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Haribolman
12-09-2002, 04:40 AM
Attention SR50 owners,

I have been told by Aprilia Australia that the SR50 comes standard with a fair amount of clutch slip. I find this unacceptable (and downright annoying and embarrassing in traffic), so I wish to modify my gearbox to allow the clutch to engage sooner (and therefore stop the bike revving so hard all the time!)

I have spent many years working on the CVT of Honda Dio's and I'm assuming that the Aprilia has a similar setup. (Front pulleys with internal rollers and a rear clutch unit with springs and shoes). I am also assuming that I should only need to change the weight of the clutch springs to achieve earlier takeup. Can someone who has worked on the Aprilia SR50 CVT tell me if this is correct?

Do I put in lighter or heavier springs? Aprilia Australia mentioned modifying the rollers...how does this work?

Thanks in advance!

amdrescher
12-09-2002, 09:23 AM
Yup you are right abut the setup.

You would need some tighter springs in your clutch, and if you have the correct setup on your bike you can install a tighter clutch release spring.

Let me hear your bike setup, and i would be able to tell you more.

Bishop
12-09-2002, 10:39 AM
Aprilia Australia are on the right track, the first thing to do is play around with variator weights, you should be able to make it take off with less revs by changing the them.

It's been a while since I played with variator/roller weights, but I'd say try .5g heavier than you got now, in theory that will raise the gearing and make the engine turn the clutch faster with less revs, so in theory the clutch will engage at less rpm.

Err, at least I think that's right, it's late and I'm tired...

Dutch Royal T
12-09-2002, 06:26 PM
Sorry amdrescher, but you are totally wrong.

He said he wanted to have the clutch engage SOONER (my question is WHY???) and in that case you need LIGHTER spring (less tension).

You could indeed also modify rollers. The rollers define on what RPM's your engine will operate.

And the heavier, the LESS rpm's. So if you want less RPM's, fit heavier rollers, but keep in mind that too heavy rollers will have the engine operate BELOW its powerband. You'll loose power and performance, and NO heavier rollers do NOT mean higher top speed. It will only STALL the engine if you fit to heavy ones.

Also keep in mind that the clutch needs slippage and the stock clutch doesn't have much, so I really question you, why on earth you want it to engage even sooner. (This will also stall the engine if it engages too early, it's like trying to drive you car from a standstill to top in highest gear and in scooters you won't ever make it to max. speed.)

jrturbo
12-10-2002, 05:03 AM
Hi there

Your assumption on how the CVT works is correct and its basically the same for all scooters.

My question is you are comparing your aprillia SR with your previous honda scoot. what exactly is it you feel is wrong with the current set up.?

Bear in mind that probably your previous honda scooter was lighter, The SR is one of the heavier scooter it weighs nearly 100 kilos with the tank full, and the engine is in standard form develops more power than your previous honda, but it needs to operate in the correct rev range.

If you make your clutch engage sooner, what will probably happen is that engine will bog down when pulling away from a standstill, once its rolling above 10 mph approx what determines the engine revs is the weight of the rollers

In order to ascertain that everything is correct you will need a rev counter and check what engine rpm your scooter is holding under acceleration.

Before you start messing around with the CVT, see if you can try another a similar bike to yours and if it drives the same, I doubt that there is anything inherently wrong with your set up, that does not mean it can not be improved, but we would need to know what engine version is fitted to your aprillia and what area of the performance you wish to improve.

Regards

Joe Rubido

Haribolman
12-10-2002, 06:42 AM
In response to amdrescher, Bishop, Dutch Royal T and jrturbo,

Firstly, thanks heaps guys for the info. This has helped a lot. It seems I have two options. Heavier rollers or lighter clutch springs. (Though I need to ask, do I fit a lighter main spring in the center of the clutch, or are we talking about fitting lighter springs on the clutch shoes?)

I've taken off the CVT outer cover for a quick look and the setup is almost identical to a Honda Dio. I used to play around with the clutch springs on some of my Dio's to reduce the clutch slip that sometimes occurred with the delivery work we used them for. So a better long term solution for me would be to replace the clutch springs, because if I fit heavier rollers, they'll be taken out every 8000kms by the dealer, and replaced with the original weight rollers when he does the service. However, non-standard clutch springs would remain untouched by the dealer for much longer.

In response to Dutch Royal T, you ask why I would want the clutch to engage sooner and you also mention that the stock clutch does not have much slippage. I would be happy if that were the case, but the way my bike revs so hard (even under moderate acceleration on the flat) just makes me realise that if I could get it to rev less and engage sooner (the same way my Dio's did) then I'd be happy. Riding my bike in traffic is embarrassing! My bike picks up revs so quickly that people think I'm trying to race them because of the noise I'm making, and the irony is that the bike isn't accelerating very quickly at all. Yet when I described these symptoms to Aprilia Australia they told me that this was normal for the SR50 and they suggested that maybe a Scarebeo would have been a better option. Does this mean that they Scarebeo CVT is geared different?

In response to jrturbo, I rode two other SR50's before I bought my bike and I think they were similar, but I'd have to ride them again to check. I didn't really try riding them "slowly" to see how hard they revved. I simply took off full throttle, so of course I expected them to rev hard. Thank you for the info you have given. I do not know what engine version I have.

One other question, when I looked into the gearbox this arvo (I didn't have an an air ratchet gun so I couldn't take the nuts off) I noticed that the front pair of pulleys was spaced a long way apart. On a Dio they sit up against each other. The dealer told me the restrictor had been removed, yet I'm surprised how much space there is between the pulleys. Is this normal? (and yes, my bike does do an indicated 90km/h)

Thanks guys!

Dutch Royal T
12-10-2002, 08:32 AM
Just one question:

Do you have the spacer removed from the front pulleys. Because this also make the scooter rev too much, because it keeps the scooter in a lower gear all the time, so basically the engine is making to much revs for its speed. I bet you have it removed, but just in case.

What you want to do is lighten the LITTLE springs. (2 or 3) These are your clutch springs.

The big spring is the spring for the torque driver. This one ALSO determines the rpm's of your scooter. The heavier the spring the more revs you make (and also makes the scooter "downshift" quicker) Most stock ones are too light (I bet you had a situation when entering a corner you let go the throttle. Ones you are in the turn and coming out of it, you go full throttle again, but your scooter seems to accelerate very poorly. That is because the not so strong stock big spring keeps the scooter in a higher gear)

What the spring does is determine how long the back pulleys stay closed (and thus the belt on its highest/higher position) A too light one will have the belt drop down to its lowest point way too soon, making it run in a high gear AND DROP REV's.

So you have many options. You have to find the right rollers, springs and big spring setup for you likeness and what the engine needs. Most of the time it's trial and error (within some borders, because you kinda know what NOT to use)

I also found out something is wrong with my setup. It should be going alot faster with the setup I have. Something must have wore out. I need a very big spring and I now rund 2,7(!) gram rollers, just to make my scooter run in its powerband (12.500~13.000rpm's)

Bishop
12-10-2002, 09:07 AM
I still say change the roller weights, as mods go I think it's the easiest to do, and as long as you tell the dealer what you did they won't change them for the wrong ones at servicing.

In the end it's most likely that the high reving is because it has been derestricted, the variator/roller weights in the bike were the right weight for the restricted engine, and now that's it's been derestriced, they are wrong.
When the bike was derestriced the weights should have been changed.
I heard one shop in another state does change the weights, and I beleive they are claiming 95+ from their derestricted models.
(I'd bet money that you too would pick up a small amount of top speed with heavier weights.)

I don't think changing or messing with the springs is a good option, it's too hit and miss, and could really mess up the ridability of the bike.
And getting lighter springs is hard because most aftermarket springs around are all stronger than stock.

Also with the pully thing, the variator in the SR will be that latest generation design, meaning it has a much larger range than the older style ones, it would have much more travel, which is why it seems so much further apart at rest.

tiba karotsu
12-10-2002, 09:53 AM
the reason most scooters today have variator halves farther apart is because they use wider drive belts, wider belts have more ply (kevlar, nylon) to make it stronger because of high power outputs of our scooters today. also the length of the drive belt determines how high the belt will climb up the pulley, having too short a belt will make your scooter a slug of the line but have a high speedometer reading while having a too long belt will give you awesome acceleration but at the expense of top speed.

the OR kits (overrange) especially Malossi made use of a wider, longer belt but didn't sacrifice both top speed and acceleration by making the front variator pulley larger than the standard Multivar for top speed and a bigger rear pulley system for tremendous off the line acceleration.

choosing the correct spring the key is experience, how well do you know the product you're about to use, as for me i've used every big spring & clutch spring Malossi has made for the Yamaha/Minarelli engine so when someone asks me what spring & rollers to use as a starting point, i ask what their current set up is and give them a ballpark answer.

Dutch Royal T
12-10-2002, 05:27 PM
Tiba, isn't having a too short belt just the other way around?

Because a short belt can't get into lowest position at the back when it would be on its highest point on the variator. This means it stays in low gearing, making more revvs and no top. Or if it would first drop in lowest at the back, it can't climb to the top of the variator, giving the same result.

tiba karotsu
12-10-2002, 07:53 PM
Dutch,

for extreme cases like that it could happen but i've tested a variety of belt lengths on various scooters (Honda Dio & Yamaha Jog), on the Honda i was using a belt (Malossi) for the Dio ZX model which has a measurement of 17 x 666 (W x L) and the top speed i got is 90kmh and that is on stock gears. then i tried using the belt from a Dio SR with a measurement of 15 x 630 with no other changes except for the shorter hub pin (narrower belt width) my top speed increased to 95kmh but the scooter was a slug at accelerating.

but this thing about belt length has been proven here by many other tuners who still use the standard Multivar variator & rear torque drive half pulley as they have a 5 kmh advantage over the OR kit when it comes to top speed. i'd like to try that set up on my Jog again but considering that my cilinder is shot i'll never be able to tune my scoot for a very long time to come.

got any spare cilinder Dutch? make it a Hebo Manston or MHR Speed if you got any?:D

Dutch Royal T
12-10-2002, 08:10 PM
I see.

It seems the new EVO 5 cilinder is the top choice. It has the MHR timing and the better Polini finish. At least that is what the rumor is here now.

Haribolman
12-11-2002, 05:06 AM
Hello Bishop,

Any chance of telling me the name of this interstate shop that is changing the rollers when they derestrict the bike? And any idea what weight my standard rollers would be? I took my rollers out this arvo and weighed them, but my electronic scales mustn't be very accurate because one roller weighed between 4-6gms, two weighed 12g, 3 weighed 18g and four weighed 26-28g. I gave up weighing at this point because of the large variation in weights.

I still prefer the idea of fitting lighter clutch springs. Once it's done then they can be left for quite some time. I doubt the Aprilia dealer would either have the correct weight rollers come service time, or if they did I doubt they'd rember to fit them instead of the original weight rollers. I found out today about a local place that has a spring measurer. Apparantly they can measure your spring, then find a lighter one! I'll phone them tommorrow and find out.

Anyway, do you know where the interstate shop is?

Thanks

Bishop
12-11-2002, 06:17 AM
I know is was one of the big scooter shops in either Sydney or Melbourne, unfortunatly I can't remember which one.

I'd actually suggest phoning one of the larger places in Melbourne or sydney, they sell a lot more scooters down there, and I'd say they would probally be able to help you better find an easy solution to your problem.
(and have more aftermarket parts)

I think Scootermarket in Melbourne is one of the biggest, and I know they were claiming good speeds from their SR's, I think their number is 03 84151800.
And I think they have a web site too.

j3rd4n2k9
08-03-2009, 12:26 PM
Attention SR50 owners,

I have been told by Aprilia Australia that the SR50 comes standard with a fair amount of clutch slip. I find this unacceptable (and downright annoying and embarrassing in traffic), so I wish to modify my gearbox to allow the clutch to engage sooner (and therefore stop the bike revving so hard all the time!)

I have spent many years working on the CVT of Honda Dio's and I'm assuming that the Aprilia has a similar setup. (Front pulleys with internal rollers and a rear clutch unit with springs and shoes). I am also assuming that I should only need to change the weight of the clutch springs to achieve earlier takeup. Can someone who has worked on the Aprilia SR50 CVT tell me if this is correct?

Do I put in lighter or heavier springs? Aprilia Australia mentioned modifying the rollers...how does this work?

Thanks in advance!

purchase a racing clutch,this would stop the "power dip",but as for the bike revving too hard,its a 2 stroke so its meant to,if u tested a 4 stroke you would find the bike woudnt rev much at all

ReplicaOwner
08-03-2009, 06:43 PM
This post was from 7 years ago. I sure hope he got it fixed by now...LOL