Predator/Cranny 2 speed

[professor]

4 to one is high gear in an old drag car. 9 to one would be good for cruising at speed, would still be sluggish off the line.
I think my bikes are in the 12-1 zone and top out at about 35, wound out, but I don't like to go that fast often. Using a 79 HF and 3 speed on one, and 212 HF single speed on the other.
The bigger the number in your ratio- the more the engine torque is multiplied but the slower you can go- just like in a car.

 

[wayne z]

8.89 is more torque at the wheel, but still a little o the tall side for good take-off performance and hill climbing.
Although, the preddy will have no trouble with the hills if you can hit them running. The ratio on my 40mph video bike is 10.8:1 . It easily accellerates on the steep hills here.

The ratio on the first bike is 9.75:1 in high gear. I had sorta sluggish take-off at this ratio but excellent cruise, so this was the bike that inspired me to add a low gear belt set to the belt/idler clutch/ friction drive tranny that I came up with on that build.

My opinoin, is that the ratio of around 10.8:1 is perfect for the 99cc Preddy with a single speed drive. It runs out of umph at 40 mph, plenty too fast , has impressive take off speed, and cruises 30 at 4200 all day. The lower gearing gives way less clutch slipping and wearing from take-off, and no pedaling at launch needed at all.

For economey right now, go ahead with your AGK plan. No extra stuff to buy now and the taller gearing uses less gas per mile. You could easily and cheaply change ratios later if you decided it's needed.

 

[motor_bike_fanatic]

all I would need to do is go to a bigger rear sprocket. if I dont like the 44t, I can go to a 56t.

 

[motor_bike_fanatic]

agk sells two versions of the maxtorque clutch, the standard version engages at 1800 rpm, the other version engages at 2200. would 2200 get me off the line better than 1800? would my hill climbing suffer?

 

[motor_bike_fanatic]

the higher rpm version will only end up costing me $5 more, but I am having trouble with the math I think. the site says the jackshaft has a 22t input sprocket and a 9t output sprocket. the clutch comes in 12t or 13t, and my rear wheel is 44t. can someone tell me the ratio, both with a 12t and a 13t clutch?

 

[wayne z]

The 12 t equals 8.96:1 = 43.1 mph at 5000 rpm.

The 13t equals 8.27:1 = 46.7 at 5000 rpm.

Personally, I would go with the 12 tooth.

 

[motor_bike_fanatic]

I was doing the math right then. 8.96:1 is twice the torque of 4.40:1, correct? and the clutch engaging at 2200 rpm will get me off the line better than 1800? how will that affect climb?

 

[wayne z]

You will need the 2200 clutch, the Preddy normaly needs to idle around 1800-2000 to keep the automatic compression release de-activated and for a smooth idle. The clutch won't have any effect on hill climbing.

Yes, those numbers mean twice the torque at the wheel.

 

[motor_bike_fanatic]

ok sounds good then

 

[motor_bike_fanatic]

is there a cheap and easy way to mount the motor without buying a plate kit? I read some other threads where people used angle iron and such from home improvement stores. that would actually save me some money vs buying a plate kit. the cheapest plate is 35 on ebay and i dont know if the holes are spaced right for the preddy. its sold by boygofast. not that 35 is a lot of money. i just dont want to buy it and find out it wont work. if someone knows if it will work, i will probably just get it anyway. its slotted to adjust the engine position. cant slot angle iron lol

 

[wayne z]

I used the BGF mounts on both mine. I had to ust two pieces of strap steel bolted to the engine parallel with the crankshaft, and drilled and tapped 1/4" bolt holes in the straps to bolt the engine mount. Had to use spacers on the bolts to the mount, to allow clearance for the engine base bolts.

I also had to tap the mount adjustment bolt holes to 1/4" because the lil metric threaded holes were weak and stripped easily, plus, I moved 2 of the holes on one end to get a little more extension of the mount..

Some people bolt on the angle irons and use the straps on that to get the engine mount width they need.
A rectangular plate could also be used instead of 2 straps.

You can slot angle iron low tech by drilling 2 holes short distance apart and cut out between then with a dremel and the good reinforced cut off wheels.

 

[motor_bike_fanatic]

so either way, its gonna take some finagling to get the motor on. i am definitely gonna need help with this.

 

[motor_bike_fanatic]

still curious about the gear ratio and torque. 8.96:1 is twice the torque of 4.40:1, correct?

 

[wayne z]

Yes, that is right.

 

[motor_bike_fanatic]

I should be fine for hill climbing then. I only have to pedal when I dont hit a hill running as it is. this is going to work out great.

 

[motor_bike_fanatic]

I have a front rim brake on my cranny. Do you think if I get the kool stop salmon colored pads, they will be good at stopping me once I install the predator? I cant afford a drum brake right now.

 

[moonerdizzle]

If you can find them buy the green Diatech Gordo pads. They are soft compound, last quit a while for being as soft as they are, and still work great wet or dry. They are the only brake pads I use on my BMX. Only down side is once and a while they make noise while stopping. But they work very well on painted and aluminum rims.

 

[motor_bike_fanatic]

those seem to be cheaper than the kool stop pads, but are they as good? they may work on a bmx, you didnt say if it was motorized, but will they stop a bike going anywhere from 25-45mph without wearing too fast?

 

[moonerdizzle]

They.last about a year on a bmx, and that's doing abubacas and tail taps every day. I also ride trails and dirty jumps and you get cruising pretty fast when you start pumping doubles and I never worried about if they would stop me. I would imagine they would do fine on a set of 26 inch rims at speed. Considering a20 rim is spinning faster than a26 inch rim going the same mph.

 

[wayne z]

Hi guys, it's time for us to speak up now. Our advice and our opinion is starting to get skewed here. I'm not going to jump on a belt drive vs. chain drive debate here. We've used both systems and we like both for different reasons.

The belts are smooth and quiet and we like that. The belt and jackshaft mounted clutch combination slips more on engagement versus a chain drive with a clutch mounted on the output shaft. Again, this is a good thing for a smooth take off from a standing start.

The jackshaft with chain drive has a very positive engagement (limited slippage). The clutch locks up quicker when it's on the output shaft of the engine because it's spinning faster than it would be if mounted on the jackshaft. As a result the shoes fly out with greater speed and provide a solid lock up. I'm not saying this is better...it's a difference we have noted in the two designs which relates to a difference in feel and performance.

We've built several bikes using both systems. Some of our customers would prefer the belt drive for its feel and smoothness. Others, like us, would prefer the chain drive. We are more focused on racing our bikes and chain is what works best for us on the track. Not saying chain is the best system...just our preference for our application.

As far as maintenance is concerned we've had to replace several belts for our customers as well as several chains. The belt change is a messy job as belt dust is everywhere and gets all over your hands. Changing a chain is no fun either as you get chain lube all over your hands. The chain will last a long time as long as you keep it lubed and maintained. And just like the EZM guys discovered with belts, if you use a quality chain it will last much longer than a cheap chain. Chain noise is not an issue for us. If the chain is aligned, lubed and the tension is set properly the chain will not be noisy. Most of us are using a chain secondary.

Those of you who have met us know we're a pretty easy going group. We're not going to put down anyone's product. We are an EZM dealer and currently have a Q-Matic with a custom shaft length for a new project. We own and ride bikes with belt and chain drive systems.

Sorry this went off topic Wayne. We've been watching your two speed as we've been playing with one too. We hope to meet you at a ride or race so we can talk bikes together. You are knowledgeable and give good advice on this forum.

Thanks Shayne, for the great post with all the info, and thanks for setting us straight.
I may have spoken out of turn by saying that I dissagreed, and assuming that you had no experience with belt drives.
I have great respect for you and your company and the dillegent research you guys are, and have been doing, on MB powerplants and drive trains. Kudos, and please keep it up :~)
We need more choices for drive trains for these things. Chains, belts, gears whatever, If it can be done, someone here will sooner or later think of it and try it.