My thoughts on a possible mini bike build

[danssoslow]

Here’s an idea of the freedom a smaller radius will afford me. With the 1-1/4’s 6.5+ radius, I had to make 45* bends just to make the offset; and that still caused the 2nd bend to be pushed back further than necessary.
Although I matched the offset angle with the 3/4” pipe (it’s inside radius is right under 5.5”), the bender’s shoe had plenty of freedom to be placed where necessary.
This will make it easer to control the alignment of the chain stay and seat stay’s “knees.”

Lining up the tubing for the seat stay is going to be interesting, as the existing tubing is in a constant arc.
The chainstay wasn’t bad, as the angle of offset allowed me to work in two planes. I’m afraid the tubing I’m adding to the seat stay will need a bit of a kick inward to meet with the original tubing. Not nearly as elegant; but we have to make due with what we have.

 

[RobertC]

Welcome back to the Oldminibikes.com forum @danssoslow !

Thanks for sharing your progress.

Keep up the good work.

 

[JimN]

I do like watching concepts become reality.

 

[danssoslow]

Thank you for the encouragement, guys! I have a small update I’d like to share. Tubing for the downtube has been prepped. Tomorrow, a gentleman is coming by the house to tig it all together. All that’s left now from me is a quick disassembly and wipe down with some acetone before he gets here. Plugs a plenty!, as I am a bit concerned with this coming apart at speed. I showed these pics to the welder; and he assured me it is good to go. Hopefully the clamps do a good job of keeping everything centered as he


That angled brace was removed so he doesn’t have to maneuver around it. A couple small angles in its place, and that upright holding the top tube is steady plumb.

I also a had a decision to make. As beefy as the original product was, I guess it was still a Murray. The engine mounting holes and the frame tubing it is welded to are not on the same plane, front to back. So I had the choice to either center the frame, or center the mounting holes.
I have decided to center the mounting holes. This means the driver’s side of the base is roughly 3/8” further from center than the passenger side of the base. The OCD side of me is doing backflips; but with the offset bends beginning so abruptly after, I figure as long as the bends begin at the same point in reference to the down tube, no one should notice.

I’d rather be sure that the engine is square in relation to the rear wheel. With the added complexity of a TC and a right side chain, I don’t want issues to stack concerning chain alignment.

 

[hermans13]

Your welding prep looks very professional ! Should turn out aligned and strong. I'm sure that a number of us are learning and gaining metal working confidence from your detailed postings. Thank you.

 

[danssoslow]

Your welding prep looks very professional ! Should turn out aligned and strong. I'm sure that a number of us are learning and gaining metal working confidence from your detailed postings. Thank you.

Wow, hermans13! I appreciate the compliments!
I will assure you though, I’m simply trying. Watching a heck of a lot of videos these days. I learned enough to no I shouldn’t attempt the welding, I guess. lol!

As of 8:14, the guy is still working on it. The garage got a good breeze flowing through, and it messed up two plugs, blowing is argon out. He’s fixing those up and is going to grind his welds down. Can’t wait to show you guys the finished product.

Hopefully on my next paycheck, I can get to purchasing the bender and/or the die. I’m stoked to get the rear end worked on. Prepping a slug to fit in between those joints will be a little more involved, as the tubing I ordered has a thicker wall than the existing tubing. I’m thinking my best course will be to purchase a 16” stick of heavy wall (1/8-1/4”) DOM, cut it into four 4” pieces, and have half of each piece machined to fit the corresponding exterior tube.

 

[danssoslow]

Here’s a Quick Look at the welded tubing. Turns out, the gap between the inner pipe and tubing was causing air expansions to blow out the last couple plugs. The welder stayed at it though, and got them done. There are some flat spots from the grinding; but nothing a little bondo won’t fix.

I couldn’t help but get to work on mocking the front tire to prep for the front forks.

 

[JimN]

I can relate. I had that happen a couple of times when I was welding mine. I didn't want to drill a blow hole, so I just planned to stop a little short, let it cool down, then finish. I forgot to stop short. Oops.

Looking good. Have you decided on how much ground clearance you want?

 

[sparkwizard]

That looks pretty low, right there. It looks good, though.

 

[danssoslow]

Ground clearance is the thickness of a double wide piece of that 80/20, right at 3-1/8”.
Which is funny. Before cutting the down tube, I had it set at 7” of ground clearance; and the steerer was darn near touching the wheel at 3-1/2” of trail; I believe I could stick one finger in between. I add 5”, lower it almost 4”, and I can now fit 3 fingers between the wheel and steerer; still at 3-1/2” of trail.

My math isn’t mathing. lol.

There’s an exponent to moving the head tube’s center line, away from the body, that I am not completely grasping; and/or there was a little bit of tilt-back to the head tube that resulted from extending the down tube.

Or maybe two of my skinny fingers add up to an inch? Lol. I feel like, if someone were watching over my shoulder, they would be tickled by my amazement over a simple magic trick.

I digress. It did move the head tube C/L out about an inch I believe. I cleaned up all my previous measurements & marks prior to deciding to extend the down tube, so I am unsure of the actual distance. I like the way it sits though. Tomorrow, the tubing I purchased to use as the Yoke should arrive; and through a side job, it appears that I may have found a tubing roller I can use. So it’s looking like the next immediate task will be working on the front forks.

-Creating the yoke, I’m working WAY above my pay grade, so I may enlist some help.
-I need to drill/tap the Spring Fork Ring to M10x1.5 (apparently, Schwinn used a proprietary M9 bolt in the spring assembly).
-get some 1/4-20 all thread and nuts to mock up the Schwinn springer parts I have now to…
-if I get a hit on that tubing roller, get some 3/4” EMT to bend and mock up some curved fork tubes

 

[danssoslow]

Update:

The Schwinn front end is put on an indefinite hold. The Whizzer spring I purchased needs to be about 2” longer (50% longer!) to make the front end look right. Plus, with me having to design a hinge that is beefy enough for the abuse; I think it is best to revisit down the road after the bike has been built.

I purchased a HF Tubing Roller; and that was a farce. Couldn’t get the EMT to NOT turn into a helix. I think the world is telling me to simplify the front end. So, for the time being, a Macargi fat tire triple tree front fork has been ordered. Info on the different triple tree forks out there can be lacking; and it was the only one that appeared to have an axle spacing wide enough to accommodate the dirt bike front wheel.

The tubing bender and shoe had been ordered. Hopefully I can gain some progress with the rear end here shortly.

 

[sparkwizard]

Off topic: Does this remind anybody of why we need build-off threads?
Back on topic: Great work and thanks for sharing!

 

[JimN]

Weeelll, I think your ride would look pretty trick with some forks like this on it, but I'm pretty biased.

 

[sparkwizard]

I love the leading link front ends. I am keeping an eye out for a used factory setup.
I am not confident that after all the math and fabrication, I can get the trail right, through the whole range of motion. The arc thing worries me.
I have built some scary spit in the past, Now I am smarter and more afraid.

 

[danssoslow]

I’d trust that design over the one I almost pulled the trigger on!


I was thinking, since the Whizzer was too short, I’ll just purchase a pit bike coilover and mount that between the steerer and yoke! Started to research parts, etc, until 1 in the morning.
RIGHT as I began to jump into bed, that voice of reason in my head told me I had no fixed points in that entire suspension. That yoke would have flopped over like a wet noodle. At least the factory Schwinn design had that 3/8” bolt to keep the spring linear. Then I feared the pivots may be a weak link, and decided back burner for now.

I want to finish this before I die, not finish it and die. So, safety first!

 

[sparkwizard]

I wasn't going to discourage you with my bad experience, but I tried one of those bicycle setups with the horizontal spring where the headlight should have been. It bent sideways at about 40 MPH. I have scars inside and outside from that one.

 

[danssoslow]

I wasn't going to discourage you with my bad experience, but I tried one of those bicycle setups with the horizontal spring where the headlight should have been. It bent sideways at about 40 MPH. I have scars inside and outside from that one.

Wow! I am sorry to hear that.
I did notice that The Cruiser Shop, a bicycle building company in Cali, made a 26” cruiser show bike called The Rum Runner that had a front fork very similar to Jesse Rooke’s front fork. I’m sure it wouldn’t be cheap; but I guess if I really want that front end, it can be purchased.

I guess this next front fork won’t come without its issues, as I’ll have to adapt a bicycle fork to fit a YZ80 front wheel. Spacers, bushings, caliper brackets OH My!

 

[danssoslow]

Ain’t nothing cheap anymore is it?!?

Not much of an update; but the bender and die came in; but now my silly goose self has to come up with a pedestal. I ordered an Infinite mount from Swag Off-road, and attempted to make a low offer on a Vevor pipe bender to use as a pedestal; but it appears my offer wasn’t even worth considering. Lol.
I contacted the seller to see if he has a missing parts unit or return that I could purchase for just the pedestal. I’ll give it until the Swag part comes in to hear back.
If not by then, I will get a grinder pedestal from HF and have both bases welded at work. So maybe next Tuesday or Wednesday I can put some meat in these potatoes.

 

[sparkwizard]

What type of bender did you get? Is it an Armstrong mechanical one, air/hydraulic?
My Vevor manual one works well in the receiver hitch on my truck. Well, it works, only works well with an extra 10 foot stick in 1 1/2 inch galvanized pipe over the handle.

 

[danssoslow]

Doggone, sparkwizard! What are you bending that needs that kind of leverage?!?

I purchased the manual JD2/Woodward knockoff on Amazon. A YouTube video comment and a poster on a tube bending page on Facebook made me confident enough to purchase a die from Grizzly. We shall see if it worked out here shortly. I sure hope so, as the Grizzly is a great deal with free shipping.
To do it all over, I’d have purchased the bender and die over the wheels and forks purchased. I’d have been soooo far ahead!

With the Schwinn fork off the table, I’m contemplating what will constitute a wash, giving the bender to the welder I am using. I will be straight up in discussing it with him, as I don’t want to reneg on our agreement; but I’m hesitant to invest in making it air/hydro. To be fair, I still think at this point it’s a wash, as there will be 4 points of attachment at the body, plus the two points out back and the axle plates.

I’ve been on the service end of things far too long to try to pinch pennies there. I want him to feel it is worth his time. I welcome any input on this from you guys, please.