49cc 4-Stroke 30 Series Torque Converter Build

[Tom from Rubicon]

Well the proof in the you tube. These little Huasheng engines area thing. My BBR kit with a 31 tooth rear sprocket functioned fine until the carb sucked up something and refused to start. Which mattered not as I was completing a Sportsman Flyer 80 build. Predator 79cc engines have challenged me from the git go.

Tom

 

[Mossy]

Your engine sounds like it's under a lot of strain. It would be very interesting to see what a tachometer reading would be. I used to have an automatic shifter the LandRider. It's reduction range was 49.21\1 to 18.82\1. I tightened up the cadence adjustment spring to where the gears needed higher speeds to change. Otherwise it would've been in the highest gear around 15 mph.

Think about a pedal only bicycle it's much easier to take off in a very low gear than it is in a medium or high gear. You can end up doing a lot of damage to your components.

Granted you must have a very strong clutch. However, when your strengthen something the next weaker point is subject to fail. Meaning something inside of your engine. I strongly suggest pedal assisting on starts.

Max torque on your engine is at 4500 rpm. If you aren't getting at least that at full throttle problems await you. Max horsepower is at 6800 rpm. Because your reduction isn't enough you'll never obtain that rpm at full throttle on level ground.

On my Robin Subaru 35 the Max hp is at 7000 rpm. If I'm in a gear doing 7000 rpm at full throttle; shifting to a higher gear won't make me go any faster. It'll still be going the same speed but the rpm level will drop. This is what engine strain is. Here's my speed formula:

(RPM × Wheel Diameter × π)÷(1056 × Total Reduction)=MPH

.... With the cvt it's more than ratios... I can't be the only one who has changed the springs on a comet clutch... Matching up the engine speed with the clutch engagement... With little power you want the front to stay small longer and the back to take long to engage... Top speed won't change just how it gets to it does... Same deal as jetting a carb... And the spring chart works the same as a jet chart... The 3 fine adjust holes... So a green on the first hole is the same as the yellow on the last one... Gold doesn't use one... What's great about the CVT and a Mikuni carb is the tuneability... But both are going to run like garbage out of the box... Unless you have by coincidence the generic enough of the setup it would work out of the box on... Same a rifle scope... Same as a lot of things...

 

[Chobiker]

I cannot believe the push back I have received over this build. Even after showing a video of it working most of the naysayers never said wow, it works, they just lurk in the background waiting for it to break and then jump in and post I "told you so" or look for something in my post to tell me how wrong I am. I don't post very often as most things have already been built or figured out before I attempt it. I've never seen a 49cc 4-stroke torque converter build so I thought I would post my success.

I will usually give it a push with my feet or 2 cranks of the pedal when starting, I just didn't for the purposes of the video. This was not a build for my 250lbs, I never expected it to move me from a stop like a slingshot, but it's still able to do so. It works awesome for my son, better than I ever imagined.

I had no idea what the WOT rpms were for this engine. I didn't use the ChatGPT reduction ratio calculator to design my build, I used what came in the box. If it didn't work I would have changed sprockets. The china branding states it's 6800rpm, but we all know how accurate their advertising is. I have an RPM gauge (picture of it below) used to measure the WOT of this engine "with and without the torque converter", no back wheel hooked up. The WOT of the engine was 3900rpms, no where close to the advertised 2hp at 6800rpm (the naysayers will tell me that's because the torque converter is sucking all the power from my engine). At 3900rpms it sound appropriate, and I don't believe this could WOT @ 6800rpms. Push mower engines are in the same rpm range and this engine is very similar. I don't remember the output rpms of the torque converter but I will check it next time I do a chain adjustment. Has anyone in these forums ever measured the WOT rpms of these engines? Just curious if mine is really low?

I have blue threadlock on this bike everywhere with sharpie marks on the important bolts to see if they move. I inspect this thing all the time looking for bending, warping, loose bolts, premature belt wear, etc. and it has required no maintenance. In person the engine sounds completely fine. Will it throw a rod through my arm or tear my thigh off with the torque converter the next time I ride it, or will it last 3000 miles without a wrench touching it? I'm sure it will be something in between. It was a mostly easy build and works better then I ever expected. I should have documented it better, but then I would have even had more of the "this doesn't work".

 

[Mossy]

Rpm

I cannot believe the push back I have received over this build. Even after showing a video of it working most of the naysayers never said wow, it works, they just lurk in the background waiting for it to break and then jump in and post I "told you so" or look for something in my post to tell me how wrong I am. I don't post very often as most things have already been built or figured out before I attempt it. I've never seen a 49cc 4-stroke torque converter build so I thought I would post my success.

I will usually give it a push with my feet or 2 cranks of the pedal when starting, I just didn't for the purposes of the video. This was not a build for my 250lbs, I never expected it to move me from a stop like a slingshot, but it's still able to do so. It works awesome for my son, better than I ever imagined.

I had no idea what the WOT rpms were for this engine. I didn't use the ChatGPT reduction ratio calculator to design my build, I used what came in the box. If it didn't work I would have changed sprockets. The china branding states it's 6800rpm, but we all know how accurate their advertising is. I have an RPM gauge (picture of it below) used to measure the WOT of this engine "with and without the torque converter", no back wheel hooked up. The WOT of the engine was 3900rpms, no where close to the advertised 2hp at 6800rpm (the naysayers will tell me that's because the torque converter is sucking all the power from my engine). At 3900rpms it sound appropriate, and I don't believe this could WOT @ 6800rpms. Push mower engines are in the same rpm range and this engine is very similar. I don't remember the output rpms of the torque converter but I will check it next time I do a chain adjustment. Has anyone in these forums ever measured the WOT rpms of these engines? Just curious if mine is really low?

View attachment 113135

I have blue threadlock on this bike everywhere with sharpie marks on the important bolts to see if they move. I inspect this thing all the time looking for bending, warping, loose bolts, premature belt wear, etc. and it has required no maintenance. In person the engine sounds completely fine. Will it throw a rod through my arm or tear my thigh off with the torque converter the next time I ride it, or will it last 3000 miles without a wrench touching it? I'm sure it will be something in between. It was a mostly easy build and works better then I ever expected. I should have documented it better, but then I would have even had more of the "this doesn't work".

Right focus only on the negative.... I suggest trying to use parts made to tune it... So it works better... My bad

 

[Chobiker]

.... With the cvt it's more than ratios... I can't be the only one who has changed the springs on a comet clutch... Matching up the engine speed with the clutch engagement... With little power you want the front to stay small longer and the back to take long to engage... Top speed won't change just how it gets to it does... Same deal as jetting a carb... And the spring chart works the same as a jet chart... The 3 fine adjust holes... So a green on the first hole is the same as the yellow on the last one... Gold doesn't use one... What's great about the CVT and a Mikuni carb is the tuneability... But both are going to run like garbage out of the box... Unless you have by coincidence the generic enough of the setup it would work out of the box on... Same a rifle scope... Same as a lot of things...

I didn't see this post of yours until after my previous post. I like the idea of tweaking the springs, just like you said, you want the front to stay smaller until the revs get up and have the back longer to engage. I might try changing the hole that the current stock spring is in. If that doesn't help I might get a different one. The carb on this engine is very basic and I have some small issues with it already, I can see this being a problem in the future. I am for sure going to look at upgrading the carb, didn't know Mikuni has one for a 50cc engine.

 

[Tony01]

Those CVTs are designed for at least 8hp. The belt drive eats a ton of power easily 2hp. I ran a 20 series symmetrical with the 7” driven on my 212. With a single speed clutch I topped out at 55-68 mph depending on gearing, but with the CVT I couldn’t get it past about 54 no matter what I did with final drive gearing. The 20 series shifts to a 1.4 reduction.

If you want more out of it you have to go to a higher reduction on the back to let the motor breathe. Most likely that motor will never exceed 3800rpm because the cvt just eats the power. For a build like that with limited HP I’d run a regular clutch. The slingshot effect is the belt initially hooking up to a motor running at idle but after that it’s pure power loss.

 

[Tom from Rubicon]

CTV's are inefficient, but Chobiker has a video. Being a Doubting Thomas just is.
But it looks like a runner to me.
My only empirical knowledge is that the die cast plate has a knit line that fails when used with a 212cc predi. A workmate suffered multiple failures of that frame plate. His only complaint at the time was of poor customer service.

Chobiker, it isn't push back so much as incredulousness. Having used a Huasheng 142 I know that they out perform and will lug uncomplaining under load.

Tom

 

[Mossy]

Good to know about the plate failing... I've been on the fence about going with the aluminum knock off or an original comet tav 1 with a steel plate... The only downside is the cover for the tav1 doesn't fit a 7" driven only a 6"... But I can modify a metal cover for a Colman 200 to fit and weld a brace on it for vibration... Not just the 4 5/16 -20 engine case bolts... But one or two of the engine mounting bolts so the whole thing slides for chain adjustment... I like to tac weld washers on the rear drop so the axle is fixed in one position so if it loosen up it won't cam out and it strengthens the drop out... Just have to grind off the welds and replace the washers when you remove the hub... I also add a plate to the drop on the inside...

 

[Mossy]

I didn't see this post of yours until after my previous post. I like the idea of tweaking the springs, just like you said, you want the front to stay smaller until the revs get up and have the back longer to engage. I might try changing the hole that the current stock spring is in. If that doesn't help I might get a different one. The carb on this engine is very basic and I have some small issues with it already, I can see this being a problem in the future. I am for sure going to look at upgrading the carb, didn't know Mikuni has one for a 50cc engine.

A slightly larger belt might help a little to get it up into the hi range but without the torque of a 8hp engine you don't have many options... Like my situation with the 79cc I'm going to have 7hp at 6k with 1/2 the torque of a 8 HP at 3k... So I'll be messing around with it to get it right for my weight and gearing... I have 42 and 46t sprocket and 25" diameter wheels...

 

[Venice Motor Bikes]

Let me start out by saying that this is actually a really good & friendly forum that has many extremely knowledgeable bike builders...
Every single day we answer the same questions from new bike builders & give the best advise we can.
We're not bashing you.. we're simply giving our honest opinions based on years of experience.

I never doubted that your bike actually runs well; I never doubted that it actually changes gears (a little); I don't even doubt that it's reliable.
I can tell you from years of experience, that that set up isn't giving you the performance that you think it is.

My point is this... if this is truly your first motorized bicycle build?, then you don't have any experience of what 'good & bad' performance really is in one of these bikes... (again, this isn't bashing you)... you just have nothing to compare this bike to.



Anyways... it looks like you've built yourself a fun little bike, & if you're anything like the rest of us here, you now have an expensive new addiction!!

Your next builds should be a 2-stroke, & then a 212cc with the same torque converter... & you'll see what I mean about performance.

Welcome to the forum.

 

[Centar]

Wouldn't something like this work better?

49cc X1 X2 Ninja Pocket Bike CVT Transmission Gearbox TM03

 

[Barnfresh]

Cool little app I’ve been using for my 30 series CVT tuning. Works best on Android Mobil devices. On Apple you can’t pre-set to mph/lbs on initial input. This Kart Calc app pretty much backs up the OP’s original claims and is real close to where I started on my 79cc Lifan when everyone told me “it’ll never work” & “your engine doesn’t make enough power”, lol I know it can be done, most are just seriously over geared for a 26” rear wheel. Currently I’ve worked my way down to a 9t-62t on a 7” driven, almost there, fun fun.

 

[Mossy]

I'm going to try a 10-46 with a 7" driven on 25" wheels with a modified 79cc that will rev 6000+... So it would do 80mph if it can push the gear? If I went with a 9or10 -56 probably be more realistic ...they make a 42 46 48 and a 56 that I can find for the pugeot 103 hub... I can use the sprockets for 2 stroke builds...
I haven't gotten anything from France in a while... Thank you for this information

 

[Barnfresh]

I'm going to try a 10-46 with a 7" driven on 25" wheels with a modified 79cc that will rev 6000+... So it would do 80mph if it can push the gear? If I went with a 9or10 -56 probably be more realistic ...they make a 42 46 48 and a 56 that I can find for the pugeot 103 hub... I can use the sprockets for 2 stroke builds... Froala
I haven't gotten anything from France in a while... Thank you for this information

I found an 5/8” bore 8t 415 sprocket for the jackshaft however 56t was as large as I could go before the chain rubs the frame stay so I’m currently in the process of swapping my final drive to #35 which should allow fitting sprockets up to 75t.

What I really need now is a 6 hole IS (44mm BCD) adapter to standard 6 hole 5.250" split sprocket pattern, if anyone knows of such a thing. This way I can utilize my arsenal of #35 sprockets leftover from Kart racing to find a sweet spot and utilize the full range of primary ratios my CVT offers, 3.13:1 to 1.12:1.



Funny you should mention the P103 moped hub because in my search for a split sprocket adapter I ran across where Sportscar Pat made a split sprocket adapter to fit his moped hub.

 

[Mossy]

I found a 60T on treatland... 6 bolts 43mm diameter...
I'll have to figure out clearance issues what I get to that point.. but a 60 is going to be better than a 46-48... Might not be ideal but like you said more usable... For $15 I don't mind having a few of each