Here at Lowbrow Customs we have focused on the Sportster platform for many years. Our goal has been to create user-friendly parts that are also high quality, and offer amazing performance. You know, just making things the way they should be made.
One of these products is a 2004-2022 Sportster Weld-On Hardtail Frame.
Our Weld-On Hardtail For 2004-2022 Sportsters shown installed on a stock Harley front frame section. This keeps the stock neck and VIN number intact, with the overall effect of having a custom frame.
Our bolt-on and weld-on Sportster Hardtails are the highest quality in the world. Made in Cleveland, Ohio, they are engineered and made by motorcyclists, for motorcyclists.
This is a Gasbox Rigid full frame for 04-up Sportsters. Instead of using the stock front frame section, a full frame is what it sounds like... a complete new frame perfect for Sportster choppers.
You may ask whats the benefits of a hardtail over a full Rigid Frame for Sportsters? When using a hardtail, you can keep your front frame loop intact and keep your VIN number right on the frame. A little less of a hassle with paperwork if, but more work and not quite as clean and tidy as using a full frame.
Tim showing off new EFI wiring harness we have developed for 2007-13 Fuel Injected Sportsters.
In 2004 Harley-Davidson changed the Sportster forever by changing the engine-to-frame mounts from solid motor mounts to rubber mounted. The goal of adding rubber mounts was to reduce vibration. This change would now give the rider a smoother and more comfortable ride, and less vibration typically leads to more reliability and power.
In 2007 Harley also got rid of the CV Carburetor and introduced the EFI Sportster. EFI stands for Electronic Fuel Injection. If you are building a 2007-2013 EFI Sportster, we have a plug and play wiring harness to help you with this build. EFI Sportsters can also be converted to carbureted as well.
HOW TO INSTALL A LOWBROW WELD-ON HARDTAIL ON A 2004-2022 SPORTSTER
Step 1: Strip Down To The Bare Frame
Start with the stripped frame, take everything off and remove the engine. Clean off any dirt or grease that might get into the welds. Save the kickstand for later, this will be reused on the finished bike. Make sure to remove the front engine mounts. Save the stock left bracket and hardware of the front engine mount, this will also be reused. The frame conversion will "Solid Mount" the engine and eliminate the rubber bushings between the frame and engine.
Remove everything from your frame completely.
Don't forget to remove the kickstand, but be sure to keep this for later because you will reuse it.
Remove all motor mounts.
Step 2: Measure And Mark The Cut Lines
Measure and mark the lower frame tubes where they will be cut. The measurement is 13-1/4" back from the CENTER of the front bolt hole.
The easiest way to find the center of the front bolt hole is to install the front motor mount bolt, and then mark the center of that bolt with a marker. Use a large square to measure straight back level with the floor or a leveled table. Make sure not to measure at an angle.
The left and right tubes get cut at the same distance back on both sides.
Both of the bottom cuts will be right in front of the lower cross brace.
Measure and mark the cut line for the backbone. This measurement will be taken at an angle. With your square, measure from the top-front of the neck cup along the backbone tube and mark where to cut at 10-1/5".
Step 3: Cutting The Stock Frame
Cut through both lower frame tubes at your marks. Use a cut-off disc or a metal saw such as a sawzall.
Next up the top backbone. But wait there's something you need to do first!
Before cutting the backbone, you will need to cut off the wiring harness clip first. This can be discarded and won't be used on your final build.
Now you can cut through the backbone.
Oh man, you just cut your bike in half! Whatever will you do!?
Step 4: Prep The Stock Front Frame Section For Welding
Using a barrel sander prep the inside of tubes for welding by removing any paint or rust. Deburr the inside of the tubes as well.
Next use a sanding disk, clean off any paint or rust on the outsides of the tubes in preparation for proper welding.
Sand a bevel around the tube cuts, this will take away the sharp edges and allow the welds to penetrate deeper into the joints for a strong weld.
Do the same for the top backbone. Use a barrel grinder to clean the inside of the tube from any paint or rust. Remember to deburr the inside of the tube as well.
Remove any paint or rust around the backbone where it was cut for proper welding.
Bevel the outside of the backbone tube end to remove any sharp edges.
Step 5: Install The Hardtail & Front Frame Section Around The Engine
The engine does the job of aligning the front and rear frame halves for welding. The first thing you are going to want to do is lay the engine down on its right side and support it level, as shown on blocks of wood. 2x4's work really well for this. You can protect the engine from scratches and damage by having a piece of cardboard or a blanket under the 2x4's on a table or ground. 
When the engine is supported properly it makes the frame installation extremely easy. Having all your hardware easily accessible will help make this job easier as well. 
You can also protect the engine from scratches with painters tape or wrapping cloths around the hardtail sections backbone and motor mount bracket. Lower the hardtail onto the engine. Line up the rear 3/4" bolt hole with the big hole at the rear of the engine.
Bolt up the rear of the hardtail. The hardtail comes supplied with the cover plate and proper bolts. Install the steel spacer through the engine, leave these bolts finger tight for now.
Install the front frame half. Slide the backbone in first, then the bungs in the two lower frame tubes. Stock frames can spring or pull when cut apart. You may have to tap the frame onto the bungs with a rubber mallet to help align the tubes properly.
Here is the top side of what it will look like with the front half pushed onto the hardtail.
The hardtail frame conversion requires the front a Solid Motor Mount Kit. Install the right side first. With the frame loose, there is room to fit the mount between the engine and the frame. Line up the peg on the mount with the notch in the frame.
The second mount gets installed next. Install the stock left bracket and reuse the stock front bolts.
Leave these bolts finger tight for now.
Step 6: Installing The Shims In The Backbone
Stand the engine and frame upright to finish the assembly. Place a 2x4 under the front and rear of the frame, this will help keep it upright. Weld prep the two shims that are included with the hardtail kit. Use a wire wheel or scotchbrite pad to remove the laser-cut scaling, rust, and or oils from the shims.
Once clean, slide the first backbone shim between the frame and the hardtail backbone. The shim will need to be slid in from the top and then rotated towards the bottom of the backbone. You can use a flathead screwdriver or a punch and tap it with a hammer to help move it.
Install the second shim on the top of the backbone. With the frame bolts loose, wiggle the frame halves and tap the shim into place between the backbone tubes.
Tap the shims flush with the frame tube for welding. The shims will center and align the frame halves. Install the top motor mount bracket you plan on using to the engine heads and the motor mount on the hardtail backbone.
This is what it will look like once you have completed all previous steps. Tighten all bolts. The front and rear frame halves are now held rigid and in alignment.
Step 7: Tack & Finish Welding
Tack weld each of the tubes in multiple locations to make sure nothing moves.
Weld the frame parts together as much as is accessible. Best practice is to place heavy tack welds at each tube joint first, then go back and finish weld the seams.
Welding it up!
The welds need to get good penetration between the hardtail backbone, shims and frame backbone.
Finish weld where you can reach. 
Lay the frame back down on cardboard and support the engine on 2x4's. Unbolt the frame and lift it off of the engine.
With the engine removed from the frame you can now get to those hard to reach places on the lower tubes that need finish welds
Finished welds on the bottom tubes.
Thats it, you have done it!!! After you have let the frame cool off, you can put the engine back down on your cardboard and 2x4's and slap your new killer frame back onto the engine. You are now ready to start making the chopper of your dreams! A super reliable chopper of your dreams.
New frame all welded up and ready to become a roller. Slap that engine back in there!
Another angle of the new frame complete.
Getting ready to put the motor back in so we can get moving on this project.
Boom!
Perfecto!
B-side in all its glory.
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