CX/GL 500/650 Radiator Removal, inc. fan and tachometer drive casing

This site will tell you how to remove the radiator, fan and tachometer (rev counter) drive mechanism. I am very receptive to comments and suggestions but you use this information at your own risk.

Skill Levels explained.

Skill Level : 2. Personally dirty : 2. Work mess : 2. Tools : 1. Space : 1.

Cooling system (left) for CXs and GLs. Hot liquid is shown in red and cooled in blue.

Coolant is pumped by the water pump impeller directly to the left and right cylinder jackets, where it carries away heat produced by the engine. The liquid is pumped upwards from each cylinder to the thermostat. If the engine is not at normal working temperature, the thermostat is closed, and the coolant recycles directly back to the pump, along the feeder pipe at the top of the engine. This helps the engine reach its full temperature quickly.

Once the temperature is raised, the thermostat opens and allows coolant to run into the top of the radiator and down through the fine chambers, where the rush of the slipstream, aided by the fan, cools it. It then runs along the chrome transfer pipe and back to the pump.

Any excess coolant overflows from the top of the radiator and into the opaque reservoir bottle at the rear of the engine. If the coolant level drops, liquid is drawn from the bottle back into the cooling system, and recycled. That is why you top-up the coolant from the reservoir, not the radiator.



You don't need to remove the engine from the frame. In most of these pictures, Valiant's engine is removed, but it was out anyway, for other work to be done.

Remove the petrol tank and radiator cap. Drain the coolant into a bin or drain tray, by removing the small plastic drain plug at the bottom of the radiator (circled, right). This plastic bolt is fragile and should be treated gently, especially when ressambling. Don't screw it in more than finger tight.


Use an allen key (left) to unfasten the top of the radiator shrouds, left and right side. Early CX500s have a one piece black plastic shroud which bolts on as per the following photos.






Another Allen key unfastens the shrouds' side holding bolts. Lift the shrouds away and give them a good clean.








Your engine has either:-

14mm bolts (left) through the radiator surround and these also clamp the engine to the black engine hanger. Your engine should not drop out when you remove all four bolts, but if you are working with the engine in the frame, it would be sensible to support it with a block of wood underneath, held up with a jack. This will save strain on the other engine bolts. These bolt holes can strip out, but can be repaired with a suitable kit.


Instead of these bolts (which are usually fitted when crash bars are added) there are steel studs which are screwed into the aluminium engine casings and poke through the engine hanger and radiator brackets, with a 14mm nut on the front ends. If you have these studs, remove the 14mm heads.


10mm dome nuts (right) hold on the three round chromed holding bolts which attach the radiator assembly to the engine hanger.






Once unbolted, these pull straight out. There's a chrome mushroom affair (left) which passes through the rubber anti-vibration mounting grommet.







Pull the overflow hose (right) off the top of the radiator, directly underneath the cap.







Unfasten the big double wire circlip which clamps the main radiator hose to the thermostat assembly, directly under main spar, and pull off the hose. These are often quite reluctant to get clear; don't use anything likely to puncture the hose or damage the radiator.








Undo the four Allen bolts (right) which hold the chrome water transfer pipe down the left hand side of the engine. The pipe then pulls off at the water pump end just forward of the carburettors, and some coolant will probably spill out.







To prevent foreign objects getting in, stuff a piece of rag or kitchen roll into the end (left).






The radiator should then just pull away. Lay it on a flat surface (right), where it can't be damaged, as the fins are very fragile. Unbolt the fan's protective screen mesh or guard.

On models with the electric fan, disconect the fan's power lead and it comes off as a complete unit with the radiator.




This leaves the fan and the circular radiator housing. The housing should also just pull off, although it needs some wriggling to get it round the frame, especially if you have the engine studs rather than the bolts.










Replace the radiator cap, and use a water jet (right) to blow out any accumulated dirt or debris. Be very careful about poking anything between the fins as they are very delicate. Use the water jet in both directions.

I was lucky and had a particularly mild late February afternoon!

Squirt the water jet down the open end of the transfer pipe to reverse-flush the radiator. Keep squirting for several minutes, at least until you can see quite clean water coming out where the top radiator hose attached.






Give the fan a good clean and particularly, check the blades for cracks and distortion. A cracked fan can explode and wreck the radiator, so if there is any wear or damage, replace the fan.

500s have the mechanical fan which is a push fit on the end of the camshaft (left).








The mechanical fan unbolts with a 10mm bolt (right) onto the front end of the camshaft. Sorry, 650 owners, but I don't have any pictures of your thermostatic electric fan. This is the mechanical fan of the 500s.





Now the fun begins, as you will need a front axle to remove the fan. Altough the fan is a simple push fit onto the tapered end of the camshaft, it tends to stick very firmly. However the thread let into the boss of the fan is the same as that on the end of the front axle (left).

I was lucky - I have a spare front axle - otherwise, prop up your bike and remove the front axle temporarily. The fork seal page tells you how to do this.

Use the axle to screw into the boss of the fan, and wriggle the fan off the end of the camshaft.

When you put the fan back, first smear some grease over the tapered camshaft end. Hopefully it will come off more easily next time!






Exposed tachometer (rev counter) drive at the front of the engine. This is held on by three 8mm head bolts, and the casing can then be teased off with gentle levering.

Remove all traces of the old gasket, on both the engine and the tacho drive casing.



This is a straightforward reversal of the removal, with new oil seals in the tacho casing and a new gasket between it and the front engine casing.

CX engines tend to leak oil from the seal inside the tacho casing, the seal which fits over the end of the camshaft, so always replace this seal, and the small one which fits deeply inside the hole where the tacho cable goes in. These seals should be part of a gasket set. Smear some grease over the camshaft end before refitting the tacho drive cover.

When refitting the radiator, use a new O ring at the junction of the water transfer pipe and the water pump. A leak here is easy to fix, but I also use Hylomar as an extra precaution. To help get the big hose back onto the radiator, smear a little grease over the outer circumference of the junction.

The O-ring at the water pump end of the chrome pipe has a compatible replacement which is easily obtained from any UK Homebase DIY store's plumbing section. The part is Tantofex 1162 and comes as a set of 2 washers and 2 O-rings. The washers are no use, but the O-rings proved to be a perfect match for the bike. At £1.75 for the pack of 2 they are much cheaper than the genuine ones.

Incidentally I have sourced the water transfer pipe and junction-to-cylinder-head o-rings at 20 pence each and I bought a dozen each of these for a fiver all inclusive. If you need these o-rings, contact Seals and Components Ltd, Village Road, Norton, Shifnal, TF11 9ED, Shropshire. Tel: 01952 730685. Fax: 01952 730665. The larger o-rings which seal between the 90-degree water junctions to the cylinder heads are BS-119 and the smaller and slighltly thinner ones which seal each end of the watertransfer pipes to the thermostat and junctions are BS-118.

Radiators can be repaired if they leak, but this is a specialised task best left to an expert.

When refilling the radiator, use a 50/50 mixture of distilled or deionised water (battery water) and silicate-free antifreeze, with its distinctive orangey-yellow colour. Silicate-free antifreeze is much better for the ceramic seal and cooling system generally. UK readers note that if you buy antifreeze from Halfords, it should be the more expensive "Advanced" formula, which does actually say silicate-free on the rear of the bottle.

Sidecar Bob from Canada comments : "Coolant is only good for a couple of years, and changing it is almost as important as changing the oil. If your cooling system hasn't been properly serviced in the last couple of years, this would be a good time to do it. You should be changing the hoses, rad cap and thermostat too.

"Take the old parts to your local AUTO parts dealer - he can supply them for much less than your Honda dealer. Depending on your model and year, the hoses may be short pieces of bulk hose, or (if sharp bends are required) may be able to be cut from an in stock heater hose. Don't forget new clamps - stainless ones aren't too expensive and you will be able to undo them without stripping something when you do it again in 2 years. The thermostat is the same one used in late '70s Civics (I have been using them in GoldWings for years). Rad cap is a standard automotive 13psi. You should replace the 0-rings at the ends of all the tubes in the cooling system. There are 5 rings, all the same size for the tubes and 2 for where the jointsbolt to the engine. They should have a perfectly round cross section - not oval or square. There is also an o-ring in the thermostat housing that should be changed.

"If you leave the rad cap on and open the cap on the overflow tank when you open the drain screw, the fluid in the overflow tank will be siphoned out. Once the tank is empty, remove the rad cap and throw it out. It's easier to change the hoses if you remove the rad. When you have it off, remove and throw out the thermostat, re-assemble the 'stat housing and flush the engine with a garden hose in the upper rad hose. Flush the rad too, and hose it off while you're at it. You wouldn't believe how much debris you can get out of the rad by spraying with a garden hose from the engine side. All those bugs &c that went in the front at highway speed and didn't come out the back for years are impeding the efficiency of your cooling system."

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