Thinking of a predator build and need opinions on the details

M

motor_bike_fanatic

New Member
My current build is a cranbrook with a 68.5cc china engine. I am thinking of having my buddy build me a 99cc predator build. to save money, I was thinking of using some parts off the cranbrook. My buddy has a schwinn cantilever frame, but its just a frame, no fork, no headset, no bearing cups in the bottom bracket. no wheels either. I was going to use the fork and wheels off the cranbrook, but only the front rim is original. the back rim is a coaster hub but with 12g spokes and is double walled steel, so should hold up fine. I have a rim brake on the front rim, I was thinking of using that on the predator build, but changing the pads to the kool stop salmon colored ones. I have an extra wide crank on the cranny bb, the kind they sell for use with the cent clutches on the china engines. will those clear the motor? I currently have a 44t rear sprocket, but would change that to a 56t for more torque. my buddy's predator bike does 46mph with the 56t rear and that is plenty fast enough for me. if I can use my wheels, fork and headset on the schwinn frame, that will give me the solid steel frame that a predator bike requires, but also save me a lot of money. 100 bucks for the engine, 300 for the transmission and motor mount, plus whatever the lighting system costs, because I want the same lighting setup he has, and 25 for the frame. that puts this bike at probably around 500 bones. I just need to know if I can use the fork, headset, and extra wide pedal crank on the schwinn frame.
 
I have found that most all cruiser type bikes have good interchangability of their parts. Sometimes you need to stick to the same fork steer tube sizes though.
 
Pedal crank shouldn't be any problem to interchange. Modern bikes with 1 piece cranks are all easily interchanged.
 
Probably will easily clear. On both my Predator builds, the engine fits high enough to clear the pedals. I re-bent them mainly to make them wide enough for my ankles to clear the engine width when cranking the pedas enough to cover the brakes LOL only pedaling ya need with these engines.).
 
ok cool. I am still on the fence about this. My current bike has plenty of speed for city driving at 31mph. I can actually break the speed limit, lol. It would cost me around 500 bones to build a predator bike. thats about equal to the cost of 5 or 6 replacement china engines. I cant make up my mind about it. I know a predator engine will have plenty of torque and outlast a china engine by ages, but even with a 56t sprocket, im still gonna do over 40mph.
 
Once you drive one of these, you'll start loosing intrest in the 2 strokes.The torque! the power! The throaty sound! The tractability! The reliability! The no premix!

All the stuff that the Happytime's dont have..

I would do the math, and gear it for about 38-40 at 5000 rpm, for rural or urban use, to allow for a relaxed cruise at 30 mph.
If you do a lot of stop and go in the city as I sometimes do, then geared for 35 at 5000 works good.
 
my buddy has the qmatic drive with 24 inch wheels and a 56t rear sprocket. he does 46 top speed. I have 26 inch wheels and was thinking a 72t rear sprocket would give me somewhere in the neighborhood of 30 top speed, which is fine with me, and with a 72t sprocket, the bike would probably drive up walls lol. I dont know exactly how to do the math. for one thing, I dont know how many teeth the qmatic drive has, not to mention that since its a gearbox, it has its own gear reduction. I also dont know how gear ratio and rpm's relate to each other to give you your top speed. I am just guessing with the 72t rear. sprocket. all i know is i dont want to go any faster than 35mph top speed. torque is what i am aiming for. being able to climb any hill without pedaling is something i have yet to accomplish with a rice burner, and I doubt I ever will.
 
26" wheels and a 72 tooth will cruise at 30 all day long ;)
I have had mine up to 35.8 by my speedo (didn't stay there very long)

the torque is what I am digging, I can pull the girls/trailer up any hill in town, even some I couldn't go up solo with the HuaSheng :)
 
motor_bike_fanatic said:
my buddy has the qmatic drive with 24 inch wheels and a 56t rear sprocket. he does 46 top speed. I have 26 inch wheels and was thinking a 72t rear sprocket would give me somewhere in the neighborhood of 30 top speed, which is fine with me, and with a 72t sprocket, the bike would probably drive up walls lol. I dont know exactly how to do the math. for one thing, I dont know how many teeth the qmatic drive has, not to mention that since its a gearbox, it has its own gear reduction. I also dont know how gear ratio and rpm's relate to each other to give you your top speed. I am just guessing with the 72t rear. sprocket. all i know is i dont want to go any faster than 35mph top speed. torque is what i am aiming for. being able to climb any hill without pedaling is something i have yet to accomplish with a rice burner, and I doubt I ever will.
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If you were to run a Q-Matic with a 2-1/2" front drive pulley, and a 72t rear sprocket, your gear ratio would be 14.4:1 which would give you 26.9mph at 5,000rpm. You would have plenty of climbing power for any hills you encounter.

dnut
 
is 5000 rpm the max on a predator? my current bike has a top speed of 31. I want my predator bike to do around that, so if 5000 rpm is the max for a predator, then I should go with a slightly smaller rear sprocket. 64t, perhaps? unless 5000 isnt the limit on a predator. then a 72t will be fine.
 
motor_bike_fanatic said:
is 5000 rpm the max on a predator? my current bike has a top speed of 31. I want my predator bike to do around that, so if 5000 rpm is the max for a predator, then I should go with a slightly smaller rear sprocket. 64t, perhaps? unless 5000 isnt the limit on a predator. then a 72t will be fine.
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5000 seems to be a safe limit on a stock Predator. I have wound mine to 6000 but it's scary.

You will prolly 14:1 too low for normal street use for this engine unless you need to drag stuff outta the woods with it.

I have my latest
preddy 2 speed geared at 10.75 to one in high, and I easily climb some very steep and long hills on my road. I'm getting about 35 mph at 5000 and can cruise all day at a rather busy 4200 and 30mph, although I think 3600 cruise at 30 is what I'm gonna change to. That'll give me a relaxed cruise rpm and about 38 mph at 5000.. I live in a rural area and I need a lil taller gearing.
Something like 11:1 will prolly suit your needs well with this lil engine.
 
scotto- said:
If you were to run a Q-Matic with a 2-1/2" front drive pulley, and a 72t rear sprocket, your gear ratio would be 14.4:1 which would give you 26.9mph at 5,000rpm. You would have plenty of climbing power for any hills you encounter.

dnut
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How about a 2&1/2" front pulley and a 44t rear sprocket at 3600 rpm? what kind of speed and torque would that give me? thinking of keeping my current rear sprocket and not removing the governor.
 
motor_bike_fanatic said:
How about a 2&1/2" front pulley and a 44t rear sprocket at 3600 rpm? what kind of speed and torque would that give me? thinking of keeping my current rear sprocket and not removing the governor.
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That combination would give you an 8.80:1 gear ratio and a top speed of 31.6mph. Torque I'm not sure of but you should still be able to pull decent size hills ok. The gearing is a little on the tall side but worth trying.

dnut
 
So, why aren't you disconnecting the govenor? These lil engines mak WAY more power at up tp 5000 rpm very reliably. The only reason the govenor is there is for this engine to run at a standard, automatic constant rpm for lawn equipment, stationary use ect.
There's no govenors on any production motorbikes for a reason. The driver is the govenor. The stock gov. limits available power.
It also limits available usable rpm range.

The average cent clutch engages and locks up around 2400 rpm. With a govenor that would leave you only 1200 rpm usable range, so performance is gonna be very limited. compared to the same engine without a gov.

You do not have to diamantle the engine and remove anything internal like some here say . There's plenty of running stock engines with govenors disconnected externaly, haven't heard of any problems happening here yet. Just the naysayeres sayin what COULD happen.
 
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not sure what im gonna do yet. trying not to spend more money than I have to. a different size sprocket means more money. the engine, gearbox and motor mount comes to $400. Im getting a frame for $25. muffler is another 36.
 
scotto- said:
That combination would give you an 8.80:1 gear ratio and a top speed of 31.6mph. Torque I'm not sure of but you should still be able to pull decent size hills ok. The gearing is a little on the tall side but worth trying.

dnut
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How about that same gearing at 5000 rpm? what speed would that give me? I am thinking somewhere in the low 40's. Would that let me climb hills ok?
 
43.9mph. With the engine turning 5,000rpm, as opposed to 3,600rpm, I would say it should climb hills much better. The 99cc Predator has ample power for a properly geared bicycle used on the street, especially when compared to an engine with half the displacement such as the HS 49cc, which works quite well.

dnut
 
the transmission I am going to use has a 22t input sprocket and a 9t output sprocket. I am going to use a maxtorque clutch with a 12t sprocket. I used a gear ratio calculator and came up with a final gear reduction of 8.96:1. at 5000 rpm's i would have a speed of 43.1. Did I do the math right?
 
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