Piston Replacement CRF450R

In this video, we show a scheduled piston replacement on a 2022 Honda CRF450R motocross motorcycle. The bike belongs to our colleague, Gennady Zyrin, who uses it for training and racing.

This generation of the motorcycle was produced from 2021 through 2024. We previously discussed the specific features of this generation:

However, this does not mean that the piston replacement procedure shown in the video applies only to those model years. The overall engine design has not changed since its introduction, so the video provides a general understanding of piston replacement for this model regardless of the production year.

According to the service manual (factory instructions), the piston should be replaced every 15 engine hours. A popular opinion among motocross riders is that on bikes like this, piston replacement is typically done at 90–100 engine hours. Gena follows a less common view: if you change the oil on time and constantly monitor the condition of the air filter, replacing the piston once every 150–200 engine hours is sufficient. In this video, we tested which opinion is correct.

The replacement shown was performed at 160 engine hours. The piston showed only initial wear, and Gena confirmed that the replacement was done at the right time — it could have even been ridden longer. The cylinder and other engine components were in excellent condition. A standard-size piston can be installed.

Turn on subtitles in the language you need to see important comments about the process.

Interesting insights from the engine builder who assisted us with the piston replacement:

• This model is very reliable in terms of durability. The same cannot be said about the 250cc version, which has significantly lower service life and reliability.
• Before removing the fuel tank, it is not necessary to relieve fuel pressure (even though this is stated in the manual). From experience, fuel does not leak when disconnecting the hose.
• After removing the seat, plastics, and fuel tank, be sure to blow off the engine and surrounding area with compressed air, as there will be a lot of dirt.
• To replace the piston, it is not necessary to remove the subframe completely (as stated in the manual). It is enough to “detach” it — remove the upper mounting bolts and pivot it down on the lower ones (see video). This saves a lot of time.
• In the video, you will also see several other simplifications compared to the service manual that make the piston replacement easier and faster.
• Before installing a new piston, it is advisable to test-fit it in the cylinder. Insert the piston (without rings) into the cylinder in the correct orientation. The piston should move freely inside the cylinder without binding. There should be no longitudinal play; slight lateral play is acceptable. Check this at different insertion depths.
• Installing one piston pin clip and fitting the piston into the cylinder is much more convenient to do in advance on a workbench (see video).
• Tightening the cylinder head bolts is a very critical procedure. The four main bolts are tightened to a high torque, which causes them to heat up. Therefore, the torque should be rechecked a couple of times, allowing the engine to cool between checks (about 10 minutes between inspections).

Some riders wonder whether to replace the piston themselves or go to a professional mechanic. Our answer is:
If you have successful experience with advanced motorcycle maintenance (for example, replacing a piston on a two-stroke motorcycle), and you are careful and patient, then with proper tools you can replace the piston yourself.

If you have doubts or lack experience (for example, even installing a piston pin clip requires a certain level of skill), it is better to consult a professional.