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An Overview and Investigation of the 4T Stella Transmission

 
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az_slynch
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PostPosted: Sun Oct 11, 2015 3:02 am    Post subject: An Overview and Investigation of the 4T Stella Transmission Reply with quote

To preface, since my 4T had a mechanical failure at low mileage which required a full teardown, I found myself with an opportunity to study the innards for the transmission. The observations and analysis to be presented in this thread are not gospel, but my own endeavor to understand the innards and come up with some tuning solutiions.

The transmission of the 4T Stella is quite similar to that of the 2T Stella, which in turn is derived from the Vespa PX line of scooters. To get a visual of how the gearing interrelates, please visiit ScooterHelp for a great description of the P/PX transmission and a gearing calculator.

The primary drive, consisting of the gearing that connects the crankshaft to the input shaft, is identical to a late model PX150 "Lusso", or EFL, transmission. The clutch is the larger, 115mm, 7-spring clutch of the style found in the P/PX 200 and later model EFL transmissions. It is fitted with a 21-tooth helical cut gear. This gear interfaces with a 68-tooth helical cut gear, which transfers engine power to the input shaft via an integrated "cush drive". The primary drive ratio is approximately 3.24:1. This ratio may be altered through the use of a 108mm clutch drive plate (plate diameter, not clutch diameter) fitted with either a 20-tooth helical cut gear (for a shorter 3.40:1 ratio) or a 22-tooth helical cut gear (for a taller 3.09:1 ratio). The latter gear is commonly found in the Vespa Rally 180 clutch, which is a direct swap into a 4T Stella. This single change is a 4.8% upgear to the primary drive and as a result modifies the final ratios of all four output shaft gears. Alterations are possible for the cush drive gear, but these changes would require a full engine teardown and reworking of the cush drive assembly for minimal gains.

The input shaft assembly of the 4T Stella is the most radical variation in the transmission. Only the kickstart mechanism is common to both assemblies. I will attempt to describe the differences.

In a traditional 2T input shaft assembly, the gears are machined as a single unit. This unit is attached to the large primary gear by the cush drive assembly. The whole assembly rides on a set of internal bearings and rotates around a fixed shaft that bolts to the engine crankcase. The clutch side bearing is a 6302 radial ball bearing which is held in the input shaft by a snap ring. The flywheel side bearing consists of a collection of needle rollers which ride in a channel machined into the central shaft.

In the 4T Stella transmission, the input shaft is constructed quite differently. The gearing is not a single assembly, but is formed from a collection of parts. The gear that drives the top gear ratio is integrated with the cush drive assembly and has a splined hole in the center. The third and second driving gears are machined as a single part and have a splined hole through the center. The driving gear for the first gear ratio is machined onto a splined shaft, which the prior two assemblies slot on to. The first gear/center shaft assembly rotates with the rest of the gearing and are supported by two external bearings. The clutch side is supported by an HK1616 caged needle roller bearing which is pressed into the crankcase. The flywheel side bearing is a 6302 radial ball bearing which is also pressed into the crankcase.

When assembled, both input shafts function in the same manner. Both assemblies consist of straight-cut gears. The unique design of the 4T input shaft prevents the interchange of input shafts with any of the traditional 2T variants. At this time, no variations on the gearing of the 4T components exist, so any gearing changes must be made with these input shaft ratios in mind. The tooth counts on the 4T input shaft are, from first to fourth, 11-13-16-20. For reference, the tooth counts on a standard PX125 are, from first to fourth, 12-13-17-21. What this means is that the 4T drive gear ratios are going to be shorter than those of a 125. Small wonder that the 4T won in the short drag races featured by Eddy Bullet.

With regard to the components of the output shaft, the selectable final drive gears, drive shaft, the shift plunger and cruciform are LML derivatives of the Vespa Lusso, aka EFL, transmission. The only items of note were that the shift plunger on the 4T is possibly .1mm longer than an OE Piaggio shift plunger and that the drive splines for fitting the hub to the drive shaft are shorter than the OE Piaggio equivalent. This would suggest that any interchange of LML and Piaggio shift mechanism parts may require shims or replacement of all parts. The final gears are straight cut and have tooth counts of, from first to fourth, 58-43-39-36.

In my next entry, I will discuss the calculation of gear ratios and some options for refining them.

EDIT: Added Attachments, so log in. Here's a couple of pictures of the intermediate shaft assembly.

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Last edited by az_slynch on Sun Oct 25, 2015 3:30 am; edited 4 times in total
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BigDaddy SnakeOiler
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PostPosted: Sun Oct 11, 2015 5:50 pm    Post subject: Reply with quote

Awesome read, thanks.
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Stilts
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PostPosted: Mon Oct 12, 2015 1:36 pm    Post subject: Reply with quote

Anxiously awaiting the next installment. My engine is in pieces right now and now is the time for any tranny rebuild.
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az_slynch
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PostPosted: Mon Oct 12, 2015 11:24 pm    Post subject: Stock Gear Ratios, Some Maths & Primary Gear Tuning Reply with quote

ProTip: Attachments included, log in to view them. Wink

If you've leafed through the Stella owners manual, page nine provides LML's record of overall gear ratios for the transmission. The question is, how did they generate those numbers? Well, here's how you calculate an overall gear ratio:

(tooth count of output driven gear / tooth count of output drive gear) * ( tooth count of primary driven gear / tooth count of primary drive gear)

To put this in context, let's calculate the overall ratio for the 4T's first gear, using the counts I shared in the transmission description:

(58/11) * (68/21) = 1st gear overall ratio
(5.27) * (3.24) = 1st gear overall ratio
17.07 = 1st gear overall ratio

Checking our work against page nine of the owner's manual, we have agreement. One note in regarding LML's calculations: it appears that they used greater than the two significant digits to the right of the decimal point in calculating their overall ratios. As a result, minor variations were observed.

In calculating ratios, I followed the model of counting the two significant digits to the right of the decimal point, and rounding up if the third significant digit was a five or greater. My calculations are in the first attachment, along with the owner's manual data for reference.

The second attachment contains the calculations for the PX125 and PX150 EFL transmissions, which the Stella's transmission is derived from. Tooth counts are from SIP, calculations are mine. Numbers were vetted against ScooterHelp's gearing calculator; I found a few very minor rounding errors for third and fourth gear output ratios in that calculator. Variances of a hundredth aside, it's clear in comparison that the Stella has a short-legged transmission. One exception stands out: second gear wasn't too far off the mark.

The third attachment has calculations based on swapping the stock 4T clutch for a 22T Rally 180 clutch. If you don't want the vintage guys hating you, you can buy just the drive plate with the 22T gear. In my opinion, this gives the transmission a decent step forward, bringing the overall ratios into the gap between the PX125 and PX150 EFL gears for minimal cost and labor. And just for funsies, I calculated the gearing with a 22T drive gear and a 67T cush drive gear. If you are cracking the crankcase open anyway, this will boost the upgear from 4.8% to 6.2%. The caution is that you will need to dismantle the cush drive and replace the gear, rivets and side plates at a minimum. Parts alone can almost double the cost of only swapping the clutch drive gear and the additional gain is minimal.

In the next installment, I'll discuss gearing options for the driven output gears.

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Last edited by az_slynch on Tue Oct 13, 2015 3:28 am; edited 5 times in total
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az_slynch
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PostPosted: Tue Oct 13, 2015 12:28 am    Post subject: Reply with quote

One other note on calculations: I observed a variance between my numbers and the numbers SIP listed on their DRT custom gears pages. It appears that SIP took an odd rounding step in calculating their output gear ratios. If the hundredths digit was a three or four, they rounded to five. Probably to make the ratios look more uniform.
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az_slynch
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PostPosted: Tue Oct 13, 2015 4:25 pm    Post subject: Output Gearing Options, First and Second Ratio Reply with quote

Attachment again, so log in. Wink

Pursuant to the evaluation of primary gear options, let's talk about the lower gears. After tweaking the primaries, the first gear ratio is markedly taller than a PX125 EFL, but still shorter than a PX150 EFL. In an endeavor to gear it more like the 150, I did a few calculations for PX first gear options. Currently, the available options for the first output driven gear are: 58T, 57T, 56T and 55T. The 58T gear is the stock gear and would need to be swapped out if we want a more usable first gear. The 57T gear is stock for a PX150 and is the most economical upgrade, especially if good secondhand spares are available. The latter two options are custom-made gears from DRT and carry a hefty price tag in the $100-$110 range each at the time of writing. Speed costs, right?

Upon review of the attached table, you'll see that even if we opt for a 55T output driven gear and are using a 22/68 primary, that short 11T output drive gear leaves us with a shorter first gear than a stock PX150 EFL. Still, I'd consider a 15.45:1 first gear ratio is a fair bit longer than the stock 17.07:1 first gear ratio. If money's no object, go for the DRT gear. If you need an upgear on a tight budget, an OE 57T gear provides a respectable 16.01:1 ratio and still provides a marked improvement over stock.

As for the second output ratio, if you upgeared the primary ratio and you're running a stock cylinder, leave it alone! It's tall enough as-is and there isn't a 44T driven gear option to shorten it with at this time. If you have a Polini 165 kit, you could run a 42T on second gear. I believe it will get you an additional half mph on the top of second. A 41T driven gear could be run as well, but the kit is probably required, that size was only manufactured by DRT and is now reported to be discontinued.

In the next installment, I'll look at meddling with the top gears. In the interim, I intend to check the dimensions of the 11T output drive gear against a 12T output drive gear, just to make sure that there isn't an issue meshing with the DRT taller gears. It's a bit cheaper than buying them to check fit...

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PostPosted: Wed Oct 14, 2015 5:19 pm    Post subject: Reply with quote

Nice info. Yes, your description of the gear cluster makes sense. That is good to know; I haven't had one apart yet.

I have used the DRT gears , with good success, in the 2T's to change things around the way I like.

The clutch gear still seems to be the best bet for a simple regear on a 4T.

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az_slynch
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PostPosted: Wed Oct 14, 2015 5:42 pm    Post subject: Reply with quote

viney266 wrote:
Nice info. Yes, your description of the gear cluster makes sense. That is good to know; I haven't had one apart yet.

I have used the DRT gears , with good success, in the 2T's to change things around the way I like.

The clutch gear still seems to be the best bet for a simple regear on a 4T.


Viney, does your shop have access to a 4T with a few miles on it and a TinyTach or similar? One task I was planning to do prior to my engine going *bork* was to figure out the rev limit for the motor and the rpm at which the "cam chain whine" started; My buddy used to flog his 4T mercilessly and I used to tell him to shift when he heard the whine.

The owner's manual lists max horsepower being achieved at 6250rpm. The maximum speed listed in the manual is 56mph. Using a very nice French gearing calculator (It lets you tweak the input shaft tooth counts so you can simulate a 4T transmission, just base it on a PX125E.), I mocked up a 4T transmission, cross-referenced top speed and estimated a max rpm of 6750-6800rpm in top gear. I'd love to nail down the rev limit in order to accurately predict possible top speeds in each gear.

And kudos to SubEtherBass on MV for indirectly bringing that calculator to my attention, it's just the tool needed to dial things in!

I'm attaching the plot for a 4T; I estimated a 90/90-10 tire and the speeds are in kilometers, but it gives us previously unknown data.

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PostPosted: Wed Oct 14, 2015 5:53 pm    Post subject: Reply with quote

One more attachment. Same max rpm and output ratios, but with the 22T primary upgear.
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PostPosted: Thu Oct 15, 2015 12:24 am    Post subject: Top Gear(s) Reply with quote

Like second gear, The third gear output options are pretty slim. The Standard gear is 39T, but a standard Piaggio or a pricier DRT gear will suit for either a stock engine or a tuned one. Attached tables for the 38T option with a 22/67 and 22/68 primary can be found below. DRT also offers a 37T option that may be a pricey-but-worthwhile option for kitted engines to help bridge the gap between third and fourth.

Fourth gear is pretty tall when one of the tuned primary ratios is used. Optional gears for fourth are 37T, 35T, 34T and even 33T. The latter two options are pipe dreams, as even a Polini-kitted engine is unlikely to be able to effectively leverage them. Even a 35T gear may be a struggle unless additional performance components like a camshaft, bigger carburetor, performance exhaust or forced induction are used. The stock gear may be most suitable for maximum theoretical speed here if the bike is kitted. For a stock cylinder, the 37T gear may be a better option. It will dilute some of the overall upgear from the primaries, but the ratio will match a little better with a 38T 3rd gear. This suggestion is based on experience with gearing in 200cc 2T Vespas. The stock 4th output gear is a 35T and the stock engine can seldom leverage it properly. Exchanging the 4th output gear for the 36T gear from a P125X shortens the gap between 3rd and 4th, allowing the engine to accelerate better in top gear and reach a higher top speed.

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Stilts
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PostPosted: Fri Oct 16, 2015 3:35 pm    Post subject: Reply with quote

az_slynch wrote:
viney266 wrote:
Nice info. Yes, your description of the gear cluster makes sense. That is good to know; I haven't had one apart yet.

I have used the DRT gears , with good success, in the 2T's to change things around the way I like.

The clutch gear still seems to be the best bet for a simple regear on a 4T.


Viney, does your shop have access to a 4T with a few miles on it and a TinyTach or similar? One task I was planning to do prior to my engine going *bork* was to figure out the rev limit for the motor and the rpm at which the "cam chain whine" started; My buddy used to flog his 4T mercilessly and I used to tell him to shift when he heard the whine.

The owner's manual lists max horsepower being achieved at 6250rpm. The maximum speed listed in the manual is 56mph.


I've got a cheapo wrap around wire tach on mine and I can definitely say that 6250rpm sounds about the limit before the limiter kicks in. The sweet spot is just over 6000, IME. I've had it up to 65 smph on flat with the 22mm carb (with slightly lean jetting) and GPR exhaust.

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az_slynch
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PostPosted: Sun Oct 18, 2015 4:38 am    Post subject: Reply with quote

Stilts wrote:
I've got a cheapo wrap around wire tach on mine and I can definitely say that 6250rpm sounds about the limit before the limiter kicks in. The sweet spot is just over 6000, IME. I've had it up to 65 smph on flat with the 22mm carb (with slightly lean jetting) and GPR exhaust.


Thank you for the info. I might need to look at some more aggressive gearing options if we're going to be able to top the "metric ton" with such a low rev limit and short gears. Going to revisit the primary options and might look at a few other output gear options.

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PostPosted: Thu Oct 22, 2015 5:09 pm    Post subject: Reply with quote

Interestingly, I have learned of a DRT rebuild kit for 125/150 cush drives which includes a special 65T primary output gear for use with 20T, 21T and 22T primary input gears. This opens up several more options for primary tuning. I've attached a table of the primary drive options with stock output gearing. A 20T input gear will result in even shorter overall ratios than stock unless the output gears are replaced with aftermarket units. A stock 21T primary input gear will give a nice overall upgear. A 22T input upgear results in a very nice overall upgear, but amplifies the odd spacing of the standard output gears. For this final option, a 165cc kit and refinement of the output ratios is recommended.

I've also included a graph of the potential performance of the 22/65 upgear with stock gears and an estimated 6500rpm redline.

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PostPosted: Sat Oct 24, 2015 12:35 am    Post subject: Reply with quote

This is amazingly thorough and useful. I need to bone up on this stuff. I've yet to do a teardown on the Stella transmission, but think it may be coming soon.

Not planning on up-gearing… yet… Smile

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PostPosted: Sat Oct 24, 2015 3:29 am    Post subject: Reply with quote

=====> Technical Section! Great research! Smile
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PostPosted: Sun Oct 25, 2015 4:48 am    Post subject: Reply with quote

More info on the cush drive! Genuine hadn't authorized my dealer to dismantle the cush drive assembly, despite our suspicion that the cush drive springs had failed and were causing the driveline noises; the lumpy and distorted side plates suggested as much. I still wanted to know what the internals of the assembly looked like, so I went ahead and bought a spare cush drive assembly from Scooterwest (thanks Max!) and took it apart. I'm glad I did, as we now know that it can be a weak link in the powertrain. The lower powered Vespas used to use six coil springs in the cush drive to absorb shock loads between the crankshaft and the transmission. As power levels increased, particularly with the advent of the 200cc engines, Piaggio inserted a second, smaller spring inside each of the large springs to aid in handling the increased loads that the engine could put on the driveline. I know that the 2005 Atomic Fireball Stellas had the double spring setup in the cush drive and assumed that other Stellas had it as well. In the 4T Stella with its loads of low-end torque and short gears, I expected to find the doubled spring configuration. I was surprised to find that it uses single-spring damping!

I've attached an image of the cush drive internals, less the center section. Yes, it was a new spare; the rust comes factory installed. The center has since been mated up to an FA Italia 67T primary driven gear and been fitted with a DRT reinforced spring kit. I'm attaching a second image, courtesy of BeedSpeed, of the center section of the cush drive with the integrated 4th output driving gear.

I would recommend that anyone tuning this engine give serious consideration to rebuilding the cush drive with a double-spring setup. I'd also recommend replacing the Indian-manufactured HK1616 needle bearing with a Torrington-branded bearing or equivalent.

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PostPosted: Sun Dec 13, 2015 2:07 am    Post subject: Reply with quote

Today, I had an opportunity to test fit a few gears onto my 4T engine block. Been waiting (and waiting, and waiting...) on some fancy parts which may or not be made out Genuine Cruiser fairy dust. Re-installed the Christmas tree and the axle assembly, then fitted the 2T gears with an eye on the fit and operation in comparison to the original 4T parts.

When assembling the transmission, top gear always goes in first. I dropped in a 35T 4th gear, found in the '05 Atomic Fireball and the Vespa P/PX200. The gear fit on with no trouble, but it had a marked amount of backlash between the gears. I refitted the stock 4th gear and found that it was somewhat sloppy too, but noticed that the gear had a fair bit more tooth overlap than the smaller 35T gear. I attribute this to the smaller 20T drive gear on the Christmas tree compared to the 21T gear of the 2T Stellas. Based on this observation, I can't recommend this combo as it would likely result in accelerated gear wear or chipped/broken gear teeth. See attached picture.

Despite the disappointment with 4th gear, I was pleased to find that a 38T 3rd gear is an easy replacement for the stock 39T gear. The gears meshed well, with ample tooth contact depth between the gears and no appreciable increase in backlash. The meshing gear on the Christmas tree is a 16T, but it is not much smaller than the 17T driven gear found in 2T Stellas. Seeing how this upgear narrows the gap betwen 3rd and 4th gear, I would encourage the budget-minded modder to consider this one if they have the crankcase split.

For second gear, I swapped in a 42T gear. This fit perfectly, as the Christmas tree's second gear has the same tooth count as its predecesor. Changing to the 42T driven gear matches the gearing with that of a 2T Stella, lengthens the usable speed range of the gear slightly and helps to correct the increased gap between second and third where a 38T third is used.

For first gear, I swapped in a 57T gear. I was a bit concerned, as the 4T has an 11T drive gear and the driven gear was a bit smaller than the 58T stock gear. I am pleased to report that the gear tooth overlap and backlash were observed to be acceptable in the upgeared configuration. Again, there is a slight increase in the usable speed range of the gear and some remediation of the spacing between first and second where a 42T second was used.

I'l add a graph of this setup when paired with a 22T clutch for reference.

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PostPosted: Tue Mar 15, 2016 4:32 am    Post subject: Important Detail...and my initial regear setup Reply with quote

Small update with images. Updated a few prior posts with extra images as well.

First, a note if you rebuild a cush drive. When assembling the inner and outer sections of the gear, look at the backside of the assembly and pay special attention to which way the driven gear is seated to the center section. When oriented properly, the ears of the center will sit flush with the plate recess in the driven gear. If reversed, the center will stick out about .5mm and you won't be able to assemble the cush drive properly. See attached for how it should look.

As for my gearing, see the second attachment for where I've settled for now. Once it's all sorted, I'll let you know how well it works.

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PostPosted: Mon Mar 28, 2016 3:50 pm    Post subject: Reply with quote

I don't think the rev limiter on the Stella is that low, I've hit it, once, in 2nd gear accelerating downhill. I think it maybe in the 7-8000rpm range. I've regularly topped out at 65ish (GPS) with my Stella with the Mikuni 22mm carb, GPR exhaust, portedish head (there's not a lot of meat to do a good port, I actually debated using some JB weld to reinforce so I could go thinner on the intake port walls), and stock gearing. I'm currently living in Japan, and my parents want me to come home for a while in the summer, if I do go home I might install the Polini 165 kit I had decked for proper squish and Cosa 22T gear clutch I meant to install last summer. Actually the Cosa clutch is a must if I want to ride, the stock clutch is beat to shit and ready to fail at anytime, gotta love LML quality. Rob Hodge at Hodgespeed recommended the Cosa clutch, much better design than the old 6/7 spring and can handle more torque and HP. I went with a 22T as a modest upgear, otherwise I would have had to use a DRT clutch gear or crack the cases for more. That's too bad about the fourth gear not meshing enough, would have loved to gear it so 1,2,3 were for accelerating and 4th was basically an overdrive for cruising.
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Location: Tucson, AZ
'16 K-Pipe, '13 Stella 4T, '12 Yager GT200i, '81 Vespa P200e and Far Too Many Others

PostPosted: Fri Apr 01, 2016 5:11 am    Post subject: Reply with quote

Neurotic-Hapi-Snak wrote:
I don't think the rev limiter on the Stella is that low, I've hit it, once, in 2nd gear accelerating downhill. I think it maybe in the 7-8000rpm range. I've regularly topped out at 65ish (GPS) with my Stella with the Mikuni 22mm carb, GPR exhaust, portedish head (there's not a lot of meat to do a good port, I actually debated using some JB weld to reinforce so I could go thinner on the intake port walls), and stock gearing. I'm currently living in Japan, and my parents want me to come home for a while in the summer, if I do go home I might install the Polini 165 kit I had decked for proper squish and Cosa 22T gear clutch I meant to install last summer. Actually the Cosa clutch is a must if I want to ride, the stock clutch is beat to shit and ready to fail at anytime, gotta love LML quality. Rob Hodge at Hodgespeed recommended the Cosa clutch, much better design than the old 6/7 spring and can handle more torque and HP. I went with a 22T as a modest upgear, otherwise I would have had to use a DRT clutch gear or crack the cases for more. That's too bad about the fourth gear not meshing enough, would have loved to gear it so 1,2,3 were for accelerating and 4th was basically an overdrive for cruising.



I'm going Cosa as well, but I'm using a 21T for now so I have upgear with some overhead if the 165 kit exceeds my expectations. Going all out on this, don't really plan to crack the case again if I can help it!

I'd love to see a 65mph all-motor 4T Stella. I'd ride it to Phoenix more often, for sure!

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martinvh
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Joined: 06 Nov 2016
Posts: 15
Location: San Francisco
Genuine Stella 4t

PostPosted: Sun Nov 13, 2016 6:01 pm    Post subject: Reply with quote

az_slynch wrote:
martinvh wrote:
Thanks all. The clutch problem is solved.

Since everyone dislikes a 'dead' thread without a fix for the posted problem:

I took the clutch apart. Found out that indeed EVERYTHING (but the clutch cover gasket) on the clutch is the same as the Vespa P200E clutch (108mm, 7 spring version, NOT the Cosa clutch).

Replaced the 5 clutch plates (3 cork, 2 metal total thickness: 11mm) with the Malossi 7 plate clutch for the P200 (4 cork, 3 metal total thickness: 11mm). I used new stock P200E clutch springs since the Malossi springs are extremely stiff, which is not needed for my stock 4-stroke. I used the Malossi plates because the additional plate will reduce heat build up per plate for all the hill starts I have (I live in San Francisco). I also replaced all the brass items, inner clutch lever etc. etc. The clutch works like a charm and is now actually a clutch instead of an on/off switch.

I do still have the rattling sound during 1st and 2nd gear though.... Does the 4-stroke have a cush drive?


Glad to hear that the clutch is doing its job now.

Yes, the 4T has a cush drive. It's built onto the 4th gear intermediate gear. Six single-springs instead of the double springs like P200s. I have more info on it in my transmission thread.


Hi,

I quoted the above from the post "Clutch shudder [Stella 150, 4-stroke]"

I think my cush gear has a (or multiple) broken spring. There's a loud series of 'knacks' during acceleration in 1st and 2nd gear. Especially uphill. I already did a full rebuild of the clutch.

Can you maybe give me some guidance on how to get to the cush gear the easiest way. I've found videos on how to rebuild the cush gear itself, but not on how to get to the cush gear.

I think I have to split the cases to get to the cush gear. The 1st questions that arise are:
- Can you leave the engine in the frame (like the 2-stroke)?
- Can you leave the cylinder on (like the 2-stroke) by removing the rights side studs only? That would spare me the timing chain hassle.
- Can you leave on the clutch cover?
- Any special tools needed etc. etc.

I do have the workshop manual. But they base there engine splitting scenario on an engine removed from the frame, with an already disassembled cylinder and clutch side parts.

Thanks so much![/list]
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az_slynch
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Joined: 12 Sep 2012
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Location: Tucson, AZ
'16 K-Pipe, '13 Stella 4T, '12 Yager GT200i, '81 Vespa P200e and Far Too Many Others

PostPosted: Sun Nov 13, 2016 9:06 pm    Post subject: Reply with quote

martinvh wrote:
I think my cush gear has a (or multiple) broken spring. There's a loud series of 'knacks' during acceleration in 1st and 2nd gear. Especially uphill. I already did a full rebuild of the clutch.

Can you maybe give me some guidance on how to get to the cush gear the easiest way. I've found videos on how to rebuild the cush gear itself, but not on how to get to the cush gear.

I think I have to split the cases to get to the cush gear. The 1st questions that arise are:

- Can you leave the engine in the frame (like the 2-stroke)?
- Can you leave the cylinder on (like the 2-stroke) by removing the rights side studs only? That would spare me the timing chain hassle.
- Can you leave on the clutch cover?
- Any special tools needed etc. etc.


I do have the workshop manual. But they base there engine splitting scenario on an engine removed from the frame, with an already disassembled cylinder and clutch side parts.

Thanks so much!


I believe that you could leave the engine in the chassis if desired, but it may make the job a bit harder. If the engine stays in, I'd suggest removing the back half in the body for better accesability to parts.

You probably can leave the clutch cover on, but you probably need to pull the rear axle. If you split the case, you will likely need to fiddle with the cam chain anyway because of the hollow pins that go between the block and the cylinder, the top end would need to be lifted at least a half-inch before the would clear the block/cylinder.

Only special tools that came to mind would be a flywheel puller and a good set of snap-ring pliers.

Before cracking the case, I'd recommend popping the cylinder head off, pulling the camshaft and checking the bigger 6202 bearing that's fitted to the camshaft. When I took the head apart on my bike, I found that the factory bearing was pretty "lumpy" and would would make an audible "tak-tak-tak" sound when you spun it. Since it runs in such an open space shared with the cam chain, clutch, valves and oil pump, the noise is amplified and difficult to track.

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martinvh
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Joined: 06 Nov 2016
Posts: 15
Location: San Francisco
Genuine Stella 4t

PostPosted: Mon Nov 14, 2016 5:30 am    Post subject: Reply with quote

Thanks!

I wil go get the flywheel tool. Is this the same as for the P200E as well?
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martinvh
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Location: San Francisco
Genuine Stella 4t

PostPosted: Tue Nov 15, 2016 5:30 am    Post subject: Reply with quote

Okay guys, this is for future reference.

I started my project of replacing the cush gear / drive of my Stella 150 4-stroke manual. My mission is to leave the engine in the frame and remove as little parts as possible.

I disconnected the rear shock absorber, which gives massive room to work when you also remove the air box. My mission to leave the cylinder on worked. You can unscrew the right side studs (you can not remove them though, since the bottom thread on the studs is thicker than the hole in the cylinder) which gives enough clearance for the bottom gasket to slip through and for the hollow pins to clear.

I am currently awaiting the flywheel puller I ordered (this is the same as for the Vespa PX and P-series (28x1mm) so I can split the cases.

Picture of the clearance:
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az_slynch
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Location: Tucson, AZ
'16 K-Pipe, '13 Stella 4T, '12 Yager GT200i, '81 Vespa P200e and Far Too Many Others

PostPosted: Mon Nov 28, 2016 3:22 am    Post subject: Reply with quote

Thanks to Martin's fearless teardown on his 4T, I'm determined to make time and commit to getting my own 4T project back in gear. Swapped out all the bearings in the block and now working on the getting the transmission section put together.

The intermediate shaft parts that I got from Beedspeed has a larger flywheel-side shaft that the 6302 bearing, which quickly goes from a snug fit to an interference fit before seating fully. I thought it was the bearing, but was able to replicate it with a second 6302 bearing. The shaft is a forged part made by an Indian company called KACE and looks to be a better-made part than the original. A trip to the machinist is in order in order to dress it lightly for a snug sliding fit, but I think it's worth it since the KACE intermediate shaft parts fit together better than the original parts. Besides, I was going to see him anyway to match the Polini manifold to the intake port on the head.

I'll post pics once I get the shaft modified and start assembly.

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az_slynch
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'16 K-Pipe, '13 Stella 4T, '12 Yager GT200i, '81 Vespa P200e and Far Too Many Others

PostPosted: Sun Dec 04, 2016 10:12 pm    Post subject: Reply with quote

Picked up the intermediate shaft shims yesterday from the shop. Installed the intermediate shaft sans the kickstart gear and spring. Popped the case together to check fhe shaft fit, everything looked OK.

Installed the felt seal for the rear hub and pulled the axle in. Lubricated the axle race where the oil seal rides prior to installation. Put the cases together again to check fit; still looking good!

I may replace the seals on the flywheel side of the case for the crank and kickstart shafts. The kicker shaft on the 4T is now sealed on the outer end with a double-lipped seal in lieu of an O-ring in the case as implemented on the 2T engines. While it seems like a design improvement, the seal lips contact the lower end of the kickstart shaft splines. Over time, the spine peaks could damage the seal. On the other end of the kickstart shaft, I've noticed two other shortcomings. Firstly, the last gear tooth on the quadrant has a thin casting and has already started bending back away from the quadrant. The kickstart return spring is also somewhat deformed and doesn't sit in the case properly. I think those two items will be getting swapped out with better parts.

Planning to install the crank thus afternoon. Hoping to install the new cruciform, then shim and install the gears next week when I can pick them up from the shop. I'll post pictures later today.

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Neurotic-Hapi-Snak
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Joined: 05 Jun 2014
Posts: 335
Location: Twin Cities, MN
'12 Stella 4T

PostPosted: Mon Feb 06, 2017 2:57 pm    Post subject: Reply with quote

I've been thinking about how to get a 2T input shaft to work in the 4T. My two ideas were either to make a shaft onto which the christmas tree would be press fit and would rotate in the 4t's in case bearings, or to modify a 2T shaft to fit into large bushings pressed into the case in place of the bearings and use the normal 2T bearings inside the christmas tree. I really need to take some measurements of both input shafts and see the insides of the case to see if either idea would work, I'll do this when I have the case open to swap out the suspect Indian bearings for quality ones and rebuild the cush gear to the dual spring setup, and when I buy some of the bearings and cush gear rebuild, I'll buy a 2T christmas tree and shaft to take measurements on. If it can work, that opens up a whole bunch of gearing possibilities, but it won't be cheap, both solutions would require a lot of machine time, and that's expensive.
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az_slynch
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'16 K-Pipe, '13 Stella 4T, '12 Yager GT200i, '81 Vespa P200e and Far Too Many Others

PostPosted: Sun Feb 26, 2017 6:51 pm    Post subject: Reply with quote

Fell behind on this one again due to life events. Started setting up the final gears last night and ran into a minor snag: The DRT gears are all slightly thicker than stock. Even when I put the thin DRT spacer at the bottom of the stack, the remaining space at the top of the stack is only 0.75mm, which is thinner than any spacer shim offered. Looks like I'll need to sand the existing 0.8mm shim down to 0.7mm and then take one of my existing 1mm shims and sand it down to 0.7mm as well in order to get the 0.15mm minimum lash for the gearbox.

Never thought I'd find myself in a spot where a Stella gearbox would be too tight to shim...

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