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BV500: Replacing the Belt and Rollers
Overview
It is inevitable. You have a Twist N Go scoot. It’s great. It also has some maintenance issues. The Continuously Variable Transmission (CVT) automatic transmission has two main wear items: the drive belt and the rollers. These are likely the biggest replacement items most owners might attempt to service themselves. The factory manual leaves much to be desired for the person who has not done a belt/roller replacement before. This document hopes to fill in the blanks for anyone who is reasonably mechanically inclined.
How the CVT/Automatic Clutch systems works:
When viewed from the left side of the scooter, the transmission housing runs from engine to the rear axle. At the engine end is the CVT itself. At the rear axle is the centrifugal clutch. Between them is the drive belt.
CVT
The CVT is comprised of two shallow cones facing each other. The belt runs between the two cones. The cones are moveable and can be closer to each other or wider apart depending on the rotational speed of the drivetrain. The thing that moves the cones in and out is a set of rollers that press against one of the cones and moves it closer to the other cone. The drive belt runs between these cones. As they move closer or further away from each other, the effective running diameter for the belt changes.
Clutch
The clutch is a little like a drum brake in reverse. The belt drives a set of pads that have weights, held back by springs. As the rotational speed increases, the pads start to move outwards against the inside of the drum. The drum transfers the power via a spline shaft to the rear wheel.
Prep
I suggest two containers for hardware. One for the external plastic fasteners and one for the ones related to the mechanicals.
You need a torque wrench that can read up to about 150 lb/ft. You can get by with one that only does 50 lb/ft with the work around I highlight below.
Socket wrenches, ½” and 3/8” drive, 21mm, 27mm, 10mm and 8mm sockets
Phillips head screwdriver
Rags
You need to make a special tool to hold the CVT still while tightening its nut. I have a picture below that you can print out or (preferred) download the pdf at the end of this article.
You need a 1/8” thick, 6 1/2” x 7 1/2” [3mm thick, 165mm x 190mm] plate of aluminum to make the tool.
You also need:
19 ea M6 x 25mm screws
3 ea M6 x 50mm bolts
3 spacers with 1/4” [6.2mm] ID and a length of about 1 7/16“ [37mm].
Print out the template. Make sure the length and width of the template are 6 1/2” x 7 1/2” [165mm x 190mm].


Template jpg...there is also a pdf at the end of the article

Using the printout as a guide, drill all holes with a 1/8” [3mm] bit. Drill all 19 holes in the circular pattern with a .201” [5.1mm] bit. Drill the center main hole with a 1 1/2” [38-40mm] bit, and the 3 along the edges with a .240” [6.1mm] bit. Tap all 19 holes with an M6 x 1.00 thread. Screw all 19 M6 screws into each of the threaded holes. I got a little anal and covered all the screw threads with vinyl tubing. The finished tool should look something like the pictures below:


Tool: Front and Back

Step 1
I like room to work. So I removed everything in the way. In my case this included the left side hard case, the fuel filler “saddle”, side plastic, and the air filter outside cover.
Removing the side cases required removal of four screws (M4 allen).
The fuel saddle plastic has four screws that hold it in place. Two are concealed under the fuel filler door and the other two are at the right and left corners. Remove the fuel filler cap and drip shield. Slide the plastic up in front and remove it from under the body panel at the rear. Replace fuel cap while doing the remaining work.
The side plastic is removed by removing the rubber mat (it pops up and out), removing two screws under it, three screws at the front wheel end of the panel, two screws that were concealed under the fuel filler saddle, and one screw under the foot “peg” for the passenger.
Lift side plastic up and off. Set aside. Your scoot should now look like the figure below.


Top: Saddle up. Note screws concealed left and right.
Middle: Screws under rubber mat
Lower: Side plastic off


Step 2 Removing Transmission Cover
Remove dust cap at rear axle.
Remove the transmission plastic cover. Four Philips screws; use #2 Phillips driver.
Your scoot should now look like:


Top: Removing Dust Cap
Middle: Removing Transmission cover (taken from Piaggio Manual)
Lower: Cover off


Step 3 Removing Transmission Housing
Remove the driven shaft nut. (21mm) I used my impact wrench. Please note this goes against advice in the manual. Use technique at your own peril. [The manual recommends using a six-seded socket to hold the middle shaft and a 21mm ring spanner to loosen the nut. It also states that you shouldn't use a 12 sided socket to hold the shaft as this could cause damage].
Remove the transmission housing. There are four main bolts (10mm socket), and an array of bolts along the edges (M8 socket). The cover should now come off. I had to lightly tap the driven shaft end to get it to come off. If you do the same, use a plastic hammer and be gentle. There are two washers that will come off the driven shaft. Don’t let them get away from you!
Your scoot should now look like


Top: Removing driven nut
Middle: Washers and housing
Lower: Step 3 done


Step 4 Removing Clutch Bell
Remove the washer from the end of the driven shaft.
Pull off clutch bell. Check inside for any abnormal wear. You should check for wear and runout. The nominal ID is 4.069” [160.2mm] with a max ID of 4.076” [160.5mm]. Measure the diameter at several places. The allowable runout is .008” [0.2mm]


Top: Removing washer from driven shaft
Bottom: Inside of clutch bell


Step 5 Removing front of CVT
Install special tool, by aligning it over the center of the CVT such that the three outlying bolt holes line up with three threaded M6 holes. Place a spacer under the plate at each location and install using M6 x 50 bolts. Be careful to not cross thread while tightening this tool in place. Tighten securely 25lb/ft [30NM].
Use a 27mm socket and remove the center bolt. This may require a breaker bar on your ½” socket drive. The nut is on seriously tight. My impact driver could not get it off! I ended up using a 4’ long / ¾”ID pipe over my socket drive to get it done. Once the nut is loose, remove the special tool.
Once the tool is off, remove the washers.


Top: Special tool properly installed
Middle: Placement of socket wrench through special tool
Lower: Removing washers from CVT


Next slide off the near side of the CVT. It simply sides off.
Check for any abnormal wear. Clean if needed. Make sure you don’t get any oil on it. If you do, wipe off immediately with alcohol.


Top: CVT near side after sliding off
Lower: CVT side should be smooth and clean


Step 6 Remove Belt/Clutch
Now remove the clutch off the driven shaft. It simply slides off. The belt will come with it. Leave the belt on it for now and set the assembly aside. Feel free to clean things up. I used a rag with some brake cleaner on it.


Transmission housing without a transmission!

Step 7 Removing Rear of CVT and Rollers
Remove washer.
The sleeve you now see moves freely. Don’t remove it yet.


Top: Remove washer
Bottom: The sleeve I am talking about


The rear half of the CVT is free to slide out. Slip some fingers behind it and hold the roller cage in place while pulling the CVT rear off. Hold the roller cage in place the whole time.
Now look at the back side to see what you were holding. Make a note of how the sliding guides are fixed into the metal cone so you can replace them properly.
Place on a work surface with the roller cage side upwards.


Top: Slip fingers behind to hold roller cage
Middle: The roller cage
Bottom: Assembly on bench, roller cage side up


Step 8 Roller Replacement
Lift the roller cage upwards. Be sure to hold the plastic guides in place while you do this. They will want to fall off as you lift them out of the CVT housing.
Set the cage on your work surface. You can now see the rollers.
One by one remove a roller, clean the inside of each roller’s running area, and replace with a new roller.


Top: Lifting roller cage. Note plastic guides around cage
Middle: The rollers!
Bottom: Lifting the sorry rollers out


Note that the rollers are different on one side than the other. Be sure to replace the rollers with the same orientation they had from the factory.
When you are done, the assembly looks like this.
I also cleaned the internal steel sleeve. It was gunky. The manual warns against lubricating or cleaning the inside of the bronze bearing it rides in.
Now, while holding the plastic guides in place, fit the roller cage back over the rollers.


Top: If you look carefully one side shows the bearing, the other side does not
Middle: All pretty now
Bottom: The sleeve after I cleaned it


Step 9 Installing the new belt
If you look at the clutch where the belt is, you’ll notice a spring at the center of the clutch where the belt runs. This spring pulls the two halves of the belt’s running surface together. You will have to spread them apart to make way for the new belt. I placed a set of rubber coated pliers in a vice, placed the new belt around the clutch and squeezed the clutch while applying pressure against the belt to get it as far as possible into the clutch. It will stay in place once this step is completed. I managed to get it about ½” [13mm] below the outside edge of the clutch. I later figured out that it did not have to be that far in. Another method is to put a piece of metal pipe on the ground and use it to massage the belt into the clutch cones but rolling it backwards and forwards while applying pressure from above.


Top: Squeezing the clutch and pressing the belt into it
Bottom: How far I pushed the belt in


Step 10 Reinstalling the CVT
Slide the rear CVT/Roller cage assembly onto the front shaft. Be sure the steel sleeve is in place. Slide the clutch/belt assembly onto the driven shaft. Run belt along its proper route to the front shaft. Reinstall washer and then the outside half of the CVT over the belt. Reinstall the two outer washers and the nut. Install finger tight. I played with the belt at this time to get the clutch to retract to the belt when in its normal slack tension.
Install the special tool. Using the 27mm socket, tighten to 120-130 lb/ft [160-175NM]. My torque wrench did not go that high. I used a 25 lb weight (bucket of water) at the end of my 4’ bar to set the torque. You can use some loctite to keep the nut from coming undone. Its also a good idea to mark the position of the nut with a dab of paint so you can tell if its coming undone in future inspections.


It looks crazy, but it works well

Step 11 Reinstalling the clutch / Transmission Housing / Cover
Slide the bell over the driven shaft.
Don’t forget the washer.
Place transmission housing over the transmission, aligning the bearing over the driven shaft. Loosely install all bolts (four large ones first). Now finger tighten all bolts. Tighten the large bolts to 17-19 lb/ft [23-26NM] and the small ones to 8-10 lb/ft [11-13NM].
Install two washers (smaller one first) and nut over the driven shaft.
Now the manual asks you to hold the center shaft while turning the nut to prevent torque from loading (and potentially damaging) the final drive. I did not do that. I held the left brake firmly while tightening the 21mm bolt with a torque wrench. I deemed this safe. You may not agree with that. Tighten to 68-75 lb/ft [92-100NM].


Top: Clutch bell going back on
Middle: The washer
Bottom: Don't forget the washers outside the transmission housing


Install round dust cap.
Position plastic transmission cover over transmission and reinstall 4 phillips screws.
Reinstall air filter cover.
Reinstall skins. You’re done. Whew!
Post job notes.
It would have been impossible to do this job to factory specs without the special tool. I did not talk about the clutch much as that is beyond the scope of this project note. My clutch pads were very lightly worn. I did this job on my scoot with about 14,000 miles on it. This is way over the factory recommended interval, but it was inspected at 10,000 with no issues reported. I was kind of surprised that the belt when it was still on the bike looked fine and was well within width tolerance. I gave passing thought to forgetting the replacement at this point. I know however that I am planning a transcontinental ride this summer, so went right on through with the project. After removal and close inspection, I found a serious crack in the belt on the inside. It is very unlikely that I could have detected this with the belt in the transmission.


The crack that really kinda scared me!

The shop that had performed the inspection at 10,000 miles had done a terrible job. Several of the plastic screws were not reinstalled or installed wrong. They also broke off one of the plastic standoffs inside my air filter. They stripped two of the screws that hold on the plastic transmission cover. It was also apparent that they had used an impact wrench to perform all the bolt removals and reinstalls. ARGGGH!!!!
It is these types of consistent incompetence from most every scooter service shop I have used that drives me to do these reports for the community.
PDF of Tool Pattern
http://www.modernvespa.com/forum/download.php?id=65491
Last Updated Thu Sep 26, 2013 12:29 pm
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