1970s Sears Spyder project

[oldhat]

Hi everyone, I found a very nice example of a 1960s Sears Spyder with a "Super 44" Drive at the flea market for $30 last week. I don't have pictures of it (yet) but this is a great looking bike. The chrome fenders don't have any dents and the paint is original but a little rusted. It came with the original ape hangers and seat. It looks like a bobber already. I bought a new pair of whitewalls and tubes and it's ready to go as a bitchin rat bike. Except I want to motorize it and make it go fast.

The rims are 20" so it's small and pretty lightweight. I'd like to use the original "Super 44" gear. I was walking around the home and garden center yesterday and I saw that Honda makes a 160CC lawnmower engine. Seems like that kind of motor would provide enough power! Looking at videos of the 6.5HP bikes on YouTube, it looks like those motors aren't really powerful enough.

Any suggestions for motors?

 

[jasonh]

I don't know how those 6.5hp motors aren't enough. The little 2-3hp 50cc 2-stroke China kit motors are plenty for a bicycle, especially with mods.

Sounds like a decent find though. I can't find anything prior to 1985 for under $75 here, and they're mostly girl bikes.

 

[oldhat]

Just guessing as far as power on those motors. What is the top speed of a BMX sized bike with one of those 50cc motors?

 

[jasonh]

25-40mph depending on what gear you use, any power mods, etc.

If it's a modern bmx size, might be a little hard to fit a motor...I think for the China motors you need 12" from the top of the bottom bracket to the bottom of the horizontal top tube.

 

[oldhat]

I live in an area with some hills so I want as much power as I can fit into the frame. I want to stay away from those Chinese pocketbike motors. They just seem janky.

It would be fun to break 50mph on a bike.

Suggestions for good lawnmower engines?

Some stuff for sale locally right now is:

3-speed Toro lawnmower
3.5 HP Tecumseh
21" Snapper commercial mower, don't know the kind of motor
Tecumseh 10 hp off a generator

 

[Bikeguy Joe]

50 mph....hmmmmm on a 20" bike? Not good martha.

I'd go for the ten horse.

 

[Bikeguy Joe]

I have a small solid rocket booster I could let go cheap.

 

[oldhat]

20" rims. Nice and small.

The bike came with a banana seat so I could either mount the motor underneath that or I could mount it in the frame...

 

[Bikeguy Joe]

How about twin weed wacker engines/two wheel drive?

Or, three engines, two driving the rear wheel, one mounted under the seat, one in-frame and the third one on the front?

SMOKIN!!!!

 

[oldhat]

Sure, how about a 4x2?

 

[oldhat]

I wonder if one of those 80cc kits on eBay would work with a 20" rim bike. Any ideas?

Looks like this guy made it work...

http://motorbicycling.com/f14/crammed-80cc-onto-my-bmx-2183.html

50mph or FAIL.

 

[Bikeguy Joe]

One will fit into a stingray type 20" bike...tight, but it will fit.

 

[oldhat]

Nice, yeah I found an old thread where a guy fit one of these kits onto a Stingray.

But these eBay specials are garbage! I wonder if it would be better to use an American lawnmower engine? More POWAR. LOL