EXAMPLE THREAD! - The Yellowjacket Speedster - Page 3

minidragbike · 04-12-2007, 08:20 PM

That manifold has been welded to the head. The angle is higher and more tilted back away from the spark plug hole. This angle makes a straighter shot to the valve head for better flow.

The head has to be cut out (large hole grind into the head at the good angle) so the intake can go in, before being welded.

**Yellowhand** · 04-13-2007, 12:33 PM

Not half moon tank...half-gallon tank...replica of the tanks Moon makes in varying sizes for custom applications...exactly the same thing as you have on your bike, except I don't buy them from Moon, I make them myself. I also make them in stainless steel instead of aluminum. They look bitchin' in copper, also.

Do you weld?

That head/manifold combo will be fun...whoever did that had to determine the alloy composition for both the head and the manifold, and select a rod that will meld with both...

Aluminum has to be pre-heated before welding, so hopefully they have made some type of fixture to hold the two pieces in alignment...

A TIG is needed to weld aluminum components that must retain their exact original shape...oxy/acetylene might warp the head.

**Yellowhand** · 04-13-2007, 01:09 PM

Ironically, the rotary floats in the Capps Manufacturing website were designed for insertion into a horse's mouth to grind away decayed tooth material, but engine builders use them for tunnel-porting because the extended and articulating shaft is much longer than a standard die grinder.

5hpminitech · 04-13-2007, 02:55 PM

hey yellowhand howm do you determine the alloy composition before welding i welded lots of cast aluminum some turns out great some so so hit or miss ta know but Im intrested if youn have a cheap way to determine that could help me

minidragbike · 04-13-2007, 03:25 PM

I don't do to much welding at all. I have a friend that welds, but now he doesn't have the tooling he use to have at his job to do it. The head is on the way here, and I'm going to install big valves in it first.

The question I have to ask is if you think you can do the job? And if so do I have to buy a manifold, or can you make one? I'm thinking about the pictures I'm going to have to take for you to see, or get the exact idea I'm thinking of.

I will shoot you a PM.

**Yellowhand** · 04-13-2007, 11:15 PM

Determining alloy composition-

For a serious job like MDB is suggesting, I'd contact the manufacturer of the components to ask what alloy they're made of, then match the rod to that alloy. If the two components are incompatible alloys, the intake would have to be remade in a more suitable grade.

There is a tremendous amount of variance in alloy composition for aluminum, and each type requires different pre-heat (annealing) procedures. Some is so low-grade it can't be welded at all.

minidragbike · 04-13-2007, 11:46 PM

The intake is made out of a much better quality aluminum alloy then the head casting. The intake is billet alluminum and the head is just a cheap casting in that picture I showed you.

The setup is basically going to be the same, but with a different head (same material) and different intake (same material)

**Yellowhand** · 04-13-2007, 11:48 PM

A little more fabrication...

Pic 1- I tacked the steering tube onto the frame after I cleaned everything up a little with a flap disk sander...there was too much old paint on the material, getting into the welds. The wheelbase is 51", a fairly long bike.

If you're building a frame without a jig, as I am, I just run a long dowel down through the steering tube as the frame is sitting on a centering line drawn on the table.

Pic 2- I don't think the frame is that interesting, so I don't want to draw attention to it, but in keeping with the Satin Black and Fly Yellow color scheme, I decided to go with the yellow on the wheels and engine, and hide the frame in satin black.

Pic 3- I bought some aluminum paint canisters at Harbor Freight to fab a gas tank. I cut the necks off, butted them together in a bar clamp mounted in the bench vise, pre-heated the aluminum with a propane torch, then used an oxy/acetylene #1 tip with a neutral flame, and Forney fluxing general purpose aluminum rod to weld the two canisters together. The fittings are aluminum tubing welded to the tank, and threaded to accept brass fittings.

Pic 4- I left enough of the neck on the two canisters when I trimmed the tops off to form a small 'waist' in the center of the tank...this allows a hand-bent heavy brass band to lay flush inside the 'waist-band'. This thick brass band will be used to mount the tank to the frame after I fab a large steel bung that will be welded to the frame, and the band will be screw-clamped through the bung. The tank holds a half gallon...four lbs of fuel when full.

minidragbike · 04-14-2007, 12:11 AM

That tank is nice!
Also is that a bearing neck you have on the front of that mini?

**Yellowhand** · 04-14-2007, 12:51 PM

Thanks...I like the way these tanks look...the size is good for minibikes...and the aluminum doesn't rust inside the tank the way steel can if not coated.

I just wish I could find the canisters as scrap, instead of buying them new.

I have made a few from aluminum fire extinguishers...Matt just found an empty one to make his Campus tank from...

This neck uses bicycle-type caged bearings with cup-style races...I make other necks on an engine lathe that are counterbored to accept 1-3/8" sealed bearings.

I never build frames that use bushing-type necks...these bushings are difficult to find replacements for, and I have posts up on different forums offering to make silicon bronze bushings at cost for people seeking to refurbish their vintage mini steering tubes...