Triumph Breather Information

Triumph 500 Breather Modifications

Spigot hole drilled to exit the timing cavity

The stock timed breather no longer functions correctly with an offset crankshaft engine. An additional line needs to be installed on a spigot going into the timing cover where a distributor was once mounted for early 500 unit construction engines. The new line should be a rubber oil line connected to the stock breather line. Do not use a clear plastic line. The breather line should then be connected to a Yamaha XS650 reed valve as this helps create a partial vacuum in the engine which improves engine performance.

A modified stainless steel bolt with a hole drilled through it is supplied with all Triumph 500 crankshafts.

Instructions on how to install the breather spigot, as well as a schematic of the breathing system, are also supplied with the crankshaft.

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Triumph 650/750 Breather Modifications

Breather line connected to TDC hole

The location of addition of breather spigot depends the year of the unit construction 650 engine. Triumph 650s for the 1970 model year, and all years after that do not need an additional breather line. Triumph 750s also do not need and additional breather line.

1967, 1968 and 1968 unit-construction 650s can have an additional breather line connected to the timing Top Dead Centre hole at the back of the barrels. The Triumph tool part # is modified to add a spigot to connect an additional breather line. The new line should be a rubber oil line connected to the stock breather line. Do not use a clear plastic line. The breather line should then be connected to the oil tank and continue on to a Yamaha XS650 reed valve as this helps create a partial vacuum in the engine which improves engine performance. A schematic of the breathing system, is supplied with crankshaft for these years of Triumph unit construction engines.

Contact us for information on breathing improvements for 1963, 1964, 1965 and 1966 engines.

Triumph Pre-Unit Breather Modifications

Breather hole is 1” to right of stud and ¾” down.

The stock timed breather no longer functions correctly with an offset crankshaft engine. An additional line needs to be installed on a spigot next to the ignition unit. The breather hose is installed before the ignition unit as the hose clip holding the line in place is not accessible after the unit is installed. The new line is a rubber oil line connected to the stock breather line. Do not use a clear plastic line.

The breather line should then be connected to a Yamaha XS650 reed valve as this helps create a partial vacuum in the engine which improves engine performance. A modified stainless steel bolt with a hole drilled through it is supplied with all Triumph pre-unit crankshafts.

Instructions on how to install the breather spigot, and a schematic of the breathing system, are also supplied with a pre-unit crankshaft.

SS breather spigot near ignition system