A Yamaha TZR125 cylinder kit can look like a straightforward replacement, but the model name alone is not enough to confirm fitment. One of the most important details is whether your engine uses the earlier 3BN00 cylinder configuration or the later 3MB00 setup.
For riders working on a 1987–1992 Yamaha TZR125, checking the bore, stroke, cylinder type, and original parts before ordering can save a lot of trouble.
Why the Cylinder Type Matters
This Champoo Selected kit is built around the 3BN00 cylinder configuration used on listed Yamaha TZR125 applications from 1987 through 1992. The cylinder has a 56.4mm bore and 50.0mm stroke, with a listed displacement of 124cc.
The product page also notes that later 3MB00 cylinders use different dimensions: a 56.0mm bore and 50.7mm stroke. Those numbers are close, but close does not mean interchangeable. The listing specifically advises comparing the replacement with the original parts before installation.
What Comes in the 56.4mm Kit?
The kit includes one 3BN00 cylinder, one forged-aluminum piston, two piston rings, one wrist pin, and two circlips. The piston pin is listed at 16mm x 47mm, while the piston height is 64.4mm.
The replacement reference numbers include 3BN-11311-00 for the cylinder, 2YK-11631-04-35 for the standard piston, 3XC-11610-00 for the standard piston ring set, and 93450-17129 for the circlips.
Check More Than Just the Model Year
If your TZR125 has already been rebuilt or modified, the current cylinder may not necessarily match the configuration the motorcycle originally left the factory with. That makes a physical comparison especially useful on an older two-stroke motorcycle.
Compare the cylinder casting, bore size, piston dimensions, pin diameter, port layout, and visible part numbers with the replacement before ordering.
When a Top-End Replacement May Be Worth Considering
Low compression, visible cylinder damage, piston wear, or a seizure can all lead to top-end inspection. However, those symptoms should be diagnosed before assuming a cylinder kit is the only repair required.
For a 1987–1992 Yamaha TZR125 using the 3BN00 setup, this 56.4mm standard-bore kit may be a replacement option once the engine configuration and dimensions have been confirmed.
