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GTR51 CVT

Mounting a CVT on a Goped scooter is not a novel idea, but this project is the first to mount the CVT horizontally to keep the engine low to the back wheel. The Goped GTR frame poses a great challenge when it comes to mounting a CVT. This is due to the actuation of the rear suspension arm and the additional stress it will put on the engine and CVT mount. This scooter's mounting system was specifically designed to handle the forces produced by the actuation of the suspension and to move the engine as far away from the heels of the rider as possible.


GalleryEdit

Mounting the engine and clutchEdit

GTR46 CVT mount design 1
GTR46 CVT mount design 2

Design of the engine mount. Due to the rotational forces created by the GTR's suspension, a novel mounting mechanism had to be created to handle the stress. This mounting method placed the main, stress-taking plate between the CVT and engine and included an additional rear support for adjustment and absorption of the massive forces created during stress.


GTR46 CVT mount block

The frame mount block. In order for the new mount to distribute the stress of the engine weight over the two welded mounting tabs of the GTR frame, an aluminum block was constructed to fit where the original engine/clutch mount sat. It is constructed of two 3/8" plates, 4 bolts and a ridiculous amount of washers. A more photo-ready design will have custom-cut spacers to go between the plates. It was to this block the the main weight-bearing plate will be attached.


GTR46 CVT mount channel aluminum

Plate constructed of 3/8" aluminum

GTR46 CVT mount channel thin

Plate constructed of 1/8" steel

GTR46 CVT mount channel thick

Plate constructed of 3/8" steel

The weight-bearing plate. Three different weight bearing plates were designed. The first 3/8" steel plate was the first to be (painstakingly) cut. Although it was plenty strong for the application, it weighed in at nearly 10 lbs, which was far too much weight

The next attempt at an appropriate plate was offered by Robotguy. He welded a 1/8" steel channel from the plate specifications and sent it along to be cut and mounted.

A third plate was constructed for testing purposes. It was cut out of 3/8" aluminum. Since aluminum weighs quite a bit less than steel, this plate weighed about as much as the 1/8" steel plate, but was a little bit stronger.


GTR46 CVT rear support plate

1/4" steel semi-circle plate

GTR46 CVT rear support

Mounted rear support

The rear support bar. A rear support was constructed from two parts, a 1 1/4" x 1/4" steel bar and a 1/4" piece of aluminum. The 1/4" semi-circular aluminum plate was cut to mount to the rubberized bolt holes of the CVT. It was then slotted for a sliding bolt to placed in it for adjustment.

The steel bar was drilled to the size of axle shaft and mounted before drilling the adjustable bolt hole in the other end. These two pieces meet together to perform both the adjustment and the support for the back of the transmission. It is because of this support that the rotational force of the rear suspension is nullified.



China CVT clutch cooling vents 2

View of cooling vents when CVT is mounted.

China CVT clutch cooling vents 1

Clutch cooling vents cut

Zocchi 78mm clutch drum

Zocchi 78mm clutch drum

The clutch bell. Since the clutch shoes of the engine were spaced an extra 1/8" - 1/2" away from the transmission, the clutch bell of the transmission needed to be extended through the mounting plate, a 78mm clutch drum designed for water-cooled pocket bikes was fitted to the CVT transmission. This extended the clutch-bell out an additional half-inch and provided a good interface between the engine's clutch shoes and the bell.

Cooling is an issue for the clutch housing in this system so a simple pattern of vents was cut into the clutch housing in order to take advantage of the fins on the clutch bell.



Switching the chainEdit

44t BFO5T sprocket

44 tooth BF05T sprocket mounted to the rim bolts

BF05T vs 25H chain

BF05T chain vs Goped 25H chain

The OEM Goped chain for all modes is a #25H. It is about 6mm wide and is barely strong enough to lead a long life on cruiser scooters. In order to strengthen the setup and make the CVT compatible with the drive train, a BF05T chaina nd sprocket were opted for. The only modifications necessary for the conversion was a widening of the new sprocket holes to match the 3/8" mounting holes of the Goped sprocket.


Flipping the cylinderEdit

Active 50 flipped

Cylinder flipped Active 50

Active 50 reversed pulse channel

Pulse channel cut on opposite side of case

Active 50 case bearings

New crank case bearings.

Since the engine had to be flipped in order to mount the CVT, the cylinder was flipped in order mount the DDM Dominator exhaust in the correct direction and keep the air filter away from the rider. Although the Active 50 is supposed to have a pin offset piston, the piston did not have any markings indicating this, so the flip was still performed. The process is pretty straightforward.

  1. Remove cylinder
  2. Cut a new pulse channel
  3. Match the case to the transfer ports
  4. Remove the piston
  5. Reassemble with piston, cylinder and gasket facing the other way
  6. Re-cut cover to accommodate flip
  7. Paint over hideous john deer green color

I ended up replacing the crank case bearings because the old ones were 10 minutes of operation from failing and causing damage.


Mounting the exhaustEdit

GTR46 CVT exhaust mounting 3
GTR46 CVT exhaust mounting 2
GTR46 CVT exhaust mounting 1

Since the cylinder was flipped, the Active 50's flywheel was no longer in the way of the Dominator's exhaust and mounting was relatively straightforward. Mounting the pipe support to the pull start cover was also a straightforward process requiring only a couple spacers and re-drilling. Pipe-wrap needed to be added to protect the rider from burns.


TestingEdit

Initial testing was done to see if the Active 50 would even run. It was a free engine and the previous own warned that it *needs work*. After the engine successfully started and ran well, all focus was on the new CVT transmission. After playing with the weights and shimming the contra spring, 5mm of shim and 27g of weights was settled on. Gearing with the 18/44 final was still too high to let the engine rev out so a new rear sprocket was cut and a larger pinion switched in for 20/54.

With top speeds of above 40mph and acceleration reaching 35mph easily in a short residential, outright testing was finished.

Two test videos where shot:

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