79cc non-kit build

[malatious]

I have built a couple of bikes from kits. One 2 cycle and one 49cc 7G 4 stroke. Since I had thrown out half of the parts that came in the kits, I decided the next one would be without the kit. I wanted to do a 79cc predator build. It has taken about 6 months to collect the parts I wanted and put it all together but I think the bike is way nicer than the two kit bikes that I built before. I pulled out the governor and added 18 lbs springs for the valves. This engine runs way better than the Hushang 49cc, Idles nicer and just sounds better. Also, used the 3D manual clutch, it is one of my favorite upgrades so far. Still need to add a headlight and turn signals and stuff but the main part is finished. Here are a couple of PICs.

 

[dogcatcher]

It looks good, what bicycle did you start out with?

 

[malatious]

It is a replica frame of an old Roadmaster.

 

[bluck]

I love your bike I have a schwinn that's close frame and same motor, im using a ezqmatic clutch and wanted to see how a 3d clutch would feel. Are you in California? Any way I can go test it out I'll bring my bike if you wish haha just want to see if it's worth getting the 3d clutch

 

[Greg58]

Good looking bikes guys.

 

[malatious]

Mine is geared a little high but the manual clutch makes up for it somewhat. The clutch is a little touchy so I might need to adjust the leverage on it a little. Still testing and will decide if I want to change the ratios. I don't mind starting off a little slower if I can get a higher top speed. Great looking bike Bluck, I always liked the Schwinn frames. I'm in Riverside, CA, don't know how far you are from here.

 

[bluck]

Mines is geared high as well, except I feel that my acceleration can be better with a 3d clutch so your gear ratios might be like mines. Yours might actually be a little higher I'm assuming but I feel your take off will still be better than mines. Oh riverside is about 30 minutes from where I live I wouldn't mind going over to test it out. Let me know if you would be willing and what days work for you. I might even ride the bike there sounds like a fun ride.

 

[malatious]

Bluck. Sent you a PM.

 

[Dan]

Suweeet, looking good!

 

[Skitch]

Very nice! I am planning a build with same engine and bike. I have not found a manual clutch for 5/8 shaft. Apparently they exist!

 

[malatious]

Manual clutch is only made for the 3/4" shaft so far. It requires a sleeve and tall key to start with. Not a bolt on and go kind of thing. I'm not sure what else you will need. In CA you can't buy the 79cc predator as a stand alone motor. I started with a 79cc predator water pump which has a shorter 15mm shaft and no key slot cut in the shaft. I had to have a machine shop make an extension piece for the manual clutch to work. I'm getting more used to the manual clutch and really like it. I like that I can pedal, pop the clutch and start the motor. Also, the clutch can be feathered to get a little burst of torque. I'm geared a little high too and the clutch gives me a little more control on takeoff.

 

[Skitch]

Thank you for the info on clutch. Kinda figured that was the case. I bought my motor yesterday. This will be my first Moto- bicycle build, however I have built / modded some road race motorcycles in the past. I plan to do the 79 on an existing bicycle frame and then build a frame for the next one using a 212.

 

[Skitch]

Manual clutch is only made for the 3/4" shaft so far. It requires a sleeve and tall key to start with. Not a bolt on and go kind of thing. I'm not sure what else you will need. In CA you can't buy the 79cc predator as a stand alone motor. I started with a 79cc predator water pump which has a shorter 15mm shaft and no key slot cut in the shaft. I had to have a machine shop make an extension piece for the manual clutch to work. I'm getting more used to the manual clutch and really like it. I like that I can pedal, pop the clutch and start the motor. Also, the clutch can be feathered to get a little burst of torque. I'm geared a little high too and the clutch gives me a little more control on takeoff.

What gears are you using. Someone else recommended a total 13:1, but it is

 

[malatious]

Not sure of my overall ratio, never sat down and figured it out. On my transmission it is 12 teeth on the clutch up to 29 teeth on the jack shaft. (I had to switch to the #35 chain on the transmission to use the manual clutch, original tooth count for 415 chain was 9 and 22) The other side of the jack shaft is 9 teeth and 44 teeth on the wheel sprocket, with the #415 chain. My bike also has 24 inch wheels, which I chose so it would be a little lower to the ground. My bike cruises good between 30 and 35 MPH at about 5000 to 5500 RPM which is about where I wanted it. For 26" wheels you would probably want to go with a bigger rear sprocket. My transmission plate is the one everyone is selling for the 79cc predator but I don't remember where I purchased it. OMB Warehouse sells different size sprockets that will fit the transmission. I hope this helps, sorry if it is a little bit convoluted.

 

[Skitch]

If I got it right your overall ratio is 11.83:1, but the 24 inch wheels would make about 7% difference, making it very close to same as 13:1 with 26".

 

[malatious]

That does sound about right. I already had the 44 tooth sprocket that I ended up not using on another build so I figured I would go ahead and try it out thinking the 24" wheels would put it close to where I needed it to be. Top speed in California is 30 MPH but it is nice to have a little extra when running with the cagers.

 

[Skitch]

The gears I have coming will put me at just under 12:1. I am hoping that with the head milled, a little porting and polishing, and a PK19 carb it will pull it.

 

[Tony01]

Malatious, bike looks great. Can I just make one suggestion, swap the 9t to at least a 10 or better an 11 or 12t and increase a driven sprocket somewhere else. Small sprockets like to eat chain.

The gears I have coming will put me at just under 12:1. I am hoping that with the head milled, a little porting and polishing, and a PK19 carb it will pull it.

You do not want to mill the head on a stock predator. Well I guess it depends how much. Problem is it has no rod bearings. Too much comp will cause the already crappy rod to wear faster.

I shaved 70 off my 212 head... Developed rod knock real quick and a leaky head gasket. And valve cover interference.

Woulda been better to weld up the cc, shave it the same 70 or even 80 and then move up to the thicker fire ring gasket.

 

[Skitch]

I am not sure I buy all that. The force of compression is a fraction of the force of expansion, and exspasion force is what we want! Improved porting, better intake, exhaust, all serve to raise combustion pressure. Can,t say why your's broke, but I suspect it was not due to to much compression. The highest performance engines in the world use plain bearings on the rod. Yes, I know there is no oil pump, but it is film strength, not oil pressure that supports the rod.

 

[malatious]

Malatious, bike looks great. Can I just make one suggestion, swap the 9t to at least a 10 or better an 11 or 12t and increase a driven sprocket somewhere else. Small sprockets like to eat chain.

Tony01, Thanks for the info, I will keep an eye on that small sprocket. I don't have a chain tensioner on the chain and it seems to be running around the sprocket without catching or binding. I would have picked a bigger sprocket but that was what came with the transmission and I already had the 44 tooth sprocket for my wheel.