4 stroke transmission issue

D

Dawelny97

New Member
Hey all. Im sorry for posting a new thread, I did it because no one replied to my old one no more (im new to the forum) But anyways, I got my 4 stroke motorized bicycle complete and I've been riding it a few times, its has plenty of torque for a 36t sprocket on the back and I've had it up to 25 mph before. Now for some reason the chain loosened itself after every ride, but moving the tensioner back fixed that. The problem is that without me realizing, I've been riding around with the big gear on the transmission (belt drive) loose. Now I didn't notice this until after I gave it gas and the motor revved up and the bike didn't move. (its been working fine for a few days) Looking at the transmission I can see that the big gear driven by the clutch is spinning, but the sprocket where the chain is, isnt? I took the transmission cover off and took out the screw that was loose, put loctite, and put it back in. Now the bike engages yea, but it jumps in and out of gear out of nowhere. Like it accelerates normally then all of a sudden the engine revs super high without moving the wheel and jerks the bike forward (even though im at a decent speed already from pedalling) Can anyone help me out with this? I've literally only been riding this bike for 2 days and its my first build:(
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the gear on the right is the one im talking about

IMG_1916.jpg
 
1. do not ride it that way, you can do damage to the shaft if the screw is spinning or key-way is lose. Take it apart and see what is the problem.

2. chain new will stretch, it is normal. ..........Curt
 
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Technically those are called pulleys and it sounds like one of them is intermittently slipping on it's shaft. Looking at the pic it looks like the rear pulley may be mounted on a spline? That's not a likely place. The front pulley looks like it probably has a keyway? And that is a likely place. They can shear off.

I'd be looking in there ....
 
Are you a large person and are there very steep hills where you live ie 20+% grade? Unfortunately trying to pull large amounts of weight up steep hills with too high of a gear ratio something has to assist or give. The belt and/or clutch could be slipping due to overload.
 
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LR its a cog belt they don't slip, but ya think when i first read it 36 tooth is high, unless you are very flat ground, ..........Curt
 
curtisfox said:
LR its a cog belt they don't slip, but ya think when i first read it 36 tooth is high, unless you are very flat ground, ..........Curt
Click to expand...

That isn't exactly true about the belts not slipping. I've had chains slip on cogs when put under extreme overloads. Granted it does take a lot of over load for this to occur and the surface contact on the small wheel has to be very little. Still the same rule applies once overload threshold is reached either something has to assist or something has to give.
 
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Dawelny97 said:
Hey all. Im sorry for posting a new thread, I did it because no one replied to my old one no more (im new to the forum) But anyways, I got my 4 stroke motorized bicycle complete and I've been riding it a few times, its has plenty of torque for a 36t sprocket on the back and I've had it up to 25 mph before. Now for some reason the chain loosened itself after every ride, but moving the tensioner back fixed that. The problem is that without me realizing, I've been riding around with the big gear on the transmission (belt drive) loose. Now I didn't notice this until after I gave it gas and the motor revved up and the bike didn't move. (its been working fine for a few days) Looking at the transmission I can see that the big gear driven by the clutch is spinning, but the sprocket where the chain is, isnt? I took the transmission cover off and took out the screw that was loose, put loctite, and put it back in. Now the bike engages yea, but it jumps in and out of gear out of nowhere. Like it accelerates normally then all of a sudden the engine revs super high without moving the wheel and jerks the bike forward (even though im at a decent speed already from pedalling) Can anyone help me out with this? I've literally only been riding this bike for 2 days and its my first build:(
:-||.spr.
the gear on the right is the one im talking about

View attachment 103606
Click to expand...

After a little more thought on this and the fact you running a high gear ratio, you're having an engine strain problem. Chances are the slow downs occur on inclines even slight ones. People with shift kits will notice this and can even see it if they have a techometer. These 4 strokes like you have reach max horse power at 7000 rpm. Therefore a shiftkit user can shift to a ratio where WOT is 7000 rpm giving max speed for that particular location. If WOT is under 7000 then down shift to a ratio where it is 7000. If WOT is above 7000 then up shift till you at 7000.

Unfortunately you're a single ratio drive system with a small engine. Therefore get a larger rear sprocket and a techometer/hour counter. Then you can use the throttle to stay around 7000 rpm. If you're going up a steep hill you should have at least 5000 rpm where max torque is. If with assist you can't at least get 4500 rpm you risk damaging the clutch or other possible damages.

The hour counter is helpful for maintenance schedules. Change the oil ever 25 hours and clean the air filter every 10 hours. The techometer/hour counter is very affordable and easy to install.
 
Thanks for all the advice everyone. But taking the transmission of the engine and trying to figure out how to take the thing apart without breaking it even more took 4 hours but after all that I looked at the big gear and I took it out and there was this key thing I think its called woodruff im not sure. Here's a picture of it, that thing was so loose I could wiggle it with my finger. Anyways I got a small screw to hammer it with and tried to hammer the key back down. It went back down but it still kinda wiggled a little bit. Is it okay to ride it like that? Also LR Jerry thank you for the advice but I dont think its overstrain. I weigh about 174 and having the bike up to around 25 mph before puts the engine at a pretty high rpm, I can hear it as it pitches up in sound and it pitches up pretty high. Also when I first had it and the transmission actually worked this thing had so much torque I felt like I had built a warp drive bike
laffxct2

Well, until the transmission self destructed :(

My questions are these - I put the key back down as far as it would go but the key is still kinda wibbly wobbly but the actual transmission gear isnt. Is it okay to ride it like this? Also its a new engine so i dont know if that has something to do with it, but when I lift the wheel off the ground, it spins and the engine accelerates by itself. Is this normal? Also since the revs were pretty high @ 25 mph, I believe the top speed would be around 30-32 mph. Is this normal for a 36t sprocket? If it helps the engine I got is a huasheng 144f 53cc engine kit from ebay with belt transmission.

Oh one more thing - there are literally no hills in my area. Everything is flat, this bike has never seen a incline before
 

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Dawelny97 said:
Thanks for all the advice everyone. But taking the transmission of the engine and trying to figure out how to take the thing apart without breaking it even more took 4 hours but after all that I looked at the big gear and I took it out and there was this key thing I think its called woodruff im not sure. Here's a picture of it, that thing was so loose I could wiggle it with my finger. Anyways I got a small screw to hammer it with and tried to hammer the key back down. It went back down but it still kinda wiggled a little bit. Is it okay to ride it like that? Also LR Jerry thank you for the advice but I dont think its overstrain. I weigh about 174 and having the bike up to around 25 mph before puts the engine at a pretty high rpm, I can hear it as it pitches up in sound and it pitches up pretty high. Also when I first had it and the transmission actually worked this thing had so much torque I felt like I had built a warp drive bike
laffxct2

Well, until the transmission self destructed :(

My questions are these - I put the key back down as far as it would go but the key is still kinda wibbly wobbly but the actual transmission gear isnt. Is it okay to ride it like this? Also its a new engine so i dont know if that has something to do with it, but when I lift the wheel off the ground, it spins and the engine accelerates by itself. Is this normal? Also since the revs were pretty high @ 25 mph, I believe the top speed would be around 30-32 mph. Is this normal for a 36t sprocket? If it helps the engine I got is a huasheng 144f 53cc engine kit from ebay with belt transmission.

Oh one more thing - there are literally no hills in my area. Everything is flat, this bike has never seen a incline before
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Two things must be known to give you a mathematical speed at 7000 rpm. They are total reduction and wheel diameter.

So far all that's known is you're using a 36t rear sprocket. What size sprocket is on the transmission. If you don't know the reduction of the transmission then count the number of spines on each belt pulley and tell me what each one is.
 
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Okay, so I probably shouldn't have, but I went out for a ride. Everything worked the way it did, just like how when I first got it. But about a mile into my ride the stupid chain loosened up again and even worse, the chain sprocket started slipping again :( so now I know for sure that its that key thats bad. Also, I don't know if it has something to do with this but when I start accelerating past 20 mph, the entire bike starts vibrating really, REALLY bad. If I accelerate a bit more the vibration somewhat goes away, but should I be concerned with that? Also I should probably let you guys know that I have been riding around with a loose chain because it literally loosens itself every ride and I think if I fixed that none of this would have happened in the first place. So I've been looking around online for spare keys, and there's quite a bit on www.bicycle-engines.com. Would any regular old key fit on my transmission? I think those keys are for the 4g transmission but I dont have that transmission. I guess the one I have is an unbranded belt drive. But would the kit for the bicycle-engines transmission fit on mines? Man, I wish you didn't have to learn by breaking things
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Dawelny97 said:
Okay, so I probably shouldn't have, but I went out for a ride. Everything worked the way it did, just like how when I first got it. But about a mile into my ride the stupid chain loosened up again and even worse, the chain sprocket started slipping again :( so now I know for sure that its that key thats bad. Also, I don't know if it has something to do with this but when I start accelerating past 20 mph, the entire bike starts vibrating really, REALLY bad. If I accelerate a bit more the vibration somewhat goes away, but should I be concerned with that? Also I should probably let you guys know that I have been riding around with a loose chain because it literally loosens itself every ride and I think if I fixed that none of this would have happened in the first place. So I've been looking around online for spare keys, and there's quite a bit on www.bicycle-engines.com. Would any regular old key fit on my transmission? I think those keys are for the 4g transmission but I dont have that transmission. I guess the one I have is an unbranded belt drive. But would the kit for the bicycle-engines transmission fit on mines? Man, I wish you didn't have to learn by breaking things
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You can always make a larger key smaller. I personally like dealing Staton Inc

http://www.staton-inc.com/store/index.php?p=product&id=879
 
Okay guys so I was curious as to whether the key loosened up again, so I took of the transmission plastic cover, took of the screw where the key was, and there it was. To my utmost confusion, it was still in the same place that I hammered it down to before. So I guess I was wrong in it loosening up the last time I took it for a ride. I hammered it down and it stayed in place. But I still got the same symptoms as if it wasn't tight??? What in the world is going on. I notice now that when I pedal, the big gear doesn't move anymore.It's like the shaft it's connected to spins, but just spins in place. But I think it's slipping on the chain sprocket. I notice that when the engine is running the engine moves the big gear and the shaft, but not the chain sprocket. Does the chain sprocket have a key too? Or am I missing something here. Is it possible that I loosened up the chain sprocket while hammering down the other key? Now it's the chain sprocket thats slipping on the shaft. My question is does that have a key too? Here's a picture of the hammered down woodruff key on the big gear. The big gear and the chain sprocket spin independently of each other.
IMG_2051.jpg
 
I think you should take the hole shaft apart and check it, if you keep riding it will grind the shaft down, or the sprockets, and you will have to get a hole new one. Get new keys, you can find some at HomeDepot or other big box stores or ACEHardware ..........Curt
 
I looked at Grainger website for key stock and made my own key. The size I remember you go look and find, and then a surprise. There are two more shown if I remember right that are offset one slight smaller and one slightly larger. In any event having a slightly larger key and sanding it down to be very snug fit is they way I had done some. Also I have beside the steel keys I use, the engine flywheel key that is soft aluminum. It is supposed to be that way unlike the power output shaft. Don't mix them up.
 
From your picture, it looks like the pulley hole is worn, out of round.....
and the woodruff key is too small.

You might have to bore the pulley to the next size and install a sleeve.
If the hole is 5/8", have the machinist bore to 3/4".
You can buy them on ebay, like this one:

5/8" x 3/4" x 3" Shaft Adapter Pulley Bore Reducer Sleeve Bushing Sheave & Key

Oh, and have them cut a new keyway in the pulley.

Don't mess with damaged goods.

Inspect your sprocket and clutch for key damage and replace.

Update: It might be cheaper to buy a new pulley from bicycle-engines.com.
On the website, it looks like they have several different woodruff keys you can buy.

Maybe that's where your problem started.

You might've had the wrong key.
Your keyway might be short and tapered.
If it is, you'll need a key that's tapered, like the bow of a boat.
Place your woodruff key in the keyway without your pulley. This is to check how deep it goes in.

From the picture, it just doesn't look right and tight in there.
 
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