First build: Two stroke 80cc mountain bike with jackshaft

Hey guys! Glad to have found this place.

This week, I started my first build, a Wildcat PK80 with a Sick Bike Parts jackshaft kit. The base is a 1997 Gary Fisher Mamba that belonged to my mother...she was about to throw it out, but I saved it from this grisly fate to give it a second chance. Right now I'm waiting on the right size chain breaker to show up; in the meantime, I plan to hang out here and pick up whatever tips and tricks I can.

Eventual plan is to add a complete electrical system with headlight, brake light, speedo, and horn, possibly with a dynamo. The grip shifter dangling off there will most likely become a tank shifter.

 

[rover528]

No doubt, if you are approaching a steep hill it's best to peddle as much as possible and get as much speed up as possible before hitting the hill and you can keep peddling to help keep the RPMs has high as possible while going up.

Sick I love it.

 

[rover528]

No doubt, if you are approaching a steep hill it's best to peddle as much as possible and get as much speed up as possible before hitting the hill and you can keep peddling to help keep the RPMs has high as possible while going up.

Can I actually shift my own sprockets manually while pedaling and the Motor running.

 

[FurryOnTheInside]

If you are running the basic set up, with the engine having its own separate single speed fixed drive sprocket, then your bicycle's gears are completely unaffected.
You can help all the time if you have the ratios to keep up with the bike.

Although you are by far the weaker engine when it comes to power output, you can stand all your weight on the pedal and that does help in a way that you can feel and enjoy and the engine seems to be enjoying it too and responding positively to you, because that little bump in RPM makes it put out more power, and that can be enough to go from a steady or decelerating climb to an accelerating climb.

It is a very fun way to ride at any speed. You need like a 52t to 11t top gear to run out of legs around 34mph.
You are not adding anything to your speed by pedaling frantically at 35mph though. It takes such an exponential amount of power to add more speed by this point and you're not making any torque once you are struggling to keep up and put your weight into the pedals.
You are however, keeping yourself warm and enjoying kicking your legs and feeling as if you're powering your bike naturally, in the same way you have learned to ride your bike since you were a kid.

I really wanted a uniquely geared bike just perfectly set up for my rides, with a genuine Shift Kit from the USA, but I wanted to get motorised quicker than I could save up money for what I wanted to do with that.
I am glad that I got to experience this way of doing the motor assisted bicycle.
The two stroke engine is strong enough to bump start going uphill and then accelerate up the steepest part of my local coastal trail, with my assistance.
It isn't geared for hill climbing because the trail is 99% flat, just has a couple of very sudden changes in the elevation of the coastal path as it goes from sandy beach to rock/ cliffs.


Later, when you try the Shift Kit (or something that you create with the Sick Bike Parts parts) it will be fun to experience closing the throttle and freewheeling without any drag to slow you down.

 

[rover528]

If you are running the basic set up, with the engine having its own separate single speed fixed drive sprocket, then your bicycle's gears are completely unaffected.
You can help all the time if you have the ratios to keep up with the bike.

Although you are by far the weaker engine when it comes to power output, you can stand all your weight on the pedal and that does help in a way that you can feel and enjoy and the engine seems to be enjoying it too and responding positively to you, because that little bump in RPM makes it put out more power, and that can be enough to go from a steady or decelerating climb to an accelerating climb.

It is a very fun way to ride at any speed. You need like a 52t to 11t top gear to run out of legs around 34mph.
You are not adding anything to your speed by pedaling frantically at 35mph though. It takes such an exponential amount of power to add more speed by this point and you're not making any torque once you are struggling to keep up and put your weight into the pedals.
You are however, keeping yourself warm and enjoying kicking your legs and feeling as if you're powering your bike naturally, in the same way you have learned to ride your bike since you were a kid.

I really wanted a uniquely geared bike just perfectly set up for my rides, with a genuine Shift Kit from the USA, but I wanted to get motorised quicker than I could save up money for what I wanted to do with that.
I am glad that I got to experience this way of doing the motor assisted bicycle.
The two stroke engine is strong enough to bump start going uphill and then accelerate up the steepest part of my local coastal trail, with my assistance.
It isn't geared for hill climbing because the trail is 99% flat, just has a couple of very sudden changes in the elevation of the coastal path as it goes from sandy beach to rock/ cliffs.


Later, when you try the Shift Kit (or something that you create with the Sick Bike Parts parts) it will be fun to experience closing the throttle and freewheeling without any drag to slow you down.

Ya. I have a fairly steep hill leaving my home and will need to see if it can make the hill by itself or if I'll need to assist in a lower pedaling gear. I'll have to wait to find out the answer to that one.

 

[FurryOnTheInside]

You should be geared high enough that you have to stretch your legs and provide some extra torque on the steepest section of your route, otherwise you would have geared your engine low for the rest of your route. You would be running it at its top rpm, limited by its port timing instead of the load on it.
With that low load most of the time, it isn't good for "breaking in" your new cylinder and rings or much fun to ride as you'll keep coming up against your top rpm which never changes.
It is really nice when you can feel your engine pulling against a high load, and when a single hard pedal stroke speeds the engine up a bit and it pulls even harder.

 

[rover528]

You should be geared high enough that you have to stretch your legs and provide some extra torque on the steepest section of your route, otherwise you would have geared your engine low for the rest of your route. You would be running it at its top rpm, limited by its port timing instead of the load on it.
With that low load most of the time, it isn't good for "breaking in" your new cylinder and rings or much fun to ride as you'll keep coming up against your top rpm which never changes.
It is really nice when you can feel your engine pulling against a high load, and when a single hard pedal stroke speeds the engine up a bit and it pulls even harder.

Thanks Furry. I'm looking for a 38 tooth sprocket for my mountain bike with 26" tires.

 

[HumanPerson]

Thanks Furry. I'm looking for a 38 tooth sprocket for my mountain bike with 26" tires.

Manic Mechanic

 

[HumanPerson]

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[Tyler6357]

Can I actually shift my own sprockets manually while pedaling and the Motor running.

Furry is right. The peddle chain has nothing to do with the engine drive, peddling will only help the engine. In fact, often when I'm going down a steep hill where I don't need the engine I will cut it off and hold the clutch handle in and just glide down the hill to save gas only using the peddles if needed.

 

[FurryOnTheInside]

I'm sure they make tuffer shift on the fly kits for those of us that are hard on gears. Lol

View attachment 95622

Pretty sure that this will be my FSB once we do some aluminum fab work...

Plus we can add the jack shaft kit at the same time,,, my fab dude will add motor mounts at same time,,, reinforce things is a good idea...

Don

You're doing aluminium fabrication? and heat treatment? And a real full suspension 2 stroke through a genuine SBP Shift Kit powered bike.
I look forward to that build thread!

I must find someone to weld my very basic Chinese high tensile steel 26"x4" fatbike frame. It isnt suspension but its probably as usable (or more, and certainly easier to design the build) than a short travel/springer/soft-tail mid 90's LTS.

I need a loner welder who is still able to work in isolation through this "end times". My dropouts are only thin plate, but I got a serious cassette driven (geared) E-motor hub especially for the build to take the load from thd right hand chain.
So that probably has greater strength than my toy fatbike frame! It is 190mm width hub versus the frame's (odd) 197mm, too.
I need a loner welder fabricator to make a thick pair of dropouts from some chunky plate had already has, and weld them in. Plus do a bit of reinforcement for my head tube.
I will need a pipe put together from the pieces I have been collecting, too.

I have purchased a Chinese jackshaft kit (a low quality knock off of the earliest SBP Shift Kit design, with subsidised carriage courtesy of the Chinese Communist Party and no taxes and fees on entering UK) because shipping steel parts plus tax/fees from USA to UK is prohibitively expensive for me.
I really need to get at least the Ultra Heavy Duty dual bearing freewheel from SBP in the USA, so I can be confident in its suitability to support all the axial load in all the (1x8 Sramano gripshiftshadowplus) gears.
But that has a build thread too! I'll write it when I put the effort in to find a loner welder fabricator who is able and available and close enough to me that I can get my frame to him.