Bonneville Two

This year Bonneville Speed Week sponsored by the S.C.T.A. will be held August 11-17. In an earlier note I described the context of this dissertation, the various motorcycle speed records during the ‘70s. It was during the lapse from 1970 when Cal Rayburn beat Don Vesco’s record and 1975 when Vesco had his revenge that this story occurs.

I mentioned Robert Leppan and his 245 mph record in 1966 on a dual Triumph powered streamliner. That victory was celebrated by the Triumph corporation naming their most recent dual carborated twin 650 the “Bonneville.” Prior to that Triumph’s top model was called the "Thunderbird," but they had licensed that name to Ford. The ultimate evolution of the Triumph Trophy or TR-6 became known after that flat area of earth in western Utah.

In ’73 I worked for a large Triumph dealer in Denver. He planned to retake the record for Triumph and built a streamliner with engines from two 750cc Triumph/BSA triples. He gathered a team, built a bike, collected vehicles and crew, and headed for the Salt Flats that August of ’73. I was the most junior mechanic in his shop having just been hired, and I got to go along. As he said, “Mickey knows the electrics better than anyone else, and we all know Bonneville salt can be bad on electric stuff.” That’s what he called it, “electric stuff,” like points and spark plugs, alternators and batteries. Yeah, I was the only grease monkey that really understood that “stuff.”

We were staying in Wendover, a dozen or so miles from the Flats. I loaded my Honda XL250 thumper in the back of the truck for personal transportation, and rode shotgun in a U-Haul all the way to Wendover. We drove over 600 miles down I-80 and arrived in the evening, checked into an old motel, ate a hearty meal at a local truck stop, and prepared for the next day out on the salt.

We were soon set up on the flats erecting tents and making practice and qualification runs. But there was a problem. We were getting high speed loss of power. The tach would quit rising, and start to sink just when you were near the top speed. Now our bike was very high geared and took a bit of time and distance to come up to top speed. That’s typical, and there’s plenty of room on the six mile run to get up to speed. But that slow going seemed to foul up the engines and they couldn’t get to full rpm in the speed run.

Most of the mechanical geniuses were focused on the carbs, jets, float bowl height, fuel flow, air cleaner plenum, exhaust system, and other fuel/air related issues. I was pretty sure it was the ignition coils. Triumph never was famous for their Lucas electrics, and I was almost certain that was the problem. But no-one would listen to me. After all, I was the most junior guy on the team and they mostly brought me along to hand them tools or get them cold drinks.

The driver didn’t think it was electrical because of some story he kept telling about throttle response. The mechanics were all focused on the fuel. So I had to figure out some way to prove my theory. I got an idea.

I rode my little bike into Wendover and went looking for a Radio Shack. Sadly, there wasn’t one. Locals told me the nearest was in Salt Lake City, some 125 miles away. So I made my plan. I was supposed to be around during the day, although I was just a glorified go-fer, driving into Wendover to get some cold drinks or something. Besides, it was a long hot ride to Salt Lake City across the dessert. I told my boss some story to excuse me for the next day, and headed out on my solo adventure. I waited for the cool of nightfall. I bought a little two-gallon gas can in Wendover to extend my range, filled the tank of my little Honda and the gas can, and set off about mid-night. I don't think there was an open gas station the whole path of the trip and the XL had a rather small gas tank, so I was prepared to make it the whole way with gas to spare.

I couldn't really keep up with the traffic on my little 250cc dirt bike, but there wasn't a lot of traffic and it was a four lane with a wide shoulder, so that didn't matter. The ride across the cool night dessert was without surprises, and I eventually arrived in Salt Lake where I waited patiently for a Radio Shack to open. There I bought my needed gear: wire and connectors and six little gauges. Another stop at a local hardware store for some metal brackets, and I was soon headed back to Wendover and the Salt Flats.

This time the hot sun made the trip less than pleasurable. I soon stopped at a rest stop and slept in the shade on a picnic table for several hours as I was also approaching over 36 hours awake. I got back on the Interstate by 6:00 PM and made it to the motel by late evening. I spent a couple of hours in my room soldering and building my little test rig, and even got some more sleep.

So I was ready when I got back to our little camp on the Salt the next morning. The bike was under a wide tent like roof and the mechanics had the side covers off the fiberglass shell and were working on the carburetors. They were poking and prodding various bike parts and arguing about the fuel lines and sand and other minutia.

I started explaining, for the fourth time, my theory that it was the ignition coils and now I had a way to prove it. I showed them my little test rig with six connecting wires and six meters. I explained that it would show the average electrical output of each individual coil.

My theory was that, since Triumph had reused the dual coil design from the Bonneville, combining that with a single extra coil for the third cylinder, this was a weak point in the ignition. The Triumph Bonneville (how ironic a name considering where we were) used a dual coil. It was two ignition coils in a single body. That saved size and weight and probably cost. They reused that in the triple with a more regular, single coil to fire the three spark plugs. The whole assembly was housed in a small triangle shaped void under the gas tank near the front to get lots of cooling air. Our special designed, double engined bike moved the coils behind the second engine where there was little air flow, and I knew it was a hot spot.

I expected to show that cylinders 1 and 2 of each engine would drop off at high rpm under the high temperature experienced inside the aerodynamic shell and cause misfiring, yet cylinder 3 that used the single coil was not as affected. The double coil was more sensitive to the heat due to working twice a hard with little extra external area to bleed off heat. I already knew from the driver comments that ventilation inside the shell was poor and engine heat was extreme. In fact, that heat was one of the suspected causes of our very problem, but they were looking for ways it was affecting the fuel system.

My meters were coupled to the ignition circuit inductively. That means they read the magnetic field in the plug wires when the pulse of electricity made the spark plugs fire. The coils produce a high voltage pulse each time the points open. The collapsing field in the little transformers that were the ignition coils jumps the simple 12 volts of the battery to hundreds of volts to create a strong spark. The faster you go, the more frequent the pulses. As long as the energy content of a single pulse remained relatively constant, my meters should show an increase due to more frequent pulsing at higher rpms.

My theory was the dual coils lost efficiency due to heat, and I expect my instruments to show a difference between the electrical power produced by the dual coil compared to the single coil. I had built a simple circuit with rectifiers and capacitors to produce a small DC current representing the average power of the spark plug pulses and fed this DC to the little dials. This is how many of the instruments in a car are designed, hardly rocket science, although this bike was closer to a rocket than a normal motorcycle. If the pulse energy was dropping at high rpm (and temperature), then it is likely the plugs will fire poorly acting like fouled plugs. The two cylinders connected to single coils were not as effected, and confused the symptoms. Otherwise the experienced mechanics would have realized the problem was spark and not fuel.

Soon I was explaining to our rider how he would check the gauges at speed and look for certain symptoms shown by comparing the six meter readings. He said he didn’t understand what I was talking about, and since it was my idea, why don’t I take the bike out on a qualification run and perform the test myself.

I thought he was kidding, but he was as serious as taxes, and soon I was clothed in a full leather racing suit and full coverage helmet and being locked into the claustrophobic cockpit of an approximately 500 horsepower rocket. In the first place, I was the same small size as our pilot and fit in his clothes. Apparently I was also just as reckless (or crazy) as him because soon I was zooming across the salt at a speed that I’m sure approached what our modern astronauts experienced just before leaving the confines of gravity and this earth. Now I knew what it was like to fly a jet plane less than a foot off the ground.

Zooming along just six inches above the salt, I barely remembered to watch the six dials as the engine moved into the top rpm range as I entered the measured mile. Just as I had suspected, dual coil for cylinders 1 and 2 (as well as second engine cylinders 4 and 5) showed a lower reading than the single unit coil. By the time I’d positively determined that my theory was proven, I’d gone the measured mile and started to decelerate. This was not a record run, so I didn’t have to turn around and make a second run. As soon as the bike slowed, lacking ventilation, it got very hot and I was glad when the crew popped off the top with the window and let in some air. I unstrapped and began the acrobatic process of climbing out of a bullet, sort of like exiting the birth canal.

After a ride in the back of the pickup with my racing leathers unfastened and tied around my waste, I finally stopped shaking. Funny how, after the danger is over, you get all butterfly stomach and queasy. At least I didn’t throw up.

As we sped back to the crew tent, the fresh air dried out my sweat soaked t-shirt and I quit trembling. I think it is like parachute jumping. They say the first time isn’t bad. The hard part is doing it the second time because now you know just how bad-ass scary it can be.

I quickly reported my results. Then they asked, “Now what do we do?” I had an answer for that too. Back when I was hopping up my own custom Triumph when I was in the Navy, I had swapped out the Lucas ignition coils for good old GM parts. A quick trip back to Wendover and we had six large automobile ignition coils which were soon squeezed into the small space within the bike and one problem was solved. I installed them in front of the hot engines, which would also help reduce any heating problem. That fixed the problem of the moment.

Sadly there were other problems that week with chains, sprockets, and transmission that weren’t so easy to fix, and we left the salt two weeks later without a record. When you link two motorcycle engines together, you have to fabricate a lot of parts and systems to marry the power plants together. That can be very difficult to get right without several tries and we didn’t bring a machine shop with us. On a positive note, my ignition coil fix did solved the dropping rpm problem and I was a hero, at least for fifteen minutes.

That was the only year my boss tried for a record, so that little bit of history and a new land speed number for the Triumph brand was never entered into the books. The Vescos didn’t have any luck that year either with their Yamaha four-stroke powered bike. The engines performed fine, but handling was the issue. Back in Denver my new reputation added some credibility to my standing among the shop personnel, so it wasn't a complete failure.

After we got back to Denver, when one of the crew members handed me a little piece of paper that looked like it came from a cash register. This was the official results of the qualification run I had made when testing the coils. Produced by the Southern California Timing Association with time and speed of the measured mile: 226.395 miles per hour. There you have it folks, Not a land speed record, but faster than I’ve ever gone in anything short of a United Airlines plane. Now drink up your beer and shake my hand as the fastest person you've ever known … on two wheels. (Unless you've met Don Vesco.)

One final comment, in case anyone important (such as an executive from Triumph Motor Corporation or Don Vesco) is reading this, I write fiction. Sure, some of this story may be true, a little bit, but in general you have to know how to tell when I’m lying. It is simple. My lips are moving.