Restoring a 1971 Triumph TR6C Trophy - Part 4

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MC Staff

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Note: This is part 4 of a 4-part article covering the restoration of a 1971 Triumph TR6C Trophy. Start at the beginning with part 1 here, or catch up with part 2 here and part 3 here. 

Six months ago we turned the first wrench on our Triumph TR6C project, and it’s now finally drawing to a close. Sharp minds will note, however, that we didn’t say it’s done. Why? Mostly because we won’t call it finished until all the little details (missing side cover caps, front turn signals, etc.) are tended to. But it’s 99 percent of the way there, and better yet, it runs. And surprisingly, it wasn’t that hard getting it there.

A little air, please

In our last report, we noted some issues installing our Mikuni carb conversion. Namely, the Mikuni wouldn’t work with the stock air box – unacceptable to us, as we think the air box side covers are a key part of the bike’s look. We couldn’t believe it, but a few calls to some Triumph specialists confirmed what we’d discovered: It won’t work. Apparently, most folks doing this conversion either don’t like the stock air box or simply don’t care. We do, and decided to see what it would take to make the stock air box work.

Sizing up our options, we turned to eBay for a used air box we could hack on without feeling too bad if we ended up destroying it. There were a few sets available when we went trolling, and the first thing we discovered was that boxes for twin-carb 650s were perfect for our planned modification. Why? Both the single-carb and dual carb inner box are made up of two mirror-image pieces that bolt together around the main frame tube. The single-carb box, once installed, has an oblong hole at the front for a rubber sleeve to join the assembly to the stock Amal carb. But the twin-carb box has a blank front, the air tract running instead from the outer air box covers. With no pre-existing hole, we could start from scratch.

Fifteen dollars and three days later, we were ready to begin the modification. With all our pieces in hand, we discovered it was a pretty straight-forward process of mounting the twin-carb inner air box, the conversion manifold and rubber spigot, and then lining up the Mikuni carb to the spigot. Carefully eyeballing the Mikuni’s position (we couldn’t install it in the spigot because the Mikuni protrudes into the inner air box), we scribed lines on the air box marking the top and bottom of the Mikuni’s intake throat. Following that, we simply scribed the Mikuni’s opening on the air box, allowing an extra eighth-inch all around for a rubber seal, and cut away with a Dremel tool.

It took a bit more fiddling after making our first cut, but everything went together perfectly, and we ended up with exactly what we were looking for: A superior Mikuni carb without compromising the original look of our classic TR6C.

Getting wired

With the Mikuni sorted we turned our attention to installing the new main wiring harness, a job we were excited about in an odd, god-I-hope-this-goes-well sort of way. The oil-soaked and fraying original harness was about as trashed as they come, tying maybe a fourth of the bike’s various electrical bit together. It was also probably responsible for taking this bike off the road in the first place, as it had a nasty habit of eating fuses every few miles. The last time the bike ran it was wired straight, with no fuse, until it stopped. Hmmm.

We made careful note of all the original attachments; labeling connections, taking copious photos and drawing out little diagrams detailing connections to items like the voltage rectifier and the ignition system. You can’t record too much when you’re taking apart old iron.

All that preparation paid off when we went to install the harness, because frankly, it was amazingly painless. We made a mistake or two (like inadvertently separating the hot white wire from the main loom to the handlebar controls, giving us no power to the horn and brake light circuits), but everything went where it was supposed to, and more importantly, everything worked. Well, almost everything, but more about that later.

Confident we were on the road to our first firing of the TR, we moved on to more mundane issues like fitting the front brake cable, the rear brake light switch, the rear light assembly and rear turn signals (we’re still waiting for a new set for the front), and the oil lines. The speedo cable’s screw-on barrel fell off when we went to install it, so we have a new cable on order.

Exhausted and exhilarated

Next up was the new dual exhaust system from Mac, which took a bit more effort to install than we’d anticipated. In hindsight it was a fairly straight-forward process, but we were surprised our system didn’t come with any installation notes. The header pipes sweep under the frame, so the first order of business was removing our freshly painted center stand. Too bad, as center stands make working on any bike easier, and that’s not a concession we really wanted to make.

Once we had the header pipes on, we slipped the mufflers in place and went to attach them with the supplied brackets to the rear foot peg hangers. As delivered, the brackets are basically 6in pieces of chromed flat bar with a 45-degree turn-up at one end, with locating holes drilled in each end. By the time we were done they had mirror 45-degree bends at both ends, with the ends that attach to the foot pegs drilled out from the supplied 3/8in hole to the required 7/16in hole.

Finally, it was time for the piece d’ resistance, our freshly painted tank from Precision Motorcycle Painting. Initially, we weren’t sure what color we wanted, but in the end we opted for stock Triumph Pacific Blue with contrasting white scalloped side panels. Precision’s Craig McGlothlen poured his talents into this tank, using modern paints with a deep clear coat to finish it off, and it shows. We knew it’d look good, but we weren’t prepared for just how much the tank, combined with the completely new saddle from Walridge Motors, would transform our tired old TR. It’s so good looking, it’s almost sinful.

But will it run?

And then came the day of reckoning, the first fire of our project TR. First up was filling the frame with fresh oil (yeah, it sounds weird, but remember, the frame is the oil reservoir), followed by the primary case and gear box. That done, we turned to adjusting the valves, which is a bit fiddly on Triumphs if you don’t have a set of angled feeler gauges. The tolerances on the 650 are tight (0.002in intake and 0.004in exhaust), and using a straight feeler blade takes a bit of checking to confirm you’ve got the valves set right. New spark plugs came next, followed by a nervous, almost tenuous filling of the freshly painted tank. Nobody wants to be the first to soil perfection, so we draped the tank with clean rags before we filled it.

With the ignition on and the fuel tap open, we gave the kick start a mighty swing and … nothing. Check the ignition, check for fuel, swing again … and again … and again … and still nothing. A quick inspection showed no spark at the plugs, even though we’d checked the wiring circuit previously and everything looked good. So, we pulled out our handy digital volt amp meter, checked the pickup coils for the Boyer, then the Boyer for output to the coils, and everything looked fine. And then we realized the one thing we hadn’t done.

Blame it on haste or excitement, but while installing our new wiring loom, we didn’t clean all the old connectors. Tank off, connectors cleaned, and five minutes later we had power through the system. Tank back on, fuel line connected, ignition on, a mighty swing and the Triumph roared to life, but not exactly the way we wanted it to. This was an out of control I’m-gonna-rev-till-I-pop roar, with smoke blasting out the tail pipes and the engine going from zero to almost-max revs in a heartbeat. Fumble for the key, shut it down and think, “S***, I hope we didn’t kill it.” A double-check, turn the idle screw all the way out, and try again, but this time ready to kill the ignition. A mighty kick and it roared to life again, but this time we killed it before it revved too high.

More checking revealed the stupidly simple cause. The Mikuni will take the stock Triumph throttle cable, but in our case the stock cable is a bit short relative to the Mikuni’s slide travel. Add in a throttle cable adapter at the twist grip (further shortening the cable) and the Mikuni’s slide was probably half way up its travel. Simply removing the cable adapter at the twist grip gave the slack we needed, and this time it fired, didn’t run away, and after about 30 seconds of adjusting we had a nice, even idle, a mellow woof coming from the new pipes, changing to a nicely subdued bark with each sharp twist on the throttle. Wow.

What’s next?

Since we started this project, we’ve poured more than a few hours into bringing this old desert sled back to life. With the exception of the paint work by Precision, we did everything else in a modest, unheated little shop. Working mostly during off hours, at times our process was slow (especially during the cold winter months), but on good days we’d walk away amazed at how much two guys armed with wrenches, spray degreaser and some paint cans can get done.

This wasn’t a restoration, and it was never intended to be. And it wasn’t a “restore it yourself and save big bucks” project, either. What we really wanted to show is what the average guy or gal can do, working with modest means, out of their own garage.

The best part is, a project like this won’t break the bank. Prices for Triumph parts are reasonable, down right cheap, really, and the suppliers who helped us represent a huge trust of information – they’ll usually know a lot more about what you’re working on than you do. With a little searching, a rough but running TR6C can be found for around $1,500 to $2,000, and expect to spend at least another $1,500 to get it clean and running, give or take a few hundred dollars depending on who does your paint job, arguably the most expensive part of the project. Not a bad admission price for classic cruising.

We’re planning a feature story on the Triumph to really highlight its cool new look, but in the meantime, look for us and our finished TR6C at the 2nd Annual Bonneville Vintage GP September 7-9 and at the Barber Vintage Festival October 19-21.

Read Part 1, Part 2 and Part 3.