We can build your mini to meet legal limits for the classes of: mx, off-road, dtx, hill-climb, and motorcycle road-racing as well as atv and shifter-karts.
There are two ways to build a mini into a supermini, big bore cylinder and or stroker crankshaft to increase the displacement and change the powerband to suit different types of racing.
One way is budget and involves just the top end, and the more comprehensive way is a big bore and stroker, which involves a complete engine rebuild and more expense. We also offer stock bottom end rebuild with big bore top end, which is less expensive than a big bore stroker. We use Hot Rod crankshafts, bearings, and seals for stock and stroker engine rebuilds.
Regarding engine maintenance issues, boosting the displacement of an 80 to 100cc plus will boost the average “maintenance cost per hour” of riding time. That dollar per hour number varies based on the “state of tune” of the engine. For example an RM85 built to 100cc and low to mid powerband for pump gas is the same cost to operate as a stock bike, approximately $20 per hour. On the far side of the maintenance spectrum is a RM112 built for a national amateur level racer runs about $60 per hour to run.
Wiseco and Vertex are piston manufacturers that make pistons in big bore sizes. We can modify your top end parts to fit the Wiseco pistons and take your mini over 100cc for $475 complete. We build these kits for youth racers of all ability from novice to national level.
In recent years big wheel 80s and 100s have been a popular choice for adults riding off-road. The lightweight, narrow big wheel minis are even easier to ride with especially more low end power. These types of big bore kits are built for durability and easy starting, plus they run on inexpensive pump gas.
All of our kits include cylinder porting, head mods, powervalve service and crankcase clearance mods on applicable models. You get your choice of 2 powerbands and 2 fuel types. All the top end parts are included too like a Wiseco or Vertex piston kit, top end bearing, alignment pins, and oversized gasket kit.
A complete package custom tuned to your wishes, with a mix of parts and labor and technical support through specialty books and free sample PDFs.
All of the piston and gasket kits used in our kits are easy to buy and available from any motorcycle shop or on-line accessory mail-order company. We also sell them for a good deal on our Paypal page with 24/7 ordering.
Our all-inclusive big bore stroker supermini performance engine rebuild for the YZ and KX85s boosts these engines to 112cc displacement to conform to AMA and NMA supermini class rules.
This performance build includes a HOT RODS stroker crankshaft and bottom end rebuild kit with bearings, seals, and gaskets. Your engine will be disassembled, cleaned, inspected, clutch and shifter parts polished, case porting and assembly.
For the top end we’ll overbore, port, and re-plate the cylinder. You’ll get the choice of 3 different porting packages and fuel types of pump and race gas. Our techs will modify the head and install the powervalves and check the squish clearance. You get the choice of Wiseco, Wossner, or Vertex piston kits and we’ll give you 20% on future spare top end kits.
Available for Kawasaki KX80, 85, 100 1990-2014 and Yamaha YZ80, 85 1993-2014.
The 2 powerband choices are:
The 2 fuel types
We machine your head flat then machine the squishband and bowl to match your powerband and fuel choices. The fuel types are unleaded pump 92 and race gas of 98-110. Pump gas is the most popular choice because you can also run race gas. We offer free updates for 1 year on porting changes and head mods.
CR80/85 1986-2014 $475
We offer 92 and 100cc. The 92cc meets 2mm/80-over rules and the 100 is legal for supermini.
Special recommendations: Magnum or Mishimoto oversized radiator, Keihin 28mm PWK carb.
KX80/85/100 1989-2014 $475
We offer sizes of 92, 99, and 107cc. The 92cc meets 2mm/80-over rules, the 99 is legal for supermini and the 107cc is the maximum oversize and combined with a Hot Rod stroker crank the displacement is 112cc. We use the Vertex 54.5mm race-forged piston in our 107cc kit, all other kits come standard with Wiseco pistons.
Special recommendations: Boyesen waterpump Pro-Circuit Kips valve, JMS head.
RM85 2000-2014 $475
We offer 4 different sizes for the RM85. The displacement range is 92, 100, 103, and 105cc. The 92 covers 2mm/80-over classes, the 100cc is our standard super. The 103 is a Wiseco Yamaha piston with a shorter timing height that is ideal for 3mm stroker cranks. The 105 is a Wiseco Suzuki piston but makes the cylinder thinner at the top o-ring groove thereby reducing reliability.
(Casemods required, send complete engine or bare crankcases)
Special recommendations: Boyesen waterpump, Wiseco clutch, FMF Fatty, Keihin 28mm PWK carb.
YZ80/85 1993-2014 $475
We offer 3 kits for the YZ. The 92cc size meets 2mm/80-over rules and we have 2 super configurations. The standard super is 103.5cc using the Wiseco GP piston and we mod your stock Yamaha parts. The 112cc option is an all-inclusive kit with no exchange needed. The kit is available from Hot Rod as a stroker bottom end rebuild kit and the top end is made by Cylinder Works and includes a cylinder, head, and Vertex piston. The crankcase needs special mods and we offer that for $100. This kit sells for $240 for the bottom end kit and $650 for the top end kit. You’ll still need a mechanic to assemble it.
(Casemods required, send complete engine or bare crankcases)
Special recommendations: FMF Fatty, Hinson clutch kit.
The 85 cannot be bored becuase the cylinder is too thin above the exhaust. However it can be resleeved and fitted with a 52mm piston kit to make it a 100. The kit for the 105 to 112cc is $550 and that includes replating not resleeving.
Just CLICK & PRINT a copy of the Service Order Form and follow the directions on packaging your parts for shipping. All the options are listed for services, powerband choices, fuel types, spare parts, shipping methods, and payment options.
Typically big bores hit hard and flatten-out and that’s what magazine testers have complained about. The reason is that tuners cheap-out and skip a step, cylinder porting. We include porting with all of our big bore kits and YOU CHOOSE the powerband type.
Our kits work with all stock and aftermarket parts. FMF Fatty pipes work great along with long silencers. Short silencers give better low end but flatten-out on top end. A 1-tooth larger countershaft sprocket makes a big difference and compliments the greater torque of a big bore. CV4 makes high pressure radiator caps and Fluidyne oversized radiators that help keep the coolant from running too hot. Boyesen waterpump impellors and covers work great too. Reed valves, ignitions, flywheel weights are all items that make little difference. Aftermarket carbs can help, you’d want a 28mm PWK Keihin or 30mm ONO carb available from Carb Parts Warehouse in Ohio. JMS makes billet heads and powervalves for most of the late model minis.
Heck yeah! A 112cc Supermini makes 30hp and the bike weighs 140lb whereas a 125 makes 34hp and weighs 200lb. The difference is suspension and handling, and most important the racer!
Technically you need to adjust the carb jetting when the air density changes but most supers can use standard 85 jetting. Jetting has most to do with where you ride and the average air temperature. Pump gas changes jetting too because of the chemicals used to make 4-stroke cars clean burning. On certain models, we supply specific jet needles and main jets with our big bore kits. Regarding pre-mix oil and ratios, we recommend Maxima Castrol 927 at 32:1 because it has additives to blend with ethanol pump gas and offers better lubricity for supers.
Always gear for more speed to compliment the increased torque. Typically you should increase the countershaft sprocket by 1 tooth.
Wiseco Pro-Lite forged piston kits designed for superminis are very close to the same weight as a stock cast piston, so there are no vibration problems caused by the bigger piston. However if you’re building a big bore, long rod stroker for top end, then you may want to have Crank Works in Tempe AZ change the balance factor for best results. The longer length of the connecting rod mathematically complicates to balance factor and www.crankworks.com is the only company that can help you. They have biggest database of balance factors for all types of racing. They’re the crankshaft Einsteins! While you’re at it, throw in a set of ceramic bearings from Worldwide Bearing in New Jersey. www.worldwidebearings.com ceramic bearings reduce the heat transfer in the crankcase and preserve maximum charge density for better power.
We build-in reliability with thicker cylinder plating, a coated forged piston, and polished port edges. Our Supers are more reliable than a stock 85. However a 112 big bore stroker requires frequent changes of the piston ring, every 4hrs. Also you’ll need to use race gas like VP C-12. Pump gas is just laded with crap to make your truck start in the winter and pollute less. National caliber racing engines need race fuel!
Wiseco is the only manufacturer of supermini pistons and features anti-wear coatings, more surface area to transfer the heat, lightening slots in the inside of the piston to balance the crankcase compression ratio and allow for really wide transfers and exhaust, and a smooth intake to boost the engine’s over-rev. Replacement cost averages $99 for the piston kit, $25 for a gasket kit, and $15 for a top end bearing or $144 for all including 3-day Priority Mail shipping! The average service life is 5-15hrs for ring and 10-30hrs for piston changes for average riders and half that time for experts.
Turnaround time is fast because we have many core cylinders in stock for immediate trade-up. And if you have a new cylinder and want to modify it, we’ll stamp your name on it and the time varies by season, longer in the wintertime because that’s our busy season. You can call and reserve a core cylinder for exchange, and we’ll hold it for 10 days. During big youth events like Mini Os, World Mini, Michigan Mafia Mini Mo-Down, Lorretta Lynn’s, Ponca City, and Branson, we get rushed so please think 30 days in advance of a big event like the ones listed.
Yes, we specialize in international business. Just CLICK & PRINT a copy of the service form and send it with your parts. Send your parts by airmail (Par Avion) or a popular shipping company like UPS, FEDEX, DHL, or Purolator. State on the customs documents that you are sending your engine block to America for repairs. We’ll resend your customs docs back with your order and declare the value under $200 USD so you don’t pay taxes. We’ll send your proper invoice by airmail, not email because the EU monitors private email. We’ll email the airbill tracking number so you’ll know when to expect the package. We are experts at international shipping and documentation.
ALL INTERNATIONAL ORDERS GET OUR RUSH SERVICE FOR FREE!