Retro-fitting A CV Carb On A Shovelhead
Article & Photos By: Will Ramsey – Faith Forgotten Choppers – faithforgotten.com
Originally Published In The December 2014 Issue Of Cycle Source Magazine
This is the second installment of a two part tech article on retro fitting a CV carb to a shovelhead motor. In the first article we fabricated a new intake manifold by welding a machined adapter to an existing manifold. In this article we will present one solution to the problem of securing the CV carburetor to the shovelhead motor. Since these carbs were originally used on Evolution motors, the support brackets were designed to bolt to the top end breather holes. As a Shovel head breathes from the case, there are no top end bolts to support the carb. So our solution is to fabricate a carb support that will attach to the underside of the rocker boxes. In this example we are using 304 stainless steel so that the final product can be polished to a mirror finish.
The fabrication of the CV Carburetor support begins at Tooling Ventures, my friend Brian’s machine shop. This is where we design and machine all of the CNC parts for Faith Forgotten Choppers. The big Hurco Mill makes quick work of machining the front of the support bracket.
After the bracket is profiled in the mill Brian uses the manual lathe to sand the radius on the outside of the bracket. We do this manually in order to create an accelerated radius which leaves a flatter area on the outer diameter. It’s really just a matter of taste and design choices. Notice that Brian uses blue layout dye so he can blend the radius up to the edge.
While the part is still in the lathe Brian polishes the outer diameter which will be visible after final assembly. Although the part will be fully polished after fabrication it is always easier to pre-polish parts when you can. It will save a lot of time during the final polish stage.
Now the new bracket can be bolted to the CV Carb. The next step will be fabricating the parts necessary to attach this bracket to the rocker boxes.
Here you can see the threaded hole in the front rocker box originally used to support the stock carburetor on a shovelhead. We will mark, drill, and tap a matching location of the rear rocker to increase stability of the support and to create visual symmetry of the entire assembly.
A machinist’s scale and a sharpie are sufficient for marking a drill hole for the rear rocker box.
When manually drilling a hole it is always better to center punch the location. This allows the drill bit to start easily without walking across the material.
*Trade Secret* Obviously the depth of this drill is important as we don’t want to drill into the box and create an oil leak. The use of Dykem (or any layout dye) is a great way to mark a drill bit and allow you to accurate gauge your drill depth. Unlike tape, the dye cannot move and the bright contrast makes it easy to see.
The hole is carefully drilled by hand for a 5/16 x 18 thread. This correct drill size is “F”. You can clearly see in this picture just how effective the layout dye is at gaging the drill depth.
The drilled hole is hand tapped for a 5/16 x 18 thread. The use of a tap guide is very helpful in keeping the tap square to the rocker box.
*Trade Secret* Whenever I machine a bung that will be welded to form a mounting bracket of any sort, I always drill the hole “on size”. This helps minimize the shrinkage during the welding. After the final weld is made I will drill 1/64”-1/32” over for clearance. This tip will ensure that any bracket you fabricate will fit back in place with ease.
This step is not necessary but I prefer to countersink the bungs to allow the bolt head to sit flush.
½” round stainless is cut to length, and a drum sander is used to fit the rod to the machined mounting bung on the rocker box.
The rods are welded to the bungs and to the support bracket attached to the CV carb.
A high performance K&N air filter and cover supplied by Joker Machine adds the final touch to the assembly. I have always used Joker Machine products for this application because I like the clean and simple look of their design. As always if you have any comments questions or concerns regarding any of my tech articles please feel free to contact me. Thank You! email@example.com References: www.faithforgotten.com www.jokermachine.com