Article & Photos By: Will Ramsey
Originally Published In The February 2016 Issue Of Cycle Source Magazine
Older vintage motors are full of exciting surprises once disassembly starts. Often times they leave you wondering how the hell they were even running before you got to them. A very common problem found in older motors is excessive wear and grooving around the breather gear. Once the damage becomes significant enough you will find yourself with yet another point of oil leakage. S&S Cycles offers an oversized breather gear that is perfect for fixing this problem. Not only is this a high quality part, but S&S has managed to improve the efficiency of the breather gear by enlarging the window and modifying the timing. This tech will illustrate the machining process we use to clean up the gear cavity in the old case, and fit the new S&S breather gear.
This American made S&S oversized breather gear features both an enlarged window and scavenge port, allowing for more efficient air flow and oil scavenging from the flywheel cavity.
Photo 2: The circular grooving in the breather cavity is common place in old motors. The more severe the grooving, the more issues you will have with oil blowing out of the bottom end. The oversized breather gear is a perfect solution.
Take an initial measurement with a telescoping bore gauge to record your starting point. This diameter will vary slightly between motors due to different amounts of wear
Mic the breather gear to determine how much material will need to be bored out of the case. S&S recommends between .0015”-.003” clearance between diameters, with a wear limit of .004”. Using patience and precision, we will shoot for the smaller side of this spec.
When preparing a new setup on the mill we always clean and stone the entire mill table. This removes any burs or residue ensuring that our set up will sit square to the table.
The last thing to touch the surface of the mill table is my bare skin. This is an important practice I learned from my friend and mentor Brian Howell. The skin on your hand will remove any remaining particles from a metal surface, allowing a precise set up.
It’s always a good idea to check the tram on your mill, especially when working with vintage motor cases. This practice confirms that the cutter is square to the table and will not inadvertently bore a skewed breather gear cavity. Take the time to do it right the first time
Rather than just setting the case flat on the table and allowing it to rest on the index ring, we use “matched” 1-2-3 blocks to set the case on the machined gasket surface of the case. Developing correct and safe set ups in the mill can be challenging and fun. Try to think critically, and always visualize a way to keep your part square to the linear movement of the mill table.
When clamping the case to the table, always be sure that the clamp is positioned directly over a supportive 1-2-3 block. This will avoid flexing the case or potentially cracking it if you over tighten a clamp.
A coaxial indicator (often called a coax) is used to find the center of the breather hole. Maintaining the center is critical to the final alignment of the gears. Check it, then check it again, and finally, check it one last time.
The boring head is secured in the spindle of the mill. In order to enlarge the breather cavity to accept the new S&S breather gear, we will bore the diameter of the case .0015” larger than the breather. The automatic quill feed on the mill allows us to get a very smooth surface finish on the bore.
It is important to take frequent measurements and think critically about the process. Advancing the cutter .001” will increase the diameter of the bore .002”. Using a boring bar takes patience and understanding. Often the cutter must be run two or three times at the same position to eliminate the flex in the cutter. Measure often and sneak up on the final diameter slowly.
Once the final diameter has been achieved we can test fit the breather. Since we took care to hit the smaller side of the diameter tolerance we have a very good fit. Precision is always king in this game and the machine work on this case needs to match the precision and quality of the S&S breather gear. Once the motor is assembled and the breather gear is shimmed to spec, we will have a trouble free case breather that is truly better than new. www.sscycle.com