CMS-Japanese Motorcycle Supply Parts

Converting the Honda CX500 or GL500 to an electric fan

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A popular - if somewhat controversial - mod is to replace the stock mechanical fan with an electric fan.


The stock mechanical fan is attached to the end of the camshaft, and spins at the same speed that the camshaft does - which is half that of the crankshaft RPM. This means that if your engine is idling at 1,100RPM your cooling fan is spinning at 550RPM, and if you're caning along at 10,000RPM your fan is spinning at 5,000RPM.

Looking at this aspect of the cooling system independently it's not an ideal setup - say you're idling in heavy traffic in the middle of summer in 45 degree C heat - you are probably going to want your cooling fan running faster than the absolute minimum speed to keep your engine cool. Conversely, when you're belting along at 100km/hr in winter and have plenty of cold air flowing through the radiator you probably don't need the cooling fan spinning at top speed. Moving to an electric fan allows you to base the fan speed on the coolant temperature entering the radiator and not engine RPM; when it's hotter, the fan will spin faster as needed - simple as that.

Some also say that reducing the amount of things that the engine has to work to move constantly will lessen the strain on the camshaft/engine in general. We haven't seen any measurable evidence that this helps.

The mechanical fans are known to develop cracks, which if unnoticed can result in the fan shattering into the front of the radiator, leaving you potentially stranded and requiring a new radiator.

You also don't see any modern bikes running mechanical fans - they've all moved to electric, which is presumably better based on that.


If it ain't broke, why fix it?

The fan is only one aspect of the cooling system; the amount of coolant flowing though the radiator is governed by the thermostat, so the fan spinning more than might perhaps be necessary is not going to automatically result in your engine running "too cool".

As a counter-argument to the "less spinning mass = good" aspect of the argument for the conversion, it has been suggested that the camshaft is balanced with the fan's spinning weight on the end and by removing it there might be some negative consequences. We haven't seen any measurable evidence that this is a problem.

The stock mechanical fans have cooled many CXs beyond 200,000km, and it's a proven design by one of the biggest motorcycle companies - can you do better with your own design?

Also, new mechanical fans are readily available, and are likely to be cheaper than the conversion to an electric fan.

If you decide you would prefer to move back to the mechanical fan down the track and have chopped your camshaft down, you need to find a new camshaft.


A writeup on this will be coming... eventually. Some of the photos are done, but it's well down the list! Some notes;


The protrusion on the end of the camshaft for the fan to mate to will likely get in the way of a new, electric fan. It is possible to cut it off without removing the camshaft from the engine; you just have to be very careful not to get any metal shavings into the engine. This is a rather permanent change.

Even after removing the end of the camshaft, you still need to find a reasonable shallow fan to fit in the available space.


Check the amperage draw of the fan for suitability! We'll add some info about what's suitable and what's not.

Fans known to work

Mounting locations for the fan switch

You could locate the temperature switch in a number of locations in the bike, but it helps to be aware of where the coolant is flowing to/from in the system.

A temperature switch for the electric fan has been seen to be mounted in the following locations in various conversions:

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