4-stroke 100cc

lmajo

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Feb 20, 2024
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Athens, GA
Hello all,

I recently have been daydreaming about cruising the mountainous gravel roads of my local national forest, wind in my hair, and whatnot. I love the idea of a dirtbike but even the cheap Amazon ones are outside my price range and will be for some time. I have looked into bike engine kits before, but have never seriously considered them because they seem finicky and I do not have the necessary tools or experience with engines. Now I think they are the cheapest way to accomplish what I want, so I figured it might be a good learning experience. My main concern is the hills; There are some long, steep climbs that I would prefer not to pedal up. I am considering buying a 100cc 4-stroke engine kit from Aliexpress. Will this engine provide enough power and torque to get me up these slopes without pedaling (I weigh 175 lbs)? I've read that the 4-strokes are more reliable but this kit looks bulky and weighs 46lbs. Would I even be able to pedal with this engine mounted? Would I be better off with the lighter 100cc 2-stroke? Are "China dolls" worth the hassle?

Thanks in advance for any responses
 
Fyi, my current build I have almost 1500 bucks into (and no, that's not because I have the money to spend. I am an unemployed high school student doing odd jobs for cash lol). It takes time and money to build thses things the right way. That being said, I understand the budget thing and I built my first bike pretty cheaply.

A few questions, how fast do you want to go? (the lower the number the easier we can get you a good gear ratio for climbing grades). Do you want to be able to stop on those hills? Do you have a welder?
 
Fyi, my current build I have almost 1500 bucks into (and no, that's not because I have the money to spend. I am an unemployed high school student doing odd jobs for cash lol). It takes time and money to build thses things the right way. That being said, I understand the budget thing and I built my first bike pretty cheaply.

A few questions, how fast do you want to go? (the lower the number the easier we can get you a good gear ratio for climbing grades). Do you want to be able to stop on those hills? Do you have a welder?
Haha, this definitely seems like a hobby that can become a money sink. In the future, I will surely buy a dirt bike but I thought this might be a budget-friendly way to achieve something similar. I would not consider myself a speed demon, but I would like for the bike to go 25-30 mph on flat ground without me worrying about the engine exploding. I understand that the hills will be slow but as long as I am going faster than walking speed I'll be happy. I do need to be able to stop on the hills and I do not have a welder.
 
Ok, this complicates things a bit. It's hard to get a good braking system for hills without discs. 25 to 30 is totally achievable.

I think we could use some help from @Sidewinder Jerry . He's a gear ratio wizzard and he has some experience with stopping on hills with rim brakes.
 
When it comes to mountian roads familiarity is by far the most important factor. For example: you don't want to be going down a steep hill 50+ mph only to discover there's a STOP 🛑 sign at the bottom of the hill. On certain roads where there's sharp curves etc techniques like bump braking needs to be used. In some locations I don't allow my down hill speed to exceed 15 mph. With rim or disc brakes high quality pads are what you should invest in. I use Kool-Stop E-bike pads. My life is worth the extra money 💵 they cost.

When it comes to rim brakes avoid water 💦 getting on your rims. Most definitely bump brake going down steep hills when a controlled speed is needed. This can keep you from overheating the rims and blowing out your tubes.

What you may want to consider is building a shifter bike or one with a CVT.
 
You may want to check in with the USFS or National Park service about operating that type of vehicle inside a National Park. There are often restrictions or equipment requirements that need to be met. Case in point, operating a dirt bike on trails in many parks, if they even allow it, requires an exhaust system with a USFS approved spark arrestor.

It also seems like you may want to temper your aspirations with reality. A Bicycle frame and chassis capable of the kind of off road use you are wanting is often not very suitable for motorizing. Remember, these are bicycles designed to handle the abuse of human power.

If long steep hills are in your future, then the standard 2 strokes are the least well suited to it mainly due to their potential to overheat when under high load at low speeds, and you will likely be at low speeds. Force air cooling is the only good solution for that issue, pretty much leaving you with the 4 stroke option.

Honestly, you may want to just save up some more and go with one of the cheaper dirt bikes. I have had a Hawk 250 since 2017, and aside from modifying every square inch of it, because that's just how I get down, it has been a fairly solid bike, and is perfect for light trail and road duty (as are any other bikes just like it, such as the Brozz 250, CSC TT250, etc). If you want something for jumps and hauling ass across whoops and such, I can point you at better bikes in a similar budget, but they aren't quite so good as on-road bikes.
 
Hello all,

I recently have been daydreaming about cruising the mountainous gravel roads of my local national forest, wind in my hair, and whatnot. I love the idea of a dirtbike but even the cheap Amazon ones are outside my price range and will be for some time. I have looked into bike engine kits before, but have never seriously considered them because they seem finicky and I do not have the necessary tools or experience with engines. Now I think they are the cheapest way to accomplish what I want, so I figured it might be a good learning experience. My main concern is the hills; There are some long, steep climbs that I would prefer not to pedal up. I am considering buying a 100cc 4-stroke engine kit from Aliexpress. Will this engine provide enough power and torque to get me up these slopes without pedaling (I weigh 175 lbs)? I've read that the 4-strokes are more reliable but this kit looks bulky and weighs 46lbs. Would I even be able to pedal with this engine mounted? Would I be better off with the lighter 100cc 2-stroke? Are "China dolls" worth the hassle?

Thanks in advance for any responses
I'll say this, by no means are these bikes perfect, but I will say the braking system especially with new Hydraulic setup of the 24' model is shockingly good, I just am tidying up putting a 224cc in mine, and it will stop 300lbs me @45mph quick and comfortably with hardly any effort.

The power stock is just Ok, since you are lighter, it'll do just fine.

Again, not perfect, but pretty good for the money.
 
I'd say don't get any kit with a bushing in the clutch they dry up fast and seize. The problem is they use plain brass instead of oillite. I would get a 49cc 4 stroke with tapered shaft and bearing mounted clutch. 4g trans is good for the 49cc. I'd use the stock transmission until it breaks then buy a 4g from grubee. The 49cc honda clone is decently lightweight I had 2 of them remember tapered shaft not 15mm with the bushing. They fit on hyper cruisers and some other bikes.
 
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