Hello and Welcome!
- Thread starter Dan
- Start date
Hi everyone, I'm new here and to motorized bicycles. I just purchased my first 80cc kit, should be here in about a week. Can't wait to put it on my bike(21 speed Trek mountain bike). I've always had a love for working with small engines. Thought this would be a great place to meet fellow riders and perhaps meet some from my area Pittsburg CA. Just wanted to introduce myself and say hi to everyone. Hope I posted this in the right area.
Yep, you did. I just want to let you know, however, that most of the newer trek frames are very, very tight when it comes to fitting any engine. I wasn't able to fit one of those engines on a Marlin 5 it was so tight. Depending on the model, you MIGHT have just enough space to rub off some paint, and not much else. If I could get the model name and year of the bike, I could help you out a bit more.
If you have an older frame, it will likely fit.
If you have an older frame, it will likely fit.
Yes it's an older frame, more than 10 years old I know for sure. I've seen many youtube videos it looks like so much fun cant wait to start riding! I'm also planning to use it as an alternate means of transportation. Have an old car on it's last leg so don't drive it much, need another way to get around.
Gotcha. Those decade old frames will fit it. They tend to be tall and open, although on the tight side. The ones from the '90s are even better. Essentially road bikes with wider wheels, slacker geometry, and heavier, thicker tubes. Im running a 79cc HF motor on a mongoose threshold, about a 20 year old bike. It fits the engine and holds up to the 5 horses I got turnin through it.
Your bike may be made of aluminum, since that got popular in the 2000s, so be very aware of any cracks forming as you upgrade for more power. They can and will be catastrophic. It may be worth your while to learn how to weld aluminum so you can strengthen and repair your frames.
Ok. I'll keep that in mind about the aluminum frame. Just for future reference, can you recommend a stronger type of frame I could get down the road less prone to cracking? If I were to keep everything stock, would the frame still be prone to cracks? What are some good frames for the 80cc motors?
For the stock motors, you can use any frame without reinforcements. Once you start getting above 4 horses though, you start wanting steel frames. 6 horses and up need some kind of reinforcements.
I'll be installing some angle iron straps to my bike once I get my head shaved down some more and improve fuel delivery. In addition, I'll be getting a longer seatpost to add some rigidity in the seat tube, which is where the highest level of strain is on my build.
Ok. Thanks for all the help so far. Down the road, I do want to do some upgrades but for now on a tight budget so a stock motor will do fine for me. I've heard some people when they install their first kit, they have to bend the tube of the exhaust a little to clear the pedal, hopefully that wont be the case with my bike. It does have front suspension too for a better ride. I like your ride btw. How many HP you running right now?
Somewhere between 4 and 5 horses. Started off with 3.5, then added a dellorto carb with a rejet, lapped my cylinder head (there came to be a gouge in the surface from a retention pin), and installed 18lb valve springs. Soon, I will be really wet sanding down the cylinder head with 400g paper and Tap Master cutting oil, and finishing it with two sheets of 1000g and the same oil. I am also going to increase the bolt torque to 18ft/lbs from the 14 on it now.
I'm really workin hard to get it to hit 50mph and hold it reliably for a full tank over somewhat hilly terrain. That's also how I will determine my minimum range. Right now, idk where my mileage sits as it hasn't been reliable enough to go through a full tank in one run, but it's getting there.
Yes, but you have to use your chain breaker and possibly a half link to get the tension right. Otherwise, that chain will hop around, and sometimes even right off the sprocket. I had that issue with every single tensioner that came with any kit. It's just not a good idea to use them.
Yeah guys the danger is very real. The motor kit style tensioner is a disaster waiting to happen...never trust it. That said every bike I've built over the last 10 years uses at least one spring type tensioner to control the motor drive chain, several use one on the pedal side as well, none can swivel into the wheel. I've posted warnings and how to's and whys of tensioners for years and I'm sure many old timers are sick of seeing these reminders to newbie and experienced builders as well. There is a big difference in properly designed and installed tensioners and the crap sold with the kits and on the internet. Multispeed road bikes and mountain bikes use a spring tensioner to control huge amounts of chain length on bikes...Shimano and Sram make fortunes on these tensioners sold in every shifter package and using a half link is unheard of on these. Chains are meant to be used and not constantly fiddled with and spring tensioners allow us to do just that. I never have to adjust a chain once it's initially installed and I don't break chains ever and I have bikes running 14.5 hp and 12 + hp two over 5 hp the rest pretty much stock kit engines. Chain wear is minimal with proper maintenance.
Rick C.
Rick C.
When I get my kit, I'm going to try first with no tensioner. There's a guy that has a YouTube channel that did a 4 stroke build without the stock tensioner and all he had to do was adjust the height of the motor on the frame a bit and it worked.
However you decide to do it, just make sure that you have no less than 1/4 inch vertical travel present in your chain. 1/2 inch is a good spot to start with.
I did motorcycle specific #420 power transfer chain from JT sprockets. My 79cc kept breaking the 415. You'll not break that #420 chain for at least 1,000 miles.
Ok I’ll keep that in mind. I’m thinking first up grade I should get is replace the stock rear sprocket mount because I hear a lot About the ones that come with the kit bend/break spokes. Then probably after that, get an hp carb.
