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Bike Profile - Posted 19th June 2009

Honda CX500, Part One
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Two decades ago, Simon Lock had just gotten used to riding his somewhat tired CX when its camchain needed some attention. Out with the engine, then...

The CX, being a transverse Vee, needs its engine to be dropped out of the frame and swivelled through 90 degrees to get the rear cover off and get at the camchain. This was all pretty straightforward but time consuming for a newcomer. Still, it all went well. The camchain tensioner had, of course, failed and the rattly camchain had been eating through a main bearing mounting bolt. It had gone quiet because it had eaten quite enough of that bolt, thank you very much.

I decided that my experienced friends had a point.

When brown was cool... 1979 Honda CX500 advert

It was all pretty simple to reconstruct until it came to the mechanical seal that separates the water pump impeller from the engine internals. This beauty is 51mm in diameter. The hole it fits into is 50mm in diameter. After 20 years there is a reason why I can still remember these dimensions precisely. The seal is a delicate little affair that cannot be safely whacked with a big hammer. My only transport was now a bicycle...

After a night in the freezer for the seal and use of a propane torch on the case it was still no go. So I cycled off to my local back street bike shop with a case and seal hanging from one hand. They swiftly gave me an acetylene torch and told me not to leave it still for any reason. After five minutes of playing the flame over the case the seal just fell in. Phew! Back together it sounded great and life continued... with a wedding planned and honeymoon to the west country planned for the following month it all looked too rosy to be true.

And it was.

Some of the CX500's more attractive features. Yes, really...

On a nice running-in trip to Coventry with a mate I stuck to 50mph on the way there. On the way back I opened it up and got to 50mph before it died and came to the well-known silent halt that the Superdream used to do. After a bit of worrying I tried the starter and off we went. Provided I kept below 50mph all was fine; above that it stopped for regular rests. After a night's thinking I deduced fuel starvation but just couldn't find a problem. So it was 50mph for a week... slower than the Superdream. Sigh…

Until I looked up the petrol pipe and saw the flap of rubbery stuff half blocking it. Job done.

Der wirtschaftliche Allrounder. Can't argue with that... 1979 Honda CX500 brochure

A week or so after that I noticed the temp gauge tending to hog the red area. Odd. Then it would be a problem to get the bike to start on both cylinders for a bit. It would start on one and smoke for a while before the other cut in. My powers of denial were still good at such a young age and even removing a plug, turning the engine over and watching the water fly out of the plughole didn't make me feel there was really a problem. I've no idea how I reasoned that the water had got into the cylinder but I wasn't going to think it was head gasket failure in a hurry. Until I stopped on the way home one evening that is, blipped throttle and watched in fascination as a jet of water shot across to the other carriageway. I did that again. Wow! That'll be the expansion tank being very pressurised then.

Off came the heads and new gaskets were applied. Naturally it only took two goes and the gaskets were bloody expensive. Still the honeymoon was fun and took in Glastonbury, Dartmoor and Cornwall without any trouble, well, not from the bike. Then I moved back to Coventry to start teacher training. At which point the World's Most Frustrating Problem reared its head.

Try and think of a way of dealing with this one. Your lovely CX runs well. Really well. Until it warms up to operating temperature. Then it runs on one cylinder, but only over 5000rpm. And only under load.

This is a difficult scenario to replicate for diagnosis purposes and there were reports of a CX rider in the West Midlands riding around leaning over the side of the bike and not really watching where he was going.

It took three weeks of this anger-inducing behaviour to make me snap. But boy did I snap. Out came the world's biggest screwdriver because I couldn't take off the plug cap with my hand whilst moving. CX plugcaps are about three inches long and seal very well into the rocker cover.

There was an angry thrash up the road to warm it up followed by me leaning over and forcing the plug cap off with the screwdriver. It promptly flew into the road and smashed into two!

Honda CXs on eBay.co.uk

CX plugcaps are very expensive and I was very poor. In a blind fury with the machine I stuffed the one inch of plug cap back on and proceeded the wring the bike's neck. And it obviously got the message at once because the problem disappeared. Turned out the plug cap had a miniscule crack which had filled with oil. Once this warmed up it allowed the spark to track to earth giving me my problem under load. The nice stubby plug cap I was left with worked just fine for the next two years.

And so life went on. A tiny bit of swarf, probably from the old camchain wear, killed the alternator one day. It's very nice when you are a trainee teacher to have to ask your Head of Department to assist in pushing a heavy shaft-drive bike around the playground in the snow to get it started... So a weekend was put aside for a new alternator. £15 from the local rag sir. My kind of price.

Sometimes the bike would jump out of second, and eventually third, but it continued to provide sterling service.

Wassergekuhlter 2/Zylinder 4-Takt-Motor mit eingebautem Radiator. Can't argue with that... 1979 Honda CX500 brochure

Like Superdreams, CX500s are indelibly linked in my life with both wonderful and awful moments. The accomplishment of that first major engine work, the touring to new places, managing 98mph in the search for a ton and the familiar whirr of the water pump all bring back fond memories. I'll try and forget the fury-inducing mechanics, probably because my own inexperience was responsible for quite few of them, along with the near-misses.

I've often thought about getting another one but I think I'll let it remain a fond memory - after all there's so much that can go wrong!

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If you're tempted to try a CX today, then the Vintage Japanese Motorcycle Club would be the chaps to help you find the bike of your dreams: www.vjmc.com


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