Scenes From Behind The Bamboo Screen: Asian Hybrid
'konketsu' (Japanese for mixed-blood)
by nick voge
Monday, January 27, 2025
Revelations tend to occur at the least expected times, perhaps because it is only when the mind is totally relaxed that clear thinking is possible. My epiphany occurred at a used bookstore when I came across a copy of Lindsay Brooke's excellent narrative, Triumph Racing Motorcycles in America. There, roaring off the pages in timeless black and white, was Gene Romero leading the pack off turn two at the Sacramento Mile on his 750 Trackmaster Triumph; Gary Scott on his short-rod 750 under the lights at Ascot; Skip Van Leeuwen on a stock-frame Bonnie, feet up, full-lock and full throttle at the Tulare TT. You fool, was all I could mutter, how could you not have a Bonneville? Which was a strange thing to ask, because I did have one, two actually, both rotting in my backyard long after some unknown heroes of yore had flogged the best years out of them in the Mojave Desert.
Desert sleds they were, the original dirt bikes picked up for a few hundred bucks from a friend suffering from what are now euphemistically called "substance abuse problems," and dumped behind the house where the rats live. It isn't hard to imagine what it must have been like: hundreds of 650 Triumphs with straight pipes thundering at full whack fast and free across the open desert, bouncing off pucker bushes and spitting out vicious streams of rocks and sand from wildly spinning rear tires. It makes the hair at the back of your neck stand on end just thinking about it!
Once enlightened, my mission was clear. A conventional restoration was out of the question. First, because there is no shortage of perfectly restored Bonnies and second, because the bikes were missing all of their road-going equipment (strewn across the Lucerne Valley, no doubt). This left me free to build a TT-style hot-rod ... or, in the modern vernacular: Supermotard, sixties style.
Choosing the best pieces from the two rolling wrecks, I set to work on the chassis. The frame went off for sandblasting, welding and assorted repairs prior to painting. After cleaning the fuel tank, I checked for leaks, coated the inside with sealer then sent it off to the painter. The seat, a fiberglass Bates TT item found at a swap meet, was sent to a surfer buddy and widened two-inches to match the frame rails. A small Bates headlight, another period piece, came from a friend.
Slowly, the chassis began to come together. Strip the wheels, check the bearings, paint the hubs, lace the stainless spokes, clean decades of filth from inside the forks ? each a single step in that "journey of a thousand miles."
Which brings us to the engine ... I had a rough idea of what I wanted: 750 kit, mild cams, some headwork, and no problems. I wanted, for once, to build an engine as well as I could, regardless of the cost, to see if all the added expense, extra time and endless aggravation (mostly aggravation) was worth the trouble. So, before opening the engine, I opened the books, reading a variety of restoration guides, manuals, speed tuning booklets, and taking notes all the while.
You cannot build a good engine without a good crank, so, of course, you have to start with the cylinder. The bores must not only be perfectly round, they must also be perfectly perpendicular to the crankcase ? not as common as you might think on these old Brit-bikes. I ordered a Morgo 750 cylinder from England then sent it off to Bore Tech in Ohio where they would check it, bore it and impregnate the bores with a witches' brew of super-tough carbide to reduce wear, improve ring sealing and help prevent seizures. When the cylinder was done, pistons were ordered from Venolia to suit the bores, and only then could the crank be sent off to Falicon for balancing, blueprinting, crack checking and various other top-shelf trickery.
While the crank was out, I disassembled the rocker boxes, replaced the rocker arm springs with shims (reduced friction), removed excess casting material from the rockers (reduced reciprocating weight), and surfaced the mating surfaces on a sheet of glass covered with wet-and-dry paper (reduced leaks!). When the crank came back, a pair of Megacycle's mildest cams were degreed in and mated with "R" followers and racing pushrods. [Lest you think you need a vast and well-equipped workshop to perform such miracles, I built the engine on a patio dining table, with nothing but a roof overhead, standard hand tools and about $200 worth of Triumph special tools.]
During this often stressful but highly rewarding process, I was once again reminded what wonderful engines these are. Twin cams give immense freedom in terms of cam timing; separate oils for the engine, transmission and primary prevent cross-contamination and ensure that each part of the engine runs in oil of ideal viscosity; direct-drive top gear means that most of the transmission is not even spinning when the engine is in top, greatly reducing friction and wear; and the low center of gravity of the pushrod design coupled with a large diameter crank contribute significantly to the Triumph's legendary handling qualities and gutsy torque. Yes, when they designed this engine, they got it right. And that valve adjustment that costs two or three hundred bucks on a modern Four takes all of 15 minutes on a Triumph. The cylinder head was a very trick piece given to me by a friend who races the gamble bikes in Japan. In the old days they used to run very highly tuned Triumph engines in these hybrid, big-money racers. This particular head was flowed by Hara-san, Japan's top Triumph tuner, and features 10mm center plugs, big valves and port shapes that put a supermodel to shame. My buddy also turned me on to a pair of blueprinted Amal carbs with light return springs (another gamble racer trick) and a quick-turn throttle off a Yamaha road racer. Two modern inventions which dramatically reduce oil leaks and improve performance are a modern semi-hardening gasket sealant such as Yamabond, and an electronic ignition. I availed myself of both.
In a project of this nature, the aesthetic decisions can be as vexing as the mechanical. I opted for silver-gray paint on the frame, rather than the standard black, in order to give the bike a "lighter" look, while the flames on the pearl white tank and seat are as red as the blood in any dirt tracker's veins.
So, you ask, was it worth the trouble? Does it run like the fabled Triumphs of which the old guys so reverently whisper? When the traffic light turns green and you drop the hammer, does your mind's eye see the green flag waving them off the line at Ascot? And when the road crests at a rise and the front wheel comes off the ground, do you imagine yourself going airborne at the Peoria TT?
What do you think?
Desert sleds they were, the original dirt bikes picked up for a few hundred bucks from a friend suffering from what are now euphemistically called "substance abuse problems," and dumped behind the house where the rats live. It isn't hard to imagine what it must have been like: hundreds of 650 Triumphs with straight pipes thundering at full whack fast and free across the open desert, bouncing off pucker bushes and spitting out vicious streams of rocks and sand from wildly spinning rear tires. It makes the hair at the back of your neck stand on end just thinking about it!
Once enlightened, my mission was clear. A conventional restoration was out of the question. First, because there is no shortage of perfectly restored Bonnies and second, because the bikes were missing all of their road-going equipment (strewn across the Lucerne Valley, no doubt). This left me free to build a TT-style hot-rod ... or, in the modern vernacular: Supermotard, sixties style.
Choosing the best pieces from the two rolling wrecks, I set to work on the chassis. The frame went off for sandblasting, welding and assorted repairs prior to painting. After cleaning the fuel tank, I checked for leaks, coated the inside with sealer then sent it off to the painter. The seat, a fiberglass Bates TT item found at a swap meet, was sent to a surfer buddy and widened two-inches to match the frame rails. A small Bates headlight, another period piece, came from a friend.
Slowly, the chassis began to come together. Strip the wheels, check the bearings, paint the hubs, lace the stainless spokes, clean decades of filth from inside the forks ? each a single step in that "journey of a thousand miles."
Which brings us to the engine ... I had a rough idea of what I wanted: 750 kit, mild cams, some headwork, and no problems. I wanted, for once, to build an engine as well as I could, regardless of the cost, to see if all the added expense, extra time and endless aggravation (mostly aggravation) was worth the trouble. So, before opening the engine, I opened the books, reading a variety of restoration guides, manuals, speed tuning booklets, and taking notes all the while.
You cannot build a good engine without a good crank, so, of course, you have to start with the cylinder. The bores must not only be perfectly round, they must also be perfectly perpendicular to the crankcase ? not as common as you might think on these old Brit-bikes. I ordered a Morgo 750 cylinder from England then sent it off to Bore Tech in Ohio where they would check it, bore it and impregnate the bores with a witches' brew of super-tough carbide to reduce wear, improve ring sealing and help prevent seizures. When the cylinder was done, pistons were ordered from Venolia to suit the bores, and only then could the crank be sent off to Falicon for balancing, blueprinting, crack checking and various other top-shelf trickery.
While the crank was out, I disassembled the rocker boxes, replaced the rocker arm springs with shims (reduced friction), removed excess casting material from the rockers (reduced reciprocating weight), and surfaced the mating surfaces on a sheet of glass covered with wet-and-dry paper (reduced leaks!). When the crank came back, a pair of Megacycle's mildest cams were degreed in and mated with "R" followers and racing pushrods. [Lest you think you need a vast and well-equipped workshop to perform such miracles, I built the engine on a patio dining table, with nothing but a roof overhead, standard hand tools and about $200 worth of Triumph special tools.]
During this often stressful but highly rewarding process, I was once again reminded what wonderful engines these are. Twin cams give immense freedom in terms of cam timing; separate oils for the engine, transmission and primary prevent cross-contamination and ensure that each part of the engine runs in oil of ideal viscosity; direct-drive top gear means that most of the transmission is not even spinning when the engine is in top, greatly reducing friction and wear; and the low center of gravity of the pushrod design coupled with a large diameter crank contribute significantly to the Triumph's legendary handling qualities and gutsy torque. Yes, when they designed this engine, they got it right. And that valve adjustment that costs two or three hundred bucks on a modern Four takes all of 15 minutes on a Triumph. The cylinder head was a very trick piece given to me by a friend who races the gamble bikes in Japan. In the old days they used to run very highly tuned Triumph engines in these hybrid, big-money racers. This particular head was flowed by Hara-san, Japan's top Triumph tuner, and features 10mm center plugs, big valves and port shapes that put a supermodel to shame. My buddy also turned me on to a pair of blueprinted Amal carbs with light return springs (another gamble racer trick) and a quick-turn throttle off a Yamaha road racer. Two modern inventions which dramatically reduce oil leaks and improve performance are a modern semi-hardening gasket sealant such as Yamabond, and an electronic ignition. I availed myself of both.
In a project of this nature, the aesthetic decisions can be as vexing as the mechanical. I opted for silver-gray paint on the frame, rather than the standard black, in order to give the bike a "lighter" look, while the flames on the pearl white tank and seat are as red as the blood in any dirt tracker's veins.
So, you ask, was it worth the trouble? Does it run like the fabled Triumphs of which the old guys so reverently whisper? When the traffic light turns green and you drop the hammer, does your mind's eye see the green flag waving them off the line at Ascot? And when the road crests at a rise and the front wheel comes off the ground, do you imagine yourself going airborne at the Peoria TT?
What do you think?
— ends —