lead to a fusion between the metal of the tubes in contact and the material from the electrode.

Welding is a complicated process that gives good results only if the welder has the capacity and experience to obtain the right fusion and melting of material from the electrode and the tubes. In fact if tension is regulated too weak no melting effect will be generated and we will only obtain a continuous and repetitive sticking of the electrode to the tubes with difficulty to take it off once it is stuck. On the other hand a too strong tension will determine an excessive fusion of material with holing of the tubes and weakening of the entire structure. The choice of tension must be done based on the thickness of the electrode and the thickness of the elements joint together (walls of the tubes).

The welding done by the welder manually usually is completed in more phases. After each weld, along the line of contact of the two tubes, the area, that has partially cooled down and from an orange-red colour given by incandescence has become grey, must be checked to see what material has really generated a good and strong link of the tubes, and which is instead only laid over the tubes and has no real joining effect. The first “good” weld shows a silver shiny area, the second is mainly a grey unsmooth surface. Best check is made by hitting hard the welded area with a metal hammer and a metallic brush (often given with the welding machine as kit, together with eye protector glasses). If the material is correctly hardened it will not come off even with the hardest hammering you can do, otherwise metal parts will come off, which means they would not anyway resist more then a few minutes when the kart is running and bending.

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A kart chassis can be complex and highly strung

Practical welding hints

Let us see how to proceed when welding two parts of a chassis. First of all be sure to position and fix well the two parts that need to be joint together. The surfaces that are in touch must be in good contact and well blocked. Then position the clamp on one of the two parts. Be sure the clamp is in good contact with the metal. If the clamp is positioned on a chassis tube verify that paint does not isolate the chassis from the clamp, in fact there must be contact metal to metal to obtain tension transmission to the area that must be welded.

Now try to set voltage on the welding machine starting from a low value, usually indicated on the instruction sheet of the machine depending on the thickness of the electrode used. To warm up the electrode touch quickly the clamp that is surely the element with better tension transmission compared to the chassis of the kart. After the electrode has lit up producing some sparks it is ready for welding. Always cover eyes with welding mask or glasses!!! This secures from sparks in the eyes and even the strong light coming from the lit electrode must be absolutely avoided since it can harm seriously your eyes and anyway partly blinds you for some time.

Start touching quickly the area to be welded and see if sparks are produced. The quickness in doing this is motivated by the fact that if the movement is too slow the electrode sticks to the metal tubes and is very difficult to pull off. The real welding must be done positioning the electrode at a certain distance from the area that has to be treated. Also the electrode must not be vertical respect to the surface to be welded, but inclined. This should permit a continuous movement of the electrode on the surface with production of a strong light and no sticking of the electrode to the metal. If this does not occur and the electrode goes on sticking to the metal we can try to increase the tension on the welding machine and this will help avoid the problem. After each weld hit hard the area with a metal hummer so all the waist material comes off and leaves a good clean surface on which to work on.

Like this article? Then read more Tech Tuesday here:

Tech Tuesday – Pistons

Tech Tuesday – Weight and seat positioning

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Tech Tuesday: Pistons

Pistons are elements that lay an important role in engine performance and reliability. They in fact act as valves on the gas produced by mixture burning in the combustion chamber. These gases at high temperature and pressure have a very high quantity of energy that can be transformed to mechanical energy through the con-rod and crank-shaft system. This system is moved thanks to the capacity of the piston in sealing the volumes over and under it in the cylinder and crank-case. Also in this passage mechanical energy of the piston expressed through a longitudinal movement is transformed in rotational mechanical energy. All this happens with great forces acting on the piston (mechanical stress) that are added to the high temperatures that the piston reaches in contact with the burned gases (thermal stress).

Roys DD2 Piston

Piston movement

Pistons move longitudinally in the cylinder, but their speed changes constantly in a sinusoidal way. This means the piston starting for example at top dead corner (TDC) has a speed equal to zero. Then it accelerates quickly reaching top speed when the con-rod is at 90° respect to the crank-shaft arm. After that speed decreases again and is null at bottom dead corner (BDC). This quickly changing speed indicates strong accelerations (both negative, deceleration, and positive). Any acceleration generates a force called inertial force. Inertia is the capacity of every body to oppose itself to acceleration (negative and positive). The opposition is the inertial force. Inertia increases with weight of the element and the square value of otational speed of the crank-shaft. Maximum negative and positive inertial forces are at TDC and BDC.

In addition to the longitudinal movement along the cylinder axis he piston has orthogonal movements that are determined by the lateral forces generated by the inclination of the con-rod respect to the cylinder longitudinal axis. Since the diameter of the piston is slightly smaller than the one of the cylinder, the piston can move sideways inside the cylinder. When the piston is moving upwards it is pressing on one side of the cylinder liner. When it passes the TDC and comes down the piston presses on the opposite side of the cylinder liner. This is due to the fact that the con-rod is inclined on the opposite side.

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Total forces on the piston

In addition to the inertial forces acting on the piston, the head of the piston has to deal with another mechanical stress, such as the high pressure coming from the burned gases in the combustion chamber, and a thermal stress as the temperatures transmitted from these same gases. In particular in two stroke engines a cycle is completed in 360° of the crank-shaft, which means the piston has less time to cool down respect to the situation of a four stroke engine. In two-stroke competition engines such as kart engines the highest temperatures are reached at the centre of the piston head and can reach 400°C (752°F) in air cooled engines and 360°C (680°F) in water cooled engines.

Heat transmitted from the burned gases in the combustion and expansion phases to the piston head is then given to the cylinder through the ring(s). From 30% to 60% of the total heat energy is transmitted this way and helps cooling the piston. Piston temperature increases around 3°C every 100 revs/min and also 15° every bar of increases of medium pressure in the combustion chamber. Also combustion timing and compression ratio influence the temperature of the piston.

PISTONS_135cc_150cc_SM

All these factors stress strongly all the structure of the piston and this is why materials and shape are well designed to obtain a very light and strong/resistant component. Aluminium for control and limitation of deformation given by high temperatures and additional elements added to the piston are key for obtaining a good result. Shapes also have changed a lot during the years, but finally they seem to be today very similar to one another especially in two-stroke competition engines for karts.

We will see in the next issue exactly how pistons are built and how the selection of the materials is made of a series of elements that help make a resistant component with also good thermal characteristics that help reduce friction, increase performance, reliability and durability of the piston and the entire engine.

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Tech Tuesday: 7 things to check on your kart

Kart prep is an ongoing thing but to get your season off to the best start you can’t beat a pre-season garage session. We’ve spoken to industry experts to get the last word in kart preparation after a winter lay-up.

1 Check for regulation changes

Every year drivers get caught out by what seem like petty rule changes and the worst case scenario is that it happens at the first round of a championship where you have to count any zero scores due to technical exclusions. So read through the MSA general karting regulations, your class regulations, and any club or championship supplementary regulations. Don’t let it be you who is chucked out for having your tyres rotating in the wrong direction!

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Most teams and kart shops are able to check your kart is straight on a jig

2 Check your chassis is straight

For better or worse, most modern frames are less stff than they used to be and more prone to bending from bouncing off kerbs or other karts, let alone more solid obstacles. This is why flat tables are a common sight outside team awnings. Many teams will check and straighten your frame for a reasonable fee, just ask!

3 Strip down and clean the kart and engine

You will want to do this more often than once a year, but a spring cleaning session is an ideal opportunity. Strip the whole kart down, including the removal of the rear axle assembly. Use a cleaning spray and make sure you get into the awkward corners, and if you’re using a pressure washer only do it after you have removed the parts with bearings. As you go along, check for cracks, worn cables and bolts and broken springs, and clean the brake discs with brake cleaner.

Laury Curran of Maranello Karts UK says “Clean the engine; the more you clean, the more you will find. Clean sprockets and chains in petrol or diesel and check they aren’t worn out then put the sprockets in order.”

A worn out chain will twist sideways and teeth on sprockets will become hooked.

Jamie Rush of R&S Motorsport says “Part of the clean that is important is to grease up the bearings, we usually use a product called Tri-Flow. It’s usually something a lot of people forget.”

At least once a year it us recommended to go over the entire kart replacing nuts and bolts, you can buy them in bulk from a local fastenings wholesaler.

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4 Check all accessible engine parts

Even if you can’t rebuild your own engine, for example in Rotax, there is plenty you can do to keep it in good condition. After you have cleaned it, take the engine apart as much as possible, using the manual that you can usually download or buy from the engine manufacturer. Many of the following need to be done as often as after each race or practice session, but get them all done in your pre-season prep session then you know where you’re starting from.

11-POINT ENGINE CHECKLIST

1 Clean and check the air filter, then clean after each wet race or practice. Clean with soap and water or brake cleaner.

2 Replace sump oil if using a four-stroke engine. You may need to do this as often as every meeting.

3 Check the starter cable if your engine has one.

4 Replace balance gear oil in engines such as the Rotax Max, and thereafter do after about five hours running.

William Pettitt

5 Replace gearbox oil and check it for metal particles by filtering through a clean white cloth. The drain plug should have a magnet that attracts metal swarf from normal gear wear and tear, but if you see an excessive amount get it checked by a specialist.

6 Check the clutch for wear, you’ll need special tools to loosen it and pull it off the shaft.

7 If you have a power valve it needs to be kept clean. Use something like Scotchbrite with carb or brake cleaner but not emery cloth as it will polish the valve too smooth and potentially make it illegal. Check it is fitted centrally and that it slides in and out easily.

8 Check the reed petals for chips at the edges or breaking up.

9 Check and replace starter motor brushes.

10 Check all electrical components are in good condition, including the earth wire from the ignition coil to the engine.

11 Check and replace exhaust wadding when it is burnt and brittle.

brake pads

5 Strip and service the brakes

Dean Golba of top TKM team DSG Racing says “Last time they were used chances are it was probably wet. Brakes don’t like moisture or dirt, they seize up and drag or bind on the disc. New pads, seals, fluid and a full bleed will make sure there are no issues and they are ready to go for the new season. Check which type of brake fluid your system should use, don’t mix DOT 5 Silicone based with DOT 5.1 Glycol Ether based.”

Using the wrong type of fluid can cause the seals to perish and lead to leakage and failure.

Laury adds “Learn how it comes apart and goes back together in case you need to do it in a hurry, and check brake discs for wear and cracks.”

And illustrating how important karting professionals think keeping your brakes in order is, Jamie had yet more tips “Always good to give the brakes a bleed, maybe re-kit and also de-glaze the pads and discs (especially gearbox and front brake classes).”

To de-glaze, rub the pads and discs with an emery cloth.

6 Check your datalogger or dash

“Something else is to clear the memory on the data logger and check all the sensors are functioning. Sometimes with the low temps and damp it can cause some problems,” says Jamie.

Also keep the cables and connectors in good condition and check that they aren’t pulled tight or chafing anywhere as this will eventually cause failures.

Dakton-Digital-System-6

7 Weigh your kart

Have you been munching mince pies or been on a new year health kick? Either way you may have some adjustments to make to your kart. If you are overweight, apart from the obvious solution, there are plenty of lightweight components to invest in such as floor trays, magnesium wheels if not already used, a seat or nuts and bolts.

You can also save weight by running a very small fuel tank. If you have the opposite problem, you should put some thought into where you put your lead, so try to use some corner weight scales and try to get the weight balance right.  If your corner weights vary on each side them you might be dealing with a twisted chassis which brings us back to point two. Driver-only weight also comes into it – several classes have minimum driver weights so if you’re a parent with a Cadet moving up to Juniors check they are eligible. If they’re underweight, you have two options; a steak-and-chips only diest for 3 months or a lead vest!

Learn from 40 years of experience

George Robinson, or Robinson Sport, who specialise in Rotax engines, has these great tips focused on Rotax engines in particular but they apply for anyone preparing a kart to go racing:

1)      A worn front sprocket is so often overlooked, as soon as the teeth start to look sharp or hooked, you are losing horsepower, the most efficient chain transmission is when all items are new or as good as new, that’s both sprockets and the chain.

Kartpix

2)      If the in-line fuel filter shows any sign of dirt in the paper gauze—change it, it will have lost some of its efficiency and could be gradually starving the engine of fuel.

3)      Earth of the Ignition pack or Coil must be in good clean condition and the earth strap must not be too close to the High Tension Plug lead, these will arc across quite wide gaps particularly if wet and will cause misfires and possible damage to the ignition pack.

4)      Make sure that the engine mounting clamps are in good condition and grip the chassis tubes evenly and securely. Also the engine bolts that secure the mount. Vibration in this area will cause carburetion problems and probably crack the chassis as well…expensive !

5)      Throttle cables are ignored until either they snap or seize up. The Pedal stop should be adjusted so there is still a small amount of movement in the cable without it being tight as a Guitar string. Too tight and it breaks.

Kartpix

 

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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