reposted below
Yamaha 3 Cylinder Stroker - Ted Broad / Barry Ditchburn
The Broad Yamaha 3 cylinder Monocoque
I posted a few pictures of this bike some months ago under a different thread and over the following few days I was asked to post more photos, I was asked about the bikes spec and then to create a separate thread for the build.
So I thought on it and finally started writing but as always I got busy on other stuff. Nowt else for it I thought, PC on lap, late in the evening, half a bottle to the good I would tap away. Great plan, didn’t work, sleep usually getting in the way — Early spring through summer is always a busy time for me completing builds for race and road or prepping bikes for the riding season.
So this diatribe must be my 5th or 6th attempt at writing something, however this time I think I have a good chance of finishing it. Fingers crossed. What follows is everything I know about the bike, the thought process behind its creation, its development, those involved and its successes, followed by the bikes rebuild / recreation. I must stress that the story may not be complete as I said its everything I know from conversations with the Broad family and from digging out period publications. I hope you find it interesting.
Ted Broad Yamaha — A little history.
For those under 45years old and/or live on the west side of the Atlantic you may not of heard of Ted Broad but in the UK (and to a degree Europe) Ted Broad was a house hold name amongst motorcycling families, he was one of the most successful privateer sponsors of the 60’s, 70’s and 80's. Perhaps in a similar way to characters like Don Vesco or Don Tilley were in the States.
Ted’s tuning career started with British bikes in the early /mid 50’s reworking Norton and AMC singles but by the end of the decade had started tuning two strokes, reworking road going Yamaha’s into race bikes and developing bikes like the Yamaha TD1’s into race winners often beating the efforts of Yamaha’s works team. Over those early years Ted built and enviable reputation and was held in the highest regard by Yamaha so much so that the full works Yamaha team would pitch up Ted’s premises and use his workshops as their base for the TT and British GP’s rounds of the world championships in the 60’s.
It’s worth mentioning that Ted spent time in Japan working with Yamaha, developing crank and gearbox reliability on everything from TD to TR to TZ of all sizes and many of his mods were incorporated into the production bikes. Not limiting himself to Yamaha he also worked with Honda GB to improve the RS500 cranks, Honda (Jap) couldn’t work out why Keith Huewen’s engines kept going bang so Honda GB sent Huewen's cranks to Ted to sort. Ted also used RG500's and tuned the new Suzuki RG500 for his race efforts and ridden by Dave Potter.
As mentioned a key thing to remember about Ted is that he was a privateer sponsor. Although he was a Yamaha dealer and taking bikes from Mitsui, whose over the counter racer bikes were often not competitive, demanded that their production race bikes must be raced as delivered did caused a little friction between Ted and Mitsui (Yamaha). Eventually Ted stopped taking complete bikes for his own race team efforts preferring to building TZ’s from spares and to his preferred spec - Proving his point Broad Yamaha won the British superbike championship on home brewed TZ750’s in 1979, 80 and was leading the 81 championship until a tragic spill at Oulton Park, Broad Yamaha also won the BEMSEE champions too.
The list of riders Ted Broad helped along include Geoff Tanner, Reg Everett, Chas Mortimer, Paul Smart, Barry Ditchburn, Dave Potter, Jim Wells to name a few. He also prepared works RD56’s for Reg Everett, Phil Read and Bill Ivy, RD05 and 05A (v4’s) too. Ted also managed the European Transatlantic match race team for several years in the early 80’s his team winning several years.
It’s fair to say that Ted Broad along with the Frank Sheene, Geoff Monty and the Padgetts put Yamaha on the map in the UK and to a degree the rest of Europe. Sadly Ted died quite recently he was 91 years old.
The Monocoque Creation
In the late 1960’s a very talented engineer called Eduardo Giro designed a monocoque chassis to house the Ossa 250 engine (which he also designed), the bike was light and handled well when ridden by Santiago Herrero resulting in a 3rd standing in the 250cc world championship in 1969. This feat did not pass Ted Broad by.
Ted had considered that if he could build a bike that could carry enough fuel to complete a TT without stopping he could beat the "works" efforts. Pondering the possibilities of a monocoque chassis, both advantages and possible pit falls by 1971 Ted started work with fabricator / designers John Chisnell and Derek York, Teds bike was not to be a copy of the Ossa but rather his version, with a stronger headstock and load beam arrangement and a combined rear swingarm / rear engine mount. The only similarity was the material just about everything else was different including the engine, whereas the OSSA was a 250cc single 2 stroke, Ted fitted a 354cc Yamaha twin. Also the Ossa monocoque carried fuel in the usual place, forward of the rider, but Ted decided to use the full top line of the bike to tank fuel. What this meant was a fuel tank with a capacity of just over 7 gallons and therefore enough fuel for a 354cc bike to complete a TT without refuelling. Carrying this much fuel is problematic, a 7+ gallon fuel load is huge, so the chassis was fully baffled to prevent surging, the low seat height of 27” permitted the tank to stretched down to just above the swing mount lowering the fuel CofG.
Below is a photo taken end of 1971 of the steering column and load beam arrangement. Note the lower tube machined to take Yamaha rubber anti vibration engine mounts, same as those fitted to the front of the Yamaha engine.
Steering column / load beam arrangement (original photo).
![Auto part]()
The load beam in position in the main chassis C beam (original photo).
![Bumper Vehicle]()
Yamaha TD2 based engine mounted in the chassis. Note the rear arm is a one off built to TR3 dimensions. Forks are Yamaha probably road YDS7.
![Motor vehicle Vehicle Car Classic Classic car]()
The chassis complete with just a few thing to sort before the season opener. Chassis builder John Chisnell coasting on the bike. This was the 1972 version of Ted Broad’s monocoque, the Mk1 if you like!
![Land vehicle Vehicle Motorcycle Motor vehicle Mode of transport]()
Below the monocoque mk1 352cc engine, finished and photographed at Brands Hatch in 1972. Ted’s rider at that time was Barry Ditchburn, Barry later to become a works rider for Kawasaki alongside Mick Grant.
![Land vehicle Vehicle Motorcycle Car Motor vehicle]()
The Monocoque Evolves
Whilst monocoque mk1 was being built Ted was working on his other secret weapon a 475cc 3 cylinder engine based on a YDS7 with an extra cylinder on the side, his experimental engine fitted into a standard YDS7 chassis. The engine used a combination 2x175cc top ends (from a 350) and a 1x125cc top end (from a 250) giving 475cc, a Yamaha based crankshaft made from 2x TR3 cranks with a firing order of 1, 3 , 2. Yamaha race cranks have 13 splines so a 120deg crank wasn’t possible (without spending big ££’s) so the crank was built out of phase.
Below is a page abstracted from a period magazine dated 1972 showing the bike and engine arrangement.
![Vehicle Car Newspaper Newsprint Classic car]()
Despite the experimental engine being mounted off centre in the standard YDS7 frame the 3 cylinder performed well winning races for Ditchburn and Broad Yamaha. The monocoque 352cc which proved to have impeccable track manners was doing exactly the same.
But why build a 3 cylinder 475cc? If you think about what was being raced in 1971/2 then there wasn’t a great deal of choice in the 500cc class, Suzuki T500 modified or oversize Yamaha TR3 both knocking out between 60-70 horses. The British singles like the Manx or G50 with 50hp were still racing but largely out powered by the Japanese strokers. So If a TR3 was making almost 60hp what could it make with and extra cylinder? 80hp? It was a no brainer for Ted.
By the end of 1972 Ted's 475cc triple was making almost 80hp, but with his eye on the UK superbike class (500cc to 750cc) he had also experimented with 521cc version using 3 x TR3 cylinders. This engine made 85hp and more than competitive against 75hp Tridents, 70hp Commando and Harley’s. The Suzuki TR750 triple was making more power but I was heavy and lousy handling, other rarities like the Crescent were unreliable. In fact most of the opposite were tipping the scales between 320 and 360lbs but Teds knew he could build his Yamaha based 85hp triple into a package weighing around 250lbs. That’s one hell of a power to weight advantage.
For 1973 it was decided rework the 3 cylinder engine with a new TR3 gearbox, later dry clutch and 3 x TR3 top ends fed by 3 x 34mm VM Mikuni carbs, sparks from a Pitsch Krober ignition. To cope with the extra horses it was decided to fit the reworked engine into the monocoque chassis fitting the engine centrally. The running gear remained largely unchanged initially but later the front end was swapped out for a Yamaha XS2 with 300m single disc. The bike tipped the scales at around 255lbs.
Below Ted Broad with his creation in 1973.
![Land vehicle Vehicle Motor vehicle Automotive tire Tire]()
…..and below the monocoque fitted with Yamaha XS2 front end.
![Land vehicle Vehicle Motorcycle Motor vehicle Automotive tire]()
The 3 cylinder monocoque had its racing debut at Brands Hatch on the 20thApril 1973.
![Poster Vintage advertisement Recreation Flyer Veterans day]()
This race meeting hosted a schedule of both national as well as the Transatlantic Trophy Match races and was part of a full international motorcycle racing weekend. The Trophy races moved to Mallory Park on the 22nd and Oulton Park on the 23rd.
Prior to the “debut” weekend the monocoque had been extensively tested proving to be both fast and competitive. Ted lobbied the European team management to allow his bike and rider into the European team but they refused. Why? I would speculate that the bike was unknown and a risk therefore. Ted entered his creation into 2 National races firstly the 750cc Superbike race and then the 1000cc race. Now Ted wasn’t the sort of man that believed in “happy accidents” and in both races all of the European team members were also entered. Below I have included the entry lists for both races, you may recognise some of the names!
![Text Document Font Paper Menu]()
![Text Font Document]()
What happened next was a bit a fairy tale and must have embarrassed the British team. In the 750cc Superbike race Ditchburn was blistering and was mixing it with works riders on the 521cc Monocoque, chasing John Cooper to the line for a 2nd place. But in the 1000cc race Ditchburn won by a country mile beating the works guys again. Broad and Ditchburn nailed their point well a truly home, the monocoque proved itself in spectacular fashion. Many more race wins were to follow. Below is press photo of the Ditchburn on the monocoque in the 750cc race.
![Land vehicle Vehicle Motor vehicle Motorcycle Vintage advertisement]()
Continued See next post.....
I posted a few pictures of this bike some months ago under a different thread and over the following few days I was asked to post more photos, I was asked about the bikes spec and then to create a separate thread for the build.
So I thought on it and finally started writing but as always I got busy on other stuff. Nowt else for it I thought, PC on lap, late in the evening, half a bottle to the good I would tap away. Great plan, didn’t work, sleep usually getting in the way — Early spring through summer is always a busy time for me completing builds for race and road or prepping bikes for the riding season.
So this diatribe must be my 5th or 6th attempt at writing something, however this time I think I have a good chance of finishing it. Fingers crossed. What follows is everything I know about the bike, the thought process behind its creation, its development, those involved and its successes, followed by the bikes rebuild / recreation. I must stress that the story may not be complete as I said its everything I know from conversations with the Broad family and from digging out period publications. I hope you find it interesting.
Ted Broad Yamaha — A little history.
For those under 45years old and/or live on the west side of the Atlantic you may not of heard of Ted Broad but in the UK (and to a degree Europe) Ted Broad was a house hold name amongst motorcycling families, he was one of the most successful privateer sponsors of the 60’s, 70’s and 80's. Perhaps in a similar way to characters like Don Vesco or Don Tilley were in the States.
Ted’s tuning career started with British bikes in the early /mid 50’s reworking Norton and AMC singles but by the end of the decade had started tuning two strokes, reworking road going Yamaha’s into race bikes and developing bikes like the Yamaha TD1’s into race winners often beating the efforts of Yamaha’s works team. Over those early years Ted built and enviable reputation and was held in the highest regard by Yamaha so much so that the full works Yamaha team would pitch up Ted’s premises and use his workshops as their base for the TT and British GP’s rounds of the world championships in the 60’s.
It’s worth mentioning that Ted spent time in Japan working with Yamaha, developing crank and gearbox reliability on everything from TD to TR to TZ of all sizes and many of his mods were incorporated into the production bikes. Not limiting himself to Yamaha he also worked with Honda GB to improve the RS500 cranks, Honda (Jap) couldn’t work out why Keith Huewen’s engines kept going bang so Honda GB sent Huewen's cranks to Ted to sort. Ted also used RG500's and tuned the new Suzuki RG500 for his race efforts and ridden by Dave Potter.
As mentioned a key thing to remember about Ted is that he was a privateer sponsor. Although he was a Yamaha dealer and taking bikes from Mitsui, whose over the counter racer bikes were often not competitive, demanded that their production race bikes must be raced as delivered did caused a little friction between Ted and Mitsui (Yamaha). Eventually Ted stopped taking complete bikes for his own race team efforts preferring to building TZ’s from spares and to his preferred spec - Proving his point Broad Yamaha won the British superbike championship on home brewed TZ750’s in 1979, 80 and was leading the 81 championship until a tragic spill at Oulton Park, Broad Yamaha also won the BEMSEE champions too.
The list of riders Ted Broad helped along include Geoff Tanner, Reg Everett, Chas Mortimer, Paul Smart, Barry Ditchburn, Dave Potter, Jim Wells to name a few. He also prepared works RD56’s for Reg Everett, Phil Read and Bill Ivy, RD05 and 05A (v4’s) too. Ted also managed the European Transatlantic match race team for several years in the early 80’s his team winning several years.
It’s fair to say that Ted Broad along with the Frank Sheene, Geoff Monty and the Padgetts put Yamaha on the map in the UK and to a degree the rest of Europe. Sadly Ted died quite recently he was 91 years old.
The Monocoque Creation
In the late 1960’s a very talented engineer called Eduardo Giro designed a monocoque chassis to house the Ossa 250 engine (which he also designed), the bike was light and handled well when ridden by Santiago Herrero resulting in a 3rd standing in the 250cc world championship in 1969. This feat did not pass Ted Broad by.
Ted had considered that if he could build a bike that could carry enough fuel to complete a TT without stopping he could beat the "works" efforts. Pondering the possibilities of a monocoque chassis, both advantages and possible pit falls by 1971 Ted started work with fabricator / designers John Chisnell and Derek York, Teds bike was not to be a copy of the Ossa but rather his version, with a stronger headstock and load beam arrangement and a combined rear swingarm / rear engine mount. The only similarity was the material just about everything else was different including the engine, whereas the OSSA was a 250cc single 2 stroke, Ted fitted a 354cc Yamaha twin. Also the Ossa monocoque carried fuel in the usual place, forward of the rider, but Ted decided to use the full top line of the bike to tank fuel. What this meant was a fuel tank with a capacity of just over 7 gallons and therefore enough fuel for a 354cc bike to complete a TT without refuelling. Carrying this much fuel is problematic, a 7+ gallon fuel load is huge, so the chassis was fully baffled to prevent surging, the low seat height of 27” permitted the tank to stretched down to just above the swing mount lowering the fuel CofG.
Below is a photo taken end of 1971 of the steering column and load beam arrangement. Note the lower tube machined to take Yamaha rubber anti vibration engine mounts, same as those fitted to the front of the Yamaha engine.
Steering column / load beam arrangement (original photo).
The load beam in position in the main chassis C beam (original photo).
Yamaha TD2 based engine mounted in the chassis. Note the rear arm is a one off built to TR3 dimensions. Forks are Yamaha probably road YDS7.
The chassis complete with just a few thing to sort before the season opener. Chassis builder John Chisnell coasting on the bike. This was the 1972 version of Ted Broad’s monocoque, the Mk1 if you like!
Below the monocoque mk1 352cc engine, finished and photographed at Brands Hatch in 1972. Ted’s rider at that time was Barry Ditchburn, Barry later to become a works rider for Kawasaki alongside Mick Grant.
The Monocoque Evolves
Whilst monocoque mk1 was being built Ted was working on his other secret weapon a 475cc 3 cylinder engine based on a YDS7 with an extra cylinder on the side, his experimental engine fitted into a standard YDS7 chassis. The engine used a combination 2x175cc top ends (from a 350) and a 1x125cc top end (from a 250) giving 475cc, a Yamaha based crankshaft made from 2x TR3 cranks with a firing order of 1, 3 , 2. Yamaha race cranks have 13 splines so a 120deg crank wasn’t possible (without spending big ££’s) so the crank was built out of phase.
Below is a page abstracted from a period magazine dated 1972 showing the bike and engine arrangement.
Despite the experimental engine being mounted off centre in the standard YDS7 frame the 3 cylinder performed well winning races for Ditchburn and Broad Yamaha. The monocoque 352cc which proved to have impeccable track manners was doing exactly the same.
But why build a 3 cylinder 475cc? If you think about what was being raced in 1971/2 then there wasn’t a great deal of choice in the 500cc class, Suzuki T500 modified or oversize Yamaha TR3 both knocking out between 60-70 horses. The British singles like the Manx or G50 with 50hp were still racing but largely out powered by the Japanese strokers. So If a TR3 was making almost 60hp what could it make with and extra cylinder? 80hp? It was a no brainer for Ted.
By the end of 1972 Ted's 475cc triple was making almost 80hp, but with his eye on the UK superbike class (500cc to 750cc) he had also experimented with 521cc version using 3 x TR3 cylinders. This engine made 85hp and more than competitive against 75hp Tridents, 70hp Commando and Harley’s. The Suzuki TR750 triple was making more power but I was heavy and lousy handling, other rarities like the Crescent were unreliable. In fact most of the opposite were tipping the scales between 320 and 360lbs but Teds knew he could build his Yamaha based 85hp triple into a package weighing around 250lbs. That’s one hell of a power to weight advantage.
For 1973 it was decided rework the 3 cylinder engine with a new TR3 gearbox, later dry clutch and 3 x TR3 top ends fed by 3 x 34mm VM Mikuni carbs, sparks from a Pitsch Krober ignition. To cope with the extra horses it was decided to fit the reworked engine into the monocoque chassis fitting the engine centrally. The running gear remained largely unchanged initially but later the front end was swapped out for a Yamaha XS2 with 300m single disc. The bike tipped the scales at around 255lbs.
Below Ted Broad with his creation in 1973.
…..and below the monocoque fitted with Yamaha XS2 front end.
The 3 cylinder monocoque had its racing debut at Brands Hatch on the 20thApril 1973.
This race meeting hosted a schedule of both national as well as the Transatlantic Trophy Match races and was part of a full international motorcycle racing weekend. The Trophy races moved to Mallory Park on the 22nd and Oulton Park on the 23rd.
Prior to the “debut” weekend the monocoque had been extensively tested proving to be both fast and competitive. Ted lobbied the European team management to allow his bike and rider into the European team but they refused. Why? I would speculate that the bike was unknown and a risk therefore. Ted entered his creation into 2 National races firstly the 750cc Superbike race and then the 1000cc race. Now Ted wasn’t the sort of man that believed in “happy accidents” and in both races all of the European team members were also entered. Below I have included the entry lists for both races, you may recognise some of the names!
What happened next was a bit a fairy tale and must have embarrassed the British team. In the 750cc Superbike race Ditchburn was blistering and was mixing it with works riders on the 521cc Monocoque, chasing John Cooper to the line for a 2nd place. But in the 1000cc race Ditchburn won by a country mile beating the works guys again. Broad and Ditchburn nailed their point well a truly home, the monocoque proved itself in spectacular fashion. Many more race wins were to follow. Below is press photo of the Ditchburn on the monocoque in the 750cc race.
Continued See next post.....
Attachments
1 - 8 of 22 Posts
PART 2
The Monocoque Recreation
The Chassis
Several years ago I was asked if I would like to get involved with rebuilding the original engine. Being a sucker for punishment and without seeing the engine up close I said yes! It can’t be too bad I thought. Shortly after I was asked about recreating the chassis, well there’s a thing about being a bit thick, you keep making the same mistake. Again I said yes.
The engine was in quite a state. The cases had suffered some damaged, threads pulled, wasted studs, case mating surfaces marked up and some corrosion. The original TR3 cylinders needed repairs and re-plating. Pistons were scrap. The heads were good but all different volumes. Gearbox missing, most of the clutch and crank missing too.
However we did find much of the original ignition, likewise the carbs. We also found the rear wheel, wheel spindles and spacers, the swing arm spindle and foot rest hanger plates and footrests. In fact quite a lot of small stuff which although didn’t seem significant it all helped to understand the scale of the bike, swing arm mounting width, swing arm fork width and so on. Original foot rest hangers and brackets helped understand exhaust mounts and routing, also the foot controls set up.
The final piece of the jigsaw was contacting the original builder of the chassis – John Chisnell (now in his 80’s). John had kept all the original drawings, dimensions, samples of the frame material and the original wooden plug mould. What a piece of luck, we were expecting faded photos and dim memories of a bike that existed nearly 45 years ago. John loaned us all of the drawings and other information he had (a huge thanks to John).
My next problem was finding someone to remake the chassis. We all know that traditional skill sets are slowly disappearing, basic engineering work, lathe or milling for example on manual machines, even people knowing how to use measuring instruments are getting thin on the ground (and on top). There are loads of CNC gurus out there, ideal for making 25000 of this or that but because I had the original drawings why pay for someone to digitise them, then programme a half dozen machines to cut or manufacture the bones of a one off? I gave these guys a miss after many wanted to make the chassis their way rather than recreate the original, altering head angle, gusseting and material spec in fact one well known competition fabrication shop was so far off the mark it would have built a pile of crap that would never have worked. And all for the cost of a motoGP chassis! I wanted someone who would build it exactly as it was and not modify or attempt to improve on the original design (which was exactly my remit). I found one good guy who I had used before but he was so busy and did nothing with the project for many months. So took the project back, then found Seargent Fabrications (highly recommended) who agreed to build the chassis. No rush I said and that’s what I got – 14 months later I had a new chassis! The swingarm is a replica of the type fitted to the Yamaha TR3 but 50mm longer, this came from another source but Seargent Fabrications modified it to fit the frame.
Below is a series of photos of the chassis in various build stages.
![Product Machine Machine tool Toolroom Tool]()
![Chair Floor Room Furniture Auto part]()
![Bumper Machine Vehicle Toolroom Machine tool]()
![Bumper Auto part Automotive exterior Vehicle Metal]()
The Engine
This engine is the original 3 cylinder Yamaha, non came before. Its the engine that started out life as a 475cc later converted by Ted to 521cc. Its a format much copied after by the likes of Rudi Kurth (his were water cooled, Ted also built a water cooled version), Dennis Trollope and Arnold Fletcher of Len Manchester Motorcycles. Even by Yamaha see the 1977 350cc bike of Takazumi Katayama.
As you can imagine the engine had suffered, the cases were basically sound but needed work. My biggest concern was that the cases sealed correctly and there was minimal distortion. I can say they were not perfect but salvageable and after a little work maximum rocking across the faces was just .0025” and when tightened down the was no measurable out of true (average) on the crank bearing seats, just a little fretting on some bearing seat which I could resolve with non-permanent machinery adhesive.
The crank is a new build using 2 good TZ 350 cranks and a box of odd flywheels - a runout of 0.001 was achieved. I didn’t build the crankshaft as I don’t have a jig for it, but occasional calls to the builder revealed that it took some hard work, trial building the crank many times using various combinations of flywheels – it took weeks of frustrated shouting, the builder walking away from the job only to return when in a better mood. But it worked out fine in the end and he’s built another crank for me since so we are still friends I think!
The crankcase cylinder top deck had been lowered to achieve a level deck for all three cylinders. But all three cylinders had different heights and the heads all had different volumes. Simple decision was to match the heads and shim the cylinders to achieve the correct piston clearance for each cylinder. After 45 years in a box the cylinders were in a bad shape, they still had original plated bores which needed reconditioning and so were sent to Lancourt, Weston-Super-Mare UK for new Nikasil plate along with 3 new TZ350 Meteor pistons (modified skirt). Once back the engine build could start. Below are a few photos of the engine going back together for the 1st time since 1974.
![Auto part Engine Automotive engine part Gear Transmission part]()
![Engine Auto part Automotive engine part Machine Vehicle]()
![Engine Auto part Motor vehicle Automotive engine part Vehicle]()
And mocked up for the exhaust fitting!
![Land vehicle Vehicle Motor vehicle Motorcycle Mode of transport]()
Final Assembly
The final assembly is the easy bit, adjust this and that, nice shiny bolts, make an exhaust, find a fairing that fits, then try to get the old girl running again.
I wish it was that easy. It wasn’t and we’re still tinkering with the bike which is hugely sensitive to atmosphere, runs nice when ambient temp is hot then into carbs and ignition when cool and damp. It’s a learning curve!
Anyways here she is, all finished and shiny. Spec as follows;-
• Alloy Monocoque – frame geometry as Yamaha TR350 with 50mm longer arm.
• YDS7 based 3 cylinder engine (safe 0.9mm piston head clearance, ignition 1.8mm before TDC)
• TZ350 gearbox, clutch and primary
• Carbs are Mikuni VM34 x 3 (from a TZ750A)
• Ignition Pitsch Krober original from 1972
• Rear Wheel TR3
• Front wheel is XS2 with TZ slotted disc on XS2 carrier. Hydraulics are Yamaha XS2.
• Forks and yokes are Yamaha XS2
• Rear shocks are custom Hagon.
• Fairing is Jawa V4 (c1968) screen is Honda CR750).
![Motorcycle Vehicle Motor vehicle Fuel tank Motorcycle accessories]()
![Land vehicle Vehicle Motor vehicle Motorcycle Car]()
![Land vehicle Vehicle Motor vehicle Motorcycle Car]()
![Vehicle Motor vehicle Auto part Engine Car]()
![Motor vehicle Vehicle Engine Auto part Car]()
![Vehicle Motor vehicle Motorcycle Bicycle handlebar Auto part]()
![Tire Spoke Alloy wheel Automotive tire Wheel]()
The Monocoque Recreation
The Chassis
Several years ago I was asked if I would like to get involved with rebuilding the original engine. Being a sucker for punishment and without seeing the engine up close I said yes! It can’t be too bad I thought. Shortly after I was asked about recreating the chassis, well there’s a thing about being a bit thick, you keep making the same mistake. Again I said yes.
The engine was in quite a state. The cases had suffered some damaged, threads pulled, wasted studs, case mating surfaces marked up and some corrosion. The original TR3 cylinders needed repairs and re-plating. Pistons were scrap. The heads were good but all different volumes. Gearbox missing, most of the clutch and crank missing too.
However we did find much of the original ignition, likewise the carbs. We also found the rear wheel, wheel spindles and spacers, the swing arm spindle and foot rest hanger plates and footrests. In fact quite a lot of small stuff which although didn’t seem significant it all helped to understand the scale of the bike, swing arm mounting width, swing arm fork width and so on. Original foot rest hangers and brackets helped understand exhaust mounts and routing, also the foot controls set up.
The final piece of the jigsaw was contacting the original builder of the chassis – John Chisnell (now in his 80’s). John had kept all the original drawings, dimensions, samples of the frame material and the original wooden plug mould. What a piece of luck, we were expecting faded photos and dim memories of a bike that existed nearly 45 years ago. John loaned us all of the drawings and other information he had (a huge thanks to John).
My next problem was finding someone to remake the chassis. We all know that traditional skill sets are slowly disappearing, basic engineering work, lathe or milling for example on manual machines, even people knowing how to use measuring instruments are getting thin on the ground (and on top). There are loads of CNC gurus out there, ideal for making 25000 of this or that but because I had the original drawings why pay for someone to digitise them, then programme a half dozen machines to cut or manufacture the bones of a one off? I gave these guys a miss after many wanted to make the chassis their way rather than recreate the original, altering head angle, gusseting and material spec in fact one well known competition fabrication shop was so far off the mark it would have built a pile of crap that would never have worked. And all for the cost of a motoGP chassis! I wanted someone who would build it exactly as it was and not modify or attempt to improve on the original design (which was exactly my remit). I found one good guy who I had used before but he was so busy and did nothing with the project for many months. So took the project back, then found Seargent Fabrications (highly recommended) who agreed to build the chassis. No rush I said and that’s what I got – 14 months later I had a new chassis! The swingarm is a replica of the type fitted to the Yamaha TR3 but 50mm longer, this came from another source but Seargent Fabrications modified it to fit the frame.
Below is a series of photos of the chassis in various build stages.
The Engine
This engine is the original 3 cylinder Yamaha, non came before. Its the engine that started out life as a 475cc later converted by Ted to 521cc. Its a format much copied after by the likes of Rudi Kurth (his were water cooled, Ted also built a water cooled version), Dennis Trollope and Arnold Fletcher of Len Manchester Motorcycles. Even by Yamaha see the 1977 350cc bike of Takazumi Katayama.
As you can imagine the engine had suffered, the cases were basically sound but needed work. My biggest concern was that the cases sealed correctly and there was minimal distortion. I can say they were not perfect but salvageable and after a little work maximum rocking across the faces was just .0025” and when tightened down the was no measurable out of true (average) on the crank bearing seats, just a little fretting on some bearing seat which I could resolve with non-permanent machinery adhesive.
The crank is a new build using 2 good TZ 350 cranks and a box of odd flywheels - a runout of 0.001 was achieved. I didn’t build the crankshaft as I don’t have a jig for it, but occasional calls to the builder revealed that it took some hard work, trial building the crank many times using various combinations of flywheels – it took weeks of frustrated shouting, the builder walking away from the job only to return when in a better mood. But it worked out fine in the end and he’s built another crank for me since so we are still friends I think!
The crankcase cylinder top deck had been lowered to achieve a level deck for all three cylinders. But all three cylinders had different heights and the heads all had different volumes. Simple decision was to match the heads and shim the cylinders to achieve the correct piston clearance for each cylinder. After 45 years in a box the cylinders were in a bad shape, they still had original plated bores which needed reconditioning and so were sent to Lancourt, Weston-Super-Mare UK for new Nikasil plate along with 3 new TZ350 Meteor pistons (modified skirt). Once back the engine build could start. Below are a few photos of the engine going back together for the 1st time since 1974.
And mocked up for the exhaust fitting!
Final Assembly
The final assembly is the easy bit, adjust this and that, nice shiny bolts, make an exhaust, find a fairing that fits, then try to get the old girl running again.
I wish it was that easy. It wasn’t and we’re still tinkering with the bike which is hugely sensitive to atmosphere, runs nice when ambient temp is hot then into carbs and ignition when cool and damp. It’s a learning curve!
Anyways here she is, all finished and shiny. Spec as follows;-
• Alloy Monocoque – frame geometry as Yamaha TR350 with 50mm longer arm.
• YDS7 based 3 cylinder engine (safe 0.9mm piston head clearance, ignition 1.8mm before TDC)
• TZ350 gearbox, clutch and primary
• Carbs are Mikuni VM34 x 3 (from a TZ750A)
• Ignition Pitsch Krober original from 1972
• Rear Wheel TR3
• Front wheel is XS2 with TZ slotted disc on XS2 carrier. Hydraulics are Yamaha XS2.
• Forks and yokes are Yamaha XS2
• Rear shocks are custom Hagon.
• Fairing is Jawa V4 (c1968) screen is Honda CR750).
The bike was 1st raced with a TR3 front drum but this was quickly swapped out for the XS2 front end, the weight saving was huge, that TR3 4LS brake weighs a tonne BUT sometimes a bit of weight out front helps the bike. The longer rear arm was fitted to counter the loss of weight over the front end. I believe the 1st racing production Yamaha to run with a disc up front was the TZ750A in 74, the smaller TZ250/350C got the disc around c1975/6 when the monocross frame turned up. The earlier twin shock A & B had a much longer trail figure than the later bikes to help that heavy wheel turn.
The bikes in Aus may have something to do with Barry Ditchburn, he built a few a put them in Seeley chassis. I think his son (Craig?) was riding them at one time. One of these Seeley framed Yamaha 3's turned up over here a year back and was for sale.
The Scitsu (Dawson built, ridden by Machin/Marshall) bike shared similarities with the Broad bike and 1st raced in 73, crank was out phase TR3 based but I believe it ran both engine sizes 475 and 521cc - I was also told that it ran a true full 500cc but not sure how this was achieved (if at all). I don't know were this bike is today. There is a replica out there, this was sold by Bonhams a few years back as the original but i have been told since that its not the original and was put together by the Gaskin brothers - Mark and Paul, proprietors of Gov'nors Bridge Motorcycles!!
The Yamaha 3 cyl 350 of Katayama was built in Holland (with Yamaha factory support, as sort of backdoor works effort) the man to speak is Ferry Brouwer - interesting info in the link below but the article credits Rudi Kurthe as the base knowledge for the engine which isn't true, not only did Ted Broad build the 1st air cooled 3 he also built the 1st water cooled 3, cylinders were made by Fahron at the end of 73 early 74 before the TZ A turned up, Kurthe's engines were all TZ based . I believe the water cooled bike 1st raced late 74 a full year before Kurthe. Ted was very close to works Yamaha.
https://motovue.net/tag/three-cylinder-yamaha/
The Len Manchester bike is TZ350 based and water cooled, its still around today and was built by Arnold Fletcher in 74 (I think). This bike was back on track quite recently and is still fantastically original and a great credit to Arnold Fletcher.
Dennis Trollope built one but I have never seen a photo of this bike.
Below is Dave Potter on the last version of the Broad 3 in 1975, frame is a TZ750A which was later converted with Foale mono-shock but the whole package was too heavy for the 3 cylinder. The following year Ted went with the new RG500mk1, but in 1976 he built a TZ750C with special Yamaha made 250cc reed top ends, this engine found its way into the TZ750A chassis (pictured) and raced on for a few more years until The TZ500 turned up. Interestingly the link above also speaks of using TZ750 bottom end but with TZ250 top ends but that's one un-rideable engine as the piston porting arrangement makes the engine absolutely savage and why Yamaha made special kit cylinders for some customs.
Potter on the same chassis but with Foale conversion and TZ750 bottom end with Yamaha kit 250cc reed cylinders (boards are white suggesting 750 but its actually a 500).
John did ride a monocoque with an AS125 Yamaha engine and running gear. I understand that this bike was all John Chisnall’s (and Derek York’s) work.
I am not aware of Ted Broads involvement - neither Ted or his son have never mentioned such. Although Ted might have worked with the engine.
When recreating and building the Broad bike I had all of the monocoque drawings which were loaned to me by John, they included a single drawing relating to the 125. All were contemporary C1971. But which bike came 1st? I don’t actually know, I have several photos of John riding the 125 all date from 1972, the same year Barry Ditchburn was to 1st ride the Broad monocoque with the twin engine. See photos below of John on his 125.
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