I have a 1984 Yamaha XS400 twin, one of the spine frame and DOHC engine types rather than the staid old SOHC model. I've owned it since 1988 and it has now done 64000 miles. The engine is on its third camchain and second tensioner. The first chain went at 24000 miles, sounded like the whole engine was going to fall apart. To compensate, servicing consisted of changing the oil - the carbs and valves very rarely need attention even at the current, high mileage. Performance does not seem to have fallen off, either... it still does 110mph, 60mpg and burns off Honda Superdreams. Which drives their riders very berserk!
Handling is a bit weird. There’s a typical mono-track back end which when brand new holds everything well in line. Problem is that the bearings all wear rapidly, a few thousand miles sufficient to have the rear tyre waggling all over the road. An expensive outlay on having some phosphor bronze bearings made... still ruined them in short order so I went back to stock bearings and a back end rebuild every 5000 miles. All I could think was that the swinging arm mountings allowed a microscopic amount of movement which was amplified under cornering forces.
The front forks were a bit spindly; use of the single front disc twisted them and bounced them on their stops. The XS weighed under 400lbs, didn’t take too kindly to the madly bouncing front end. Riding smoothly, the Yamaha was nicely flickable and didn't weave, with newish back end bearings. The riding position was comfortable for a couple of hundred miles at a time; although this was not an opinion shared by the pillion; too cramped for anyone other than a dwarf.
I had a continuous battle with the caliper, which did the usual Japanese trick of seizing in winter. I won out when I found out that LC components could be fitted, which meant they were cheaply available from breakers. The wheels were so ugly they tried to hide under a rash of corrosion; it was a waste of time to polish or paint them. The rear drum brake was rod operated, had a wonderful feel and shoes that lasted 20000 miles. Along with a modicum of engine braking, it was a lot safer option for wet weather work than fighting with the front disc which either lagged or locked on solid. Various brands of pads had no effect, so I bought the cheapest - they lasted 10 to 12000 miles.
The engine was the most interesting part of the bike. Lots of easy going torque below 6500 revs, then a slight stutter which turned into a seamless surge of power up to an improbable 10000 revs. Thereafter, vibration became fierce, the motor a little rough at lower revs but smooth at 60 to 90mph cruising speeds. The power surge wasn’t wild like a YPVS, but the way the motor came on cam gave the bike an appealing feel that the bland SOHC model lacked.
I was impressed with the tireless 90mph cruising ability, that put me in mind of much bigger machines. Although no vibration that I could discern got through to the rider, it was evidently attacking the chassis in an insidious way... a pillion peg, indicator, number plate, horn and rectifier unit that all came loose bore testament to the high frequency vertical twin vibration that the whirring engine was putting out. Pillions also occasionally complained of feet going dead.
The rectifier was the only serious casualty. Bulbs started blowing and one battery got so hot it threatened to blow up, the whole bike pervaded by the smell of acid. Shortly after I fixed that by fitting an XJ rectifier, new wiring and battery, paint started falling off the frame around the side panel area, which I put down to the invidious nature of the boiled battery acid.
Finish, wheels apart, stood up to the rigours of too many winters better than I’d expected. I'd seen some two year old Yamahas that were so rusted they looked fit only for the breakers. The black engine finish only came off at the front, down to the layers of road dirt that was thrown off due to the skimpy front mudguard. Tank and panel finish are still excellent, helped by weekly polishing sessions. Most of the frame is hidden away. The silver painted swinging arm is a bit of a rust trap and is painted every time I pull it out to replace the bearings.
The wheel bearings need replacing every 15000 miles, the rear going first. Just the slightest looseness threw the Yam into some wild wobbles. At one point I had worn wheel and swinging arm bearings at the same time! That made the XS a real pig above 30mph. As did the front forks at 32000 miles. I didn’t bother putting any gaiters on them with the result that the chrome was badly pitted and the seals quick wear by 25000 miles. A few thousand miles later there was enough slop to destroy the seals in 250 miles!
I could’ve had the forks hard chromed, put in some new bushes and seals but it was cheaper to buy a GS450E front end for fifty quid together with its much superior single disc and caliper. This time I added some bright red gaiters; had no more problems since then. The rear shock has survived - it never had much damping to begin with but kept the back wheel in line when turned up to its highest setting.
The latest sign of chassis malaise is the frequency with which I have to clean out the fuel tap filter, the petrol tank rusting from the inside outwards. It rather reminded me of the silencers which shone brightly until one day spots of rust appeared. The next day one dissolved as I was riding along; the other did the same trick when | gave it a gentle probe with my boot. They last about five years, which is good going for Japanese exhausts! A pair of universal megaphones were hammered on, didn’t make much extra noise but put a 3000 to 4000rpm flat spot in the power band. Fuel improved from 60 to 64mpg, so it’s probably running more than a touch lean.
It's always been a lean starter, needing loads of choke and ten minutes to warm up. The lack of a kickstart caught me out a couple of times when the battery went dead - they last 14 to 16 months before refusing to churn the engine over. A lot of choke juggling was required, varying with the weather conditions. Push-starting was possible if I was feeling fit, but it needed about 400 yards before I could risk leaping on the seat and dropping the clutch. Unless I was in a desperate hurry I preferred to put the battery on the charger.
Even a fresh battery didn’t help the front light, which was only up to 25 or 30mph country road hauling. The square headlamp made it impossible to put in a different reflector. Most of my riding was in town or on the motorway so it wasn't that much of a hassle. More trouble was the starter burning out at 49000 miles - it was so obscure that I couldn't get it rebuilt, had to order a new one all the way from Japan! Took six weeks to come. I was incredibly fit from the bump starting by then!
This model was always very rare, I’ve only ever seen one other on the road. That means when the engine finally fails I’m going to be stuck for a replacement... the frame is so unique it’s unlikely that I could shoehorn any other engine in there. Not that I would want to replace it with anything other than the original mill, it’s so versatile and so strong that I’m overwhelmed with good feeling.
I've got the chassis sorted, as well, so the Yam runs along like a newish bike. Commutes every day, runs wild on the weekend and is as cheap to run as many a 250. I can’t help but feel that Yamaha and the punters both missed out on a wonderful chance to take over the world with this marvellous little 400!
Alex Mearle