Can-Am Dirt Bike Build, Part 2

Aug. 11, 2010 By Dan Paris
In part-one of Project Can-Am we outlined what we planned to do with my Dad’s old Can-AM TN’T 175 to prepare it for vintage motocross and hare-scramble racing. That seems like a million years ago … time may fly for you and I, but when it comes to restoring a vintage dirt bike time just drags on and on and on.

In any case, with the Ormstown Vintage Off-Road Festival coming up, our resto-racer project hit the afterburner. Here’s how we’ve made out so far.

Once we had the frame stripped it became obvious that, while in decent overall shape, this was a former race bike. The lower frame rails were squashed and the area near both footpegs was broken. There were a few other minor cracks as well. Dad, the blacksmith, welded things up properly and added some reinforcing to strengthen the lower cradle of the frame.

Once the frame was repaired and strengthened it went to Niagara Custom Powder Coating. Locally known for their work on Custom Harleys and flat-track race bikes, they did a great job making our old Can-Am frame look better than new!

Early Can-Ams featured steering head bearings that were offset and keyed to fit into the frame’s head tube. You could mix and match them in all sorts of ways to change the handling. We’ve settled on the stock setting that gave us 30-degree rake, at least for now. New thrust washers, needle bearings and seals made it work like new.

At first my father wasn’t all that keen on this project, but as it came together he got more excited about it. Together we spent a lot of time bench racing while reassembling his old race bike, which was really cool. See, there is more to vintage motocross than old motorcycles! In part one of the build we pulled apart the motor to find things were still within spec. Rotax engines had a reputation for being indestructible, but we still had Kevin Annette from Vintage Parts4U split the cases to have a closer look. He found our initial measurements to be spot on. The engine, with two racing seasons off-road, another couple seasons of ice racing and 30-odd years of sitting in a barn, was internally like brand new. The porting had already been cleaned up, but Annette jazzed it up further with a lighter flywheel, a new clutch assembly and new crank seals. The carb was treated to new floats, but that was it. It was bolted back together and deemed ready to race.

The original airbox had cracked, so Vintage Parts 4U supplied us with a new-used one and a brand new Uni air filter element. Old Can-Am airboxes are weird, with the filter sitting in a tray under the seat on top of the big empty airbox.

Bombardier makes snowmobiles, and some of the best in the world. When they went dirt racing in the early ‘70s they used some of their snow machine technology to make dirt bikes that were not only powerful but very quiet. This oddly-shaped muffler was part of their formula for success. Back in the '70s dad tried other, much noisier, mufflers but according to him none worked as well as the stock kidney-shaped thing. With that in mind we left it alone ... for now

Vintage Parts4U supplied a set of nice Renthal Vintage-bend bars. We added a set of MSR quick-adjust levers and our favorite AME grips, along with a new clutch cable and kill button. We’ll be replacing the hastily repaired old-school throttle housing and cable with a more modern unit ASAP!

The Can-AM has a very slim profile, so slim in fact it’s hard to hang on with your knees. We actually prefer the slightly wider TN’T tank over the MX tank (pictured) for that reason. Vinylocity (905/658-0359) makes complete restoration graphics for the old Can-AMs. Their replica decals will go on our gnarly TN’T tank we will use for racing, while the mint-condition MX tank will go back on the trophy shelf. Speaking of skinny, Vintage Parts 4U is working on mounts that will let you bolt modern footpegs onto old Can-AM frames. Until they’re ready we’ll stick with the tiny originals. We’ll be trying to find a shifter with a folding tip as well.

Cycle Improvements/MX-Tech rebuilt the Betor front suspension on our bike. The tiny 35mm fork tubes were straightened before being polished for smoother action. The internals were also polished and de-burred, but under strict orders ‘not to do anything they couldn’t do in 1975’ Cycle Improvements/MX-Tech limited major modifications to replacing the 0.39Kg springs with stiffer 0.42Kg units. They tried to rebuild the Koni shocks Dad had raced with, but they were unable to source a replacement seal head for one of them. We’ve since ordered new four-inch travel shocks through Vintage Parts 4U, but until they arrive we’ll use these old ‘mystery’ shocks. We also slipped a new Maxxis Millville tire on the rear and a Dunlop Geomax up front, just because we had them laying around.

The Can-AM started on the first kick once we got it back together, quickly settling into a nice idle. A few blasts around the yard showed it ran well, the clutch was smooth and it shifted ok. Unfortunately a split in an oil-injection line made the bike spew two-stroke oil. Adding to the mess it also dribbled fuel all over itself, thanks to a leaky petcock. With the Ormstown Vintage Offroad Festival just around the corner and the Gopher Dunes Vintage Races a month after that we’re still running wide open to get this bike ready to race.

Right away, aside from new fuel and oil lines, we’ll be installing new shocks. We’ll be changing the gearing from high-speed ice-racing 15-44 to a more moto-friendly 14-50 combination, along with a new chain. We’ll also bolt on a chain guide, a new throttle and cable and a new petcock. Hopefully we can at least ride it a couple hours to get the jetting and suspension dialled in before we drag it all the way to Quebec … in three days!

Our future plans include lacing up some lighter aluminum rims with new spokes, making the engine looking pretty, a folding shifter, trying a couple different exhaust systems and figuring out a way to improve the notoriously mediocre Can-AM brakes. And maybe, just maybe, we’ll even drag home a trophy or two … after all, this bike has done it before! Newsletter
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