Saturday 19 March 2011

Honda CB125S/CB125J


TAN 26N was bought in the summer of ’84 for the princely sum of £100. On arriving to look at the bike, it appeared to be in good condition for the year with both chrome and paint still in evidence. The engine looked good externally with no visible oil leaks or signs of butchery.

It had no MOT or tax but according to the owner had recently been rebuilt by him. This last point made me a little suspicious. Why, if the bike was in such good condition for its age, hadn’t the owner put a years MOT on it and another £100 or so on the asking price? I decided to give the beast a test ride. I started the engine first kick and listened for any unusual noises from the 125cc OHC single cylinder engine, in particular the cylinder head.

If oil changes are skimped on these machines the head is easily ruined due to blocked oilways allowing drying up of the camshaft bearings. If this happens a replacement head is needed and costs more, new, than the bike is worth secondhand.

No nasties were evident as it ticked over evenly and quietly. I took it for a spin around the block and everything appeared fine. It pulled well throughout the rev range in all the gears and seemed lively for a four stroke single. That was it, I decided to buy it.

It failed the MOT, according to the tester the frame was out of alignment. This pissed me off excessively, with visions of the machine being a write off due to the expense of frame replacement, especially as the rest of the bike was good. I took it to another MOT tester where it passed with a compliment about it being in good shape for its age! I put the bike through another three tests in the time that I owned it and all it required was a new exhaust.

Servicing was simple. Just change the oil every 800 or so miles and check the tappets at the same interval. Usually, no adjustment was required but when it was, patience was needed as adjustment is a little awkward. Two thou is a ridiculously small gap to set accurately. Each time the gap was set and the locknut tightened, the gap invariably went down to one thou or disappeared altogether.

Perseverance is the answer as it is important with such a small gap to set it accurately. Ignition timing is dead easy to set and rarely seems to go out anyway. In all the time I had the bike (about four years), I only ever bought one replacement spark plug. It just never seemed to wear out.

Performance for a 125cc single of its age was quite good. If wound up in the gears, acceleration was quick enough to out accelerate most cars in the city and it cruised at 60mph without having to thrash it (I prefer whipping myself anyway). Top end was a bit over 70mph. One had to be careful of artics breathing down one’s neck. When this occurred I always felt that this great hissing monster was about to devour me (well, at least it makes life exciting). Headwinds took their toll on performance with the bike having to be worked hard to maintain a high cruising speed.

Starting was always a one kick operation. The bike always lived outside, and no matter how freezing cold or wet, the bike never failed to start and warm up quickly without fuss. This used to give me a perverse form of pleasure as I listened to numerous cars in our roads churning their engines over and over on cold winter mornings. 2CVs seem to be particularly prone to this activity in cold weather.

It was light enough to hold upright when slides started by just sticking both feet down and praying hard. I never came to any grief so I must have been doing something right. Generally, overall handling was not good. On bumpy surfaces the suspension felt far too soft and when bumpy surfaces were combined with bends at any reasonable speed, all sorts of unwanted contortions took place. Modern 125s show just how much suspension has improved since this machine was made.

Lighting, is another story. Although the electrics were always reliable (never any problems with flat batteries, etc), the power of the 35 watt headlamp left a lot to be desired. Even in poorly lit streets I found the beam inadequate for safe riding much above 40mph. I considered fitting a higher wattage bulb, but on looking at the electrical specifications I found that the total alternator output was only 45 watts. A bulb of any higher wattage would not leave enough power for the ignition and rest of the lights.

As it was, the engine would sometimes stall on tickover when the headlamp was on and indicators in use whilst waiting at junctions for any length of time. I can only assume that the drain on the system was such that the voltage dropped enough so as to stop the coil producing an efficient spark. Once riding along there appeared to be no problem except that the headlamp beam dimmed significantly each time the indicators flashed. Later models had 75 watt alternators which must have improved things a lot.

Braking also left something to be desired. Brake fade from the front SLS drum was noticeable. Locally, this was particularly apparent when speeding down Grapes Hill in Norwich and the lights turned to red at the bottom. The front would start to fade when applied hard although the rear held up well. This also seemed worse in hot weather. It seems that the cooling of the linings must be the problem here. However, at least the braking was unaffected in the wet.

Given that I was not a high mileage rider or used the brakes particularly hard, the life of the shoes seemed rather short. This was true for both pattern and genuine parts. I always cleaned out the drums and made sure that all the spindles were lubricated so as to ensure the brakes were not binding on. I can only assume that this must be something to do with the lining quality.

I finally sold the little Honda just before Christmas last year for £200. Not bad considering that I only paid £100 for it and got four years of basically trouble free use from it. My reason for the sale was that I finally got round to passing the bike tests and wanted something with more zap.

I ended up with a rebuilt air cooled RD250 which certainly fulfils the zap department. However, it has recently cost me more money in parts and running costs that the Honda ever did. I still see the bike around the city and it appears to be going well and still looks in good shape. The bloke that bought the Honda never even bothered taking it for a test ride. He looked it over, listened to it running and said, It sounds like a good 'un, and handed over the £200.

Would I have another? Yes, if I were to use it just for commuting to work, but since I also like a bike for entertainment ppurposes I really want something with more performance. A Honda CB125S is an excellent and inexpensive way for someone to get into biking provided that a good example can be found. In many way I found it a rewarding machine to own and hope that it gives its new owner the same service it gave me.

Steve Crook

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For fifty quid I thought I couldn't go wrong. The engine still ran. The MOT certificate was only a month old. The consumables had plenty of life left. The object of my attention was a 1976 Honda CB125J. The mileometer read 49,560. Red Hermatite on the engine joints gave away its hard life. As did the puddle of oil.

The CB125J has an OHC, two valve single cylinder engine. It roots go back to the sixties and the CB150. Engineering on these little thumpers is rather spartan. None of later excesses, like balancers or twin choke carbs. Simplicity and natural ruggedness were its calling cards. The compactness of the motor is echoed in the chassis.

The engine is slapped into a single down tube frame, straight out of the fifties. The CB floated like a duck on ragged, worn out suspension. When they were new they might've had some damping. The shocks and forks were now both weakly sprung and prone to sticking. The road bumps played havoc with my backside and arms.

But that was the least of my troubles. Nearing home a canine rushed out under my front wheel. I grabbed the front brake and twisted the bars. The dog escaped except for having its tail shortened. Judging by the screams of the huge dog and little old lady owner it'd been castrated. The CB has a curious disc front brake. The caliper is operated by cable, a worm mechanism translating the motion of the cable into braking forces. That was the theory, anyway.

The brake hadn't worked very well until I'd applied adrenalin inspired muscular input. That had squealed the front tyre. A dubious Taiwanese import that threatened to slide away from under the bike. Often felt like I was skating along on the wheel rims. I was quite impressed with the stopping distances. Until I realised the front brake was locked on solid. Dropping the clutch with 9000 revs up just stalled the engine dead.

I sort of pushed and dragged the bike the remaining couple of hundred yards home. Screams from my once friendly neighbour echoed down the street. She was acting like I'd put a hand up her skirt. Rather than mildly attacked her fido. Hammer and spanners soon released the caliper. The pads were so worn they had started to crack up. I was riding around on a potential death-trap. New EBC pads and some grease on the mechanism. Half a dozen washers in the forks to help out the springs sorted the front end.

Starting had proved elusive. Trying to remove the spark plug was no fun. Felt like it was corroded in solid. Left it to soak in penetrating oil overnight. Whacked the socket wrench with my biggest hammer. It moved a fraction, groaned as I carefully undid it. I was relieved, the last thing I wanted was to break off the plug in the cylinder head. The old plug was so corroded and covered in crud it was a wonder the CB had ever started. The shiny new one started to cross-thread but I caught it in time.

Despair set in when I clocked the points. So worn they surely must've been the originals. I found a set that almost matched from an auto-accessory store. Needed a bit of filing to make them fit. A deep blue spark at the plug was my reward. A new battery completed the electrical renaissance.

Starting became a one or two kick affair. A serious lunge was required despite the lack of capacity. The lights were pathetically dangerous. Discouraged riding in the dark. For loitering in the well lit town centre they were marginal. Most of the wiring seemed newish. The horn was a gruff bleat. It didn't matter as the rotted silencer gave a warning bark to wandering car drivers. The whole exhaust was hidden under a thick layer of rust.

The engine ran quite well. The main hassle, a 5000 to 7500rpm flat spot. I put this down to the rotted silencer affecting the mixture. It was so annoying that I bought a new OE exhaust system. It was heavily discounted, cheaper than buying a universal megaphone. The flat spot was still present but a less traumatic 5000 to 6250 band.

Riding around this proved difficult. The gearbox had only three ratios that could be relied upon. Fast progress demanded revving the hell out of the engine whilst punching the engine through the gears. Old Honda gearboxes have a strong reputation as anti-theft devices.

Anyone who rides old Honda hacks should expect as much. What I was getting for my fifty quid was an engine that ran nearly faultlessly, within the above constraints, for the past year. Top speed was a splendid 75mph. It wasn't sustainable. Down to the thumper vibes and chassis wobbles. A constant cruising speed was more like 55 to 60mph. I could live with that for most of the time.

The only engine faults were a rattly camchain and copious oil leaks. The bore and piston are supposed to be short-lived but mine gave no trouble. Maybe the piston was an improved design, I doubted that it was original. The camchain tensioner wasn't automatic but could be bodged. The oil seemed to weep out of every engine joint. The sump didn't hold much oil, could be run dry in about 200 miles. The few long runs I did I strapped a five litre can on the back. Once it ruptured, laying down an oil slick. I think it was the vibration that split the can.

Such runs were always a bit of an adventure. It felt like I was battling against the elements. The seat wasn't original and wasn't much cop. Went hard after about fifty miles. Doing 250 miles in about six hours left me with a John Wayne stagger. A total disinclination to get on the bike again. That lasted for three days.

By riding like a complete jerk I could keep up with modern (restricted) 125s. The ones I tried had brilliant handling and excellent suspension. But the speeds they could legally travel meant none of that mattered. What counted was the willingness to make wild overtaking manoeuvres. And, hang on come what may. As both brakes were seriously useless I didn't have much choice but to charge forward.

Even when thrashed fuel was a remarkable 85mpg. The more usual commuting chores meant a gallon lasted 110 to 120 miles. I think it was more expensive on oil than petrol. What kept surprising me was that it didn't get any worse when the engine went off tune. Or when I'd added 11000 miles to the clock during the year I'd owned it. The tyres, as they were like iron, still had a bit of life left in them. The EBC pads lasted about 9000 miles.

One benefit of owning the CB125 was that complete strangers would come up to me and rave about the little Honda. They usually reckoned that it was a brilliant bike that hadn't given a moments trouble. Two of them had mouldering old wrecks stashed away. Mine for free if I came to take them away. One had been crashed, had quite a few salvageable engine bits. The other had seized, spent about a decade rusting away. There was nothing that was worth keeping. The frame, for instance, had rusted right through. A few hammer blows reduced it to dust.

The bike isn't often found in breakers, getting a bit too old for that. CG125 chassis parts can be adapted. I reckon it's even possible to shoehorn in a CG engine. I've actually put most of the cosmetic bits into a reasonable state with a rub down and paint job. My latest improvement was a pair of Girling shocks. They are a bit stiff but stop most of the wallowing. A little sideways play in the swinging arm was removed with a couple of washers.

The last MOT was the usual laugh. A dingy back street centre notorious for its laxity. A gruff old bugger reckoned he couldn't hear the horn nor see the lights. He didn't cop the dubious swinging arm or pathetic brakes. I distracted him by asking about his days on British bikes. Exited with certificate in hand.

To be honest, I just bought the bike to ride into the ground. After the first couple of months I began to realise that the engine wasn't go to blow up. I rather liked the amount of effort needed to get it to flow through traffic. Perverse, perhaps, but it's all about arriving at a destination full of satisfaction.

R.L.L.