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Chain and sprocket orientation
Q: I have several Japanese 2-strokes from the late 1960s and early 1970s and have an issue that has plagued me on countless motorcycles, both new and old, over the decades. I’ve never received an explanation that would seem to justify the sheer volume of instances I have run into.
Every time I align a chain and front and rear sprockets, I find the chain will almost never run centered over the sprockets. Now, I’ve known for over 45 years that the little factory indents/alignment marks on the swingarm are generally useless for alignment purposes, so I have used all the alignment methods I have ever seen, from name-brand alignment tools (which work great, by the way) to measuring and equalizing the distance between the swingarm pivot and the axle shaft, the string method, etc. I always check the sprockets themselves to ensure they are flat as a pancake and not tweaked. Most recently, I had a piece of steel machined to be exactly straight and laid it up against the two sprockets of my current project, finding they were misaligned by 1.65mm. I then removed 1.65mm from the countershaft sprocket spacer as there was more than adequate clearance and got those two sprockets aligned within a gnat’s behind, but to no avail. For clarification, the sprockets and chain are new and correct factory OEM parts. The result is always the same: The right inner link of the chain rides up against the right outside edge of the sprocket. Thus, the chain is slightly to the left of center. I always make sure I have the correct play in the chain measuring it multiple ways, including with the shocks removed and the countershaft, swingarm shaft and rear axle all in the same plane.
Of course I am also aware that frames and mounting points, etc., were not always perfectly in alignment from the factory 40-plus years ago and can get out of whack from living a hard life over the years. Therefore I also do my best to ensure the frame is not tweaked before I ever start on a project and rectify any noted problems I find.
Out of curiosity, I recently visited my local multi-brand dealership and I nosed around the street bikes checking the chain alignment on every brand new street bike on the showroom floor. Every single bike I looked at but one had the exact same issue. The chain was to the left of center and riding on the right inner edge. Even the used bikes I looked at had the same issue. The only bikes in the dealership that didn’t have the issue were the dirt bikes. I’ve often wondered if the issue was that the front and rear sprockets were not vertically parallel and I don’t know how to check that. But after seeing all the new bikes with the exact same issue, well, I give. —Chuck Floyd/via email
A: You’ve certainly put a lot of time and thought into this, and my answer is going to be so short you may be disappointed. Once you put any load on the gearbox the shaft deflects just enough to cause the chain to pull to the outside. It’s really that simple. MC
