Rubber Mounted Triumph Motor Project

In 2004 I built a Triumph motorcycle. The motor is a 750 from a 1978 Bonneville. The frame is pre-oil-in- frame, which means the down tube is not enlarged to accommodate the oil bag (as designed for a dry sump motor). The engine mounts match regardless of the gap in years.

When I put this bike together I didn't realize the amount of vibration that the 750 produced. So much so that components would literally sheer off  at high RPMs. My first solution was to make beefier connections on everything, but the relentless and constant vibration would wreck everything including my hands and brain.

So last winter I took on the idea of rubber mounting the motor, without looking too chunky or overdone. Below is a picture of what the lower mounts look like on a stock Triumph frame.

These are rigid mounts. They flush right up to the aluminum case of the motor. My plan was to cut these out and replace them with mounts that accommodate rubber isolators. The following photos are the succession of the lower mounts only. I'll take photos of the front, rear and top mounts for a future post.

Above are the rubber isolators I found at a company called HA-King $8.00 a piece. They make motor mounts for any and all motors imaginable. I priced Norton stock rubber mounts, (they made a rubber mounting system for their late 70s model bikes) For one set they wanted $900 bucks! The steel is a design I had cut from mild steel. The center hole is roughly one and a quarter inch inside diameter. The outside diameter of the rubber mount is two inches.

Below is what the front two mounts look like after modification.

Above is the rear mod. This was the toughest design hurtle as the mount had to be moved back about an inch to accommodate the rubber mount. So I had to cut the T shaped mount and add a new mounting stud an inch rear of the original, not to mention designing a new plate with a modified bolt pattern.

In the above photo you can see the top mounts, sometimes referred to as head steadies, modified to accommodate the same isolators. If anyone is interested in doing the same thing to their bike, I'd be happy to take more detailed photos or answer questions, but holy shit it took a long time and lots of design, trial and error. My bike makes the same growl but doesn't bite me so hard anymore. All my lights,  pipes, license plate, oil tank, carburetor and gas tank stay attached to the motorcycle. Freeway riding is much more pleasant. I also took some of the high RPM vibration out by putting in a larger rear drive sprocket as well.