Home » Features » Rotax Max Column » The Max Column: September 2006

The Max Column: September 2006

karting-mag-logo-15I promise to take a rest from standing on the political “orange box” and spend these few words extolling the virtues of the Max classes rather than taking pot shots at the state of the industry and the ineptitude of all those officials we love to hate!

I have recently had a very interesting number of trips abroad to France, Italy and Germany all Kart related and all influenced by my involvement with the Rotax Max.
The Rotax phenomenon as it has become known abroad has had a huge effect on the shape of Karting in the last ten years.

Ten years ago short circuit Karting was in decline, the cost of competing at a good level in the 100cc classes had caused it to become too elitist and we had not as yet heard of the Max. The following year 1997, the very first Max engines started to appear, little did we know at that stage that this was to be the biggest revolution in the sport ever.

The first Max was of course what we now know as the Senior engine. The price was good and the specification was very comprehensive when compared to what we were used to. At top dealer level the engine was greeted with nothing more than passing interest. Championship organisers declared that they would never run the class as it was for “hobby” drivers only and some clubs followed suit by refusing to accommodate the Max owners, believing that it was a passing faze. Today the Super 1 Max meeting attracts the largest entries of any and the Rotax interest at the Kartmasters can only be described as huge. The engines in Senior and Junior form have brought new levels of reliability to the sport and a warranty witch was hitherto unthinkable.

The engines have evolved over the last nine years with various detail changes that have not dramatically changed the performance of the unit. I recently had an engine in for its first service, which was over seven years old; it had been lightly used when new and then stored for over five years. The engine was in good condition but really needed updating with the latest components so the rebuild was not the cheapest. The owner, however, now wants to race so he was not averse to spending whatever was required, safe in the knowledge that all the new components fitted would be warranted. A new con-rod, balance shaft, piston, bearings and gears were fitted. After running in the owner phoned to say that the engine had never performed better and that it appeared to be more than a match for other drivers on the day. It would be quite impossible to build a Formula A type engine of such an age and expect it to be competitive. When you buy such a unit all you get is the unit with ignition and exhaust bend, sometimes the exhaust is thrown in but not always. There is certainly no warranty. Furthermore there is almost certainly an evolution model already in the pipeline, which will destroy the value of your investment before the ink is dry on your cheque! It is no wonder therefore that this form of racing was already in decline before the Max came along to finish it off.

The Rotax Max really struck a chord with the British. The UK has far the highest ratio of Max per licence holder of anywhere in the world. As such we are a very important market for all the related equipment including Karts accessories and tyres. These elements have been the reasons behind my various trips abroad recently, not that I am involved with the decision making process. It is however very interesting to see how much work goes on behind the scenes to keep the sport running smoothly.
That was not political was it? Now for the technical bit.

The Exhaust valve is a source of anguish to some and in more or less every case this can be solved with some careful maintenance. First of all we need to get the names right. As you take the black plastic cover off you will find a black plastic disc with the green (or red if very old) bellows secured to it by a circular spring. This plastic disc is known as the Exhaust valve piston. Having taken out the two M6 cap head bolts that retain the assembly, you will be able to withdraw the whole unit from the engine, the alloy component which fits into the back of the cylinder is the Exhaust valve, pure and simple, it is also sometimes known as the guillotine but for identification purposes in the price list and manual, it is the exhaust valve.

The Exhaust valve works by back pressure from the exhaust system inflating the bellows and forcing the piston away from the cylinder thus drawing the exhaust valve up. This has the effect of raising the exhaust port and so producing more power at higher RPM. In its closed position the valve keeps the port low which helps to give good torque at low RPM. For the engine to perform at its best, the exhaust valve must be in perfect working order and be smooth in its operation.

All components of the valve must be spotlessly clean, but care must be taken not to damage the original surface finish of the exhaust valve itself, this could lead to exclusion from the results if a zealous scrutineer believed it had been modified. It is most important that the stud that holds the valve to the piston is perfectly clean. I always grease this where it goes through the body. It is necessary to put a small amount of “Loctite” into the thread at each end as the stud can unscrew in use which in a worst case scenario will reduce the power to below that of a Junior engine! On reassembly the stud should not be over-tightened into the piston as it is only soft plastic, the stud will force its way through the end of the piston, destroying it. The assembled length will also be far too short for best performance.

On assembly it is vital to ensure that the gasket is the right way up, there is only one way to fit this and there are four options! Make sure the holes line up or it will not work whatever you do. The green bellows with their strong spring are now well accepted although at first there was a belief that it made the exhaust valve lazy, at least it is now much more secure, the bellows is very unlikely to be unseated. Rotax have recently introduced a smaller spring, which fits at the bottom of the bellows, which helps to make the seal between the rubber and the body more efficient.

This can only improve the operation of the valve so it has to be a worthwhile retrofit. Having rebuilt the unit, it is time to refit it to the engine. It is quite easy to line up the boltholes before screwing them home. When the exhaust valve is remounted and the bolts are tight it is most important that the piston is very free when pushed down.

It should spring back easily, if not then it must be adjusted by moving the piston round on its thread until the piston and valve are perfectly aligned. Refit the cover and start with the red adjustment screw between fully screwed home and fifteen clicks out. This is tuners territory and they all say something different so I am not about to stick my head over the parapet! The exhaust valve can be a source of difficulty as the performance loss can be very gradual. If you are unsure, borrow a whole assembly from another engine, which you know is OK. This will at least eliminate the valve from your enquiries.

Balance gears are an area often overlooked. I believe in checking them every time the engine is used. Because the two large gears are really just like an oil pump, they will absorb some power if they are overfilled with oil or the oil is too heavy. The first rule of thumb is to loosen the drain plug, the lowest M6 bolt on the gear cover, and see what comes out! If the oil is discoloured or, worse still has white specs in it you must investigate further. Take the cover off and check all the gears very carefully. It is usual to replace at least the two large gears.

These are fitted flat side out on the balance shaft and boss side out on the crank, you will see what I mean when you look at them. If the balance gears are damaged I would change all five gears to be sure. If any of the others fail afterwards the water pump will cease to operate, the results could be disastrous, a seized engine for the sake of a couple of £5 gears.

Check the condition of the circlips and replace them if they look worn. It is also easy to stretch them when taking them off, only expand them as much as is necessary to unseat them and they will be fine. Fitting the gears is made a lot easier if they are warm, I use a powerful hairdryer which is quick and easy, better than heating them in water as the plastic is hydroscopic and this can adversely affect their life expectancy. If the engine is standing flat on the bench then the balance shaft will automatically align itself, the line on the end of the shaft should be vertical, pointing at the edge of the filler casting.

The crank should be rotated to top dead centre, the mark on the crank should point at the triangle mark on the casting which is at approximately 11 Oclock to the vertical. Make sure there is a very small amount of backlash between the two balance gears. Refit or replace the other three gears, don’t forget the circlips, check and replace the gasket if necessary and refit the cover. The bolts with the copper washers go at the bottom and one up to the left. Now the oil A straight SAE 30 or 40 will do the job as specified by Rotax, or there are gear oils manufactured by the proprietory suppliers that are made specifically for this type of plastic gear cluster. 50cc is the recommended fill level, I know that many are now using less oil, but if that is the case then even more care must be taken to check the gears regularly.

In an older engine where the crank may be worn this can slightly compromise the oil-seal and the engine will quickly drink its own oil. Again regular checks are the key!
All very sensible this month and loads of words, don’t worry I will be back to normal next month, talking bollocks as usual!.