2-Stroke Gas Bike Build

[blsnelling]

No, it's not a chainsaw, but it is a 79cc 2-stroke none the less. These are super cheap Chinese clone engines used on "gas bikes" or "motorized bicycles". They're typically built on cruiser bikes like those you can get from Walmart as cheap as $80. The engines come in a kit that includes EVERYTHING needed to build a gas bike. These kits run about $90-$130.

My brother built one of these over his Christmas break. He has a total of $150 in his.

 

[blsnelling]

After helping my brother with his, I decided that I wanted one. I found that there are many different versions of these engines. There are different strokes, bore, rod lengths, pistons, and cylinder heights. After much research, I went with a Zeda 80 engine. It has the longer rod, longest stroke, and biggest bore. It also has several other upgrades that set it apart.

http://www.bicycle-engines.com/Firestorm-Z80-Complete-80cc-Bicycle-Engine-Kit.html

 

[blsnelling]

I've also decided to upgrade several of the components that come in the kit. I've purchased the following parts separately.

1. Spring loaded chain tensioner
2. CNC high compression head
3. CNC rear hub adapter
4. CNC front engine mount

 

[blsnelling]

I purchases 3 different pipes to try out. We haven't had a chance for any definitive testing, but here they are.

This pipe is WAY louder than I want. I plan to put a silencer on it.

I have two different versions of what they call a banana pipe. This one is much better fit to the frame and has butt welded seems on the pipe.

Here's the other version. It doesn't fit nearly as tight and the pipe sections are like welded flanges.
`

 

[blsnelling]

Here's the bike I bought. It's a 7-speed Schwinn that I picked up for only $60 off the FB Marketplace. I installed the white wall tires, chrome springer forks, and new fenders. The originals were rusted. The rest of the bike cleaned up really nice. I've cleaned and greased both axles, bottom bracket (crank), and the headset (fork bearings). Even after these mods, I still only have $130 in this bike.

 

[blsnelling]

Here's my engine. It does not come with the chain tensioner that's on it or the billet intake.

One thing I love about these is how cheap they are to work on. This billet intake manifold was only $10.

Here's the billet front engine mount.

This is the billet sprocket adapter. I'll be using the sprocket that comes in the kit and it hasn't arrived yet.

 

[blsnelling]

This is the high compression billet head I bought. This one has a 5.5cc combustion chamber. This head was only $40

 

[blsnelling]

Now to the fun part.....engine mods. The first order of business was to check the deck height. I had take a bunch off my brothers cylinder to get the piston crown close to flush at TDC. Mine is spot on. You'll find tremendous difference in these engines as they are clones of clones of clones and tolerances are all over the place.

The next order of business was to degree the cylinder.

Exhaust - 105
Transfers - 114-116 (Uneven from one side to the other)
Intake - 65

Yes, you read that right. It only has 9* of blowdown. My brothers was the same way. The only other difference was that his intake was at 60.

My goal is to raise the exhaust in order to gain some blowdown. The intake will be widened, but not lowered. Most porting recommendations I've seen on these suggest leaving it with less duration than I'm used to in a chainsaw. The transfers will require a TON of work, but I will not be widening or raising them, other than as needed to clean and even them up.

Here's the exhaust. I'll be raising it to the red line.

Here's the intake.

Here are the transfers. They are nasty. The bottom edge needs tapered. The back corner and wall needs a ton of work.

Notice how much lower this transfer is.

 

[jakethesnake]

Ported?

 

[stihl_head1982]

Has this thing been hacked up inside?

 

[zero_sum]

A friend of mine has built several of these things, they are a blast to ride.

 

[blsnelling]

That's all for now. I did the degreeing yesterday morning and still haven't ported it. I'm recovering from surgery 6 days ago, so progress will be slow at times.

 

[blsnelling]

I don't normally work on the kitchen table, but special times call for special measures

 

[blsnelling]

My chainsaw mind is wondering what it would take and how much might be gained by adapting the pipe to one of my chainsaws

 

[paragonbuilder]

Very cool!
Subbed


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[jakethesnake]

Are we racing these things.

 

[B440]

I like that banana pipe.

Here's one I built back in 2010 using a 4-stroke engine. Wasn't fast enough

 

[blsnelling]

Are we racing these things.

Oh, I' sure we will!

I like that banana pipe.

Here's one I built back in 2010 using a 4-stroke engine. Wasn't fast enough

Why am I surprised to see one of these pipes already on a chainsaw?

 

[blsnelling]

One of the recommended mods for these is to remove and true the crank. I did my brothers by mounting it in my 3-jaw chuck and putting a dial indicator on the opposite end. You would be amazed how easy they are to tweak! Dialing in the crank in the 3-jaw chuck has proven to be difficult. I'm going to make a cheap set of v-blocks to set the on.

I really wish someone made a billet crank for these. These things appear to be made out of junk steel. I called Millenium yesterday and they would true and weld one for $60-$70. I might just try my MIG on one. They're <$25.

https://www.ebay.com/itm/66-80cc-en...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649

One the really cheap engine kits they recommend replacing the bearings. They're simple 6202 bearings on both the crank and the driven shaft. Nachis should be a great choice here. I've seen it recommended several times to replace the wrist pin bearing with one from a Stihl 028 chainsaw

 

[Deets066]

Guy I know bought one of these and wanted me to port it also. Just don't have the time, told him no