CR125,250,500R aluminum frame conversion ③Cooling System Details


What you can learn from this article

This article shows the best way to rebuild the cooling section of a 2021-2023 YM CRF450 frame with a 1995 YM CR500 engine!

Review Aokuma-kun’s concept

おさらい あおくま君のコンセプト

Radiators are a consumable item in motocross.

It crushes easily when it falls over. In many cases, when it collapses, the only way to replace it is to replace it,

Welded repair parts are costly and time-consuming to produce each time.

In addition, welded repair products have difficulty in weld joint reliability.

There are two main difficulties: one is the difficulty of welding aluminum material and the other is the functional requirement of welding the water path.

Therefore, I wanted to use the mass-produced product as it is.

Confirmation of layout 1995CR500R

レイアウトの確認 1995CR500R

This is typical of the water routes employed in the two-cycle era.

The route for supplying cold water to the cylinders seems to vary somewhat from year to year.

My year model receives cold water from the right side from the water pump.

After the water from the cylinder head is distributed independently to the two radiators in parallel,

The water from the cylinder head is distributed independently and in parallel to each of the two radiators, and returns via a common route.

The water hoses themselves are minimal and of simple design.

The water hoses on the inlet and outlet sides to the water pump are close to the chamber,

It seems to be common to the 125, 250, and 500 that the inlet and outlet hoses to the water pump are close to the chamber and require attention.

Confirmation of layout 2022CRF450

レイアウトの確認 2022CRF450

On the 4-stroke 450, only the right radiator has an inlet to the water path from the cylinder head.

The left and right radiators are connected at the top by a large diameter connecting path.

The joint diameter of the final return path from the right radiator is

The joint diameter of the final return path from the right radiator is narrower than the joint diameter of the return path from the left radiator,

water flow distribution is adjusted.

Water hose connection path found by observation of actual equipment


The final water path found is shown in the diagram above.

The 450 mass-produced radiator is used as is,

The concept of the water route follows the existing CR500 as much as possible.

The key point was to use 3-way joints in two locations.

The first 3-way joint is a “Y” type HONDA mass-produced product.

The other 3-way joint is a “T-shape” type, which is a general-purpose product available on the market.

Avoid joining 3-way joints near the side of the chamber where clearance is tight,

We decided to join the 3-way joint at the rear of the cylinder, where there is more space.

What we used


The first 3-way joint is a “Y-shape” type, mass-produced by HONDA.

The other 3-way joint is a “T-shape” type, commercially available general-purpose product.

The water hose is cut from the part that can be used for CRF450 and CRF250 mass-produced products.

The connection is made with a commercially available general-purpose aluminum joint.

Find a usable “bent R” water hose and assemble it like a puzzle.

If I was asked to make another set, I don’t think I could. LOL!

Photographs of actual equipment


The chamber will have escaped perfectly~.

Cooling performance is


There is no particular problem with the situation, although we have not checked the temperature measurement or measured the flow rate.

The use of a CRF450 radiator and some extended water hoses have increased the absolute amount of water being used.

The cooling performance may be slightly affected by the increased water volume due to the use of the CRF450 radiator and some extended water hoses.

The above is a reference for the cooling system piping layout.

Thanks for reading.

2022CR500R aluminum frame conversion ①eng mounted