Yamaha XJ 900F

Sensible bikes are small, and motorcycles never have long production runs. As generalisations, it's fair to say that these are mostly true, but then along comes Yamaha's XJ900 to be the exception to prove the rule -whatever that means. For this air cooled, transverse four cylinder machine has been churning out of the Hammamatsu factory for almost exactly a decade,now,
and with an engine capacity that's anything but small. At its launch at the end of 1982, the XJ appeared to be aimed at filling the sports-tourer role, but at first fell between the two stools rather than straddling them confidently. Shaft drive gave the lie to any sporting credentials in many people's eyes, while the small, bar mounted nose fairing wasn't really adequate for a proper tourer. In addition, the first models were found to have
a high speed weave problem, serious enough for them to be recalled for a frame mounted, slightly larger version of the fibre to be fitted which has appeared on every XJ since. But gradually, over the years, the 900's positive qualities have taken the upper hand, and it's since sold steadily enough to be retained for a whole decade in the Yamaha line up (let me tell you, one dealer I've spoked to this year has sold four XJs, no GTSs and no YZFs. Modifications over the years have been relatively few; after the fairing change, in February 1985 the bore was increased from 67 to 68.5 mm, raising capacity from 853 to 891 cc and upping the low rev torque usefully, as well as improving the top end power slightly. Other changes have been mostly cosmetic, though very recently, the clocks have finally been moved from the handlebars to a console on the inside of the fairing. Though now old fashioned in many respects, the XJ900 still has some qualities yet to be taken on board by some other bike designers.

The generous 4.8 gallon fuel tank and 45 to 55 mpg consumption allow two hundred miles to be covered before the reserve tap even needs to be cocked, and the roomy riding position doesn't make this a particular feat of endurance, though the forward slope of the seat is less than ideal. Low down torque is excellent, enough for the bike to comfortably pull from two thousand rpm in top gear, making for a relaxed, long legged feel. In fact revving it is nothing like as satisfactory anyway, mainly because the motor becomes harsh and vibratory when spun much above six thousand.

But another feature which appeals to
potential XJ buyers is the relatively simple servicing requirements. After all, at £4500 new, the Yamaha is clearly a budget machine, so will already have attracted the home mechanic or at least those competent enough to affect roadside repairs. The first advantage the XJ has over more recent designs is immediately obvious - the engine and ancilliaries are very much more acce-sible, so far less time is spent in simply getting to the parts you want to look at. What does have to come off, almost inevitably, is the fuel tank, but before that remove the seat (undo the lock then operate the two levers under it on either side at the back). The sidepanels can now be pulled off, and practically the same procee-dure applies to the tank. Instead of bolts at the back, only a spring clip needs to be pulled out before the back of the tank can be lifted. The fuel tap should be left in the 'On' or 'Reserve' position and the fuel and vacuum pipes to it disconnected, as well as the electrical connecter from the fuel level sender.

Once the tank is off, it's worth smearing a little grease on the two locating rubbers at the front, to make life a lot easier when it comes to replacing it. The fairing doesn't have to come off, though many people assume otherwise -instead remove the two 6 mm bolts at the back of it, near the engine,- as there's enough flexibility in the panels for them to be bent out of the way when necessary. Dave Sterry at Hamil-tons in Streatham, who kindly did the necessary to this particular XJ for us, then prefers
to blow around the spark plugs with an airline to clear any muck and grit away -if it falls into the cylinders it can cause a lot of damage. You probably don't have an airline at home, so either do the same with a footpump (or even bicycle pump) or blow through a piece of tubing. This of course applies to any bike you're removing the plugs from, not just the XJ900. The small, vestigial-looking belly pan comes away after the four Phillips screws attaching it are undone, and the bike's now ready for your attentions.

Working down the engine, the spark plugs themselves are very easily taken out (with or without the fuel tank in place) as they're angled towards the outside of the engine. The leads are not only numbered one to four from left to right, but colour coded as well in case the numbers wear off, so there's not much excuse for putting them back wrongly. In fact, the plugs last well, as long as fifteen thousand miles if the bike's not used too hard. Next, if the engine's cold, the valve clearances can be adjusted. The cam cover is held on by eight bolts with 10 mm heads and 6 mm threads, with thick rubber washers to seal them. All are very easy to get at, and all are the same. Once they're out, the cover itself lifts off and will come quite easily away out of the left hand side of the engine, exposing the eight valves and their shimmed clearance system.

The shims are on top of the valve buckets, so the cams themselves don't need to be disturbed. If you want to play safe, undo the left hand crankshaft end cover, so the timing marks can be seen, and align the T' scribe with the line on either side of the ignition pickups. Two of the cylinders will be at top dead centre, and one of those in its compression stroke, when the cam lobes will be facing away from the valves. That's the cylinder to work on first, so check with a feeler guage that the inlet valve clearance is between 0.11 and 0.15 mm, and the exhaust between 0.16 and 0.20 mm. If one is outside the tolerance, you'll need to replace the shim with a fatter or thinner one to bring it back (usually you'll be after a thinner shim, as the gaps tend to close up in use). If you're not confident about levering the valve down, clear of the cam, with whatever you have lying around your shed, you'll need the special
Yamaha lifting tool, which isn't an exorbitant price. First rotate the bucket so the notch in its rim is easily accessed - you'll need this to lift out the shim, so make sure you can get an electricians' screwdriver to it. Then turn the engine over (stabbing at the starter button is fine, as long as the plugs are d i s c o n -nected...) until the valve you're working on is fully opened by the cam, and insert the tool into position behind the cam lobe, so it rests on top of the valve (locating on the edges of the bucket) and bolt it to whichever cam cover bolt hole is nearest (it'll only align with one). Be sure that it's completely square on to the cam. Now turn the engine over again so the cam lobe moves back to facing away from the valve, which the tool should still be holding fully open. If you've turned the engine so the cam lobe moved away from the tool, then you'll be busy lifting out the shim. If you rotated the engine the other way, the valve lifting tool will have obstructed the cam lobe, and part of the cylinder head could have snapped off, (seriously) so you'll be busy phoning your local Yamaha dealer to discover that a new one, without the labour costs of swapping over your cams and valves or fitting it, costs a breathtaking £1031.25. Still, that includes VAT, so it could be worse...

Definitely worth noting. Anyway, the shim can now be lifted out with the dextrous use of pliers and fine screwdriver, and hopefully its thickness will be inscribed on the back. If not, it was fitted the wrong way round and this wore off, so you'll need (...to get a dealer...) to measure it with a micrometer. Then the size of the new shim can be calculated. Once all the needy valves are seen to (usually only one or two at each service) the cam cover can be replaced. The rubber gasket will still be sitting snugly in its groove in the cover, and doesn't need to be replaced or assisted with any gasket cement, though it's worth cleaning up the rubber washers on the cover bolts, as with even a small piece of grit, they'll start to weep oil. Replace the timing cover, too.

Now the enigne can be started and fully warmed so the carbs can be balanced. This is quite conventional, apart from the fact that a special tool is needed again to blank off the YICS valves. These are passages within the cylinder head linking the inlet tracts and which have a significant effect in boosting the low and mid-range power of the motor, but do interfere with carb balancing. Remove the bolt in the left side of the cylinder block, insert the special toll and crimp over the end - the passages are now suitably blanked off, and the vacuum gauge pipes can be connected to the brass stubs on top of the inlet tracts. On cylinders one, two and four these normally have rubber caps on, while the third cylinder's is connected to the fuel tap vacuum switch, but note that on older bikes the rubber hardens and cracks, so that air can leak into the inlets and upset the carburation. Replace them with new if you're in doubt. If you're using the fuel tank remotely, you'll have to set the tap to the 'Prime' position, or there'll be zero flow, but Dave Sterry uses an old oil bottle which holds enough gas for the balancing operation. The recommended method is to balance cylinders three and four to each other, then one and two to each other, and finally equalise the two pairs of cylinders with the central butterfly adjuster. If you can get all the carbs to read within 1 cm of mercury of

each other (the absolute value is unimportant, unless it's obviously absurd and needs investigating) that's ideal, but 2 cm is acceptable. The carburettor air mixture screws are located on tops of the bodies, just to the engine side of the diaphragm housings, and are covered by rubber plugs. These don't normally need attention until the engine's covered quite a high mileage, but do ensure the plugs are securely in place, as otherwise water gets to the mixture screws and they seize up - the only cure when they do need to be moved is to drill them out, and that often doesn't work.

Now that the engine's fully warmed, the oil and filter can be replaced. The drain plug is well hidden but accessible with a socket wrench beneath the filter housing, which itself is on the lower front of the crankcases. That won't come out directly through the exhaust pipes, but needs to be twisted to one side first -you don't have to take the pipes off though...
The motor needs no more attention than this, as even ten years ago electronic ignition and automatic cam chain tensioning were the norm, so you can move onto the rest of the machine. Starting at the front, the brakes are prone to seizing during winter use (aren't they all on Yamahas?) so even if the pads aren't worn it's worth removing them and cleaning up the callipers. This involves extracting the bent over 'R' clips in the pins, sliding out the front one, lifting off the spring plate then sliding out the rear pin. The pads should now come out, though some makes (EBC, for example,) can be a tighter fit than others. If you're applying Copa-slip -which is worthwhile if done sparingly -add a touch to the sides of the pads as well as the back to get them operating more smoothly (Dave Sterry's recommendation again).
 

Under the left sidepanel (which should already be off...) is the air filter housing, though you'll have to unclip the toolkit holder before removing the four Phillips screws that hold the cover on. The filter itself now comes out easily enough, but as it's paper will have to be renewed rather than cleaned, and at about seventeen pounds a time isn't cheap. On the other hand, even at something like five thousand miles old it can affect fuel consumption noticeably, so don't leave it too long - it's a false economy. A K& N washable airbox filter is available for the XJ9, so if you're keeping the bike for a while, is a good investment. Meanwhile, make sure the lip in the edge of the filter (on each side) engages properly with the slots in the housing and cover, or again the carburation will be upset by airleaks. On the other side of the bike is the battery, which is very visible so checking the level isn't a chore.
At the back the shaft drive bevel box oil should ideally be changed at each service, with an EP80 or 90 gear oil. The drain plug is on the bottom, while the filler plug is halfway up, and this also doubles as the level check - fill the oil to the bottom of the threads and no more. Overfilling causes oil to blown out of the breather (the domed nut on top of the housing) and all over the rear wheel, in which case you might as well have opted for chain drive in the first place...

Source Witch Motorcycle 1993