Angle For Drop Loop

Forbidden Tuna

Active Member
Sep 3, 2019
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Kings Mountain, North Carolina
Hey guys, I'm working on a new project. I'm using an old Columbia women's cruiser as the donor bike and I'm trying to figure out what the angle is for a drop loop frame? If you compare the seat tube to the down tube with a protractor what angle would it usually be? It's not quite a 180 degree bend obviously.

I have a manual bender for tubing so getting that curve won't be much of an issue, I'm just trying to get a ballpark degree range. Engine will be a Honda 200cc clone. Only parts of the Columbia I'm saving are the rear end and the head tube, and the rear end will be modified to make room for a belt sheave for an attempt to use a serpentine belt as well as strengthening with gussets and maybe even re-welding all the attachment points.

I know not all drop loops are the exact same between the different makers, but say for example a classic Harley Davidson like a 1912 Model 8A.

Any suggestions will be much appreciated.
 

curtisfox

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Dec 29, 2008
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Get a box cardboard box and set the bike next to it so you can draw on it. then get some bendable material like Pax tubing, then forum a drop loop to what you want could even put a wire inside to hold the shape the draw around it for a pattern. draw around the bike frame also, and go from there. ..........Curt

Would love to by the 24" frame for my wife?
 

Forbidden Tuna

Active Member
Sep 3, 2019
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Kings Mountain, North Carolina
Get a box cardboard box and set the bike next to it so you can draw on it. then get some bendable material like Pax tubing, then forum a drop loop to what you want could even put a wire inside to hold the shape the draw around it for a pattern. draw around the bike frame also, and go from there. ..........Curt

Would love to by the 24" frame for my wife?
Sounds good, I'll try that
 

indian22

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Dec 31, 2014
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Curt's right cardboard layout. Big cardboard box flattened out and sketch out the whole frame and include the motor you will use in the sketch. You won't believe how much space is required to fit a clone in that frame. I do like the girl bike conversions to four stroke. Unique character of their own.
Rick C.
 

Forbidden Tuna

Active Member
Sep 3, 2019
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Curt's right cardboard layout. Big cardboard box flattened out and sketch out the whole frame and include the motor you will use in the sketch. You won't believe how much space is required to fit a clone in that frame. I do like the girl bike conversions to four stroke. Unique character of their own.
Rick C.
For that 24" BF Goodrich I might use a HF 79cc in the future. I'm pretty well acquainted with the 79cc engines and they really fly with a 13:1 gear ratio and a 19mm carburetor.

I might not use the rear end from the old Columbia though, the dropout tubes are pretty thin. Since my bender can do 180 degrees I might just fab up the rear end as well.
The Honda clone I was told is meant for go kart racing, has a billet flywheel with I think a 20 degree advance built in. When I bought it I got the old worn out engine and a brand new one he intended to swap parts onto.
I am building this frame with a charcoal gasifier in mind, it's one of my other hobbies and the gas produced loves a spark advance and high compression(woodgas can withstand up to a 17:1 compression ratio), only issue is woodgas also derates your horsepower from 50% power to 80% power depending on design. It'll run on either gasoline or char-gas when I'm done with it. Reactor mounted on a rear rack that I'll probably weld to the rear end which is another reason why I'm leaning towards building my own from the get go.

I'll see about sketching it out first though. For forks I'm not gambling and just going to get those nice eBay girder sprung forks.
 

Oldbiscuit

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Oct 3, 2020
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Wow ! I always wanted to build a wood gas plant and hook it up to one of my antique single cylinder twin flywheel hit and miss engines. I’ve never seen any one put one on a bike before, but I have seen them on several pickup trucks in the past.
 

Forbidden Tuna

Active Member
Sep 3, 2019
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With charcoal as the fuel you can get away with almost anything. The tar has already been burned out. My 86 Mazda B2000 runs on charcoal and the reactor is literally a 55 gallon barrel with a pipe welded at the base running through perpendicularly and holes drilled in the pipe that make it look like a flute, gas exit is at the top running to a bag filter.

I'll make sure to take lots of pictures to show how I will build this one for the Honda clone.
I'm basing it off of a Swedish gasifier for motorcycles that mounts on the rear rack. It's just a little more complicated than the one I run my mini truck on. I asked the guy that documented it and he said it was made for a BSA 500cc bike.
 

Forbidden Tuna

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Here's a few videos showing gasifiers on motorcycles or ones made for motorcycles.
This one is an Updraft I'm assuming, meaning air comes from below and the gas flows up through its own fuel. Very simple but not as fuel efficient, they use up about half of the fuel and the gas gets weak and you have to refill.
Updrafts have one major advantage that the gas is almost ambient temp when it leaves the reactor so you don't need to build a cooler for the gas, just a filter to get the soot out.

Here's a video showing the aforementioned Swedish gasifier, it is what's called a Down Draft meaning the gas is generated somewhere near the middle and flows down, through a constant amount of its own fuel to scrub the gas. These will typically make weak gas once fuel runs down to the nozzle level.
Unfortunately no subtitles if you don't speak Swedish but he does a good job of showing the guts.
Down Drafts are fuel efficient but require a cooler for the gas, usually just a group of pipes to increase surface area and you going down the road, and then a filter or a cyclone and then bag filter as he shows with this one. It's only complicated because they had stamping machines to mass produce these. I use mostly scrap and hardware store found parts.