The Imperiled Life of the Kickstarter Cotter Pin

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Cotter Pin

Dave Porter Portrait 2

‘The Imperiled Life of the Kickstarter Cotter Pin’

By Dave Porter, Customer and Technical Support at The Bonneville Shop

One of the hallmarks of vintage BSA and Triumph motorcycles is the kickstart feature, a very simple and effective way of turning over the engine to initiate starting. In most cases, the transmission is engaged by the action of the kickstarting lever, which in turn rotates the primary drive to turn the engine’s crankshaft. Electric starting became the norm by the early 1980s, although the ubiquitous kickstarter remained in place on the late Triumph T140s, as a back-up system when the battery or starter motor wasn’t up to the task of turning over the engine.

“When the cotter pin becomes distorted from use, it can allow the kickstarter lever to rotate slightly on the spindle, effectively reducing the amount of sweep the lever moves on the downstroke.”

One very important component common to all of the pre-unit and unit-construction BSA and Triumph singles, twins, and A75 and T150 triples was the kickstarter cotter pin. The cotter pin was essentially a wedge-shaped pin constructed from mild steel that was designed to lock the kickstarter lever to the kickstart spindle. There had to be a provision allowing the lever to be removed from the spindle so the outer gearbox cover could be removed for transmission service, so the cotter pin was employed to join the lever to the spindle.

Unfortunately, the cotter pin is subject to a fair bit of abuse, both during installation and in use. Most BSA and Triumph twins in stock condition are not too difficult to start, at least compared to larger displacement single-cylinder engines, such as the BSA B44 and B50 models, and as a result, it takes a long time to develop a worn kickstarter spindle or lever. Other parts in the system are also prone to wear, such as the kickstarter quadrant and kickstart pinion. When the cotter pin becomes distorted from use, it can allow the kickstarter lever to rotate slightly on the spindle, effectively reducing the amount of sweep the lever moves on the downstroke. This condition contributes to hard starting, particularly in the case of motorcycles using electronic ignitions, which require several revolutions of the engine to fire the ignition. Hard starting means more frequent use of the kickstarter, which accelerates the wear on all of the aforementioned parts.

Options for Cotter Pins:

Since the kickstarter levers and spindles are subject to wear, often exacerbated by worn cotter pins, we offer the pins in three conditions:

57-4356 is the standard replacement cotter pin, measuring 9.5mm O.D., with a body length of 1.33”, and a threaded length of .550”. The flat cutaway runs the entire length of the body. This cotter pin is suitable for use where no discernable wear or distortion is present on the kickstarter lever hole, and the flat on the spindle is unworn.

57-4356 OS also measures 9.5mm O.D., with a body length of 1.33”, and a threaded length of .550”. The difference from the standard cotter pin is that the flat cutaway runs up to the head of the body, so more of the circumference of the cotter pin body is available to fill the void left by the wear on the lever and spindle. This cotter pin is intended for use on levers and spindles that show a moderate amount of wear, and the slight variance in the design will compensate for the wear when fitted correctly.

57-4357 A is noticeably different in appearance, not only in color, but in that while the O.D. still measures 9.5mm, the body of the pin is shorter, measuring 1.258”. The threaded stud measures .600”, longer than the standard 57-4356, and the flat cutaway runs up and terminates at about 2/3rds of the body length. The result of this profile is that more of the circumference is being pulled into the void left by wear and distortion. The threaded stud has to be slightly longer to allow for proper thread engagement of the nut on the stud. The 57-4357 A cotter pin is intended for use on considerably worn levers and spindles that are near or at the end of their service life.

“I had to cut through a kickstart spindle once due to the lever being welded to the spindle!”

Over the years I have encountered shims, nails, and ground down bolts in place of the proper kickstarter cotter pins, and in fact I had to cut through a kickstart spindle once due to the lever being welded to the spindle! As I mentioned earlier, the cotter pins are made of rather soft steel, and are easily damaged during installation. To prevent this, I suggest carefully drifting the pin into place once the cutaway flat on the pin is aligned with the flat cut into the spindle. This minimizes the load on the threads of the pin when the nut is tightened. The nut should not be used to draw the pin through the lever, as it will likely strip the threads or snap off the threaded stud from the body.

Need other parts for your Triumph transmission, check out our comprehension selection: Transmission (Gearbox) – The Bonneville Shop

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