Motorized bike project

***Longshot270*** · #1 Wed, May 2nd, 2012, 03:49 PM

One of my many irons in the fire, this one being the most time consuming (by choice).

A few months ago a neighbor gave me the frame to a Specialized Rockhopper. I already have a hard tail trail bike so it was laying around unused. About a month ago I stumbled onto a motorized bicycle kit that was on sale for $179, I figured it would be cheaper to go on small errands and to nearby fishing holes.

After about 4 hours after picking the engine up from the Post Office I had the bike "running"

After working out some big bugs like sub-standard chain and engine sprockets. Then working out some smaller electrical issues and adding a rack and other cosmetics, I had this.

Got past the 50 mile break in and started trusting it for better trips. With the finiky carb working well I could cruise easily around 20 and had a top speed ranging from 27 to 33 mph.

After riding it yesterday I realized that I'd like some more speed. The first issue, which I knew was going to be a problem early on, was the mountain bike frame was just too tall. I had originally toyed with the idea of putting it on my blue commuting bike but having no suspension was not going to a fun ride. I needed to lower CG and wind profile some so I decided to do an engine swap. I fabricated a new front assembly with parts from a scrap bike to give me front suspension. Next, is to work on the exhaust. It currently doesn't have one because the pedals did not clear the muffler...but a hack saw fixed that real quick. This weekend I'll find someone to weld it back together in a way that will work. I've also got a smaller rear sprocket in the mail that should arrive in a day or two. Switching from a 44 tooth sprocket to a 36 tooth sprocket should bring my cruising RPMs down quite a bit and make have my power band end around 30-32 instead of the current 24-26 mph range. I'm not expecting the claim of 8-10 mph increase because that comes out to be a calculated estimate, not a tested one, but I do expect my top speed to be load based rather than RPM based.

***Power Hungry*** · #2 Wed, May 2nd, 2012, 08:07 PM

That's really cool!

Does anyone remember these?? I used to have one and I LOVED it! Never pedaled anywhere for almost 2 years. LOL I think I paid $100.00 for it brand new and bolted it right on my 10 speed bike.

***88Racing*** · #3 Thu, May 3rd, 2012, 03:36 PM

Nice project there Longshot!

Before to long you'll have a Harley......

***Longshot270*** · #4 Mon, May 7th, 2012, 08:43 PM

Got the new sprocket installed today.

It added an extra 5 mph with the carb running really bad. The carb is running rich and so it four strokes at WOT. Before the gear swap this would have limited me to ~18 mph. Today I was able to cruise at 22-23. I'll probably just cut back the fuel shutoff to run correctly at WOT since messing with the main jet is a PITA and a huge gamble for it to turn out correctly.

Then my rear tire tube blew out so I'll be swapping both tire and tube tomorrow. There is something wrong with the tire because this is the third tube to blow out.

ticopowell · #5 Tue, May 8th, 2012, 12:19 AM

Quote:

Originally Posted by Longshot270

Then my rear tire tube blew out so I'll be swapping both tire and tube tomorrow. There is something wrong with the tire because this is the third tube to blow out.

Maybe you need speed rated tires? I bet most bike tires aren't rated for continuous highway speeds, or maybe just the ones you have. I have seen bikes go pretty fast, but they usually don't hold that speed for long periods of time.

***Longshot270*** · #6 Tue, May 8th, 2012, 08:51 AM

Quote:

Originally Posted by ticopowell

Maybe you need speed rated tires? I bet most bike tires aren't rated for continuous highway speeds, or maybe just the ones you have. I have seen bikes go pretty fast, but they usually don't hold that speed for long periods of time.

No, the tire blew while sitting, just like the two before it. I think there is a spur or thorn in the sidewall somewhere.