Frame and Front Fork Modifications

In his last update, custom bike builder Brent Mayfield detailed his plans for building a “FrankenHarley” to participate in the 2014 Motorcycle Cannonball.

His choice in machine was to use a 1930’s Harley Flathead powerplant and a 1920’s Harley chassis. Obviously these parts were never meant to work together, so extensive modifications to the frame and front end were necessary to have a rolling bike.

Here’s Mayfield’s next progress report. Enjoy!

 

Hi Team,

Frankenstein's motor and transmission now fit smoothly into the JD frame, which they were never designed for.

Frankenstein’s motor and transmission now fit smoothly into the JD frame, which they were never designed for.

Here’s the next update on my 35VJ project.Last update covered a little history on how I came to decide to build the VJ. It also covered the work required to the frame to accept the V motor.

There is still modifications to be done to the frame (top motor mount, adding a seat-t bracket, removing the two J top motor mounts, etc). but I’m done with working on the frame for now. I had also mentioned making the modifications to the rear fork leg. What I forgot to mention was that I also installed a new fork stem and put new tubes in the front fork leg. A front brake anchor will also need to be added to the rear leg but I can’t do this until I have my front wheel assembled and brake in place (more on this later).

New Fork Stem :

Mayfield added a whole new front fork stem to replace the garbled threads on the original

Mayfield added a whole new front fork stem to replace the garbled threads on the original

The threads on the fork stem were pretty much worn away and I decided a new stem was the best way to go. You can buy the new stem but it’s really not made to replace the entire length of the old stem. You need to cut the old stem off a couple of inches above the lower tree, cut the new stem to the appropriate length and weld them together. The bottom 1/4′ of the old stem, right above the tree, is the correct diameter for the lower ball race to be a press fit. The I.D. of the old stem and the new stem are not the same. A stepped sleeve was made that had 2 O.D.’s to fit the I.D.’s of the old/new stem. The sleeve still had a I.D. large enough that a steering damper rod would still pass through if desired. cross holes were drilled in the old & new stems so they could be plug welded to the sleeve. The stems were also heavily chamfered so they could have a nice butt weld. The butt weld was then ground down so the lower bearing race could be installed or removed from the repaired stem. The top tree is installed before any welding to help make sure the stem location is as it should be.

 

Front Fork Tubes :

New front fork tubes were added by Mayfield to replace the weakened originals

New front fork tubes were added by Mayfield to replace the weakened originals

The original front fork tubes were really rusty and weak and needed to be replaced. You can buy new tubes and lower castings but you need to use the original cross casting that is also the spring perch. I also decided to use the original lower castings. I cut the old tubes 1 inch above and below the cross casting and 2 inches above the lower castings. All the joints between the castings and tubes were originally brazed together. I then slit the pieces of tubes lengthwise, with a die grinder, that were attached to the lower castings. Next I heated the lower castings and tubes to the point that the braze was melting and then pealed the slit tubes from the castings. I kept the heat on the castings and wire brushed as much of the brass off as I could. The same procedure was then done to the cross casting. The new tubes were then silver soldered into the cross casting at the proper length. Fixturing was used to make sure the tubes were parallel and that the spring slots were in line. The lower casting were then silver soldered in place with a fixturing rod between them to insure they were aligned.

After extensive work on the front end, adding the rockers is one of the final steps

After extensive work on the front end, adding the rockers is one of the final steps

Fork Rockers :

The rocker studs and bushings were worn and needed replaced. I pressed out the old bushings and put in new. You want to make sure the studs are a nice slip fit in the installed bushings and that  the bushings stand a little proud of the rocker castings to make sure they do not bind when the stud nuts are tightened down. I also opened up the axel hole in the rockers to fit the axel I’ll be using with the front wheel I’ve chosen.

 

Final fitment :

For this project, Mayfield machined a custom set of axles to fit the Bultaco Pursang wheels he is fitting

For this project, Mayfield machined a custom set of axles to fit the Bultaco Pursang wheels he is fitting

Next I assembled the front and rear forks, cross adjuster shaft with sliders, rocker arms with studs and axel but not any of the springs (internal or external. You want to make sure that when all is assembled and tightened up, there is full travel of the front fork without any binding. I did have to do a little tweaking of the rocker studs and the sliders and slider slots to get full uninhibited travel of the front fork. Next I took the fork apart and installed the springs. I installed the fork in the frame and will now work with the front wheel & brake to make my brake anchor rod and bracket.

 

 

Mayfield chose to use Bultaco Pursang wheels front and rear for the superior braking ability. Harley Davidson didn't offer a front brake until 1929, so this is a needed update.

Mayfield chose to use Bultaco Pursang wheels front and rear for the superior braking ability. Harley Davidson didn’t offer a front brake until 1929, so this is a needed update.

Till next time,

Old #77

Brent