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Old 05-30-2011, 04:25 PM
nate-m nate-m is offline
Motorized Bicycle Newbie
Join Date: May 2011
Location: Georgia
Posts: 13
Default Re: Motorbicycle commuter

My 'NaterBuilt' Motorbicycle revision 1.3:

This is how my first creation turned out. It's built using a Trek steel-framed 820 bicycle with a GT4 Grubee 66cc motor kit bought from Pirate Cycles. Shopping with Pirate Cycles was a good experience and the 150 dollar kit is a fantastic value.

This forum was a invaluable resource and has given me lots of great ideas. Thank God for the internet. It's a fantastic resource and makes all sorts of things previously impossible and expensive, very possible and cheap.

My observations on the GT4 kit:

The engine is fine. It's extremely low-tech, but put together decently. For the price offers a unbeatable value. I don't like the mounts through. Custom frame mounts are a very good upgrade. Unless the mounts match your frame exactly I expect that any long term installation (several years) will result in metal fatigue failures around the mounts if you keep them 'stock'.

The carburetor is fine. It doesn't leak and it does it's job reliably. Suppose to be a upgrade compared to the normal fair that you get.

The 'rag' type rear sprocket is irritating to put on, but it works great. I have no problems with using a rag-mount type rear sprocket!

The controls are 'ok'.

I don't care for the throttle controls. It's very cheap and a bit complicated for what is needed. But they work just fine. So it's ok. A metal replacement from NAPA auto stores would be on my Todo list.

The clutch control is fine. Just a generic child bicycle style brake lever. Works as advertised but people with weaker hands will have problems with it. The lever probably should be longer for more leverage.

The chain is cheap. It stretches way to much when it warms up and shrinks back down bizarrely. I don't understand it, but makes it nearly impossible to get the right tension without using a spring-mounted idler wheel. A new chain from Tractor Supply of the same size would probably be a good idea for people wanting a lot of use. But it's strong and big enough that it will work out as advertised. It was not damaged, rusted, or stiff when I got it... unlike other people's experiences with other kits. I was fine enough with it that I used it. It's just not optimal.

The gas tank was fine. It has a cheap cap that is crying out for a upgrade. It was dirty inside also. Not full of crap, but it's not something that can be eat off of and surface corrosion will cause problems with the carb. But I ruined the tank trying to screw in the cut off valve. MY FAULT. I don't blame the kit for that.

YOU NEED A SEPARATE FUEL FILTER. You WILL run into issues with the carb without it.

The 'tensioner' is a piece of crap. Very easily the worst designed and most dangerous part of the kit. It is abhorrent in all forms and there is not a single positive thing to talk about it. The world is simply worse off as a whole that this crud even continues to exist. It makes babies cry.

Basically this is what will get a HUGE number of people into trouble:

* You buy the kit and put it on.

* The last bit you will probably mess with before driving for the first time is fiddling with the chain tension. You know if it's too tight it will cause problems, and too lose it will flop around and probably do something bad.

So you get it on so it's 'ok' tight.

* You get on your bike and ride around a bit. You get back and notice that the chain is flopping around a tiny bit. So you sigh and work on the tension a bit more.
* Eventually you get brave enough that you take it out for a long distance ride. Plus you go fast. Things seem to go well.
* When you get back you notice your chain is flopping all over the place. It's VERY loose. So you swear a bit and fix it before going inside....
* A couple days later you get back on your bike and take it for a spin. A few blocks later the stupid real-wheel chain thing EXPLODES on you. The chain will break shredding something. Or pull the tensioner down into your spokes and ruin your rear wheel while causing you and your bike to crash hard. Something really bad.

What happens is that you put the tensioner on and tighten it down while the chain is still warm and lose. When the chain cools and sits for a while it tightens back up and will create a HUGE amount of pressure. When you combine that with a 2-3 HP motor it WILL do something very bad. Something WILL break.

So the only right way to run this kit stock is with a floppy chain. Upgrading the tensioner is a MUST. It won't stay tight, it won't do it's job, it will eventually rotate down into your spokes. The bolts are cheap crap, the plastic wheel is not only weak and won't line up right, it's brittle. The thing will sit at the wrong angle always since it's clamped to the chain stay that probably is not parallel with your chain. The bearing surface will probably fail and the wheel will stop turning and your chain will be forced to slide across it. For as long as you use it you will need to keep a eye on it and do a inspection EVERY time you ride your bike.

The final big part of the bike is the exhaust manifold/muffler. I hate it. It's just not designed well. It's restrictive, it doesn't do a good job of muffling, and I lost the bolt and the bottom cap of the muffler the first time I drove it any distance. This is even after I inspected it and tightened down the bolt since it had started to come lose. Supreme irritation.

A proper expansion chamber would be a MASSIVE upgrade that nobody will regret as long as it fits on your bike. Not only increase power and fuel economy, but just sounds and looks better.

All in all it's a good kit. It's a great starting point for a a great bike. The 66cc motor has a lot of potential and it should be reliable enough and parts are cheap.A very suitable toy.
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