Gear Set Install

[eDan]

I do NOT recommend this Buddy mod. Skip down to Update 9 for the explanation.

Long-time lurker now first-time poster.

I have been on MB for many months now gleaning quite a bit of useful info on Buddy voodoo. Thanks to all who have shared. I figure it's now time to give back what I've learned, especially since I haven't found much info on Buddy gear sets.

What I have detailed below is my voodoo saga, which has mostly revolved around the gear set. I began writing this some time ago and have added updates as I learned them, although it is just now being posted. It got much longer and more detailed than I intended. So, if you want to get right to the tranny part <insert joke here>, then skip down to INSTRUCTIONS.

A little bit about my Buddy: It's a 2006 Buddy 125 with 19k miles. I use if for commuting about 8 months out of the year, when I'm employed Those are mostly highway miles too riding WOT. Top speed is 61 mph (gps) and lifetime economy is 76.6 bmpg. I had no engine voodoo on it until now, but had done a few things over the years:
- a short windscreen (which gave me between 3-5 bmph more out of the top end speed)
- stebel nautilus horn
- activated the body blinkers
- upgraded all the turn signal bulbs to SilverStars
- PIAA halogen head lamp
- front rack
- rear rack and topcase

I had been planning on doing the big bore kit plus some other upgrades, and when my Buddy died on the highway last August (that's a whole 'nother story involving the police declaring my legally parked ride on a side street abandoned and towing it for over $200, damnit), I figured it was a good time to start - especially with ScootwerWorks "Buy More, Save More" deal.

Here's the voodoo:
- 161cc big bore kit (done)
- Large cylinder head (done)
- Rejet stock carb to 110 (done)
- Replaced right crankcase (done)
- New crankshaft (done)
- Prima exhaust (done)
- Uni air filter (done)
- 1,500 lb clutch spring (done)
- 12g sliders (done)
- Gates belt - (done)
- NCY Transmission Kit (done)
- 16/36 gear set (done & TBD)
- Vee 351 tires (done)
- Tire stems (done)
- NCY front brake rotor (done)
- Front brake pads (done)
- HID Kit (in process - tough to fit it in to an '06)
- Decompression tube (tbd)

Yeah, I dropped a chuck of change, but saved 30%. I figured after four years of reliability I was willing to reinvest in my Buddy.

I hadn't planned on splitting the crankcase, but one of the four cylinder bolts broke off in the right crankcase, which is why I believe Buddy died (loss of compression, no power, burning oil). I tried drilling out the bolt and using a bolt extractor. It too failed. I then tried drilling out the extractor and broke three cobalt bits. Since I was into the fix for about $30, I decided to stop and just buy a new crankcase, which was $80 new and just $54 with the 30% BMSM discount. So I figured I 'ate' the discount by buying the bits and extractor set and gained some experience.



And since I was into the crankcase, might as well replace the crankshaft assembly too.

I've completed the engine rebuild, but have spent way too much time tuning and retuning the carb, playing with weights and contra spring, doing time trials all to no avail. I am underwhelmed and disappointed with the top speed and acceleration. Nothing more happens between half and full throttle. I'm not expecting the front wheel to come up considering the new gear set, but certainly be more zippy and a bit faster than it was before these mods. 40 mph just won't cut it. Something is seriously wrong and it can't just be the jets and weights.

UPDATE 1: I think I had a break through last night. I simply stood over the Buddy with feet firmly planted on the ground and throttled up. I was able to easily prevent the scoot from going forward using my feet a la Flintstone brakes. It is the stock clutch with 19k miles on it. Is there too much power from the engine slipping the clutch? I think I need to replace my clutch. Good, more to buy.

UPDATE 2: Installed the NCY Transmission Kit. I now cannot prevent the scoot from overpowering my feet-brakes, so that's an improvement. However, no improvement in speed or acceleration, which means the clutch wasn't the root cause.

Now, onto the gear set...

According to ScooterWorks, the stock gear set on a Buddy 125 is the 15/42 gear set. For the gear-challenged that's a reference to the tooth count on each gear - 15 teeth on one gear and 42 on its partner.

UPDATE 3: I had decided to test all my assumptions on the voodoo and began with the stock gears. I counted the teeth myself, which I should have done when I first removed them. It's NOT a 15/42 set, it's a 13/42 set! There IS a 15/42 gear set in the tranny. However, the upgradeable set is the 13/42 set with a splined ID on the LEFT handed helical 42T gear. The other RIGHT handed helical 42T gear has a continuous bore and is pressed on. Well that's a bit confusing. FINALLY, after three months I think this is the real problem! I just got the new 14/37 set two days ago, which SW special ordered. they only carry various 15T and 16T combos.



Below is the stock 13/42 gear set. Notice the splines on the ID of the 42T gear.



I bought the 16/36 set , which I (and Scooterworks) believed to be a drop in replacement. Spoiler alert: It's not.



I want more top end speed to keep up with traffic better and the 16/36 gave the biggest ratio improvement at just over 24%.

15/42 = .357
16/36 = .444
.444/.357 = 1.244 or 24% ratio increase

So I figure at my previous 61mph (gps) I should be doing nearly 76mph regardless of engine mods, assuming the stock engine had enough torque. So the big bore should do quite nicely since it adds about 25% power over stock.

From ScooterWorks:


UPDATE 4: I really went from a 13/42 to a 16/36 set, which is a 44% increase, not 24%. No wonder my engine can't get me going beyond 40mph.
13/42 = .310
16/36 = .444
.444/.310 = 1.436 or 44% ratio increase

UPDATE 5: Withe the new 14/37 set that I have yet to modify, I'm back to where I want to be:
13/42 = .310
14/37 = .378
.378/.310 = 1.221 or 22% ratio increase

The 13T pinion and its shaft are one piece, not a gear pressed onto a stubby shaft. The 42T gear is then pressed on to it.



Although assemblable (I'm declaring this is a word) without mods, you will ruin as I did, the two bearings supporting the gear/shaft. I figured since this was billed as a drop-in upgrade and it fit into the rear brake/transmission housing that I could trust the thicker gears would work. Not so much. With the cover completely on and no gap between the two aluminum housings, I torqued all the fasteners down and could barely turn the shaft with the clutch housing by hand - I knew something was wrong. A shout-out to Brandon at Scooterworks - he sent me out replacement bearings at no charge, but I had to get the gears machined to work. Oh - and getting the bearings out of a blind hole without a puller is a beyotch.






********************* INSTRUCTIONS *********************



Welcome skippers.

Disclaimer: Repeat at your own risk. There is no implied nor should you infer any guarantee of success doing exactly what I did. Manufacturing variations will yield different measurements and perhaps results. Wear eye protection, look both ways before crossing the street, blah, blah, blah.

Again, the upgradeable stock gear set for the Buddy is a 13/42 set - at least for my '06. Once you have your new gear set...

1 - Machine 'em: (read above if you don't)

- Remove .076" MIN (I took off .080") off the shaft boss
- Remove .079" MIN (I took off .080") off the shaft length - also one may add a slight chamfer for easier assembly with the bearing



AND do one of the following:

- Remove .105" MIN off the entire gear and hub face
OR
- Remove .0525" MIN off each side of the entire gear and hub face
OR
- Remove .055" MIN off the gear tooth face (yellow surface) AND remove .105" MIN off the gear hub (red surface) to work with the retaining ring.



I chose the last option so there was a bit more more tooth-to-tooth engagement. In the end it really doesn't matter for power transmission since the spline/shaft engagement remains the same, yet the gear gap was very minimal. I would take a couple more thou off if I did this again.

UPDATE 6: I will be! Actually, now I am planning to keep is symmetric and mill material off both sides.



2 - Drain the gear oil: I was pleasantly surprised that my oil looked fresh, although having 4,500 miles.

3 - Disassemble the transmission:

I suppose this could all be done without pulling the engine, but at a minimum one would need to:
- Remove the muffler
- Remove the rear wheel
- Disconnect the rear brake cable
- Remove the rear brake/transmission cover by loosening the 8 bolts.

Remove the 13/42 pressed gear set, just pull.
Then remove the output shaft, it should slip out of the bearing. The splined 42T gear will slip off, so be careful. No need to remove the retaining ring.

It should look something like this when done:



4 - Un-Press & Re-Press:

Press off the stock gear from the small pinion gear/shaft and press it on the upgrade gear/shaft. Scooterworks' site mentions needing a 50 ton press, I did it on a 20 ton and I suspect a 10 ton might work. Since most people don't have this, give a machine shop a call. The set up takes as long as the pressing. With an experienced machinist/technician it should take all of 5 minutes.

5 - Install modified gears:



The gap between the 42T and 36T gears is very small at .003". It works, but I think I'd like a .010" gap next time.





6 - Replace Gasket:

You may be able to get away with reusing the old one provided it's still in good shape. I didn't want to take any chances.

7 - Install tranny cover: Make sure you can hand-turn the gear train without the cover on to get a feel of the system torque. Turn the clutch bell, you will feel resistance, but you should easily be able to turn it with one hand. Install the cover and slowly install the fasteners and continue to check for binding by hand-turning the transmission. If it gets tougher to spin, then something is binding. Stop and figure it out! If it's all good then torque them down. From the page 69 in the manual: M6 @ 1.0-1.2 kg m, M10 @ 3.5-4.0 kg m.

8 - Refill with gear oil: Check for leaks.

9 - Ride captain ride...

UPDATE 7: I finally got to riding the new 14/37 gear set this weekend. It was better than with the 16/36 set, but still not great. It tops out at only 50 bmph. I think this foray into messing with the gears is proving to be a tricky deal. So now I'm planning to revert back to the stock set and make sure it's not an engine or tranny issue, which I don't believe it is. In the mean time I am searching for a more modest ratio increase of 5%, such as a 13/40 set.

UPDATE 8: Reverted back to the 13/42 gear set. Nothing. Installed the stock contra spring. Nothing. Installed stock roller weights. Nothing. Inspected the valve clearances. Just fine. Installed the stock intake. I did find the o-ring for the large-flow intake was pinched and cut though, perhaps altering the mixture by sucking in more air. Nothing. I basically had a stock setup now with a 161 kit. So nothing I did significantly changed performance, which shifted my focus from power delivery to fuel delivery.

I cleaned the fuel filter, disassembled the carb. Cleaned the idle and main jets, the needle jet base, the needle jet, inspected the diaphram and slider, the float valve, everything. Reassembled and VOILA! The engine ROARED to life like I had never heard before! It was deep and throaty and reeked of power! I hopped on and HOLY $^*&! Even with the 14g weights it was smokin' (figuratively).

You mean I have been screwing around for the past four months with springs and weights and gears and clutches, when it was a dirty carb all along? That is silly. Especially since I had completely disassembled, cleaned and rebuilt the carb and fuel filter last fall. Gahhhh! AND I use seafoam every few fill-ups. The particulate and gum gods were against me.

As a former colleague often said: "The answer is obvious once you know it."

So, now that everything is largely stock with the 161 kit, I want to ride it for a bit before I try any more gear swaps.

For what it's worth, in this process of trouble shooting, I measured the contra spring forces when each were compressed to 1.96", which is what I determined to be the compressed state in the NCY clutch.

Stock spring: 69.2 lbs
1,000 rpm: 77.6 lbs (12.3% greater than stock)
2,000 rpm: 84.8 lbs (22.7% greater than stock)

I will post photos later. I need a beer.


********************* Update 9 *********************

Update 9: I do NOT recommend this mod, at least with the NCY gears.

2011 was a bad year for my Buddy. I was so focused on several (yes several) engine rebuilds last year that I forgot (sorry) to post about this VERY important discovery about the gears - a broken tooth.



When I went back to reinstall the stock gear set, I found a broken tooth on the aftermarket pinion gear.

Now, with either aftermarket gear set installed I had noticed a lot of play - or gear slop - when turning the rear wheel by hand. I didn't like it, but believing these were drop-in replacements (once machined) I didn't persue it further until I saw the broken tooth.

I discovered that the center-to-center distance of the Buddy gear set is farther apart than these aftermarket gears, perhaps by a mm or two. So the gears were not meshing at the pitch diameter, but farther up the tooth, where the tooth is weaker. This is why I believe that tooth failed. It is further troubling because I had hardly any miles on this set, 50 at best.

I inserted each gear set into the case to gauge the play, check out these videos:

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I mis-spoke in the third video, the stock set is a 13/42 gear set, not 15/42 as I stated.

I tried to reverse engineer the gears to determine the correct center distance, but didn't come up with a 'good' number. I was expecting a nice whole metric number.

Buddy is back to the stock gear set. If I can't find better gears, then I have fanciful (read: expensive) dreams of having custom gears cut one day.

[Kaos]

Wow, welcome to MB, and FANTASTIC first post!

Rear gears are one of the least upgraded parts of the Buddy, so its awesome to see a good writeup on them.

Just to answer what I think might have been a question in your post: With the stock gears, a new head, the spring upgrades, and a 161cc kit, you should have been able to wheelie it. And definitely not been able to hold the bike still with just your feet.

[eDan]

Thanks Kaos, you're one of the prolific posters on MB with gobs of great info that I've been following. Thanks to you.

Yeah, a wheelie I wasn't expecting and didn't even get close with this setup. BUT I wanted more, not less and that's what I got.

We just got about 8 inches of snow over the weekend, so when I do get my gears modified it will be some months before I can take the Buddy out for a test drive.

[BootScootin'FireFighter]

that's a lot of great information, thanks for the write up. can that be archived over in the technical library forum?

[Kaos]

Thanks Kaos, you're one of the prolific posters on MB with gobs of great info that I've been following. Thanks to you.

Yeah, a wheelie I wasn't expecting and didn't even get close with this setup. BUT I wanted more, not less and that's what I got.

We just got about 8 inches of snow over the weekend, so when I do get my gears modified it will be some months before I can take the Buddy out for a test drive.

Ahh, thats a shame. I know how hard it can be waiting to test new mods!

[bigbropgo]

Great post. And welcome to modernbuddy. I am sure members are thankful for the R&D. Looking forward to the results. Ride safe.

[Keys]

...now if only I could find a gear-set for my Rattler 110...

--Keys

[bigbropgo]

...now if only I could find a gear-set for my Rattler 110...

--Keys

spi-parts has some. Same company weezool found his. I went as far as an email to them to verify, but that's it. At the time the part #'s were the same ( for 50 and 110) and that bothered me. The reply said, "yep, it will fit". I can't verify if they fit though.

[Bcon]

eDan - Great post!

With respect to your power disappointment after the mods, there's definitely something going on there. I'm sure you'll get it worked out. Mine took quite a while to break in after the big bore install. It smoked a bit for the first 50 miles, so it definitely didn't have peak compression. After 200 miles, there is a very noticable increase in power and top speed. I also noticed the carb needed re-tuning as it broke in.
However, like you, I'm down for the winter due to snow and single digit temps so further tuning has been delayed until spring.

I didn't do the big valve head or the Uni filter, and am running the stock CVT/clutch with 11g sliders, and it'll pull the front wheel sightly going up the very mall incline on my driveway. For my use, I'm very happy with the mods, tons more torque and a slight increase in top speed.

I'm looking forward to hearing how it goes once you can get back out!

[Howardr]

Great post. Now the suspense of waiting til spring so we can hear results from these mods.

FWIW, I was led to believe the 62mm piston was "plu-n-play for my Buddy 150. NOT!

Howard

[ericalm]

This is the most technical post in MB history. Anyone who posts mods without full installation instructions and dyno results is slacking off!

[eDan]

that's a lot of great information, thanks for the write up. can that be archived over in the technical library forum?

I'm happy to share, though I'm not sure how to move topics to other forums.

eDan - Great post!

With respect to your power disappointment after the mods, there's definitely something going on there. I'm sure you'll get it worked out. Mine took quite a while to break in after the big bore install. It smoked a bit for the first 50 miles, so it definitely didn't have peak compression. After 200 miles, there is a very noticable increase in power and top speed. I also noticed the carb needed re-tuning as it broke in.
However, like you, I'm down for the winter due to snow and single digit temps so further tuning has been delayed until spring.

I didn't do the big valve head or the Uni filter, and am running the stock CVT/clutch with 11g sliders, and it'll pull the front wheel sightly going up the very mall incline on my driveway. For my use, I'm very happy with the mods, tons more torque and a slight increase in top speed.

I'm looking forward to hearing how it goes once you can get back out!

Hey thanks. I have 150 miles now on the big bore. The engine sounds healthy and responsive, except when riding. I even bought a compression tester and it's north of 175 psi. So I'm confident the engine is fine. I think my biggest performance gain will be with the correct gears - well until I try them and discover something else I missed.

This is the most technical post in MB history. Anyone who posts mods without full installation instructions and dyno results is slacking off!

Aww, shucks...thanks, and there are some detailed posts in here! Not to misrepresent, but I merely reposted that dyno graph from ScooterWorks - perhaps I should note that in the post. I did rely on it on which to base my gear choice, but did not generate it.


I'll definitely be posting updates as they happen. I figure in the next week or two I'll get my new gears modified. I'll need to wait for a warm spell, something in the 30s will do just fine, to open up the gear case. I don't have a garage so all my work is done outside.

[gearhead]

great write up!

[eDan]

I posted Update 7 in the body above to keep it all centralized, and also included it here:

UPDATE 7: I finally got to riding the new 14/37 gear set this weekend. It was better than with the 16/36 set, but still not great. It tops out at only 50 bmph. I think this foray into messing with the gears is proving to be a tricky deal. So now I'm planning to revert back to the stock set and make sure it's not an engine or tranny issue, which I don't believe it is. In the mean time I am searching for a more modest ratio increase of 5%, such as a 13/40 set.


Does anybody know of a source for a 13/40 gear set? I can't seem to find any scooter or buggy shop that sells them. They apparently exist though. Or a 14/43 set?

Also, other than Harbor Frieght, any sources for an inexpensive hydraulic press in the 10-20 ton range?

I'm getting to the point of buying my own rather than running to the machine shop for my pressing needs.

[ericalm]

Is it screaming off the line or are you suffering in acceleration and top speed?

The basic truism for modifications that's at least mostly true for Buddys is that once you have a cylinder kit, pipe and transmission upgrade, you'll see diminishing performance returns for every dollar spent on additional mods.

[eDan]

It is definitely not screaming, unless on the centerstand. So I'm reasonably confident in the engine mods, but not the gears.

It is zippy off the line until 20-ish, but then begins the mismatch between the expected engine revs (sound) and speed. The engine wants to do more rpms, but I think the added torque of the new gears prevents it from winding out.

[ericalm]

Hm. Had you played with your transmission setup (roller weights) much before installing the gears? How was it performing before the gear install?

[eDan]

All of these mods were done at once, big bore, NCY super tran and gear set.

Before the mods (and the engine fail) things were all stock and it was running well.

I probably have some tweaking left on the roller weights as well as the main jet, but I expect those to be fine tuning, not gross tuning.

To me, everything keeps pointing back to the gears.

[Lagerhead]

Did you use the torque spring that came with the NCY trans kit?

The spring that came with my kit was the wrong one. (too short / weak)

[eDan]

I did use the NCY spring. The spring seemed to fit fine. I do have several others from all the trial and error, but wanted to stay with a "known" setup.

Hopefully this weekend I'll get the stock set back in and see how that performs.

[ScooterTrash]

Did you use the torque spring that came with the NCY trans kit?

The spring that came with my kit was the wrong one. (too short / weak)

Mine sucked as well. switched back to the stock spring and got 5 mph back on the top end

Mine was the right size but is for acceleration, not top end

[Lagerhead]

I can't imagine that all of the NCY kits came with the wrong spring but mine was 105mm in legnth. A worn out stock spring I have measures 150mm.


TorqueSpring by benandangie, on Flickr

I did try running the red spring and it made it seem like I was starting out in too high of a gear. I never tried the "Flinstone brake torque" technique but I think my results were similar to what you're describing.

Good luck!

[ScooterTrash]

Yeah, mine was the same size. Just softer

[jrsjr]

The basic truism for modifications that's at least mostly true for Buddys is that once you have a cylinder kit, pipe and transmission upgrade, you'll see diminishing performance returns for every dollar spent on additional mods.

There's actually some physics behind that. The relationship between power and top speed is exponential, not linear. 25% more power does not deliver 25% more speed. Just for fun, try messing with the Aero-Horsepower & Drag Loss Calculator. Without knowing the exact parameters, it's impossible to do exact calculations, but I played around with it (as shown below) for fun. Since I don't know the actual numbers, I just tweaked the calculator using 6 horsepower and 63 MPH and made close approximations for the coefficient of drag and frontal area until I got close. Then, I used those same parameters and changed the desired speed to 76 MPH. Look at what a whopping difference in horsepower it makes! If that calculator is to be believed, it would take more than 10 horsepower to push a Buddy through the air at 76 MPH. Using my parameters, a 20.6% increase in top speed required a 68.3% increase in horsepower. That's crazy!

The gearing thing is crazy cool (Welcome to Modern Buddy, eDan!), but you're going to have to find more horsepower to go with your gearing in order to go fast. The gods of physics do not negotiate! Sorry.

[ericalm]

[eDan]

There's actually some physics behind that. The relationship between power and top speed is exponential, not linear. 25% more power does not deliver 25% more speed. Just for fun, try messing with the Aero-Horsepower & Drag Loss Calculator. Without knowing the exact parameters, it's impossible to do exact calculations, but I played around with it (as shown below) for fun. Since I don't know the actual numbers, I just tweaked the calculator using 6 horsepower and 63 MPH and made close approximations for the coefficient of drag and frontal area until I got close. Then, I used those same parameters and changed the desired speed to 76 MPH. Look at what a whopping difference in horsepower it makes! If that calculator is to be believed, it would take more than 10 horsepower to push a Buddy through the air at 76 MPH. Using my parameters, a 20.6% increase in top speed required a 68.3% increase in horsepower. That's crazy!

The gearing thing is crazy cool (Welcome to Modern Buddy, eDan!), but you're going to have to find more horsepower to go with your gearing in order to go fast. The gods of physics do not negotiate! Sorry.

Yeah, I kinda lost sight of air-resistance in spec'ing out the gears. I'm eager to get the stock set back in this weekend and scoot about.

[jrsjr]

Yeah, I kinda lost sight of air-resistance in spec'ing out the gears. I'm eager to get the stock set back in this weekend and scoot about.

Hang on to that modded set of gears! There's a group of folks who are all about making scooters go fast, the Motor-Scooter International Land-Speed Record Association. All you need is a big carb, cam, and a performance head combined with your gear set and you should be ready to go chase the official Buddy land-speed record.

[Kaos]

Yeah, I kinda lost sight of air-resistance in spec'ing out the gears. I'm eager to get the stock set back in this weekend and scoot about.

Hang on to that modded set of gears! There's a group of folks who are all about making scooters go fast, the Motor-Scooter International Land-Speed Record Association. All you need is a big carb, cam, and a performance head combined with your gear set and you should be ready to go chase the official Buddy land-speed record.

Just outa curiousity, why 6HP? The 125 is 11HP, I'm not sure what the 50's run, are they around 6?

[eDan]

Check out Update 8 in the main post.

I'm finally on my way!

[ericalm]

Check out Update 8 in the main post.

I'm finally on my way!

Ha! Awesome.

This is why I think these kinds of mods should be done incrementally. It makes it way easier to eliminate culprits if things aren't going right.

Now that you have a good baseline, it'll be interesting to see where things go from here.

[eDan]

Check out Update 9 in the first post for the latest development.

[rick71454]

Hello eDan:

Thanks for this post. Makes me leery about modifying final gears to get top speed.

Rick71454

[gitsum79]

If there's clearance with the engine case, why not try a taller rear tire? It would be just like using a taller final gear ratio. You could even install a slightly shorter rear shock if you wanted to keep the ride height stock.

You can check for belt wear on the variator face. If the belt has a little extra room to ride further out, you can shave the boss down 1/2mm to 1mm or so, depending on how much further the belt can go out.

[rick71454]

Hello Gitsum79:BuddyLand:

It would be so simple if a larger diameter tire than stock, could be mounted in the rear. I made measurements myself and no other tire larger than stock size would fit properly.

If anyone says otherwise, please provide photographic proof.

Thanks
Rick71454