150cc Transmission System Upgrades

Upgrading the CVT system on a 150cc buggy

This CVT upgrade guide is based on an original work authored by “dewmanity” (Randy) 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 150cc GY6 motor 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. Though the photographs featured in this guide show the work being performed on a buggy, once the transmission cover has been removed, the process is identical for almost every CVT system used in any kind of scooter.

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

1. The muffler on many 150cc buggies is attached to the CVT cover and must be removed for access to the CVT system. Additionally, the left rear tire may need to be removed on some models.

– If this is the case for your buggy, lift up and stabilize the rear of the buggy with a jack and/or jack stands. Remove the left rear tire, if necessary.

Image 2: Exhaust bolts on underside of engine
Image 1: Exhaust bolts on underside of engine

2. On the underside of the engine, remove the two exhaust bolts.

Image 3: CVT cover with exhaust removed.
Image 2: CVT cover with exhaust removed.

3. Remove the single bolt that connects the exhaust to the outside of the CVT cover.

– Note: If there is a removable kick-start shaft used as an exhaust mount, remove that as well. You can see the bolt on the side in the above photo.

4. Remove the bolts around 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 4: CVT cover removed. Variator on left, Clutch assembly on right
Image 3: CVT cover removed. Variator on left, Clutch assembly on right

5. Take off the CVT cover. Be careful to damage the CVT gasket as little as possible. If the gasket does become damaged, it’s OK. This is not an air or water-tight chamber and the gasket does not necessarily need to be replaced.

6. Remove the 17mm 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 strap wrench held by an assistant can be helpful.

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

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

Part II: Changing Roller Weights

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

9. Remove the old rollers and set aside.

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

Important Note: If installing Dr Pulley slider weights, refer to this article for specific instructions on the proper orientation for slider weights.

Image 5: New rollers installed.
Image 5: New rollers installed.

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: Many Dr. Pulley variators come with three small washers that can be optionally installed as spacers. In most cases, they are not necessary on buggies and can decrease overall performance. 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

13. To access the clutch, remove the clutch bell nut. The size may vary by buggy model, but is commonly 17mm on a 150cc. 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.

Image 6: Clutch Bell
Image 6: Clutch Bell
Image 7: Inside the Clutch Bell
Image 7: 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 surface, it is probably time to replace it.

Image 8: Clutch assembly
Image 8: Clutch assembly

15. Remove the clutch assembly.

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

16. Tighten a strap wrench around the clutch. Use a pipe wrench to loosen the large flat nut holding the assembly together. Alternately, you can place the clutch assembly into a towel and lock it into a vise for more stability. Use the pipe wrench to loosen the flat nut as mentioned above, then slowly release the pressure of the vise to contain the pressure from the main spring.

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.

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

Part IV: Changing the Clutch Main Torque Spring

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

18. Lift the old spring off the clutch pulley plates, and remove the spring guide from the end of the spring.

Image 12: New spring with spring guide
Image 12: New spring with spring guide

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

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

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.

Image 13: Clutch
Image 13: Clutch
Image 14: Clutch on compressed spring.
Image 14: Clutch on compressed spring.
Image 15: Completed clutch assembly
Image 15: Completed clutch assembly

– 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.

Image 16: Replaced clutch assembly
Image 16: Replaced clutch assembly

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 17: Belt replaced on variator side
Image 17: 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 slack to 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. The belt may be slightly squished when initially putting the fan plate back on. The process that we advise using is to tighten the nut into the fan plate until it is about 1/2 tight, then manually rotate the transmission (using the variator or clutch assembly) about 1/2 turn (you can remove the spark plug to release engine compression and make this easier). Then, tighten the variator nut more, repeat turning the CVT 1/2 turn, tighten the nut, etc until the nut is tight and the belt is no longer pinched. The belt will be gently squeezed through this process up the variator face plate a small amount to its natural resting position.

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

Image 4: CVT cover removed. Variator on left, Clutch assembly on right
Image 18: CVT system

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

Image 3: CVT cover with exhaust removed.
Image 19: CVT cover reattached

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

26. Reattach the exhaust by reversing the steps at the start of this guide, and put the left rear tire on if you had to remove it. Remove the jack stands and place the buggy back onto level ground.

27. 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.

28. 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.

29. Have fun with your newly upgraded CVT system!

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

Copyright 2013 Buggy Parts NW