Read valve breather and catch can for the 74 TX650.


Active Member
Like most bikes of the era the TX650 had a basic engine breather breathing into the airbox. I've done quite a few mods to this bike, including VM barbs and pancake filters. The pancake filters don't lend themselves well to engine blowby being fed into them, plus I don't like the idea of feeding the blowby gasses into the inlet tract, so I made this reed valve engine breather and catch can.

Reed valve breathers allow air in the crankcase to be expelled on the pistons downstroke and drastically slow the flow of air being sucked back in on the pistons up stroke. thus maintaining a sligtly negative crankcae pressure. As a secondary positive, they also prevent excesive pressure on the piston on its downstroke and prevent some oil seapage through jointing surfaces.

The petal was taken from a pit bike read valve and cut in half, two holes drilled and screwed to the base plate. Base plate was tapped M3 10mm deep to take the petal. Not fun tapping this small, but, this time around the tap survived.

Main body was carved out with an endmill to give the petal room to move and air to flow. Base plate has a channel on the engine side for any oil to run down back into the rockers. Topside was channelled either side to get the Allen heads level with the top surface. Outlet spigot is 16mm with a 12mm hole.

Air from the engine enters the main body from the reed valve is channelled upward, does a U turn and travels downward to the outlet spigot, losing a little oil on the way. Any oil trapped before the reed valve is channelled back to the rockers.

The catch van is made from 42mm tube with four baffles. Instead of welding the baffles inside of the tube, I fixed them together with a 4mm screwed and peened the end so it wouldn’t come apart, the baffle cartridge was then pressed into place resting on top of the intake tube so it won’t float around. The intake tube stretches across the diameter of the 42mm tube and has three exit holes underneath. For the blowby gas to escape it has to exit via the four baffles and finally through some stainless mesh before exiting through the air filter on top, set between the two carb filters.

There is a tap underneath connected to the catch can by a rubber hose. The filtering medium inside the can is replaceable via the top plate secured on top by four 4mm stainless allens. The can is mounted to an aluminium bracket by two rubber gromets and two threaded T nuts to stop the gromet from being squished too far, then fixed to the right, rear engine bracket.

Mounting the can proved a little troublesome: behind the motor over top of the swing arm pivot is the only place I could find to mount it. To make it less noticeable I painted it black and welded an outlet on the side so I could mount the final filter between the two carb filters. It is only a small catch can with around 220ml capacity, that’s in total of course, realistically only around 100mm under the baffles. If it proves too small, I can fit a larger container under the swingarm connected to the catch can outlet by a rubber hose.


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I almost always run into the same issue with racebikes. If I have to run the stock airbox, I don't like the idea of running the oil vapors in there and if I am running superbike classes without the stock airbox, the rules state it has to run to a catch can. I usually use a brake fluid can it is easy, cheap and works really well. I guess I could post up a bunch of pictures of me making mine but it is pretty simple and doesn't require any reed valves or machined aluminum pieces. just a hose a can and a hose clamp to the frame. Sometimes I use green zip ties.
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