Want to swap 66cc 2 stroke for 79cc predator. Any and all advice welcome!

[TheNecromancer13]

So yea, my 66cc chinagirl engine breaks like clockwork every 3 weeks or so, never the same thing twice, but always something new to fix, and I'm sick of it. Plus it's really underpowered and has no hill climbing power and (at least in my opinion) pretty mediocre speed. So, I want to swap it out for a 79cc harbor freight predator engine. I am thinking of doing some of the mods listed in this thread: https://www.affordablegokarts.com/99cc-predator.php provided that the 79cc is just a smaller version of the 99cc as I suspect. So yea, free for all, any and all advice welcome, tips, tricks, issues you ran into, etc. Here is the old bike: http://imgur.com/a/f9Mpn and before you ask, yes the engine will fit into the same spot as the old one, it's tight, but it will fit. Also any idea of how much this will cost me to do, and what stuff I will need to buy? I own a bunch of tools, including an oxyacetylene welder, so fabrication of mounting brackets and exhaust systems shouldn't be an issue.

 

[culvercityclassic]

I will give this advise... That 79cc will never perform like a well built and tuned 66 two stroke. It's just a dog from my experience. Plus to do it half way right you will spend three times as much. Sure you want to do it?

 

[TheNecromancer13]

Once I get it running, will it be more reliable? I use mine as my only mode of transportation, so I value reliability over extremely good performance. Also, I have sunk over $500 into repeatedly fixing the 66cc 2 stroke I have right now, and it still breaks down every 3 weeks, so somehow I think given a year, I will come out ahead even with the higher startup costs.

 

[culvercityclassic]

Yes it would... Give it a shot.

 

[KCvale]

So yea, my 66cc chinagirl engine breaks like clockwork every 3 weeks or so, never the same thing twice, but always something new to fix, and I'm sick of it.

Welcome to the 'I am sick of 2-strokers' club.

I want to swap it (66 2-stroke) out for a 79cc harbor freight predator engine.
Also any idea of how much this will cost me to do, and what stuff I will need to buy?

Yep, I've built 2 79er's like this.

You'll need your tools, skills, and a fat wallet.

Sure the engine is<$100 with a coupon, but it has no internal gear reduction or clutch like your 2-stroke, nor is it designed to take a handlebar active throttle.

Start researching transfer cases with an automatic (Centrifugal Force) clutch and gear reduction with a chain sprocket output that will bolt to the engine.

One of the first things you will find is a Torque Converter, a belt system that is designed to act like gearing.
Ignore them, you need to sacrifice alot of horsepower just for them to function.

I went with a $300 Q-matic belt drive.
Ouch.

This will help with the other details like getting rid of the goverener and attaching your throttle.
http://kcsbikes.com/topic.asp?TOPIC_ID=639

They do haul donkeys though, especially on a big bike like that 29" wheeled Micargi.

Good luck with it!http://motorbicycling.com//www.pinterest.com/pin/create/extension/

 

[TheNecromancer13]

How fast we talking here? My bike has 29" wheels as well...

 

[KCvale]

How fast we talking here?
My bike has 29" wheels as well...

The ones I built would do ~40 mph but I don't know full top speed, we don't like running faster than the brakes.

 

[TheNecromancer13]

The ones I built would do ~40 mph but I don't know full top speed, we don't like running faster than the brakes.

What size rear sprocket?

 

[2Stroken]

So yea, my 66cc chinagirl engine breaks like clockwork every 3 weeks or so, never the same thing twice, but always something new to fix, and I'm sick of it. Plus it's really underpowered and has no hill climbing power and (at least in my opinion) pretty mediocre speed. So, I want to swap it out for a 79cc harbor freight predator engine. I am thinking of doing some of the mods listed in this thread: https://www.affordablegokarts.com/99cc-predator.php provided that the 79cc is just a smaller version of the 99cc as I suspect. So yea, free for all, any and all advice welcome, tips, tricks, issues you ran into, etc. Here is the old bike: http://imgur.com/a/f9Mpn and before you ask, yes the engine will fit into the same spot as the old one, it's tight, but it will fit. Also any idea of how much this will cost me to do, and what stuff I will need to buy? I own a bunch of tools, including an oxyacetylene welder, so fabrication of mounting brackets and exhaust systems shouldn't be an issue.

I hear ya man. That's exactly what I did. The stock 79cc does not have the power to climb the hills here in my neighborhood. I removed the governor, and purchased the 19mm intake, carb, and pipe from AGK. That made all the difference in the world. I was also running a 56 tooth sprocket on the back.

 

[KCvale]

What size rear sprocket?

Just a 38T I think but I can't remember.

Nice clean build!
Very nice work!

I do have a suggestion though...
Make yourself a chain guard 'disc' larger than your back sprocket you can put on the sprocket with the 3 bolts there.

The 'bite point' is at the bottom where the sprocket grabs the chain, and your pant legs are.

If your pant leg get caught in there for whatever reason, it's going to suck your leg into it, and eat it up like a chain saw and it's no fun.

Apparently you can't just put a bandaid on a wound like this.

I rode home, had some liquid courage, and then took a shower to clean and access the damage.

5 days in the hospital and a really big skin graft.
Whip yourself up a little disc guard as that was no fun all and would have been prevent had I had one.



http://motorbicycling.com//www.pinterest.com/pin/create/extension/

 

[2Stroken]

Just a 38T I think but I can't remember.

Nice clean build!
Very nice work!

I do have a suggestion though...
Make yourself a chain guard 'disc' larger than your back sprocket you can put on the sprocket with the 3 bolts there.

The 'bite point' is at the bottom where the sprocket grabs the chain, and your pant legs are.

If your pant leg get caught in there for whatever reason, it's going to suck your leg into it, and eat it up like a chain saw and it's no fun.

Apparently you can't just put a bandaid on a wound like this.

I rode home, had some liquid courage, and then took a shower to clean and access the damage.

5 days in the hospital and a really big skin graft.
Whip yourself up a little disc guard as that was no fun all and would have been prevent had I had one.



http://motorbicycling.com//www.pinterest.com/pin/create/extension/

Wow! That is a nasty injury. I am sorry to see you were hurt. I hate to see people getting hurt when they are just trying to have some fun.

My 79cc bike has now been taken down to pieces. I have a new frame that I am building up and going to try and build something a little more "legal". I am using the 49cc 4 stroke now.

 

[racie35]

2stroken, is your pedal chain always turning with engine running?

 

[2Stroken]

2stroken, is your pedal chain always turning with engine running?

Nope. The setup on that bike was typical (like most other setups). The engine drive was completely separate from the pedal drive.

 

[KCvale]

Wow! That is a nasty injury.
I am sorry to see you were hurt.
I hate to see people getting hurt when they are just trying to have some fun.

Ignorance on my part about the hazard, stupidity trying show off on my part.
I am just helping others not start with ignorance, an advance warning of the potential, once you know and take the chance anyway is where stupid comes in.

Not knowing something is simply ignorance.
Knowing something and repeating the same mistake is Stupidity ;-}

My 79cc bike has now been taken down to pieces. I have a new frame that I am building up and going to try and build something a little more "legal".
I am using the 49cc 4 stroke now.

I can help with that in private if you like.

2stroken, is your pedal chain always turning with engine running?

Only if the bike is a 'fixie' with no freewheel pedal hub which by the way is a REALLY poor choice for a motorized bike.

 

[jatgm1]

absolutely yes, the most annoying part is getting the gear ratio right with the transmission, (if your not using a qmatic which is more expensive, 300$) and getting the exhaust in the right place and away from the groin region. also, getting the universal mount setup so you can reach the screws mounting it to the engine from underneath is a must, you gotta get the alignment right. but it hauls ass, and although i just got mine going, it works well for me. wont perform as well as a china girl? i mean, maybe if you have some crazy reworked 9hp chinagirl, but it doesnt brake down nearly as much. havent had an
oil leak
blown gasket, or
problem with carb
yet. ill tell you if i do.

 

[Mouse]

Got a 79cc predator and 79cc predator transmission 44t rear sprocket. And no performance upgrades except straight pipe. And I get 40 mph.