Advice on frame modification

[TadNugent]

So I got this Baja Warrior on Friday, swaped in a Predator and Tav30. Greased and loctited everything. Runs great....Lot of fun. But I would like the seat to be about as high as shown in the picture. Notice the boards stacked beneath the seat. My plan is to chop the top tube, seat tube, and seat stays, and replace them with new steel built to accommodate the proportion shown. This would make the top tube pretty much level to the ground. Basically I'll take any advice before I attempt a project like that. Examples; will it handle poorly? Will the stock portion of the frame be able to handle the added stress of a larger frame?

I have all the equipment/ skill to do this, I'm just not that experienced with mini-bikes. I think it would work. Thanks.

 

[massacre]

Personally I would not cut the frame, but would instead just weld on some tubing with brackets to raise the seat.
Cutting the frame doesn’t seem to add anything, and can be returned to stock easily by just cutting off what you welded on. This is just what I would do if it was my bike, though. Ymmv

 

[TadNugent]

Personally I would not cut the frame, but would instead just weld on some tubing with brackets to raise the seat.
Cutting the frame doesn’t seem to add anything, and can be returned to stock easily by just cutting off what you welded on. This is just what I would do if it was my bike, though. Ymmv

At frist that was my plan.... Just chop of the seat brackets.. make longer ones. When I placed the boards in there and could actually
see the distance the seat would be off the frame. I just thought it would look bad. Perhaps I could weld a temporary bracket/ sub frame on there just to test it out. Then I could ride it see how it handles with the higher seat. Maybe it wouldn't look too bad, maybe I shouldn't care how it looks. LOL.

Thanks for your input!

 

[SAT]

I would duct tape the temporary stuff in place and ride it enough to make a decision. Add a short spliced-in top tube and seat risers. Easy to remove down the road. Just a thought

 

[Charles S]

Good time for a suspension seat mod.

 

[Charles S]

I would duct tape the temporary stuff in place and ride it enough to make a decision.

Good idea!

 

[Charles S]

https://www.oldminibikes.com/forum/index.php?threads/check-your-frame-s.153828/

 

[TadNugent]

Good time for a suspension seat mod.

Excellent idea

 

[TadNugent]

https://www.oldminibikes.com/forum/index.php?threads/check-your-frame-s.153828/

Wow... seeing all that, maybe I shouldn't mess with this thing after all. A crack like that is caused by low quality steel.

 

[massacre]

Wow... seeing all that, maybe I shouldn't mess with this thing after all. A crack like that is caused by low quality steel.

It could just be a bad design too, or neglect or hard riding over time. You could weld up some gussets in that area which is pretty far away from the seat imho. It’s a single down tube and single top tube design, yeah the tubes are beefier but there might be a reason most minis have doubles. Just IMHO

 

[Charles S]

Wow... seeing all that, maybe I shouldn't mess with this thing after all. A crack like that is caused by low quality steel.

Not necessarily, it's a stress crack, which can occur with any grade of steel. It's Chinese mild steel, same stuff most Harley-Davidson frames have been made of for many years. It's a design problem mainly, IMO.

 

[Charles S]

The frame could be improved with a few easy modifications, as mentioned in the linked thread.

 

[Charles S]

@noseoil has been blasting through the dessert for a couple years on a Baja he built, exceeding 50 MPH. I think he has built and sold a few, too. If anyone knows what these bikes can/can't take, he should. Search his posts, send him a message (PC: put your cursor on his avatar to the left of his post and click "Start conversation" in the popup/box that appears; you can also click "Start conversation" on his profile page).

https://www.oldminibikes.com/forum/index.php?members/noseoil.55039/#recent-content

https://www.oldminibikes.com/forum/index.php?threads/new-baja.143372/

 

[Havasu Dave]

There is absolutely no problem with cutting your frame and splicing it. To accomplish that, you insert an inner tube or solid (I use solid) that extends an inch on either side of the cut. Leave a 1/8 gap for bead between the butt ends of the tube.

Drill a small hole- I use .25- on either end of the splice, just getting into the inner splice. Do it again 180 degrees out. Weld the holes to join the inner splice with the outer tube. Now fill the gap on the outside of the tube. It is stronger than the original tubing.

To deal with stress fractures, it's the same thing, but you need to drill a hole at the end of the crack on both sides. Called stop drilling, it mitigates further migration of the fracture. Now you simply dress the crack and weld.

If I had "this" bike, I'd cut the rear end off, and build a swing arm suspension for it- only because I like doing stuff like that, not because this bike warrants that kind of time. You can get a pit bike with full suspension anywhere after all, and all it needs is an engine.

You can get a lot of this information from the Chopper websites. Feel free to PM me with any questions.

 

[cleatusj]

Why not take a tube, with the inside dia. of the top tube, and split it. Then you could weld on a short tube to support a pivot, for front of seat. This split tube could be clamped to top tube and shocks on rear of seat could mount to rear down tubes.

 

[TadNugent]

Thanks to all for your insight. I'm definitely going to add a suspension seat. I've looked more closely at the head tube/down tube juncture, mine is intact. But that area looks sketchy. So I'll weld some gussets in there. I'll have some fab time this weekend, I'll post pictures if I actually accomplish anything.