40 series cvt questions

vegasboy

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All right, where to start. LOL I bought a 40 series for my 420 predator. The plate was strong enough but somebody welded the back pipe with bearings crooked. I cut the plate almost in half and bend it at the seam and rewelded it to get the pulleys to line up. Then I noticed if I kept the rear pulley the way it was meant to be then the driver was slid comically far off of the engine shaft🤔 I looked online and some folks were talking about flipping the driver to the other side but I did not know what the results would be so I did not do it. I ended up with my 10th sprocket on the outside. I do not know if it'll work in that configuration however I also noticed the belt going on to the driver pulley was pushing hard to the right so I reduced my spacer and slid the pulley back towards the motor more in align with the belt? Can somebody look at my pictures and tell me if my pulleys are close to correct in alignment? And if anybody has any knowledge about the baby sprocket being on the outside and to whether it'll work or not? And the last but not least what is the most popular 40 series torque converter used for the predator 420? And yes I know the chain is loose I will be welding a tensioner for it soon.
 

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rockman96

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You need to replace the red spring with a yellow spring to run it in that orientation.
 

itsid

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You need to replace the red spring with a yellow spring to run it in that orientation.
you must NOT!
(that's a stupid idea in this case unfortunately!

Well that answers one question, anybody want to take a gander at the other two questions?
No it infact answers all but the sprocket placement questions

here's the thing.. you opted for that stupid backplate setup.
that's unfortunate but we can deal with that.
(by flipping the driver inside out!)
allow me to explain:

the series 40 as you should know is a symmetrical TC, and with that it's driven should run inboard
(cam pointing towards the engine) .. that is required for the belt to run true.
and that's what the standard spring (red) is wound for.
If for some odd reason you cannot run the driven inboard,
you can swap to a yellow (reverse wound) spring and run it outboard.
BUT that requires the driven to have one beltwidth worth of float Inwards (again towards the engine)
and THAT is impossible with the stupid backplate thing.

So the only viable solution to keep the belt running true at all times is to instead flip the driver inboard.
that way the sheaves move in the same direction.
(and that again requires the red spring to be installed...)

having the sprocket on the outside is not a smart move.. it should be braced with another bearing to
stop deflection by the chain..
I haven't answered that part since if it works or not depends on your exact setup and load (unable to tell from here)
if the chain slips or jumps you can't.. if it runs true and good.. no problem!

What series 40 to use is up to you.
most (if not all) chinese copies we've seen so far are of decent quality and can surely be used.
a true Comet is always your best bet of course, but actually a clone will do nicely if used correctly.

And yes.. having messed with the backplate you might have messed up..
but frankly.. that thing is a BS piece of steel anyways.. so if you have..
just get a 'normal' jackshaft instead, mount the driven inboard as it supposed to be according to the original makers (Comet)
and you have a good setup in no time.

'sid
 

rockman96

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you must NOT!
(that's a stupid idea in this case unfortunately!

here's the thing.. you opted for that stupid backplate setup.

If for some odd reason you cannot run the driven inboard,
you can swap to a yellow (reverse wound) spring and run it outboard.
BUT that requires the driven to have one beltwidth worth of float Inwards (again towards the engine)
and THAT is impossible with the stupid backplate thing.

Be careful who/what you call stupid... Sitting behind a monitor thousands of miles away, calling people or what they say "stupid", is easy.

That said, you work with what your setup allows. If you don't have room to run as intended or designed, flip it and swap out to a yellow spring, no big deal... That is why they make the yellow springs. If you set it up right, the stationary sides of the drive and driven will line up and the variable sides will line up under a loaded condition. It may look a bit out of kilter when not running, but it will run true under normal operation. Just think before you do. And that goes for calling people stupid too.
 

Joe-405

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The moderator didn’t call anyone stupid. It’s the fact that most people just don’t agree with that particular setup.

I on the other hand have had a few with no issues other than the one time I forgot to switch the spring.
 

rockman96

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The moderator didn’t call anyone stupid. It’s the fact that most people just don’t agree with that particular setup.
Well, he may not have directly called anyone stupid, but what he did call stupid is what I said, and what someone else is using. Which, in and of itself is pretty much the same thing. Its the lack of respect and lack of tact in those statements that annoys me. Just because you don't like or agree with something doesn't make it "stupid".

This is my 420 big block with some upgrades, and it works fine with a yellow spring setup. There was simply no room to install with a red spring. And yes, the frame is stretched in the front, the rear section heavily reinforced with gussets, and a third axle bearing/plate added. Sure, there are things I could have done better, and things I'd do differently next time, but I wouldn't call any of it stupid, the yellow spring included.

Complete_left_zps0a795f45.jpg
 

itsid

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Be careful who/what you call stupid
I am...

The setup still is!
There is VERY GOOD reason Comet themself never offered such backplate setup for the series 40
(it's just not a good idea at all!)

The moderator didn’t call anyone stupid. It’s the fact that most people just don’t agree with that particular setup.

I on the other hand have had a few with no issues other than the one time I forgot to switch the spring.
great .. it still costs you unnecessary powerloss and additional beltwear.
And while -if I recall some of your minis- that isn't exactly troublesome,
(going by the power the engines likely had and the rather short travel distances you are facing at a drag race)
I do agree on very few occasions, that it does indeed make sense to swap ease of installation and spacial benefit against powerloss and beltwear
if there isn't another option and you can afford to loose some more power and money to the transmission
whereas you cannot afford to install a usual jackshaft lacking the space to put it.
IIRC you were one of the early adopters of that GPS backplate right?
Which qualifies you and those minis as one of those occasions,
since the yellow spring was the only known way to mount that thing at all.

BUT since the flipped driver idea came up.. there is an option that is just about as easy to install,
and promising less powerloss and less beltwear.
since it has been used quite a few times and has proven to be as reliable as the yellow spring flipped driven setup.
So I can't see any major drawback that causes this to be the inferior of the two options with the backplate.

And that's where we are now...
flipping the driver, keeping the red spring and a mostly straight belt at all times loosing less power causing less belt wear
or
flipping the driven, buying a new yellow spring to do so, having a kinked belt most of the time (except idle) causing more wear and powerloss.

Given those two options..

what he did call stupid is what I said
since it IS!
Suggesting to waste power and money -for no apperant reason- is not good advice.

TC on Backplate/Yellowspring sucks likely more than 30% of the engine power out of your system..
roughly 5% more than with the red spring.. that power is only used to chew on the belt to wear it down quicker.
with say a 15horse engine that means you are spending 3/4hp just to ruin your belt for absolutely no benefit.
to me that qualifies!

'sid
 

rockman96

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The setup still is!
There is VERY GOOD reason Comet themself never offered such backplate setup for the series 40
(it's just not a good idea at all!)
The inverted set up is not stupid. At the worse, it is inferior... If you are ale to run the driven inboard, by all means do it.

I do agree on very few occasions, that it does indeed make sense to swap ease of installation and spacial benefit against powerloss and beltwear
if there isn't another option

Which qualifies you and those minis as one of those occasions,
since the yellow spring was the only known way to mount that thing at all.
And there it is... Sometimes there is no other option. Is it still stupid? I have no back plate (we call them motor plates in the bike world) on my kart, the jackshaft/bearing supports were fabricated from plate steel, lined up, and welded. I had no other option than running inverted due to the physical engine size, brakes, sprockets, frame interference, things of that nature.

And that's where we are now...
flipping the driver, keeping the red spring and a mostly straight belt at all times loosing less power causing less belt wear
or
flipping the driven, buying a new yellow spring to do so, having a kinked belt most of the time (except idle) causing more wear and powerloss.
If you have a kinked belt most of the time except at idle, then you aren't setting it up correctly.

since it IS!
Suggesting to waste power and money -for no apperant reason- is not good advice.
I only answered his question with a viable option since that is the setup he has and wants, I was not advising.

TC on Backplate/Yellowspring sucks likely more than 30% of the engine power out of your system..
roughly 5% more than with the red spring.. that power is only used to chew on the belt to wear it down quicker.
with say a 15horse engine that means you are spending 3/4hp just to ruin your belt for absolutely no benefit.
to me that qualifies!

'sid
Where are you getting these figures from? Are they WAG's, something culled from the internet, or backed up scientifically with dyne runs and experimentation?
 

itsid

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At the worse, it is inferior
picking worse and paying extra for it..... I mean do I have to spell it out?
Sometimes there is no other option. Is it still stupid?
you misunderstood.. when (chronologically) there was no known alternative,
that backplate thing was a -maybe- acceptable drawback for very tight ocasions (mini bikes!)
NOW (chronologically) since there is a known to work alternative that has less drawbacks
requiring exactly as little space ... it's still stupid.

And I know that people tend to stick with things and setups they know and are familiar with (I'm no exception to that)
but that is at best lazy.. at worst it's again stupid.
I only answered his question with a viable option
asking him to spend more money for a yellow spring he doesn't need to end up with an inferior setup.
ah well.. we turn in circles.

backed up scientifically
indeed there was a research paper published a couple of years ago,
it described in great (mostly boring) detail how a non-positive-traction CVT
cannot be more efficient than (i think it was) 79.8%,
it described how a taller belt contacting surface requires higher bending forces and the resulting kneading forces
as well as a bigger slip due to circumference difference of the inner vs the outer edge of the
moving belt eating up the benefit of a bigger contacting surface from a certain point on.
(less contacting surface equaling less potential to transmit power of course)
and it also brushed over the topic of how less than perfect alignment quickly raise the powerlosses
to additional kneading forces required to move and laterally shift the belt to align with the second pulley.

Then the details escape me tbh but it also explained that those effects are actually growing with engine power
to remain a percentage of instead of a fixed wattage.
IIRC it's the torque related clamping force to keep the belt rotationally stable while accelerating
pinching the belt requiring more force to break free from the pulley... I think there was something else.. but I don't quite remember.

Powerloss was scientifically correctly measured by induced heat btw.
generally speaking thermal mass of involved parts, heat delta and out comes power loss.
forced air cooling of rotating pulleys and moving belt was taken into account by running those fully enclosed
and measuruing the temperature change of the known air volume as well.
So no false dyno reading could compromise the data.

Now.. I think we do agree that the belt WANTS to run true, don't we?
let's do a simple test..

The belt get's offset by one belt width on a series 40 with your setup.
(you can measure that yourself if you like.. but it's 7/8" according to comet)

so get a 7/8" thick board and place it on your bench, lay your belt in a 5" OD semi circle onto the board (~4" off the edge)
and a 5" semi circle onto your table your center to center distance apart
now put weights on the two half circles so that the belt is perfecly flush with the bench and board.
combined weight in kilograms times 9.81m/s² is Newtons of force, distance of the two semi circles in inches times 0.254 to get torque (in Newtonmeters) which is equal to wattseconds of energy
engine rpm times Pi divided by 12 times the belt OC to derive your belt rotations per second at you favourite speed
and you can then simply multiply the wattseconds with the belt rps to get the static powerloss in watts for the offset belt
clamping and kneading forces not fully included but I'd bet you'd be surprised already
and I'd also bet you'd be considering getting the red spring back in to flip the driver instead just to make use of the few hundred watts you are already loosing there.

with a 33.8" belt at 8 3/16" ctc
and just 1kg *(2.2lbs) combined weight we talk a powerloss of roughly 711Watts static for 4.5k rpms (570 Watts @3600 rpms)
(6.44% loss on a 15horse compared to my 5% WAG [ 5.16% @3600 rpms... just so you know where the 5 came from] )

So yeah.. test it, be surprised, change to red spring and flipped driver.. PROFIT!

'sid

* I don't own a series 40.. so I tried to get an estimate with my series 30 belt...
I need MORE than just 1kg combined weight to get them flat on the bench and 3/4" thick board so yeah...
 
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rockman96

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picking worse and paying extra for it..... I mean do I have to spell it out?

you misunderstood.. when (chronologically) there was no known alternative,
that backplate thing was a -maybe- acceptable drawback for very tight ocasions (mini bikes!)
NOW (chronologically) since there is a known to work alternative that has less drawbacks
requiring exactly as little space ... it's still stupid.
You keep saying there is a this known to work alternative that takes up the same space... What is it? I'm not up to speed.

There is NO WAY to run inboard on my kart due to space requirements. Wish there was, but there simply isn't. Thats why I'm getting a little annoyed by your "stupid" blanket statements. Maybe its just a keyboard versus face to face issue.

need to end up with an inferior setup.
ah well.. we turn in circles.
He asked a question about HIS setup... I told him how to make HIS setup work as-is. Simple as that, no more no less.
 

Snaker

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indeed there was a research paper published a couple of years ago,
Hey Sid, do you have a link or some way to find that?
I look for all I can on small engine CVT's.

When digging deep its helpful to keep in mind that the Torque Sensing function (angle cam, slots, etc) is a add-on feature.
Early small engine CVT's didn't have it.
It adds a huge benefit to the operation and also adds compromise's.
 

Joe-405

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You guys are making me wanna turn my driver around now just to see if there is a difference.

here’s mine currently..........
 

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itsid

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You keep saying there is a this known to work alternative that takes up the same space... What is it? I'm not up to speed.
I told OP above in the first post..
Flip the DRIVER INboard (driven remains pointing outboard and with the currently installed red spring)
He asked a question about HIS setup
and that's why I answered the way I did ;)
(keeping his red spring)

Hey Sid, do you have a link or some way to find that?
I look for all I can on small engine CVT's.
Unfortunately I couldn't find it yesterday..
it's been a few years since and it seems I haven't saved it to my harddrive back then *shrugs*
There's been a similar paper (from 2008 but much shorter AFAIR)
"EXPERIMENTAL INVESTIGATION ON THE EFFICIENCY OF THE PULLEY-DRIVE CVT"
and I cannot recall if the extensive one was referenced in that, or the other way around.
maybe even with a step/paper inbetween.
it's been too long for me to trace back my steps...
I could've sworn I saved the most valuable information .. but I can't find it...
maybe it's been on a now defunct laptop *shrugs* Sorry

When digging deep its helpful to keep in mind that the Torque Sensing function (angle cam, slots, etc) is a add-on feature.
Early small engine CVT's didn't have it.
well you need to take a loooong step back in history to find a time where torque sensing wasn't a thing really..
Even the earliest Salsbury CVTs I can find documentaion for had Torque sensing units
(they sold both: speed as well as torque variating driven units)
and that's 50 years ago.
I think even the very first Comet units already had both as an option.
I couldn't track any 80yo docs to find the first TCs or say CVTs to make a judgement
I think the motobecane scooter hat a torque sensor [1940s: about the first motorized bicycle with a variable transmission.. later called mobymatic]
but I cannot tell for sure. it's also hard to tell if that was before or after the salsbury patent tbh.
*shrugs*
But I think with 50+ years we can assume torque sensing is a known concept to whatever vehicle we usually come across.

'sid
 

rockman96

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I told OP above in the first post..
Flip the DRIVER INboard (driven remains pointing outboard and with the currently installed red spring)
What are we missing here? You said there is a "known to work alternative that takes up the same space"... That implied to me that there a different design, because running inboard does take more space than running outboard. My drive would have to be 2" into the engine to run inboard and have the sheaves line up straight, and obviously I can't do that.
 
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