Yamaha TX500

Twin cam 4 valver

Old Bike Australasia - - CONTENTS -

‘Lo­gis­ti­cal com­pli­ca­tions’ meant that the me­dia lolled around a sea­side re­sort, slurp­ing cock­tails and lis­ten­ing to Caribbean mu­sic when they should have been rid­ing, or at the very least, gaz­ing upon the lat­est mod­els from Ha­ma­matsu. As the pick­led press was poured on board for the re­turn trip, the bikes ar­rived on the op­po­site dock. Oh, well, bet­ter late than never.

Of course, this un­for­tu­nate event had an eerily fa­mil­iar ring in the very brief his­tory of Yamaha four stroke twins, for scarcely twelve months prior, many of the same press mem­bers had been present at the launch of big brother, the ill-starred TX750, which al­though fun­da­men­tally an ex­cel­lent mo­tor­cy­cle, was be­set with more glitches and grem­lins than could be imag­ined. But Yamaha is noth­ing if not re­silient, and soon af­ter the un­for­tu­nate Catalina in­ci­dent, sev­eral run­ning ex­am­ples of the new half-litre model found their way into the hands of road testers. Vis­ually, there were many styling cues to the TX750, and even, vaguely, to the now fa­mil­iar TX650, nee XS1, but the 500 was in fact new from the tyres up. For a start, it marked the com­pany’s first ven­ture into mo­tor­cy­cle four-valve tech­nol­ogy, an area only re­cently ex­plored by Honda via its XL250 Mo­tor­sport road/trail ma­chine. And in the head were twin camshafts,

an­other first for Yamaha, at least in mo­tor­cy­cling terms, for Yamaha’s twin cam de­sign had been used by Toy­ota for a num­ber of rac­ing and sports car en­gines, and went into pro­duc­tion in the form of the Cel­ica GT. The most ob­vi­ous dif­fer­ence be­tween the 500 and 750 was the use of wet sump lu­bri­ca­tion on the smaller en­gine, whereas the 750 used dry sump. In­side the cam box, there was a world of dif­fer­ence. With each cam lobe op­er­at­ing two valves, ac­tu­a­tion was via a rocker arm with con­ven­tional tap­pet ad­justers. This gave the vis­ual im­pres­sion of an over­head-valve en­gine, with­out the usual cir­cu­lar en­clo­sures on the cam box. The spark plugs were lo­cated cen­trally in the hemi­spher­i­cal com­bus­tion cham­ber, and there­fore, dif­fi­cult to ac­cess. Sin­tered ti­ta­nium al­loy valve seats were press fit­ted into the cylin­der head to re­duce wear and al­low the use of un­leaded and low oc­tane fuel. Down be­low in the bot­tom end, the TX500 used a forged one-piece crank­shaft with split-shell main bear­ings, three of them, with con­nect­ing rod jour­nals set op­po­site each other for a 180 de­gree fir­ing pat­tern. A pair of straight-cut pri­mary gears took the power to the seven-plate clutch and fivespeed trans­mis­sion. On the right side of the en­gine, a dou­ble-row chain with slip­per ten­sion­ers drove the over­head camshafts, with fin­ger-type cam fol­low­ers, forked to op­er­ate the pairs of in­let and ex­haust valves in each cylin­der. A dual ro­tor high ca­pac­ity tro­choidal oil pump supplied the vi­tal fluid, while a sec­ond pump re­turned it. One of the quirks of the TX750 had been what Yamaha called the Omni-Phase bal­ancer, which be­came an out-of-phase bal­ancer as the driv­ing chain wore and stretched– a fault cor­rected via a re­vised ten­sioner in later mod­els. Ba­si­cally the idea was to can­cel the forces which caused vi­bra­tion, with equal and op­po­site forces. On the 500, the coun­ter­ro­tat­ing bal­ancer was com­pletely re-en­gi­neered and much sim­pli­fied, now lo­cated in the top of the crank­case be­hind the cylin­ders, ro­tat­ing counter to the crank­shaft, and driven by yet an­other chain from the left end of the crank­shaft. The shaft ran in ball bear­ings, whereas all other bear­ings were plain. By all ac­counts, the sys­tem worked, cre­at­ing a silky smooth en­gine, but only once a few revs were ap­plied. The com­plete al­ter­na­tor had to be re­moved to per­mit ad­just­ment of the bal­ancer chain, a task re­quired every 10,000 km. How­ever sev­eral testers com­plained of an an­noy­ing whine at around 5,000 rpm in any gear, which ap­peared to orig­i­nate from the bal­ancer hous­ing. Yamaha had also re­sponded to crit­i­cism of the in­ner­most work­ings of the TX750 en­gine, and es­pe­cially the num­ber of spe­cial tools re­quired to work on it. The 500 was much sim­pli­fied – the only spe­cial tool needed for dis­as­sem­bly be­ing a puller for the al­ter­na­tor. And un­like the 750, the rocker box cover could be re­moved with the en­gine in the frame, al­low­ing for quick and easy ad­just­ment of the camshaft fol­lower clear­ance. The ease-of­main­te­nance theme car­ried through other ar­eas too; the air fil­ter could be changed in sec­onds, as could the oil fil­ter.

Chas­sis-wise, the TX500 owed lit­tle to its brethren, the frame be­ing a be­spoke item. Fuel tank, side cov­ers, muf­flers, rear mud­guard and seat were also cre­ated es­pe­cially for the 500. The in­stru­ment

clus­ter, while rem­i­nis­cent of the 750, ac­tu­ally came from the RD350, with a few ad­di­tions such as an oil pres­sure light. In­cluded in the var­i­ous light and read­outs was, like the 750, a red light that glowed when the front and/or rear brake was ap­plied, and flashed when the stop light globe fil­a­ment was blown. The in­stru­ment clus­ter con­tained no fewer than ten 3 watt bulbs! The key – which also op­er­ated the steer­ing lock, fuel tank cap and the seat – sat in the mid­dle of the in­stru­ment clus­ter.

Like the 750, the twin-pis­ton front brake cal­liper came from the RD350, and al­though the TX500 weighed 50kg more than the 350, the brake still worked quite well. Stan­dard fit­ment was the fa­mil­iar 270mm sin­gle disc on the right hand side, but the op­po­site fork leg had the nec­es­sary lugs cast in to per­mit the fit­ting of a sec­ond disc. Not sur­pris­ingly, the 750’s mas­sive rear drum brake had been dropped in favour of a smaller 7-inch item orig­i­nally found on the XS650. The TX500 had some stiff com­pe­ti­tion in the halflitre class, ranged against the best sell­ing four­cylin­der Honda CB500, and the Suzuki and Kawasaki two strokes, (as well as Yamaha’s own ex­cel­lent RD350 and later RD400) and it’s fair to say that it failed to cover it­self in glory. Ad­mit­tedly, the 500 avoided the built-in foibles of the 750, but in­vented new ones for it­self. A com­mon com­plaint was that the en­gine would not per­form prop­erly un­til fully warmed up suf­fi­ciently for the choke to be turned off – a tough call if you were run­ning late for work. It also had an an­noy­ing habit of stalling for no ap­par­ent rea­son – usu­ally at traf­fic lights. This was gen­er­ally at­trib­uted to the de­sign of the Kei­hin CV carbs, which were also found on the Honda CB450 twin and which of­ten dis­played sim­i­lar traits there. At the low speeds en­coun­tered in city traf­fic, the TX500 could be a bit lurchy – a com­bi­na­tion of the very light 180 de­gree crank and cush drive springs fit­ted to the clutch. There were also re­ports of leak­ing head gas­kets due to the warp­ing of the head it­self. The head gas­ket is­sue came to be more than just a quick fix. Like the TX750 prob­lems, dis­quiet over the smaller model’s ap­petite for head gas­kets spread via the grape vine and it soon gained a rep­u­ta­tion as some­what of a le­mon – a rep­u­ta­tion not re­ally de­served. Usu­ally, the head gas­ket, and the cam box gas­kets, would leak and when the head was re­moved, cracks could of­ten be seen be­tween the spark plug hole and one or more of the valves. In the ex­treme case, the valve seat would ac­tu­ally fall out, with disas­trous con­se­quences. Sub­se­quent mod­els be­gin­ning with the XS500C, had the lower cam box and cylin­der head cast in­te­grally – a mod that was vir­tu­ally in­vis­i­ble from the out­side but which elim­i­nated one of the prob­lem gas­ket sur­faces. This also had the ef­fect of stiff­en­ing the head to help pre­vent it warp­ing. Like the TX750, the TX500, lasted just two

pro­duc­tion years, 1973 and 1974. The sec­ond ‘B’ model fea­tured up­graded front forks with re­vised damp­ing and springs which im­proved front end sta­bil­ity markedly. Slightly higher gear­ing, and a re­vised, qui­eter ex­haust sys­tem with a bal­ance pipe be­tween the muf­flers, which was claimed to im­prove torque, also ap­peared on the ‘B’. The B model also re­ceived a hefty price rise in Aus­tralia, from $1199 to $1399. In 1975, as if to ex­punge once and for all the mis­eries of the TX ap­pel­la­tion, it be­came the XS500C, with the afore­men­tioned one-piece head and lower cam­box, changes to the carbs from the trou­ble­some Kei­hins to 38mm Miku­nis, heav­ier fly­wheels, slightly lower (8.5:1) com­pres­sion and much at­ten­tion to re­duc­ing the low-speed trans­mis­sion lash. A slightly larger ca­pac­ity (15 litre) fuel tank was fit­ted. Just why this should have taken so long re­mains a mys­tery. The 500 twin was fi­nally laid to rest with the XS500E of 1978, by which time the 500cc class it­self was seen as fairly old hat among the cur­rent crop of big bore mul­tis. The XS500C had a styling makeover that made it rem­i­nis­cent of the RD 400, with al­loy wheels from the two stroke model and a flat-sided an­gu­lar fuel tank and side pan­els, as well as a rear disc brake also sourced from the RD400. Showa front forks re­placed the pre­vi­ous Kayaba units, with the brake caliper mounted be­hind the fork legs in­stead of in front. Euro­pean and Aus­tralian mod­els were fit­ted with twin front discs, whereas US mod­els had a sin­gle disc.

A trio of TX500s

The new­est of the three TX500s fea­tured here is ac­tu­ally a 1975 model XS500B (above), which shared its dé­cor and de­cal treat­ment with the XS650 of the same year. Other changes in­cluded re-jet­ting the car­bu­ret­tors with a bal­ance tube be­tween the in­take man­i­folds – mods that did lit­tle to cure the poor throt­tle re­sponse. Clas­sic Style Aus­tralia at Seaforth, Vic­to­ria im­ported the mo­tor­cy­cle from USA and owner Jon Munn says it is a very tidy and orig­i­nal bike. Apart from the re­moval of the metal tank and side cover badges in favour of de­cals, there is very lit­tle dif­fer­ence to the ear­lier mod­els. With only 11,600 miles from new, this TX500 is typical of the East­ern US mod­els that were gen­er­ally locked away for win­ter and rid­den only in the sum­mer months.

An hon­est orig­i­nal

Peter Dun­ster, from Can­berra, owns the 1973 TX500A shown be­low; an orig­i­nal, if slightly faded rose. “When I was about 18 I was work­ing at Genge’s (Can­berra dealer) and had a Rocket 3 BSA as my ev­ery­day ride. Then we traded one of these TX500s in on a new Suzuki and for a while it be­came the ‘shop’ bike that we used for odd jobs, and the more I rode it the more I liked it. Com­pared to the BSA it had an elec­tric start, it was lighter, han­dled nicely, and went quite well pro­vided you kept the revs up to it. It would cruise at 140km/h

all day if you wanted, and had plenty in re­serve for easy over­tak­ing. Like all of these, it had a war­ranty re­place­ment job on the head, but since then it’s given no trou­ble at all. The CV carbs are still hard to tune prop­erly but the main prob­lem is low speed run­ning, so I just ride it flat out!”

And an­other

Our fea­tured bike (above) is Ray Nicholls’ 1973 TX500 in the colour cat­a­logued as Oyster, and sports dou­ble disc front brakes as well as a home-fit­ted Per­spex screen. It has been the sub­ject of an on­go­ing pro­gram of restora­tion and re­fine­ment by the owner and he says it is a very pleas­ant mo­tor­cy­cle to ride. The right side muf­fler is show­ing signs of the in­ter­nal baf­fles swelling due to rust, which causes rip­ples in the long chrome mega­phone it­self – a prob­lem that also be­set the TX750. But orig­i­nals of these muf­flers are vir­tu­ally im­pos­si­ble to come by, so there is no im­me­di­ate cure at hand. For­tu­nately the left side muf­fler is in per­fect con­di­tion.

for the next day’s run. A CB500 Honda was in­cluded in the test to give com­par­a­tive re­sults. The ini­tial test­ing equip­ment from Ja­pan was some­what in­ef­fec­tive. For­tu­nately, Bob van der Zy­den, with his air­craft en­gi­neer­ing back­ground, or­gan­ised Euro­pean ther­mo­cou­ple tem­per­a­ture sen­sors which we fit­ted in­side the sump, rocker cov­ers, un­der spark plugs, oil pump pickup ar­eas, and around the out­side of the en­gines. The sen­si­tive gauges were taped to the top of the tanks, so that rid­ers could mon­i­tor tem­per­a­tures on the high speed runs. This was all very in­for­ma­tive, so Bob took it a step for­ward, and or­gan­ised, a high tech (for 1973) data ac­qui­si­tion sys­tem. Al­though it was about the size of a large top­box, we man­aged to mount it onto the rear of the seat. Due to the bad weather, the ex­pen­sive unit was wrapped with plas­tic to keep it safe, and we just kept our fin­gers crossed that the rider didn’t crash and de­stroy the unit. When the tapes were read, and the oil tem­per­a­tures, speed, el­e­va­tion, and rpm were cor­re­lated, it was ob­vi­ous that tem­per­a­tures were ex­ces­sive. The CB500 showed a rea­son­able 250 de­grees, whereas the TX500 showed up to 300 de­grees. In the lim­ited work­shop con­di­tions we adapted sev­eral oil cool­ing sys­tems. These were fit­ted in var­i­ous po­si­tions, and it re­duced the tem­per­a­tures to an ac­cept­able level. The oil cooler be­came an add-on fit­ment in Europe. This was not the only prob­lem, as the nu­mer­ous top end gas­kets were sand­wiched to­gether be­tween the long cylin­der studs. Pro­moted by the el­e­vated en­gine tem­per­a­tures, all the gas­kets grad­u­ally set­tled, which in turn re­duced the ten­sion on the studs, and al­lowed ex­ces­sive oil and com­pres­sion leak­age. The Yamaha en­gi­neers took all this on board and re­turned to Ja­pan to re­design a trou­ble free one-piece cylin­der head. With this, and other im­prove­ments learned from this test­ing, the later model XS500 was a well sorted bike. How­ever its rep­u­ta­tion had been dam­aged by the early prob­lems, and its fu­ture sales were lim­ited. Yamaha learned from the ex­pe­ri­ence, and was now con­scious of the im­por­tance of do­ing se­ri­ous long dis­tance sus­tained test­ing be­fore re­leas­ing a new model, rather than rush­ing the model onto the mar­ket to gain ini­tial sales. A funny aside was that the Ja­panese in­ter­preter who came with the team was only flu­ent in Ger­man, and not in English. When we needed to con­verse with the Ja­panese en­gi­neers on tech­ni­cal mat­ters, the English had to be trans­lated to Dutch, then to Ger­man – and fi­nally to Ja­panese! It was a long-winded way of get­ting the cor­rect in­for­ma­tion. For­tu­nately most me­chan­ics seem to have a log­i­cal com­mon think­ing, and we ended up work­ing things out our­selves. It made the in­ter­preter a lit­tle re­dun­dant, but saved a lot of time....”

The TX500 mill laid bare.

TOP LEFT Twin disc front end was an early op­tion, and stan­dard on the XS500C. CEN­TRE LEFT Metal side cover badges and tank badges on the orig­i­nal model. ABOVE A happy muf­fler. Twin-cam top end with four valves per cylin­der – novel in 1973.

Bulges in the muf­flers sig­nify cor­roded in­ter­nal baf­fles. De­cals in­stead of metal side cover badges was one of few vis­i­ble changes on the TX500B. 11,614 miles in 45 years – not such a tough life!

ABOVE 1975 Yamaha XS500B. TOP LEFT Kei­hin CV carbs had a rep­u­ta­tion for rough run­ning at low revs. LEFT US mod­els had sin­gle disc front ends.

ABOVE Ray Nicholls’ 1973 TX500. Re­vised styling on the XS500D for 1977.

Peter Dun­ster’s 1973 TX500A.

RIGHT Rod Tin­gate on one of the test mules in Ger­many. LEFT Tem­per­a­ture sen­sors strapped to the TX500. BE­LOW LEFT Ready to roll in Ger­many.

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