Making a 55mm cylinder out of a original mbx cylinder.
The original GE3G cylinder of a German mbx can easily made into a 55m setup. The problem is not the bore, but it is the usage of the right piston. The original cylinder has already have big ports in the cylinder. When using for instance a euro or athena or autisa 55mm piston it goes wrong. The pistonseals do not match the intakeports. But there is a solution. Polini produces a 55mm alu kit for the liquid cooled RD80. Just use this piston, it has great intakeports on the piston itself and the pistonseals match the 55mm bore of the original mbx cylinder perfectly. Now you can start grinding the exhaustports. The original German GE3G cylinder has a deckheight of 24mm. Raise the exhaustports by 2mm and widen alot the 'butterfly' shaped exhaustports. This cylinder performs very well in combination with the original GE3G german mbx 80 exhaust. Why? The pipe gives it power between 5000-9000 rpm. It delivers its power in lower rpm's and is therefore easy to ride and to maintain. Since you have raised the exhaustports by 2mm you can also use a Tecno pipe if you want to have a different form of powerdelivery. 18 hp can easily be achieved with minor adjustments. The original cylinderhead can be used, but a o-ring adjusted head is recommended. For gearing, in combination with the original pipe you can use a gearing of 17-36 with the 18 inch wheels and achieve a topspeed around 115km/u
, even with a small 18mm carb. When using a bigger carb you gain alot in bottompower.
, even with a small 18mm carb. When using a bigger carb you gain alot in bottompower.
Metrakit 54mm for mbx/nsr 80
The metrakit for the nsr/mbx 80 isn't produced anymore. The cylinder is made out of ironcast and comes with a 54mm vertex piston. The exhaustport is oval shaped and the cilinder is timed around 180°. The intake ports are bigger than the original mbx ones. The cylinder looks like a good torquecylinder instead of more highrev orientated. It is a fine cylinder used with the original honda mbx 80 GE3G exhaust, powerband between 5000-9000 rpm. Sometimes you can find one on the net, but mostly in Spain. In Belgium, Netherlands and Germany it is very rare. Not the best cylinder but a good performer for daily usage. When you find one and you don't have a piston, use the rd80 polini 55mm piston and bore the cylinder 1mm out.
Malossi 53mm for the mbx 80
The malossi cylinder for the mbx80 is still produced and one of the most popular ones. The cylinder is made out of iron cast and has a displacement of around 90cc. The cylinder has a oval shaped exhaustport which is timed around +-182°. The malossi cylinder performs well with a tecno exhaust, delivers then a powerband between 6500-11000 rpm, not more. The malossi is good tunable. The easiest way is to shave 2-3mm off the top of the cylinder with a turner. Than raise the whole cylinder by +-2- 3mm. Than you can use the turbokit carr0603 or equivalent for a 192° exhausttiming setup. The disadvantage of the malossi is the pricing of the pistons. They are not cheap but availabilty is good. Their are two types of malossi cylinder: the 3737 and the nowadays made 4747. The 3737 is better timed, around 190° on the exhaust and has extra ports in the casting. The 4747 is the more tame version. Also a big disadvantage is that the cylinder can run hot and break. So you must leave out the cooling plug in the cylinderhead in order to get more coolingwater circulated. The malossi must be broken in very good, minimal 250 km and on a very low pace. You also have to put a much richer main jet in the carb. As of consequence you always get a stutter around 6500 rpm when using a tecno pipe. A innerrotor solves that problem, but that's only for trackusage. I use to use this setup and was mildly tuned and rode around 130 km/u, using a standard ignition. With standard ignition a also mean the usage of a fast ignitionplate and a nsr 50 (ac08) flywheel, in combination with a open, unrestricted CDI, like the honda mps300. The malossi works particularly well with a oko 30mm and tecno pipe and tuned to a 190° exhausttiming and innerrotor. The cylinder has then a strong bite and goes like a little crossbike. It is not the fastest cylinder, no, the original mbx 80 cylinder tuned to 192° with for instance the turbokit carr0603 is way faster, around 10km/u. The malossi comes with a bigger jet and other needle for the standard 18mm carb.
Athena 55mm for the honda mbx 80.
The athena 55mm is a cylinder formerly known as the eurokit. The cylinder is made out of aluminium and has a chrome sealing. The piston used is a vertex 55mm. Since it is made out of aluminum it has a better cooling factor than the malossi above. The athena has two nice boostports in the intake, and has six ports and and one little oval exhaustport. The cylinder is very low timed on the exhaust, like the original mbx GE3G. For better performance you should atleast raise the height of the exhaustport with 2mm and make it wider. Pay attention to the sealing, as the chrome seem to blister of when grinded on with a dremeltool. The cylinder has good potential but the big disadvantage is the lack of a butterfly shaped exhaust. The cylinder is a good daily performer when used with a standard GE3G exhaust and original carb. Topspeed can be achieved around 115 km/u with a 2mm raised exhaustport. Without tuning it is very tame in comparing with its features and boresize. The cylinder can be used with a tecno pipe, powerband between 6500-11000 rpm. With a gilardoni or giannelli ns1 pipe the cylinder performs between 9000-12000 rpm but will break fast. Top speed is like the malossi, around 130 km/U when used with a fast ignitionplate, honda nsr 50 (AC08) flywheel and mps300 cdi, big carb and tecno pipe. The cylinder is still available, but be aware the prices can vary from country to country. I recommend to use the cylinder only as a daily driver, using a original exhaust. The piston doesn't seem to like highrevs and breaks ratherly fast.
Which piston to use?
for the original bored out 55mm GE3G cylinder of the mbx, you can use the polini yamaha RD80 piston. As the image shows, the intakeports on the piston are huge and will add that little performance to your setup. The piston is still available, mainly in Germany for around 50-60 euro. Do not use this piston in a bore out malossi or athena kit. The pistonlocks do not match the cylinders ports. Although the piston can be used in the autisa 55mm cylinder.
The piston on the left is to be used in a standard honda mbx GE3G cylinder with its original bore. The piston has to be shortend 5mm and you can give it a little 'gap' of 3mm to match the intakeport. Weightloss is gained but also timing is alterned. Advantage of these pistons is that their are easy to get and for a straightforward price.
The piston on the left is to be used in a standard honda mbx GE3G cylinder with its original bore. The piston has to be shortend 5mm and you can give it a little 'gap' of 3mm to match the intakeport. Weightloss is gained but also timing is alterned. Advantage of these pistons is that their are easy to get and for a straightforward price.
Autisa 98cc for the mbx/nsr 80
The autisa is a very nice cylinder with good potential. The cylinder is rare and isn't produced anymore. When you get hold of one, just keep it. In its standard form it performs rather good, especially when used with a original honda mbx 80 GE3G pipe and carburettor. The cylinder has a wide 'butterfly' shaped exhaustport and a 'mushroomshaped' intakeport like the honda cr80. The cylinder is made out of aluminum and has a nicasil sealing. The cylinder does not run hot, unlike the malossi. Pluspoints are its exhaustports, sealing and alucasting, minuspoints are its too little intakeports. This cylinder just asks to get more fuel into it. But it is still a nice cylinder, although the manufacturing is a liltte bit rough. Pistons are hard to find, you can recognize them by looking at it: it has a little hole drilled on the front of the piston to lubricant the space between the two exhaustports. Topspeed with original pipe is around 115 km/U but it gets sooner in the powerband than a malossi or euro/athena kit. Only the bored out original GE3G mbx cylinder is faster, but the last one lacks the advantages of the autisa (alu + nicasil). Topspeeds can be achieved with this pipe ranging from 115 to 145km/u, depending on the pipe (tecno vs turbokit carr0603) and carbusage. The bore is 55mm, so it has a displacement of 98cc. When using this cylinder on a HC04 (mbx 80 engine), than you must cut of the cylindersleeve in order that it will fit the casings.
Ports of the autisa
I would like to thank the person who made this one. Here you can see the ports of the autisa. Untuned is has a timing around 180° on the exhaust.
Italkit 54mm for the mbx nsr 80
The italkit I have no experience with. There are two versions: 1)gilardoni or italkit cylinder for the ns74/mbx80 with ovalshaped exhaustports + two extra ports in the outlet and a bore of 48mm, stating 74cc 2) this one, the W-shaped exhaustport, bored to 54mm. The cilinder uses a 54.2 mm vertex piston. The cylinder has a big intake, bigger than a original mbx cylinder. The cylinder I believe is still produced by italkit but is extremely rare. I have no experience about performances of this cylinder. I believe it is made of alu with a nicasil sealing and has a very nice finish. It also has two big boostports in the intake.
I would like to thank the unknown maker of this portmap. This is a portmap of the gilardoni 74cc 48mm bore version. As you can see it has two extra exhaustports, like the metrakit pro race cylinder for derbi/am6. It is in its standard form nothing like the metrakit prorace though.
Kitaco 98.3cc for mbx/nsr 80
The kitaco big bore 55mm is produced by kitaco. I have no experience with it, but my guess is that is is a ironcast bored out standard GE3F mbx/nsr cylinder. I could be wrong ofcourse and even could be aluminium with nicasil. There is very few information to find in Europe about it. I think it is made for the mini nsr 80 and comes with a single ring piston. The kit looks performant and comes with a good base 'butterfly shaped' exhaustport. Pricing is expensive, as the kits costs between 420-500 euro. So my guess is, that it is in alu and nicasil (hopefully for that price!). Otherwise a selfmade 55mm original mbx cylinder with a rd80 polini piston would be a much more cheaper substitute. For sale in the US and Japan and perhaps in Europe. Since the rise of the internet more 'exotic' parts are easier to obtain.
First of all I would like to thank the owner and maker of the portmap (cfr. mbx forum). It is a map of a GE3F cylinder. Take notice of the exhaustport, it must be widened alot. Just make sure you keep a distance of min. 2mm between the ports and exhaustport. The top of the exhaustport must not be in a straight line, yet curved (not wel demonstrated on the pic). Otherwise the pistonrings won't last too long... A original honda mbx 80 German GE3G 79cc cylinder can easily be made like this. In combination with a good pipe, timed at minimum 190° you get good performance (in the upper revs of course). Just keep in mind to work patiently and secure when grinding the exhaustport. A mistake is quickly made, like making the gap between the two exhaustports too thin. For lubrication you can drill two or one hole(s) in the frontside of the piston, this to improve lubrication of the space between the exhaustports. Keep in mind that the drilled hole must be well sealed when it is installed in the cylinder, otherwise the engine won't run. With these timing a turbokit carr0603 exhaust with innerrotor and big carb achieves easily 135 km/U . To add more performance and revs, a o-ring cylinderhead with minimum a squisharea of 0.8 must be installed. It will gain 5 km/u. This setup is way faster than any bigbore cylinder. The bigbore cylinder can of course be set to these specifications. But behold, the engine will seize much faster. Another easy gain of hp (+- 0.5) is to install a electric waterpump and to drop out the balance axl. Getting rid of the balancing axl is only for race purposes. On the road, your crankbearings will only last 1000 km. So keep in mind: losing the balancing axl is adding more revs and throttle reaction, but it shortens the life of the engine with 50-60%. I keep the balancing axl on a mbx 80 engine installed: the 80cc has 30cc more displacement. On a 50cc race setup I leave it out...it's a choice you have to make...if your not afraid to change/revise your crankbearings alot. If you want good race performance and more reliabiltiy go to a specialised company who does balancing of rotating parts.
Kitaco 55mm pistons for the nsr 80
a set of kitaco single piston ring pistons for the honda nsr 80 (minibike). Still available in Japan but at very high prices...
Examples of tuning the exhaustports of a standard honda nsr/mbx/ns1 80 cylinder.
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