Beta EVO Air Box Drain Plug

Beta EVO Airbox Drain Plug Fitting.

Most trials involve streams or water crossings of some sort, so it is always possible to get water in the air box. For trials like the SSDT and Scott Trial where water is a big factor, it is essential to have an efficient, watertight and easy to use drain arrangement. The current plug is just a poorly designed plastic moulding which is difficult to operate/remove due to it’s shape and if fitted too tightly at the factory, the plug cannot be easily removed whilst on the bike.

My design, allows full thread contact, once carefully fitted, the plug is easily operated by a wet or muddy hand as it only needs to be unscrewed a couple of turns to expose the drain hole. When screwed up, the o-ring provides a good seal against external water ingress.

To fit the new plug, it is easier to remove the air box and mud flap to allow full access, then, carefully screw the plug out. If it has been screwed in too tight, you will have to use some mole grips to be able to unscrew and pull at the same time. With the box upside down and if the thread is ok (they usually look a bit rough), lightly grease the thread and screw in the new plug. Take care that the plug goes in absolutely square to the air box joint face and is not cross threaded, then run it in and out a few turns to make sure it is free.

If the thread is damaged or not square, an M14 x 2mm tap is required to dress the thread and ensure that it is square to the air box sealing face.

Beta Evo –Replacing the air-box drain plug.

The original air-box drain plug can be difficult to remove & replace due to it’s odd shape, and is usually a very tight fit which does not allow easy operation with wet, muddy or cold fingers in wet events. It may actually need pliers or grips to remove it, and the thread may need to be re- tapped to ensure an easy and square fit for the new plug.
For easiest access to remove the old plug, remove the back wheel, slacken off all the lower mud-flap screws so that it can be moved aside, then you can get grips on the plug to assist removal if necessary.

Once removed, you may be lucky that the new plug will just screw into the thread, but make sure that it is absolutely square and not cross threaded, otherwise the o-ring will not seal properly on the drain boss of the air-box. Most likely the rough formed thread may be too tight for the new plug, so the M14 x 2mm pitch tapping tool can be used.

Set the tool so that the start of the thread protrudes just enough to enter the air-box thread. Add a bit of grease to the tap so that any plastic swarf will stick to the tap.

Screw the tip of the tool as squarely as possible into the drain hole to just catch the thread, make sure the washer is held up tight and flat to the air-box drain boss (screw the washer up to touch if necessary), then screw the tap up into the thread using the bottom knurled nut keeping upward pressure on the washer.

After checking the air-box for any plastic swarf, fit the new drain plug. In this case the drain hole is still visible.

Screw up to the closed position, just squeezing the o-ring against the drain boss. Once fitted & with the flap back in place, the plug can be easily operated without having to remove anything.

Remember to remove the air filter and check that no plastic swarf is in the bottom of the air-box before fitting the plug. This plug now allows an easy two-finger operation by unscrewing a couple of turns to drain water from the air-box!