250cc Transmission System Upgrades

Upgrading the CVT system on a 250cc buggy

This 250cc CVT upgrade guide is based on an original work authored by “Alfordap” (Adrian Alford) and posted here on www.Buggynews.com. The original photos and text captions used by permission.

Introduction:

This guide will detail how to disassemble, upgrade, and replace elements of the CVT system on a 250cc motor (both CN250 and CF-Moto) used in many brands of mini-buggies and scooters.

This guide has instructions on replacing the variator, rollers, clutch, main torque spring, and CVT drive belt.

Please send any feedback on this guide to: webmaster@buggypartsnw.com

Tools:

– Bolt sizes may vary by model of buggy, so have a set of standard and metric sockets and wrenches handy. 17mm nuts are a common size.
– Strap wrench
– Pipe wrench or Impact wrench
– Blue Loc-tite
– 1 extra pair of hands (or an assistant!) if doing clutch mods
(Actual tools needed may vary by the mods being performed.)

Optional: An impact wrench will make this process much easier, but is not necessary. If using an impact wrench, you should consider our reversible impact wrench socket that works for both 150cc and 250cc engines. You can find it in our store here.

Safety Notice:

Before starting, allow the engine to cool completely. Exhaust and CVT systems achieve very high temperatures from normal operation.

Clutch assemblies are under significant spring pressure. Caution must be taken when removing the final clutch assembly nut.

Part I: Accessing the CVT system

Image 1: CVT cover.
Image 1: CVT cover.

4. If applicable, remove the stock air intake box. Remove the bolts securing the CVT cover and take the cover off. Some bolts may be different lengths so be sure to keep track of where they came from for reassembly.

Image 2: CVT cover removed. Variator on left, Clutch assembly on right
Image 2: CVT cover removed. Variator on left, Clutch assembly on right

5. Take off the CVT cover. Be careful not to damage the CVT cover gasket.

6. Remove the nut (size may vary by buggy model) on the variator fan. An impact wrench will make this an easy removal. If you do not have one available, you must secure the fan plate so that the fan does not rotate when loosening the bolt. A variable hole spanner or strap wrench are good tools to consider.

Note: Be very careful when removing the variator nut to not damage the variator fan plate or break off any of the “fins”.

Image 3: Variator fan removed.
Image 3: Variator fan removed.

7. Remove the variator fan plate and drive belt. Set them aside.

Note: On some buggies, the rear shock may need to be unbolted at one end and swiveled out of the way to access the variator nut with an impact wrench.

Part II: Changing Roller Weights

Image 4: Variator assembly and ramp plate.
Image 4: Variator assembly and ramp plate.

8. Remove the variator assembly, being extra careful to hold the variator, ramp plate (behind it), and center dowel pin together as one unit. The center dowel pin can be set aside. Holding the variator with the smooth pulley side down, lift off the ramp plate to expose the rollers.

Image 5: Variator assembly, ramp plate removed. Note condition of rollers.
Image 5: Variator assembly, ramp plate removed. Note condition of rollers.

9. Remove the old rollers and set aside.

Image 6: New sliders installed.
Image 6: New sliders installed.
Image 6.1: Reinstalling ramp plate.
Image 6.1: Reinstalling ramp plate.

10. Insert the new rollers or sliders into the variator, one to a slot.

Important Note: If installing sliders, see this article for specific instructions on the proper orientation for slider weights.

Image 6.2: Reassembled variator assembly with ramp plate.
Image 6.2: Reassembled variator assembly with ramp plate.

11. Place the variator ramp plate back on the variator, matching the three plastic guides around the edge.

12. Holding the variator and ramp plate as one piece, replace the center dowel pin, and put it all back on the shaft, sliding it all the way to the back.

Note: Dr. Pulley variators come with three small washers that can be optionally installed as spacers. In most cases, they are not necessary on buggies. We recommend only installing them if the original variator used washers or you have a specific reason for using them.

At this point, if you are only changing the rollers you can begin to reassemble the CVT system. Skip to Part VI for instructions.

Part III: Removing and Opening the Clutch Assembly

Image 7: Clutch Assembly
Image 7: Clutch Assembly

13. To access the clutch, remove the clutch bell nut. The size may vary by buggy model. Again, an impact wrench makes this an easy job, but you can remove with a regular socket it if you restrain the clutch bell from turning with a strap wrench or variable spanner tool.

Image 8: Inside the Clutch Bell
Image 8: Inside the Clutch Bell

14. Remove the clutch bell. Examine the inside of the clutch bell. The inside edge should be clean and will be a relatively smooth surface, not smooth like clean glass. A polished-smooth interior inhibits a good engagement of the clutch with the bell and decreases performance.

– Note: If your clutch bell is purpled and very smooth on the inside edge, it is probably time to replace it.

Image 9: Removed clutch assembly
Image 9: Removed clutch assembly

15. Remove the clutch assembly.

Image 10: Strap wrench and pipe wrench used to remove nut
Image 10: Strap wrench and pipe wrench used to remove nut
Image 11: Clutch assembly after nut removal
Image 11: Clutch assembly after nut removal

16. Tighten a strap wrench around the clutch. Use a pipe wrench or impact wrench to loosen the large flat nut holding the assembly together.

WARNING: The clutch assembly in under spring pressure. When the clutch nut is removed, the clutch assembly will spring apart with force. Use extreme caution when removing this nut, or better yet – have an assistant hold the clutch assembly down as the nut is removed.

Part IV: Changing the Clutch Main Torque Spring

Image 12: Spring assembly with clutch removed.
Image 12: Spring assembly with clutch removed.

17: Lift the clutch off of the spring assembly and set aside.

Image 13: New vs old spring comparison
Image 13: New vs old spring comparison

18. Lift the old spring off the clutch pulley plates, and remove the spring guide from the end of the spring. Your new spring may vary in overall height relative to the stock spring depending on the chosen replacement spring.

19. Set the new spring onto the clutch pulley plates, and insert the spring guide snugly into the open end.

Important Note: For some aftermarket springs, the spring collar may not fit into the new spring. In these cases, it is OK to omit the spring collar during reassembly.

Part V: Installing a New Clutch (or reinstalling the original clutch)

Image 14: Clutch
Image 14: Clutch
Image 15: Clutch on compressed spring.
Image 15: Clutch on compressed spring.

20. Place the clutch on top of the main spring and compress the assembly. The new spring is much stiffer than the old one and will be a lot harder to compress. You will need to align the small hole in the center of the clutch with the shaft on the clutch pulley plates. Reattach the flat clutch nut.

– Note: This process is much easier with a 2nd pair of hands, so an assistant may be necessary. 

– Note: Use of blue Loc-tite on these nuts is recommended. It is vitally important that they do not come loose during operation.

21. Slide the clutch assembly onto the splined shaft. Replace the clutch bell and tighten the 17mm nut.

– Note: Use of blue Loc-tite on these nuts is recommended. It is vitally important that they do not come loose during operation.

Part VI: Replacing the CVT belt and putting it all back together

Image 16: Belt replaced on variator side
Image 16: Belt replaced on variator side

22. Replace the CVT belt over the clutch side pulley plates, then stretch it over the shaft on the variator side onto the variator dowel pin.

– Note: You may have to pry apart the clutch pulley plates to get the belt enough slackto get onto the variator dowel pin. This can be a difficult process and care must be taken to not damage the pulley plates or the belt.

23. Replace the variator fan, and tighten the nut on the variator side

– Note: Use of blue Loc-tite on these nuts is recommended. It is vitally important that they do not come loose during operation.

Image 17 CVT system
Image 17 CVT system

24. Once the variator fan plate and clutch bell are securely attached and bolted down, rotate the CVT system to settle the belt into position. This can be done by manually rotating the pulleys..

Image 1: CVT cover.
Image 1: CVT cover reattached

25. Replace the CVT cover and all bolts in their proper location.

26. Start the buggy, let it idle and listen for any abnormal noises from the CVT area. Rev the motor a few times, listening for problems.

27. If all sounds well, take it out for a slower speed drive. If the buggy bogs or does not have smooth acceleration, the rollers may have shifted when putting the variator and ramp plate assembly back on. Stop driving and follow the steps to disassemble and verify correct installation.

28. Have fun with your newly upgraded CVT system!

This 250cc CVT upgrade guide is based on an original work authored by “Alfordap” (Adrian Alford) and posted here on www.Buggynews.com. The original photos and text captions used by permission.

Copyright 2013 Buggy Parts NW