Seeking drive train guidance

Squonker

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Dec 15, 2019
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I have seen on this forum many examples of two and four stroke shifter builds. And I like the idea of these and would like to build one as well but since I have not built one before, I come seeking guidance.

My thought was to use a 49cc four stroke with an EZM drive or a GT type reduction drive. Then to a jack shaft transferring power to the right side and ultimately to a XL-RD3 3 speed internal gear drum brake hub.

The bike will have 26'' wheels and I come in at about 220#

So I suppose my main questions are (assuming proper gear ratios); will the 49cc be able to drive 3rd gear with, if I recall correctly a 33% overdrive on relativity level ground? And would 30 - 35 MPH be reasonable to expect from this? Or is this thought just crazy and I need a bigger engine?

Thanks in advance;
Dave
 
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Tony01

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My vote goes to the 79cc predator. Standard kit, governor removed, minor port/polish, single speed geared 11:1 for 42mph top speed at 6000rpm with a nice 31mph cruise at 4500rpm.

The 49cc is a POS... and while many do run the shift kits... it’s really gimmicky... you have the belt primary drive, then a chain to the shift kit, then a chain on other side to cranks, then the rear chain going to a shifter... and you have to shift constantly just to get up to 35mph with no engine braking... yuck
 
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Squonker

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Thanks for the reply!

With the 79cc predator scenario, what rear hub and rear brake options should be considered?

Thanks again,
Dave
 

indian22

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Dave glad to see a new build being considered. Do you have a frame? If so it's helpful to post good photos on the thread it really helps answering questions. Lots of frame brands, styles and sizes out there and not all are suitable for motorizing for varying reasons.

Best of luck.

Rick C.

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Squonker

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Hello Rick,

Thanks for the suggestion.

Yes I do have a frame it is the Mustang stretch cruiser. Not really sure yet how to post a picture but I will find out. Arizona Bill's success with this frame and the style of his build is the catalyst for my inspiration.

Being a stretch cruiser was the reason the jackshaft is being considered to hopefully get the rear chain line lower to clear the frame constraints. My thought was to put the shaft at the base of the seat tube and the horizontal frame section similar to one built by I-paint on this forum. Creating one of the gussets that are anticipated on this frame. And if the jackshaft is a viable solution why not take it to the right hand side to get 3 speeds and a drum brake?

Thanks again,
Dave
 
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indian22

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The stretch bikes with 135mm axle spacing out back should have enough space Dave and having pedal bracket forward does present chain issues, but as you've seen they are manageable.

I've absolutely no issues with either 2-stroke or 4 cycle being used. 50cc is legal max in many areas and some fine builds with 50cc motors abound, that said with your weight and what you're considering I'd also suggest that Tony makes some relevant observations, larger displacement is a good thing until it warrants a ticket. I'm also not a fan of shift kits and again there are some great ones that appear in this forum, Tony and others have built some tremendous shifters with great skill & they work. He listed several details that are reasonable concerns.

I'm also not a big fan of taking the drive to the right. Clutch and reduction drive on the left and pedal on the right. Two separate drive lines with chains of the appropriate size for each task; pedaling and motoring...independent or utilized in unison. Break one and you've got the other to help get home with. Bike chain is relatively weak for driving with a motor and so are multispeed hubs designed for pedal power. This again isn't hating builds utilizing these I'm simply stating my preferences and my observed opinions as to drawbacks encountered in riding. I ride everyday year round, except in driving rain and icy road conditions...cold heat whatever I ride. So I place great emphasis on dependability and safety whether I'm motoring or pedaling, I do both on some.

At the end of the day I'd hope you build a bike based on what you decide & which pleases you.

Have fun during the process and post photos, it's easy, along the way. We love photos!

Rick C.
 
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Squonker

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Rick,

Thank you for your response and the recommendations. And I will use them as the new direction in my planning.

Regards,
Dave
 
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LR Jerry

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I'm going to assume you're using 26" wheels. I'm also only going to talk about small cc 4 stroke engines that reach max horsepower at 7000 rpm. The clones of the Honda 50 aren't it's equal. They neither match it in torque or horsepower coming from the factory. The clones are closer to the Robin Subaru 35 in horsepower and torque. I have an RS 35, I weigh 250 lbs and my bike weighs 100 lbs. I can go up 25% grade hills with no pedal assist. To go up 30% grade hills I need to pedal assist. My current lowest reduction is 49.21:1; with a 55:1 reduction I wouldn't need to pedal assist at all up a 30% grade hill.

So what I'm telling you is at your weight the build can't exceed 60 lbs and the terrain must be fairly flat to obtain 30-35 mph using a 3 speed hub.

To do 35 on level ground using 26" wheels in the highest gear 3 the minimum reduction has to 15.46:1. Gear 2 would give you a reduction of 20.61:1. The lowest gear would give you a reduction of 27.48:1. So at best the low gear would only be good for take offs on level ground and climbing less than 15% grade hills. If your overall weight is low enough you should be able to reach 35 on level ground with this set up and the Honda 50.

To do 30 mph on level ground gear 3 the minimum reduction has to be 18.04:1. This would put gear 2 at 24.05:1. The lowest gear would be 32.07:1. With your weight low enough and using a Honda 50 you should be able to climb 20% grade hills with no problem. You may need to pedal assist if you use a clone on a 20% grade hill.
 
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Squonker

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Hello Jerry,

How much more HP and torque would you estimate that the Genuine Honda produces? I have read on this forum that they do cost more, but that is not an underling decision maker, if the performance is something that can be noticed.

That said, it does seem as though many on this forum that are using 4 strokes are going larger than the 50cc's. Many retailers are frequently sold out, or on backorder of the 79cc kits. The reasons for this could be several things for sure, nonetheless it does appear that the current trend is heading in that direction.

Does your configuration comfortably go up a 25% grade? And what kind of speed are you able to maintain doing such?

Thanks for your reply,
Dave
 
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LR Jerry

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The RS 35 has 1.6 hp at 7000 rpm. The torque is 1.6 ft/lbs at 5000 rpm. This is about what the 49cc clones produce at roughly the same rpms. The Honda 50 produces 2-2.5 hp at 7000 rpm and 2 ft/lbs at 4500 rpm.

Most places have a 50cc limit to be legal where self built motorized bicycles/mopeds are allowed. Unfortunately large people and steep hills means you need gears with these small engines. I can do roughly 8 mph up 25% grade hills without having to pedal assist. The 30% grade hills I do have to pedal assist. Most places have an automatic transmission clause. Meaning the operator can't manually shift engine driven gears. This is why I built a bike that can shift gears automatically. Currently a legal loop hole.

What could give you a wider reduction range is to use a 5 speed IGH instead of a 3 speed IGH. Then if you do have to climb really steep hills you'd be able to drop into a reduction low enough to do it.

With the 5 speed IGH you'd have the following reductions in order to do 35 mph on level ground (1) 39.58:1 (2) 32.98:1 (3) 24.74:1 (2) 18.55:1 (1) 15.46:1

To do 30 mph the reductions would be (5) 46.18:1 (4) 38.49:1 (3) 28.86:1 (2) 21.65:1 (1) 18.04:1.
 
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indian22

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Jerry good info on the IG ratios and how these correlate to weight, power and incline changes & in conjunctions. This information is indeed useful for those contemplating shifter builds.

Rick C.
 
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LR Jerry

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What I also suggest getting is a tachometer/hour counter. Then you can be in a gear where the tach is around 7000 rpm at full throttle. If you can't reach 7000 then you need to down shift. If you're in the highest gear and going over 7000 then throttle back some (very common when going down hill).

With the hour counter it'll let you know when to do an oil change and air filter cleaning. I change my oil every 25 hours of use and clean the filter ever 10 hours of use.
 
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LR Jerry

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Jerry good info on the IG ratios and how these correlate to weight, power and incline changes & in conjunctions. This information is indeed useful for those contemplating shifter builds.

Rick C.
The IGH are nice in that the pedals don't have to be moving to change gears. So even at a dead stop you can shift back into first gear unlike a derailleur where you have to shift back into first before coming to a stop. They're also easier to disguise as a single ratio build as well.
 
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Squonker

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Very good information indeed, and being the novice that I am, provides much food for thought as well.
I really like the tachometer / hour meter tip. is there a device that will also give mph?
Just out of curiosity, could you provide some information on your automatic shifting set up?

At this point it seems the less complicated drivetrain Tony and Rick suggested may be my best course to follow for my first build.

Thank you,
Dave
 
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indian22

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The inductance tach/hr. meters are handy and require only minimal setup wrap a single wire around a the plug wire a few times and secure, zip tie or permanently attach the small meter housing to an appropriately located position and calibrate according to instructions, simple fast and clean. They are useful as Jerry stated and I've found them to be fairly accurate, though not quite real time ( they read out a good bit behind the actual engine speed) so it's always a few hundred rpm's behind information. The final readout, however, is very close to the actual high rpm, it just lags.

I really like to run these during engine break in and for verifying engine rpm with GPS speed while fine tuning the ratio setup for cruising...I don't like the engine to stay too busy while maintaining my pace and checking head temp as I ride, as well as informing me of an efficient ratio setup I can ride for hours and not punish the engine for it.

These little meters are inexpensive, but have good value when employed with purpose and on the 4 strokes as Jerry stated the hour meter is a nice reminder for scheduled oil service.

Rick C.
 

LR Jerry

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I simply use a bicycle computer for a speedometer. As for the auto shifting I use a LandRider derailleur. Shifts 7 gears automatically on a custom built freewheel 34,28,24,21,18,15,13.

I have a Honda 50 plan to switch to it in the future. Then the freewheel will have this setup: 34,28,24,21,18,16,14.

I'll also be trying out a new design on the rear derailleur soon. It'll involve putting contraction springs on the weights, which should improve the down shifting even more.
 
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