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.

 

[Captain Rainmaker]

Was riding home the other night from a nice dinner out. Got most of the way home and the motor just quit and refused to start back up (felt like it was down on compression, figured the head gasket blew or something). Tore it apart a day later and found this.

RIP.

It would appear the wrist pin clip popped out. You can still see a piece of it stuck in the bore. I don't think any of it wound up in the bottom end--the crank still spins smoothly and I can't hear anything rattling around--but before I return the motor to service, I'm going to check thoroughly.

Anyway, does anyone have any experience with this kit here? I know I'd need a windowed piston to go with it (which is fine; I need a new one of those anyway), but it'd be a great way to kill two birds with one stone: replace my ruined top end and bump the power up a bit.

Zeda 80 Dio Reed & OKO Carb Performance 2 Stroke Bicycle Engine Bike Motor Upgrade Kit

Your source for 2-Stroke and 4-Stroke Bicycle Engine Kits, Performance Parts, and Accessories!

www.bicycle-engines.com

 

[Wrench]

I've heard many stories of the piston pin cir clip popping off and doing damage.
I guess CG engines have cheep cir clips and need to be replaced with quality cir clips before ya even start any of their engines

 

[Chainlube]

Was riding home the other night from a nice dinner out. Got most of the way home and the motor just quit and refused to start back up (felt like it was down on compression, figured the head gasket blew or something). Tore it apart a day later and found this.

View attachment 102221

RIP.

It would appear the wrist pin clip popped out. You can still see a piece of it stuck in the bore. I don't think any of it wound up in the bottom end--the crank still spins smoothly and I can't hear anything rattling around--but before I return the motor to service, I'm going to check thoroughly.

Anyway, does anyone have any experience with this kit here? I know I'd need a windowed piston to go with it (which is fine; I need a new one of those anyway), but it'd be a great way to kill two birds with one stone: replace my ruined top end and bump the power up a bit.

Zeda 80 Dio Reed & OKO Carb Performance 2 Stroke Bicycle Engine Bike Motor Upgrade Kit

Your source for 2-Stroke and 4-Stroke Bicycle Engine Kits, Performance Parts, and Accessories!

www.bicycle-engines.com

You don't absolutely need a windowed piston but a good expansion chamber exhaust is needed.

 

[Captain Rainmaker]

You don't absolutely need a windowed piston but a good expansion chamber exhaust is needed.

I already have the SBP exhaust, but I could never quite get it to stop leaking. There's a good looking MZ65 clone on that same site; might be time to upgrade.

 

[Chainlube]

I already have the SBP exhaust, but I could never quite get it to stop leaking. There's a good looking MZ65 clone on that same site; might be time to upgrade.

You can put double gaskets to keep it from leaking. I make my gaskets from Fel-Pro exhaust gasket sheets and put them back to back, they seem to compress perfectly that way.

 

[Captain Rainmaker]

You can put double gaskets to keep it from leaking. I make my gaskets from Fel-Pro exhaust gasket sheets and put them back to back, they seem to compress perfectly that way.

That's not quite the issue. The SBP exhaust has a handful of different pieces: the muffler, the J pipe, some bits of copper plumbing pipe, and the flange. The copper pipe bits are supposed to connect the J pipe and the flange and allow you to "tune" the exhaust to an extent by changing their length, but I've tried a number of ways to get them to seal properly to each other and to the J pipe (short of just welding them) and none of them held up.

 

[Frogslayer]

I've heard many stories of the piston pin cir clip popping off and doing damage.
I guess CG engines have cheep cir clips and need to be replaced with quality cir clips before ya even start any of their engines

You need to at the very least orient them correctly

 

[Chainlube]

That's not quite the issue. The SBP exhaust has a handful of different pieces: the muffler, the J pipe, some bits of copper plumbing pipe, and the flange. The copper pipe bits are supposed to connect the J pipe and the flange and allow you to "tune" the exhaust to an extent by changing their length, but I've tried a number of ways to get them to seal properly to each other and to the J pipe (short of just welding them) and none of them held up.

s**te design.

 

[Captain Rainmaker]

Update time.

New parts:
-Cloud9 saddle
-Rock Bros cargo rack (More for aesthetics than anything else, though I plan to add a basket and a toolbox.)
-MZ65 clone from bicycle-engines (Actually a pretty nice MZ65 replica; the whole thing's made of 1/8" steel, and the welds, while not pretty, don't show any signs of cracking or porosity. I did have to file down one of the cooling fins on the cylinder head to make clearance, though.)
-DIO reed and OKO carburetor (I know the OKO isn't everyone's favorite, but it came with the new jug so I'm gonna try to make it work. Already have a jet kit.)
-Windowed piston
-12-volt stator
-Light and horn switch (Had to remove the grip to get it on, and since it was the Chinesium grip that came with the kit, I figured I'd just cut it off. Ordered some moped grips from Treatland to replace them.)

I've also ditched the silly screwdriver shifter and went for a more sensible Shimano Tourney thumb shifter.

More plans:
-The front fork is shot, and the rim brakes aren't far behind. New front fork is inbound, along with a TRP HY/RD mechanically actuated hydraulic disc brake for the front. Figured it was a good way to kill two birds with one stone.
-CDI with adjustable timing curve. Looking at Jaguar's but am open to suggestions.
-Considering a different tank, either on the top tube or the rack.
-Electrical system. It'll be fairly simple: low and high headlights, taillight, brake light, and horn. I plan to add a small 1 or 3 amp-hour lead-acid battery and use the 12-volt stator to keep it charged. I've put together a simple little rectifier/regulator for that purpose.

-Still debating whether or not to spring for an internal gear hub. I've been screwed a fair number of times by broken or tangled chains, and I find myself skipping gears with the 7-speed just because the ratios are so close together. If I were to get something like a Sturmey Archer 3-speed, I could run a stouter chain and still have the same or better ratio spread as the 7-speed. But my budget has already ballooned, so I think for now I'm going to hold off and re-evaluate once it's back up and running again.