27 Mar This is how we Triumph – 1968 Triumph Bonneville
Bikes may be a rarity on the blog, but we do all sorts of work on motorcycles, take this 1968 Triumph Bonneville Motorcycle Custom Bobber Fabrication project for instance. Between 1959 and 1974 the Triumph Bonneville was a bike based on the company’s Tiger T110 650 cc parallel-twin cylinder motorcycle. 68 was actually a defining year for the Bonneville. A couple of significant improvements were set in place that, for about 2 years, really made the Bonneville the pinnacle of performance motorcycles. These improvements were the Amal Monobloc carburetor and a new 8-inch front brake called a twin leading shoe replaced the antiquated old single setup. This very brief window when the Triumph Bonneville was in its heyday made the Bonneville the performance motorcycle of choice, just before the Japanese bikes changed the game.
This Bonneville bobber came to us as a project in need of some help. The engine wasn’t running, oil leaks were everywhere, the fuel tank inner coating would clog the carburetor, and parts that needed to be fabricated to hold the bike together were delivered in a box. It was a bit of a mess! Our first goal was to get it running to see what it would need. A check of fuel and spark produced neither. A wiring issue was also not allowing spark via an improper ground of the ignition. On top of this, the carburetor was clogged with what appeared to be red goo! The red goo turned out to be the lining from inside the gas tank. When mixed with gasoline the liner would deteriorate and clog the filter and the passageways. The red coating needed to be sealed, so we turned to a product we use often on performance builds as well as repairs, Por-15. If using, just follow the directions exactly. For better results take extra time; if you rush this you will wind up with similar results to the red goo, uncured contaminate clogging fueling components.
With the Por-15 cured and the gas tank sealed, we unclogged the carburetor with very small drill bits and brushes. This got the fuel flowing, meaning that we were ready to start it. After a few kicks, the bike roared to life. After a few minutes of running; however, we soon noticed a new issue, smoking. Plumes of thick, whitish/blue smoke would billow from the tail pipe. Being that this is air-cooled, that just means one thing, oil! After a check of compression and leak down turned up no evidence of obvious ring blowby, that suggested that the oil was coming from outside the cylinders. This meant the next obvious place to check was the valve stem seals.
Upon removing the valve cover, it became apparent that the valve stem seals were indeed the culprit of the smoke issue. There was too much clearance between the valve, the stem seal, and the engine that was allowing oil onto the valves and thus into the exhaust. Whenever dealing with specialized machining of rare components that we don’t see too often, we differ to other industry experts that do. So we called up Franz and Grubb Engine and had the cylinder head on the way for repair.
In the meantime we took care of some cosmetic fabrication issues that were the primary reason the bike found its way to our fab guru, Craig Hegland. A few bits were designed by Aaron Maslin at Fluid Design Studios. These included clamps to keep the pipes from flying off, spacers to keep the seat from bottoming out and falling off track, a battery hold down, and some rear fender mounts.
Right about the time we were finishing with the fabrication, we received the cylinder head with fresh valve stem seals. We popped the new head on with fresh seals and gaskets and got the bike running again. With the smoke greatly reduced, we began adjusting the carburetor, so that the bike ran as good as it looked. After a few rides this bike was ready to go back to the owner, who hadn’t even ran the bike in 5 years. But as luck would have it, this bike wasn’t ready to leave. As we were loading the bike onto the van for its return ride, the cast clutch lever cracked. Cast components mounted to a hardtail bobber with a solidly mounted engine is always a recipe for trouble.
A new lever was ordered and this bobber was on its way to its new home, a condo at the car culture center of Chicagoland, Iron Gate Motor Condos. If you’re ever in the Naperville area on the second Saturday of any given month, stop by and you might be able to see and here this classic in all its glory!