Post by Pardee on Jun 25, 2014 13:37:13 GMT -5
1972 YAMAHA TX750
Smooth Cruise
Classic Bike, November 1994
John Wyatt of "Rising Sun Restorations"
Some say the seventies are best forgotten. An era of bad haircuts, ill-fitting clothes, lurid paint schemes and poorly designed motorcycles. Others buck this trend of thinking and embrace metalflake colours and flared trousers whole heartedly.
Such people appreciate the sort of performance that can be had for minimal outlay, and favour the high profile, sweet wrapper looks associated with the decade. They also know that poor reputations can be easily acquired, but difficult to lose.
Yorkshire restorer John Wyatt falls into the latter category. He specialises in rebuilding Honda CB750 Fours--turquoise green or orangey gold, you name the colour and he's restored one. Honda monkey bikes and CBX sixes are another pair of oddball favourites.
But none are as obscure--in Britain at least--as Yamaha's TX750. If you live in this country, you've probably never seen one in the flesh before because the Hamamatsu firm never imported the TX to Britain. If you live in Holland, France, Germany or the States you may have seen such a beast. But no matter where you come from, you won't have seen a TX in such pristine condition. Not one like John Wyatt's that goes as well as it shows.
Restoration began in 1989, when a friend who imports early sandcast Honda CB750s discovered the Yamaha in northern California. Its first and only other owner clocked up 11,000 miles before going to Vietnam and stepping on a land mine. He didn't come back. Since then the machine was stored in a rickety shed.
'I paid £400 for it, rusted but original, and thought to myself, do I really want this? Well, it's a hell of a challenge and it'll give people something different to look at.' explains John, a long-time Vintage Japanese Motorcycle Club (VJMC) member.
The parts hunt was on. One rear shock absorber was found in England, but precious little else was unearthed over here and despondency set in. Then a stroke of luck--a cache of TX750 parts turned up in Rome and John was onto them: 'All the hard to find stuff was there. I got three cranks, two or three barrels, pistons, carbs and service items like gaskets, clutch plates, oil filters and the other shock absorber.'
Before work was started on the single overhead cam, dry sump engine, John contacted Yamaha Europe's development engineer Ludi Boemer. Ludi was sent out to America soon after the TX was launched on a trouble-shooting mission to find out why cranks failed repeatedly. He sat and watched as West Coast street racers revved their new Yams into the bloodline, dropping the clutch in a frantic effort to keep up with Honda 750 Four riders when the lights turned green.
This sort of abuse gave the TX a grenade-like reputation that further refinement couldn't dispel. Boemer discovered that the chain driven omni-phase balancer, which smooths out vibration from the big parallel twin, also frothed the oil to the extent that the crank was starved. The solution was simple--fit a deeper sump.
So Wyatt fitted a deep-sump conversion on his 1972 model and added an optional oil cooler, offered in the hotter US states. Neat chromed oil cooler pipes that wrap around the engine were found in Nevada. John now runs with a generous seven pints of PJ1 in his engine, a decent increase over the oil tank's five pint capacity.
The chain driven balancer was still a worry. Early versions of the balance system used 1mm offset drive sprockets to keep the chain from lashing. Yamaha later added an external chain tension adjuster. But to fit this requires modified crankcases. Through painstaking measurement, Wyatt found that he had the right size link extractor to replace his chain with a stronger, riveted DID product. This meant he could keep his early cases and rest confidant the balancer wouldn't give trouble.
Needle roller bearings for the TX engine's bottom end were specially made for Yamaha and difficult to obtain. John had to break another engine and liberate its bearings. New clutch plates, valves and pistons from the Rome stash were installed in the engine, even though the old units were hardly worn.
The TX's odd looking cylinder head with kidney-shaped combustion chambers was treated to cleaned ports by polishing out some casting flash. The cylinders now flow equal amounts of gas.
A pair of fresh 32mm CV carbs replaced the original units which had suffered 20 years of corrosive US petrol and complete the engine rebuild picture.
Most of the cycle parts were refurbishable. Original DID alloy rims, copies of Akront items, polished up better than new and the exhaust system chromed up beautifully. The seat had a tear in it so John searched for a cover in the US and Japan. Eventually a British source come up with the goods for just £7.
The only minor piece of bad luck came when John found it impossible to source the Electric sidepanel stickers. He ordered some spot-on examples to be made, then in tragic style John found a deposit of original decals.
Instead of mounting its engines in rubber, Yamaha tried to solve the parallel twin vibration problem at the source. The TX boasts two counter rotating flywheels which are spun by a chain running directly from the crank. This introduces opposing vibration to combat excess shakes. It works, but only an owner can say whether the extra complexity is worth the maintenance grief. Crankshaft is forged steel with both con rods positioned in-line so that the pistons rise and fall together. The 360-degree crank is supported in three car-type bearings. Claimed power is 65bhp at 6500rpm which results in close to 110mph on the road.
But omni-phase balancer apart, the engine is unremarkable--unlike the electrical layout. The TX sports a fail-safe lighting system. If your headlight high beam fails, the system will transfer the unused current to low beam--and if your low beam blows, high beam steps in.
Other ahead-of-their-time mods include a brake wear sensor on the rear brake cam with console-mounted red light indicator. And every time you apply either brake, another red light shows you the rear bulb is working.
All very trick, but I was more interested in learning whether the balancer works. 'Most people who see the TX say: "Oh, that pile of junk." Then I let them ride it and they come back saying what a great bike it is. It's as smooth as a Honda Four.' claims owner John Wyatt.
The extravagant statement had me itching for a ride, a desire heightened by the engine's amazing grumble. Thumbing the electric boot produced a deep purring from those big bore pipes, like a dozing grizzly bear.
Down into first and--he's right you know. Turbine-like smoothness all over the rev range. Corners were a bit worrying at first, a combination of wet roads, soft suspension and aquaplaning front brake pads on the disc. When the sun eventually made it to Tadcaster, I tried again with the shocks knocked up two settings.
This improvement made all the difference, and although I bounced out of the saddle, the bike held its line stoically. Left-handers chafed the sidestand, right-handers were negotiated safely, largely thanks to modern Metzeler rubber.
Odd for a tourer, the gear ratios are closely spaced. The advantage of this is that fifth (top) gear can be notched early at around 60mph, and from there any speed up to the ton is simply dialed in. But accelleration is not the TX's strong suit--hardly surprising for an upright tourer weighing 518lb.
What does surprise is the excellent turning circle. Slow speed work is no chore with good handlebar leverage and instant throttle control from the constant velocity carbs. But a heavy clutch--the cable goes right round the houses--and an elusive neutral tarnish the picture.
Overall impression is of a solid, but not outstanding, performer. An adequate tourer that may have gone on to greater things if Yamaha had tested more thoroughly. And if US bully boys hadn't thrashed the life out of it.
Smooth Cruise
Classic Bike, November 1994
John Wyatt of "Rising Sun Restorations"
Some say the seventies are best forgotten. An era of bad haircuts, ill-fitting clothes, lurid paint schemes and poorly designed motorcycles. Others buck this trend of thinking and embrace metalflake colours and flared trousers whole heartedly.
Such people appreciate the sort of performance that can be had for minimal outlay, and favour the high profile, sweet wrapper looks associated with the decade. They also know that poor reputations can be easily acquired, but difficult to lose.
Yorkshire restorer John Wyatt falls into the latter category. He specialises in rebuilding Honda CB750 Fours--turquoise green or orangey gold, you name the colour and he's restored one. Honda monkey bikes and CBX sixes are another pair of oddball favourites.
But none are as obscure--in Britain at least--as Yamaha's TX750. If you live in this country, you've probably never seen one in the flesh before because the Hamamatsu firm never imported the TX to Britain. If you live in Holland, France, Germany or the States you may have seen such a beast. But no matter where you come from, you won't have seen a TX in such pristine condition. Not one like John Wyatt's that goes as well as it shows.
Restoration began in 1989, when a friend who imports early sandcast Honda CB750s discovered the Yamaha in northern California. Its first and only other owner clocked up 11,000 miles before going to Vietnam and stepping on a land mine. He didn't come back. Since then the machine was stored in a rickety shed.
'I paid £400 for it, rusted but original, and thought to myself, do I really want this? Well, it's a hell of a challenge and it'll give people something different to look at.' explains John, a long-time Vintage Japanese Motorcycle Club (VJMC) member.
The parts hunt was on. One rear shock absorber was found in England, but precious little else was unearthed over here and despondency set in. Then a stroke of luck--a cache of TX750 parts turned up in Rome and John was onto them: 'All the hard to find stuff was there. I got three cranks, two or three barrels, pistons, carbs and service items like gaskets, clutch plates, oil filters and the other shock absorber.'
Before work was started on the single overhead cam, dry sump engine, John contacted Yamaha Europe's development engineer Ludi Boemer. Ludi was sent out to America soon after the TX was launched on a trouble-shooting mission to find out why cranks failed repeatedly. He sat and watched as West Coast street racers revved their new Yams into the bloodline, dropping the clutch in a frantic effort to keep up with Honda 750 Four riders when the lights turned green.
This sort of abuse gave the TX a grenade-like reputation that further refinement couldn't dispel. Boemer discovered that the chain driven omni-phase balancer, which smooths out vibration from the big parallel twin, also frothed the oil to the extent that the crank was starved. The solution was simple--fit a deeper sump.
So Wyatt fitted a deep-sump conversion on his 1972 model and added an optional oil cooler, offered in the hotter US states. Neat chromed oil cooler pipes that wrap around the engine were found in Nevada. John now runs with a generous seven pints of PJ1 in his engine, a decent increase over the oil tank's five pint capacity.
The chain driven balancer was still a worry. Early versions of the balance system used 1mm offset drive sprockets to keep the chain from lashing. Yamaha later added an external chain tension adjuster. But to fit this requires modified crankcases. Through painstaking measurement, Wyatt found that he had the right size link extractor to replace his chain with a stronger, riveted DID product. This meant he could keep his early cases and rest confidant the balancer wouldn't give trouble.
Needle roller bearings for the TX engine's bottom end were specially made for Yamaha and difficult to obtain. John had to break another engine and liberate its bearings. New clutch plates, valves and pistons from the Rome stash were installed in the engine, even though the old units were hardly worn.
The TX's odd looking cylinder head with kidney-shaped combustion chambers was treated to cleaned ports by polishing out some casting flash. The cylinders now flow equal amounts of gas.
A pair of fresh 32mm CV carbs replaced the original units which had suffered 20 years of corrosive US petrol and complete the engine rebuild picture.
Most of the cycle parts were refurbishable. Original DID alloy rims, copies of Akront items, polished up better than new and the exhaust system chromed up beautifully. The seat had a tear in it so John searched for a cover in the US and Japan. Eventually a British source come up with the goods for just £7.
The only minor piece of bad luck came when John found it impossible to source the Electric sidepanel stickers. He ordered some spot-on examples to be made, then in tragic style John found a deposit of original decals.
Instead of mounting its engines in rubber, Yamaha tried to solve the parallel twin vibration problem at the source. The TX boasts two counter rotating flywheels which are spun by a chain running directly from the crank. This introduces opposing vibration to combat excess shakes. It works, but only an owner can say whether the extra complexity is worth the maintenance grief. Crankshaft is forged steel with both con rods positioned in-line so that the pistons rise and fall together. The 360-degree crank is supported in three car-type bearings. Claimed power is 65bhp at 6500rpm which results in close to 110mph on the road.
But omni-phase balancer apart, the engine is unremarkable--unlike the electrical layout. The TX sports a fail-safe lighting system. If your headlight high beam fails, the system will transfer the unused current to low beam--and if your low beam blows, high beam steps in.
Other ahead-of-their-time mods include a brake wear sensor on the rear brake cam with console-mounted red light indicator. And every time you apply either brake, another red light shows you the rear bulb is working.
All very trick, but I was more interested in learning whether the balancer works. 'Most people who see the TX say: "Oh, that pile of junk." Then I let them ride it and they come back saying what a great bike it is. It's as smooth as a Honda Four.' claims owner John Wyatt.
The extravagant statement had me itching for a ride, a desire heightened by the engine's amazing grumble. Thumbing the electric boot produced a deep purring from those big bore pipes, like a dozing grizzly bear.
Down into first and--he's right you know. Turbine-like smoothness all over the rev range. Corners were a bit worrying at first, a combination of wet roads, soft suspension and aquaplaning front brake pads on the disc. When the sun eventually made it to Tadcaster, I tried again with the shocks knocked up two settings.
This improvement made all the difference, and although I bounced out of the saddle, the bike held its line stoically. Left-handers chafed the sidestand, right-handers were negotiated safely, largely thanks to modern Metzeler rubber.
Odd for a tourer, the gear ratios are closely spaced. The advantage of this is that fifth (top) gear can be notched early at around 60mph, and from there any speed up to the ton is simply dialed in. But accelleration is not the TX's strong suit--hardly surprising for an upright tourer weighing 518lb.
What does surprise is the excellent turning circle. Slow speed work is no chore with good handlebar leverage and instant throttle control from the constant velocity carbs. But a heavy clutch--the cable goes right round the houses--and an elusive neutral tarnish the picture.
Overall impression is of a solid, but not outstanding, performer. An adequate tourer that may have gone on to greater things if Yamaha had tested more thoroughly. And if US bully boys hadn't thrashed the life out of it.
