first four stroke build - advice needed

[Toby woodman]

having been thinking about buying a four stroke kit. I have decided that the transmission on those kits is just not up to the task. I thought about a jackshaft or shift kit but I think the engine would get in the way of a shift kit. I have decided to build a bike using a 79cc vertical piston engine made by lifan. it is a lifan 152. I will mount the engine in the centre of a frame and use a 5/8 bore centrifugal clutch which goes to a 32 tooth jackshaft sprocket mounted behind the seat post. the jackshaft output sprocket will be a 12 tooth sprocket and that will drive a 36tooth sprocket on the back wheel. this gives me about a 29 mile per hour top speed. this setup it is similar to what is used on the phatmoto rover bikes. I'm just wondering whether this setup will have enough power to push me up sustained gentle hills (I'm not very heavy). advice on any tips with engine mounting would be appreciated.

 

[Sidewinder Jerry]

Don GruBee makes a 5G transmission for a Predator engine. Performance wise they're similar to the Lifan 152. His recommended total reduction for flat land and lite riders is around 18.6\1 for a speed around 15 mph on 26" tires. For steep hill country he suggest a total reduction around 24\1 for a speed of 11 mph on 26" tires.

SkyHawk 4 Cycle________ ENGINES, KITS AND PARTS

GruBee Skyhawk T Belt drive 4G transmission kits and service parts for motorizing standard bikes and also Multi Speed Shift for Gru-Bee Gt2A frames with built in Gas tanks.

www.grubee.net

Since the 2 engines are similar Performance wise; research past threads on both to find out what past builders said worked best for them.

 

[Toby woodman]

I’m more concerned about being able to climb a sustained hill at a decent speed not really steep. Just moderate. Surely a 36 tooth sprocket would give similar performance on hills to a two stroke bike with a 44t.

 

[Toby woodman]

With the setup I said above. A 36 tooth sprocket gives me about 30mph top speed with enough torque with an engine like that for gentle hills

 

[SirLurksAlot]

I run a lifan 152f-3. Phatmoto all terrain. At 4000rpm and stock gearing, i get 22mph max (enough for me and keeps me legal in my state), with enough oomph to climb most grades well. Disable the governor and 31mph is possible, but i can't recommend that myself. Over 5000rpm, and the lifan isn't happy with that. Sounds like it's over revving and lifespan is reduced enough to matter. My original lifan is worn out from doing that, after less than 2 yrs of light use. The Predators might tolerate that better, but i have no experience with those so i cannot say yay or nay about them in this regard. Hope this helps!

 

[Sidewinder Jerry]

I run a lifan 152f-3. Phatmoto all terrain. At 4000rpm and stock gearing, i get 22mph max (enough for me and keeps me legal in my state), with enough oomph to climb most grades well. Disable the governor and 31mph is possible, but i can't recommend that myself. Over 5000rpm, and the lifan isn't happy with that. Sounds like it's over revving and lifespan is reduced enough to matter. My original lifan is worn out from doing that, after less than 2 yrs of light use. The Predators might tolerate that better, but i have no experience with those so i cannot say yay or nay about them in this regard. Hope this helps!

What was your total reduction and did you use 26" tires?

Math wise to do 22 mph on 26" tires at 4000 rpm the total reduction would be around 14.06\1.

By standard do you mean

10>[32/10]>44 ????

 

[ImpulseRocket]

I run a lifan 152f-3. Phatmoto all terrain. At 4000rpm and stock gearing, i get 22mph max (enough for me and keeps me legal in my state), with enough oomph to climb most grades well. Disable the governor and 31mph is possible, but i can't recommend that myself. Over 5000rpm, and the lifan isn't happy with that. Sounds like it's over revving and lifespan is reduced enough to matter. My original lifan is worn out from doing that, after less than 2 yrs of light use. The Predators might tolerate that better, but i have no experience with those so i cannot say yay or nay about them in this regard. Hope this helps!

Over 5k rpm and it's probably floating the valves. Not that I would want to spin that motor a whole lot faster, but some heavier valve springs would likely tame the valve float.

 

[Toby woodman]

when people tank about gear rations and hill climbing torque. The only other motorised bike I have is a 66cc two stroke with a 44 tooth rear. Comparing the four stroke with a 36tooth which would make the bike top out at 29mph. How much better or worse would the four stroke be than the two stroke with a 44t

 

[Sidewinder Jerry]

when people tank about gear rations and hill climbing torque. The only other motorised bike I have is a 66cc two stroke with a 44 tooth rear. Comparing the four stroke with a 36tooth which would make the bike top out at 29mph. How much better or worse would the four stroke be thank the two stroke with a 44t

You need to keep in mind though both the L-152 and a China girl have around 3 hp; the China girl is turning around 6000+ rpm VS the L-152 turning around 3600 rpm. It's sort of like a bicycle do you pedal slower/harder in a higher gear or do you pedal faster/easy in a lower gear?

 

[Toby woodman]

if you were comparing these setups. which would you think would climb sustained gradual hills better