My First; doodlebug engine swap

[Man Scout]

This is my first minibike but not my first rodeo. I fix up small engines for fun I went through my first 2 stroke scooter ( I had 2 of the same tanakas one was a complete rebuild), my first chainsaw, my first wood chipper, my first go cart, and now my first minibike all within a year. After learning small engines I wanted something cool to attach them onto and demonstrate them. That and I really like to drive stuff.
I needed more room in the garage so I traded a chinese go cart I swapped the bad motor on, for a minibike and some cash. The minibike is a Baja Dirt Bug just what I was looking for to start with.

I had a Honda gx160 sittin around and a briggs 5hp however the gx160 has a crack in the crank case I didn't want to deal with and the briggs I believe to be a 1 in shaft so that is a no go.
I bought predator 212 that was on sale and got to work. This all came together in a few hours.

A comet centrifugal clutch is added and 35 chain I also blew a bearing while testing it and those had to be changed after a 30 minute walk back to home base.

Green paint was applied during the bearing change while waiting for the parts to arrive.

Next for this bike is the gearing I ordered a split sprocket adapter for the DB that should be coming today I will be testing out different # tooth sprockets to see what I like. Engine modifications when I can afford to do them.

 

[Docdc]

Welcome to the boards. Looks good. That's a great frame to work on.

Doc

 

[Man Scout]

New Sprocket

I got my sprocket adapter and sprocket in the mail today from OldMiniBikes pretty nice adapter. I just had to run out and grab some 1/4x3/4 bolts and the fixins to put the split sprocket on the adpater plate.
Pictured Below: db sprocket adapter with 60t sprocket for 35 chain. Sitting on top of the stock 70 tooth.

I was able to install the new sprocket on the bike however without the lock nuts on the inner bolts that hold the sprocket to the hub as they caused the hex bolts to scratch against the frame.

Tested the speed with my phone GPS and my top speed was 45 mph. Great balls of fire I didn't need the speedo to tell me it went faster. The bike still has enough torque to wheelie but now as it gains speed it begins to feel slightly unstable it is hard to explain. I feel like the rear end of the bike rises up higher. I suppose there a few kinks to work out I'm starting to think I get a weird feeling with the bike at high speeds because I have knobby tires on it.

 

[Camjamsdad]

What brand tire is on the back? I experienced the same thing when I went over 40mph

 

[Man Scout]

What brand tire is on the back? I experienced the same thing when I went over 40mph

The tire is the stock oem WANDA tire 145/70-6. If I decide to go any faster I may have to consider better tires.

 

[GustoGuy]

This is my first minibike but not my first rodeo. I fix up small engines for fun I went through my first 2 stroke scooter ( I had 2 of the same tanakas one was a complete rebuild), my first chainsaw, my first wood chipper, my first go cart, and now my first minibike all within a year. After learning small engines I wanted something cool to attach them onto and demonstrate them. That and I really like to drive stuff.
I needed more room in the garage so I traded a chinese go cart I swapped the bad motor on, for a minibike and some cash. The minibike is a Baja Dirt Bug just what I was looking for to start with.

I had a Honda gx160 sittin around and a briggs 5hp however the gx160 has a crack in the crank case I didn't want to deal with and the briggs I believe to be a 1 in shaft so that is a no go.
I bought predator 212 that was on sale and got to work. This all came together in a few hours.

A comet centrifugal clutch is added and 35 chain I also blew a bearing while testing it and those had to be changed after a 30 minute walk back to home base.

Green paint was applied during the bearing change while waiting for the parts to arrive.

Next for this bike is the gearing I ordered a split sprocket adapter for the DB that should be coming today I will be testing out different # tooth sprockets to see what I like. Engine modifications when I can afford to do them.

You should get a nice clutch/chain cover for safety reasons since a clutch spinning at 3600rpms can cut like a knife. Brad at Hotrodminbike.com make a great looking PMR aluminum one with quick release twist retainers.

 

[catfishman]

Manscout, wondering where in illinois you are? I am in missouri, by lambert.

 

[Man Scout]

You should get a nice clutch/chain cover for safety reasons since a clutch spinning at 3600rpms can cut like a knife. Brad at Hotrodminbike.com make a great looking PMR aluminum one with quick release twist retainers.

I've been meaning to fabricate a clutch guard myself... I just haven't gotten around to it yet.:wink:

Manscout, wondering where in illinois you are? I am in missouri, by lambert.

I'm in northern Illinois. I'm a fair amount closer to Wisconsinland. But I've been to Missouri its a nice place even though all the locals told me the state was pronounced, "misery", I think they were messin with me.

 

[T-Town Mini]

...
Tested the speed with my phone GPS and my top speed was 45 mph. Great balls of fire I didn't need the speedo to tell me it went faster. The bike still has enough torque to wheelie but now as it gains speed it begins to feel slightly unstable it is hard to explain. I feel like the rear end of the bike rises up higher. I suppose there a few kinks to work out I'm starting to think I get a weird feeling with the bike at high speeds because I have knobby tires on it.

The soft sidewalls on the tire allow the tire's diameter to expand at speed due to Centrifugal force:
(start watching a 1:22 mark)

https://www.youtube.com/watch?v=4aKmlQ7U27w

 

[Bama Jama]

If you watch a car tire when it is during a burnout you can see it.It really shows on drag slicks.It gets taller and narrower.

 

[Man Scout]

The soft sidewalls on the tire allow the tire's diameter to expand at speed due to Centrifugal force:
(start watching a 1:22 mark)

https://www.youtube.com/watch?v=4aKmlQ7U27w

If you watch a car tire when it is during a burnout you can see it.It really shows on drag slicks.It gets taller and narrower.

Thanks for the tire information! That answers that question. But I just realized something.
The thing about me is that I've never owned or ridden a full sized motorcycle and bicycles don't count there is just not the same physics I can powerslide a bicycle at its full speed and it feels...how should I say; comfortable. But this minibike I wouldn't dare slide it there is too much power in there that I can't always account for like I can with my legs.

I have never thought about what to do if you lose a tire. The faster I make this bike go the more serious that realization of I could die becomes more evident. Also when I do pop a tire it will sure as hell be at high speed because I built my bike to go in straight lines as fast as it can and that is exactly how I drive it.

I suppose the front wheel going would be the worst I would lose steering and a lot of fork height. But a rear wheel going would be pretty bad too I imagine the tail sliding out from under me (as I would most certainly brake) and me laying the bike down and getting thrown off.

Getting the bike up and running used to be my first priority before I was riding it around. But now I think I have to invest in safety. My front tire has a patch so thats no good that could go while I'm riding. I need new tires and my helmet is far from adequate I need to invest in some proper riding gear I'll look like a dork but at least I'll feel cool.

Any recommendations for tires I was looking at the snow hogs and x tracks they look more like car tires which seem good but I'm not sure how tire measurement goes with minibike tires I know the 145/70/6 where the first number is width and the second is height and the third is hub diameter. however most of the aftermarket tires I see are sized something like 410x6.

I think that the 410 is the diameter still and it is bigger because of the tire design and the 6 should still be the hub dimension. I don't know if you are still following me here but my question is does the hub dimension only have to be correct for me to mount a specific aftermarket tire like a snow hog or x track on my bug OEM hubs??

 

[Camjamsdad]

Typical snow hog size is 15x5 6

The 15 is height. 5 is width and the 6 is the hole in the middle of rim size. The width is the limiting factor. Some 6" tires will fit but others will hit the brake caliper.

I had the same thought when I broke 40mph. The tracks and hogs have a stiff sidewall and take decent air pressure. I had some kenda scorpions that took 3.6 lbs. Those ballooned bad and scared me

 

[Man Scout]

Typical snow hog size is 15x5 6

The 15 is height. 5 is width and the 6 is the hole in the middle of rim size. The width is the limiting factor. Some 6" tires will fit but others will hit the brake caliper.

I had the same thought when I broke 40mph. The tracks and hogs have a stiff sidewall and take decent air pressure. I had some kenda scorpions that took 3.6 lbs. Those ballooned bad and scared me

Awesome thank you for the information. I ended up finding some threads about the tires that will fit in the DB so I will research this more and analyze my findings to conclude which tire I will purchase in the end. In fact I think it was you who posted pictures in one of those threads comparing the x trac to the snow hawg. Oh man I should have looked harder you answered my question before I even asked it.
I found some 18 dollar snow hawgs that have a 4 in width that I think should still clear the caliper. If not I guess I move the rotor and caliper.

 

[jdogg]

:thumbsup:

 

[Justpassedu]

Awesome thank you for the information. I ended up finding some threads about the tires that will fit in the DB so I will research this more and analyze my findings to conclude which tire I will purchase in the end. In fact I think it was you who posted pictures in one of those threads comparing the x trac to the snow hawg. Oh man I should have looked harder you answered my question before I even asked it.
I found some 18 dollar snow hawgs that have a 4 in width that I think should still clear the caliper. If not I guess I move the rotor and caliper.

Please post a link to your findings as I am looking into a doodle bug shortly and would like a tire that can take some snow , thanks and nice build , I will prob be going with the same engine to start.

 

[T-Town Mini]

Please post a link to your findings as I am looking into a doodle bug shortly and would like a tire that can take some snow , thanks and nice build , I will prob be going with the same engine to start.

Carlisle X-trac 15 x 5.00-6

 

[chipper]

The xtrac fits perfect and a great tire too !

 

[Man Scout]

A wealth of information has just flooded this thread. Thank you to everyone posting in here You're charts, images, and recommendations are setting me straight on this project.

Please post a link to your findings as I am looking into a doodle bug shortly and would like a tire that can take some snow , thanks and nice build , I will prob be going with the same engine to start.

Will do. As soon as I get the capital to do so but for now here was the snow hog I was looking at. http://www.ebay.com/itm/271090411274?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
I had never even thought about driving in the snow. Soon enough the snow will be back again.
I'm starting to lean towared the x tracs due to their looks.

Carlisle X-trac 15 x 5.00-6

Thanks for that picture T town that gave me an idea for my clutch/chain gaurd I'm fabricating.

 

[T-Town Mini]

...
Thanks for that picture T town that gave me an idea for my clutch/chain gaurd I'm fabricating.

The first one I made was for my Bonanza when the Tec H30 was mounted on it. I originally wanted to make one like that modeled after the ones I've seen on a lot of minis out of aluminum but, since I had some Lexan laying around I used that instead.

I fabbed up another one and made a new mounting bracket for it when I installed the engine on my DB. I've got the patterns for them now so I'll be able to make one for any bike I may build next.

 

[Man Scout]

The first one I made was for my Bonanza when the Tec H30 was mounted on it. I originally wanted to make one like that modeled after the ones I've seen on a lot of minis out of aluminum but, since I had some Lexan laying around I used that instead.

I fabbed up another one and made a new mounting bracket for it when I installed the engine on my DB. I've got the patterns for them now so I'll be able to make one for any bike I may build next.

I just found an old reflective street sign in someones trash. Pretty darn thick material I think aluminium or tin. Should make for a good clutch guard. Will update as time passes.