MX | ROADRACE | KARTING | MOPED
This year VHM exists 25 years! A lot of stories unfolded throughout these years and we’ve dug some of them up! We’ll be posting an old VHM story every month this year, starting with the blue VHM carburettor as first VHM part.
Posted at 14-03-2020, written by Chantal van Haandel
From the first two stories it became clear how VHM rolled into the karting and motocross world. In meantime, VHM also got caught up in the 2-stroke road race scene. That eventually lead to the first VHM exchangeable combustion chamber, or in short: insert. How did it come to that? We’ll tell you all about it here, starting with two persons that meant a great deal in entering the race wold.
Team principle Frits Hillebrandt
‘’As a reaction to the VHM kart carburettor, we got some questions about it from other race scenes,’’ starts Ad as a warming-up to the VHM road race narrative. ‘’Eventually I came in touch with the road race through Frits Hillebrandt, team principle of a 250cc racing team. That played out as follows. At that time, Frits also worked at the FOCWA, an institutional body for car paint shops. My father Harrie was a board member of the FOCWA, so they regularly runned in to each other. One day Frits asked my dad ‘’there’s a guy in Boekel that made a carburettor, do you know him by any chance?’ ‘Well yes of course!’ was my father’s reaction. That’s when I got in contact with Frits and with that the road race.’’
So again, the blue carburettor formed a significant link for entering a new race division. The carburettor was even tested on a Honda 250cc from Frits’ team at the TT circuit of Assen in the Netherlands and Circuit Zolder in Belgium. From a few saved notes the VHM carburettor was supposedly better at high rpm’s, but less strong at the bottom. After a scarce amount of tests the VHM carburettor project in the roadrace was stopped. However, through the new contacts that were made, the VHM road race story was just about to begin.
Tuner Olivier Liegeois
Thanks to Frits, Ad also met Olivier Liegeois. ‘’Frits knew about almost everyone in the race scene and one day he asked me if Olivier could come and have look at what I did at VHM,’’ explains Ad. ‘’That was more of an honour for me than a question. In my opinion, Olivier was THE technical man in the race. An absolute fanatic of everything that goes fast.'' Him visiting meant an ushering of parts that VHM created with or for him. Among these parts was the first VHM combustion chamber, or insert as we often call it.
First exchangeable insert
‘’The idea to create an exchangeable insert came to me through Olivier,’’ Ad continues. ‘’He was continuously busy with the cylinder heads of those racers. The original heads were not divisible yet, but many in the sport were pioneering with it, as was Olivier. However, this often lead to problems of leaking and huge detonation. That’s why Olivier asked me if I could create something for it. In the Winter months of 1996, together with Olivier, I started working on creating our own inserts. Those inserts were meant for modified original heads. We didn’t made our own, yet.
Maybe this picture below represents the historic moment where the VHM insert was first discussed. Or maybe not and this is just one of the uncountable moments of discussing anything relatable to a 2-stroke engine. Who knows… Anyways, quite a lot to see on the picture. Our old VHM logo, a gift from Mark van der Linden on the wall and if you look very closely, you’ll even see a picture of Ad’s biggest idol (Ayrton Senna) hanging in the office.
But why making a divisible cylinder head, consisting of two, instead of one part? The main advantage is that you do not have to throw away a complete cylinder head when the detonation has been sky high. With an exchangeable insert, you can easily use another insert and keep the cylinder head itself. Furthermore, you’re able to test and change your engine’s tuning on track, for less money. Multiple one-part cylinder heads with modified insides are far more expensive than a two-partly cylinder head with various inserts that can be exchanged. In addition, the heads at the time where castings, which material isn’t really resistant to detonation. Creating an insert from aluminium increased the detonation resistance.
Manual production and calculation
It was quite a challenge to create the first VHM insert according to Ad. ‘’We needed to deal with a changing heat transference and stability of the loose insert in the head. In addition, creating the correct volumes needed some attention as well. I’ve manually turned the first inserts myself. To end up with the right insert volume, I needed to turn, measure, modify, measure again, and so on. Together with Jeroen de Koning, we came up with a formula to determine the volume of the combustion chamber from the drawing and complementary parameters, so I didn’t had to produce and measure before I knew what the volume would be. That was a huge step for us, it saved a great amount of time in production. The next step was letting a software do the calculations for us. That was set up in Tensor, were various scripts, A until G, were created for different inserts forms.
The very first VHM inserts were meant for Honda RS250 and RS125 racers, with the afterward part numbers of 32007-A until -G and 32011-A/-B/-H/-J/-K/-L. Soon an insert for the Aprilia RSW125 followed as well. Shortly after, a wide range of inserts were made for karting and motocross too. The price for those very first inserts were 99 gulden (Dutch currency at the time), according to a pricelist from 1998. Custom inserts were immediately offered as well, for 135 gulden. The delivery time for such a custom insert was 10 working days at the time. The prices haven’t changed much when you convert gulden to euro, but the delivery time has substantially been shortened, to nowadays around 1 or 2 working days (with the exception of Holidays).
Piston height measurement tool
During development of the inserts, the following question came up very soon according to Ad: ‘’How can we ensure that people can easily check if their values like the volume are correct when mounting the insert? When we deliver an insert with for example a volume of 8cc, a certain base gasket, piston height and squish should accompany to match that volume. It’s really important that this is all matched properly. One way to check is by a squish measurement, with the usage of tin wire. However, that’s quite sensitive for error measurements. Results will deviate too much if a different tin hardness or thickness is used, but also the amount of tin pieces matter. So another measure system was needed.
That leaded to the piston height measurement. Ad initially saw it from HRC Honda in one of the pitboxes at a Grand Prix. They put a square strip on top of the cylinder and looked how high the piston would come when turning the crank. This was not 100% fool-proof, when the strip was hold in even the smallest angle, the measurement was not accurate enough. That’s when Ad came up with the VHM piston height measurement tool.
With the piston height measurement tool, the piston height is the only value you need to check and possibly correct. When that’s been done, the squish and volume of the specific insert will automatically be correct as well. This tool turned out to be a good solution and is still sold until today. The oldest pricelist we could find was from 1998, so the VHM piston height measurement tool is at least 22 years old. A couple of years ago we created an instruction video for the usage of this tool.
Volume measuring gauge
Besides the piston height measurement tools, at the beginning of the insert sales, VHM also produced and sold many volume measuring gauges. The gauge was supposed to be a cylinder with a symbolic, fixed piston in it, which was for example set at +2mm piston height. The gauge furthermore consisted of an O-ring and bolt holes for the cylinder head. Without this gauge, the volume needed to be measured on the engine itself. But that’s not easy when the engine is mounted in the frame. Furthermore, a small amount of liquid leaks at the piston ring, so the volume measurement is not 100% correct. With the gauge, only the cylinder head needed to be disassembled from the engine and onto the gauge to do the volume measurement. It worked quite well, but there were many gauge’s needed, as it only worked for one piston height, piston crown, etc. In addition, the piston height measurement tool worked so well, the volume gauge kind of became superfluous.
After talking about the measurements, back to the combustion chamber itself. A fun fact is that they starred on their own stickers! Theo still knew about the existence and origin of these. We’ll have to leave the road race scene for this short story and swap it with motocross. ‘’After Grant Langston became World Champion in 2000, with VHM cylinder head and insert, he went to drive in the United States. Due to factory agreements, he couldn’t drive with our cylinder head anymore, but thanks to Harry Nolte they still used our inserts. To have a relevant appearance on the bike, we created the VHM insert sticker, with yellow glow.
Today we still produce lots and lots of inserts for our customers. For each VHM cylinder head, we have a VHM standard insert, an insert advised by us for that engine. Furthermore, we offer a range of optional inserts with a higher of lower compression for experimenting with your own tuning. A blind (blanc / unmachined) insert is also possible, with which you are able to machine your own specifications into the insert. Finally, we also offer the option of making a custom insert. We’ll then machine the insert with the specifications you want. If you want to see more about the production of our inserts, we have many video’s where they appear as the main subject.
Next up: First VHM cylinder heads
This story addressed the VHM combustion chamber. The next story will cover the first VHM cylinder heads. Expected online next month, halfway April. Stay tuned!
Posted at 14-02-2020, written by Chantal van Haandel
For the ’95 go-kart season, the regulations changed and our blue carburettor was banned in the national competition. What to do now with our blue piece of art? Our focus shifted to the motocross! Blue VHM carburettor part one told about karting, this part, part two, will elaborate on the 2- and 4-stroke dirtbike, enduro and trial carburettors from VHM in the period ’94 until ’99.
First tests with Martin van Laanen
Ad remembers Martin Van Laanen as the first one to drive with the blue VHM cross carburettor. Many tests with proto types were done by him in December ’94 and January ‘95. In Martin’s hometown Uden, but also at tracks like Berghem in the Netherlands. He drove with a 125cc 2-stroke. Many test results, formulas, drawings and ideas were written by Ad in a notebook, that contains 289 handwritten pages starting from ’94 until ’97. As if that wasn’t enough, Ad also kept separate handwritten test result pages in paper archive folders related to each driver. Until today, those papers are still in good shape, enabling us to dive in and take some of the stories out for you guys. Besides Martin van Laanen, we’ll also discuss three other drivers here: Wim Oerlemans, Mark van der Linden and Eric Verhoef.
Tribute to technician Wim Oerlemans
For the VHM carburettor entry into the cross-world, we have a lot to thank to Wim Oerlemans. As one of the first drivers he tested the VHM carburettor in the cross, with his 620cc 4-stroke machine in February ’95. He still remembered that first test at cross circuit Venray, when asked about it in August 2019 when he dropped by at VHM. ‘’It almost went wrong. A Teflon part within the carburettor expanded through the heat, causing some problems. Difficult to take the jumps without risking a serious crash. Soon after, it was made from nickel, solving the issue right away.’’
In the period ’95 until ’97, Wim tested many VHM carburettors. Himself, but he also as technician in collaboration with other drivers. He went to the track to test the blue carb with among others Erik Davids, Lemmens, Frank Lach and even Joël Smets. Constantly trying to find the perfect jetting and settings. He gave us very good and usable feedback, regarding the 620cc’s and 400 LC4 4-strokes to the 360SX and 300EXC 2-strokes. According to Theo: ‘’Wim was the guy that did all the fieldwork. When we thought of something new, Wim did the testing.’’ Ad about Wim: ‘’He was one of the few people who fully understood what we made. He fine-tuned the carb settings for many drivers. Once I received a gift from Wim. A wooden case with an electric turntable, surrounding mirrors, spotlight directed on the carburettor and including our flyers from that time. I kept it al those years and it still works!’’
Carter pulsed 2-stroke Trial with Mark van der Linden
A third driver we’d like to point out is Mark van der Linden. His first test with a VHM carburettor was at December 20th ’94. As with all tests, the findings from this one were carefully documented by Ad. In his notes we can read Mark’s thoughts regarding the carb: ‘’Engine runs good stationary, picks up well from third gear, no drowning or defect spark plug. Only when partially accelerating, Mark feels it running too lean. Conclusion: bringing the needle a point back or enlarging the needle-nipple.’’ In total, Ad has handwritten 26 A4-paper sheets from all the tests done by Mark, mainly in ’94 and ’95 and a few from ’96 and ’97. Something unique we’d found in those notes was the existence of a red carb. On October 17 ’95, ‘’Mark tested a blue and red carburettor, whereby he found the red one a bit stronger. Presumably due to a lower valve-pressure, resulting in in a less lean mixture.’’
Ad regarding the trial bike: ‘’The trial engine is one of the hardest engines for creating a carburettor. If it doesn’t work or react once, it could mean the driver falls down from quite a bit of height. It comes down to a lot of precision. Mark drove multiple years with our carb and in ’95 he ended up 3rd in the final rankings of the Dutch Trial championship with our carb. As with many of our carburettors, we experienced some pump pressure issues. Especially with a trial bike, as de bike ends up in all kinds of positions. The column height and associated pressure thereby varies enormously. With a 2-stroke engine however, we could make use of the carter pulses. In addition, the fuel tank in those trial engines was positioned quite low, so the drivers didn’t bump into the tanks with their knees, which prevents peek pressures. With that in mind, we built a pump with a non-return valve that used those pulses to put extra pressure on the fuel tank. So now we didn’t only had the pressure from the fuel column height, in other words the weight of the fuel, but also some extra air pressure. I’ve added a fixed valve that was adjusted to 100 milibar to the pump, so the pressure was constant, whatever angle the bike was in.
Flipped 4-stroke Enduro with Eric Verhoef
Another driver that was among the first to test our blue mx carb was Eric Verhoef. From a note dated 23-10-95 we can read ‘Eric has won a Dutch Championship round with the VHM carb, everything was okay.’ Eric participated that year in the Category I Inters Dutch Open Enduro 4-stroke until 350cc. With start number 177 he finished 2nd in the final rankings that year. Ad remembers an acrobatic move from Eric’s KTM GS that year. ‘’In Enduro they rush past small canals. Once Eric’s bike ended upside down in such an, luckily empty, canal. OEM carbs at the time that rolled-over stalled. Eric could pull out his bike from the ditch and could just ride on. Our carburettor consisted of a closed circuit, so it stayed functioning in whatever angle it ended up. With our carburettor, the engine didn’t stall anymore with a drop of a hat.’’
Old pricelist and benefits
From an old pricelist from March ’97, it’s clear that there were 8 carburettor models available at that time for the motocross: KTM 620 LC4, 360SX, 300EXC, 400 LC4, 620 Duke, Honda CR125, Husaberg 600 and Husqvarna 600. The carburettors were sold as a complete set, but many parts were also separately available, like gaskets, rings, nipples, plugs, bolts, filter, pump springs and so on. All these parts were drawn in the period ’93 until ’97, mainly by Ad and Jeroen de Koning.
The advantages of the cross carburettor were summarized back then as follows:
By using a closed circuit, the bike will:
First VHM employee Theo and assembly
The blue carburettor and the expansion to the motocross eventually led in ’97 to the first VHM employee, former top rider Theo Bouw. His official first project was to support the whole VHM carburettor project, something he was actually already been doing for a few years in his spare time. We were able to trace a lot of correspondence back between Theo and for example Erik Davids, who drove a lot with the VHM carb in ’97. Theo arranged the necessary communication towards the drivers and assembled uncountable many carburettors.
To mount the VHM carburettor on the bike, for example the VHM2008 for Honda CR125, many steps were to be followed. We’ve found one instruction manual back, containing 17 steps, explained by 3 drawings. The fact that so many steps were necessary, might say something about the complexity of the carb. Looking back, Ad mentions that the complexity was a huge pitfall of the carburettor. ‘’Our 4-stroke carburettor was really good, I dare to say even better than the original at the time. It ran so smoothly. But we made a completely different system. Float chamber carburettors were known, but we had a combination of a butterfly valve carburettor and a float chamber with many adjustment options. Too many options for most.
A year after Theo officially joined VHM, it was decided to slowly reduce the project. When there was something wrong with the engine, many settings from the carburettor were rapidly changed, as if that was always the cause of the problems. Those sudden adjustments in settings often worsened the running of the engine and frequently we needed to assist in getting in right again. Overall, the complexity and the time it took to assist many drivers led to putting the project on the shelve. We only dusted it off for this story, but we’ll keep it there.
Next up: new subject, new story
The first and second part covered our blue carburettor story. We’re now working on a third part with a complete new subject, which is expected online next month, halfway March. Stay tuned!
Posted at 14-01-2020, written by Chantal van Haandel
The official foundation date of VHM is March the 14th 1995. However, it can be argued that, in thougth, VHM already existed a few years before that date. We’d like to mark the blue go-kart carburettor from 1993 as the unofficial start of VHM. This carburettor has been the catalyst, the reason why VHM was created. That’s why we start our storytelling with this blue piece of art. We even devided this in a part one regarding karting and part two regarding motocross.
In his blood
Founder Ad was a passionate go-kart driver and engine mechanic in his young days. As driver of the ISBL, he mainly competed in streetraces in the Dutch provinces Limburg and Brabant. In 1981 though, he switched to the ‘big races’ and became Dutch champion with Zip Shadow and Parilla 100cc engine. Quitted driving himself in ’83 to focus on his business, to get back at it for one more year in ’86. In 1990 he stepped in his wife's (Gise) Kombikart with Rotax R100 engine for doing some ‘fun’ laps. That ended him in the hospital for a week, as an accident left him with a few broken spine bones. Now you might think it’s over, but what can we say about it, it’s in his blood. Somewhere in ’92 he liked to try the 125cc shifter category. That’s were the blue carburettor entries this narrative.
Changed regulations part one
In ’92 the regulations changed regarding the engines and existing complementary carburettors. All carburettors where free to use, with the intention to enable the exchange of the existing carburettors across the existing engines. That also cleared the way for possible new carburettors to join the playing field. That’s when Ad jumped in with his own ideas. He thought that the existing carburettors were difficult to finetune, to adjust the right settings.
The basic idea of the VHM blue carbuerror was to make a slide carburettor of which you could quickly fine-tune the jets and which was precisely adjustable at any point of the gas position. However, right beneath the carburettor the membrane was positioned, so no needle could drop down, like many familiar slide carburettors. That’s why Ad made a static needle and a gas valve with an internal tube that could slide over that needle. So the principle of a slide carburattor vice versa, with a ‘conversal needle’ so to say.
The conventional vacuum carburettor at the time for the 125cc shifter had no slide and needle, only a simple valve. Slide carburettors already existed for other applications, like drawn by Ad in sketch 1 below. His ‘conversal needle’ slide carburettor was based on sketch 2, not with a float chamber, but with a membrane.
Ad made many proto types to work out his idea. Together with Jeroen de Koning all parts for the carburettor were precisely drawn and produced. Ad tested the first prototype himself, with a Kombikart and TM 125cc shifter engine at kart circuit de Landsard. He even attached the carburettor upside down at some point. While designing, it was taken into account that the carburation should remain working, even when the kart would skew on its side. Maybe a bit overdone, but it proved that the carburettor kept on working properly.
During prototyping and testing, the looks of the carburettor needed to be considered. VHM didn’t officially existed and the signature ‘golden’ color wasn’t in the picture yet. Ad wanted to choose one color for recognizability. But which color? The prototypes were anodized in almost all colors of the rainbow; red, yellow, green, light blue, even brown and dark blue. Blue, that seemed to be a returning pattern. Thus the choice eventually fell on blue, so it became ‘the blue VHM carburettor’.
So the VHM 81000, the blue kart carburettor, was born. With a price of 1.140 gulden (old Dutch currency) at the time, definitely not a cheap bargain. But for this technical blue piece of art, it sold well. It was compact, easy to fit, had adjusting screws on the outside which where easy to reach and adjust, was completely sealed from external air resulting in faster ‘pick-up’ and ensuring correct fuel/air ratio at every angle. The sentence ‘The driver who understands his engine and the VHM-carburettor will only need a few laps to obtain a more than perfect setting for his engine’ was used in flyers at the time.
Dutch champion Jean-Pierre Wouters
One of those drivers that understood the VHM carburattor well was definitely Jean-Pierre Wouters. In 1994 he became Dutch Champion 125cc with the blue carburettor on his Husqvarna engine. In the final classsification, about 5 drivers from the top 10 drove around with the blue machined part. It was looking very good!
Changed regulations part two
Sadly, the results from ’94 could not be repeated. A new regulation adjustment concerning the Dutch championship stated that the carburettor was free of use, provided that you use Mikuni, Dellorto or Keihin. In other words, the VHM carburettor was no longer allowed. That was a huge setback. On international and club level, the carburettor was still free of use. With no additive. So the narrative goes on there.
Clublevel and opposite world Theo & Ad
In the years ’95 and ’96 Ad, together with Jos Souren, kept on testing with the carburettor. Mainly at kart circuit Raceway Venray with a rotary TM engine on a Tonykart chassis. At that time, Theo Bouw, also known as ‘Mr VHM’, was already involved in the carburettor project. Even before he started working for VHM in ’97. In his free evening hours he assembled the VHM carburettors. Well, Theo actually tested Ad’s first motocross carburettor already in ’85! But that’s a whole different story. Anyways, Theo was certainly early involved in the VHM carburettor, which led to a brief opposite world. As Ad, back in the days, once drove with the old Suzuki dirtbike from Theo, Theo now once drove with Ad’s 125cc shifter kart at Venray. Funny how things can go!
Overseas to Steven Spielberg
Also at international level some drivers have used the VHM carburettor. Mike Hezemans, among others, has tested with it. Also Eddy van de Hoek used the carburettor when he worked for KUKA-kart team. He even brought the blue piece of art ‘overseas’. In 1995 they went to an internatonal kart exhibition called ‘Kart EXPO-international’ in Riverside, California, USA. An article about it, that Ad has kept al those years, appeard in the German ‘Dimo-Sport-Journal’. With the title ‘Ein VHM-Vergaser für Steven Spielberg’. In English, a VHM carburettor for Steven Spielberg. Apparently, an employee of Steven Spielberg came tot he exhibition to arrange a go-kart for some special effect filmwork. A piece of art for a piece of art.
Next up: Blue VHM carburettor part two
This first part concentrated on the kart carburettor. The second part will tell all about this carburettor for the motocross. Expected online next month, halfway February.