Restoring a 1971 Triumph TR6C Trophy - Part 3

Rejuvenation not restoration

tr6c 1

It may look like it has a long way to go, but we’re closing in on the final stages of our TR6C rejuvenation. Major jobs remaining include fitting our new wiring harness and sorting out carburetion issues.

MC Staff

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Note: This is part 3 of a 4-part series of articles on the Motorcycle Classics restoration of a 1971 Triumph TR6C Trophy. You can go back to part 1 here or go here for part 2 and here for part 4. 

Blame a long, cold winter, but progress on our 1971 Triumph TR6C moved at a glacial pace after our last report in the March/April issue. But with spring’s welcomed arrival, we finally had a chance to get back into the shop and make some headway. And as the pics show, our project bike is starting to come together.

Frame up

The last time we showed off the Triumph we had finished stripping it down to the frame and laying it bare, giving us a better idea of what we were up against. We discovered the frame had more dirt on it than paint, and we considered going whole hog and having it powder coated. But in keeping with our “rejuvenation not restoration” approach to this bike, we decided to keep it simple. After cleaning the frame thoroughly and giving it a good going over with Scotch-Brite pads and sandpaper, we gave it a final rinse with a surface cleaner followed by a coat of primer and three coats of black enamel, all from spray cans. The biggest problem with rattle can paint jobs is getting enough paint on, but it looks like we did OK. The finish came out better than expected (then again, anything’s better than what it was), and given enough cure time it should be fairly durable, as well.

While the frame was curing we treated the front forks to a thorough cleaning and new fork seals, and likewise cleaned and greased the steering head bearings. We also cleaned and greased the wheel bearings, discovering in the process that the rear brake shoes had been installed with their locating “shoes” at the wrong end, causing a bind in their action. We also discovered that someone was in the front hub before us, evidenced by one replacement wheel bearing and a missing locating clip.

The swingarm bushings were still good, so we got off easy there, leaving us with the simple chore of cleaning and repainting the swingarm. We also cleaned and painted the steering yokes, the engine mounting plates, center stand, side stand, battery box, ignition tray, license plate frame and other assorted hardware.

Into the mill

Aside from a thorough degreasing, we’ve pretty much left the engine alone. An inspection of the cylinder barrels and the inside of the cylinder head with a boreascope (basically a flexible, pencil-thin optical tube featuring a small light to illuminate the cylinder and an eyepiece to view through) showed the insides to be in good order. The bike ran well the last time anyone tried, and we haven’t seen anything to make us think it won’t again. It did have a nasty habit of blowing fuses thanks to an intermittent dead short, but our new wiring harness from Klempf’s should take care of that.

The engine slotted back into the frame relatively easily, although with an odd twist on our experience removing it. The manual says to take it out the left side, but it would only go out the right, so we figured assembly would be the reverse of disassembly. To keep from marring the freshly painted frame, we set the engine down on its right side and lowered the frame down over it, right side down — but there was no way to get it in. After a few minutes of head-scratching we reversed everything and it went right together. Go figure. Once we had a few bolts to hold the engine in place we simply righted the frame and hoisted it up on our work bench.

Trying to breathe

With the engine in the frame we turned to installing the Mikuni carb conversion we got, but discovered there are some trade-offs with the Mikuni. If you’ve converted a Norton from Amal carbs to a single Mikuni, you know it’s a simple swap requiring almost zero fabrication. The problem here is with the Triumph’s stock air filter box, which is a two-piece, Siamesed affair. Installed, it wraps around the main frame tube, reaching forward to meet the carb intake, where it sandwiches together. The air box opening is offset just a little above the carb throat, and a corresponding offset rubber sleeve joins the two.

However, the Mikuni conversion won’t let you use the stock air box (it comes with a pancake air filter), because the Mikuni’s longer throat means it wants to protrude into the air box, as opposed to the stock Amal, which doesn’t. Plus, the Mikuni’s throat is larger than the air box opening. Compounding the problem, at least for us, is the fact the air box is also the infrastructure for our newly-painted side covers.

We’ve decided the bike won’t look right without the stock side covers, so after pondering this for a bit we’re going to attempt some modifications to the air boxes to make the Mikuni fit. We’ve bought an extra set of air boxes off eBay ($15), which we’re offering up as sacrificial lambs to the project. Our plan is to work out where they need to be cut to give clearance, and see if we can adapt the Mikuni to a modified air box.

And just in case our modification doesn’t pan out, we’ve sent the original 30mm Amal off to be modified with a chrome Mikuni slide replacing its warped and sticking aluminum slide. Amal carbs might be great for their simplicity, but unless you sleeve them or replace the slides they just can’t compare with a Mikuni. One way or another, we’ll be running, and we’ll let you know what worked in our next issue.

Grip and shine

Our new tires are mounted, and we think they look perfect. Aggressive but not too knobby, Kenda’s K761 dual sport tires are street oriented but should be good in the dirt. What’s the chance we’ll actually go offroad on our TR6C? Probably pretty slim, but the tires look the part, and that’s at least half the fun.

Since these pics were taken we’ve installed the engine side plates, front and rear foot pegs, the headlamp shell, license plate brackets, tail light and front wiring. That gets us pretty close to being done, with only the main wiring harness, ignition system, carburetion, exhaust system and final fettling to get us on the road.

Although it’s looking like a motorcycle again, the biggest visual change to our project TR6C will be the fresh coat of Pacific Blue and contrasting white paint that Craig McGlothlen at Precision Motorcycle Painting is laying down. Craig’s refinished the air box outer covers and the side covers in contrasting gloss black, and once the tank’s done we’ll have an exceptionally good looking Triumph.

We expect to have our Triumph up and running by the next issue, and then out on the road for its first public outing at the AMA’s Vintage Motorcycle Days at Mid-Ohio Sports Car Course in Lexington, Ohio, July 27-29, 2007. And with any luck, we’ll actually make it!

Back to Part 1 and Part 2On to Part 4 

Project TR6C Trophy Suppliers
• Complete seat - Walridge Motors Limited 
• Headlight wiring harness - MAP Cycle 
• Tubes and rim strips - Coker Tire Co. 
• Mikuni carb conversion - Sudco  
• Final drive chain - Britech New England 
• Hagon shocks - Dave Quinn Motorcycles 
• Fuel petcocks - Job Cycle  
• Paint work - Precision Motorcycle Painting 
• Footpeg rubber; front turn signals - Baxter Cycle 
• Engine gaskets/mirrors - M&S Cycle 
• Main wiring harness - Klempf’s British Parts 
• Headlamp bracket; shifter lever rubber - Countryside Cycle Shop
• Exhaust system - Mac Products
• Tires - Kenda Tires