Drain Plug in Gearboxes

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Drain Plug in Gearboxes

Postby Schoobytwo (Bruce) » Sun Jun 05, 2016 5:00 pm

Hi all,

I've always been a proponent of not over-filling a gearbox with oil. If you fill the gearbox to the level of the side plug, it is guaranteed to leak as the gearbox is just not sealed in such a way that it will keep the oil in. So I always recommend 4 to 6 ounces of oil for starters and then if the chains are wet after you roll the Diablo over, then it should have plenty of oil in the gearbox.

These gearboxes have no drain plugs in them, so it is difficult to know what is really going on inside of them. But this weekend, I seen some things that are changing my perspective.

I've started to put drain plugs in my rebuilt gearboxes. A simple 1/4" pipe tap into the bottom of the aluminum casing making sure not to thread the tap in too far as to not make the threads very deep. Then installing a plug just enough so it does not get up inside the gearbox where the chain can catch it. A flush plug is best, but a hex head plug will work too.

DSC04614.JPG (164.61 KiB) Viewed 5317 times

The epiphany happened when I decided to install a drain plug in my daily Diablo 500 runner. I raised the front end to gain access to the gearbox and drilled the hole (3/8" for a 1/4" pipe tap) and very little oil came out which surprised me. So I grabbed my daily Diablo 503 runner and did the same thing and found the same results. Grabbed my buddies daily Diablo 503 runner and the same thing. None of these gearboxes were leaking, so where the heck did the oil go? :o

My new perspective is all gearboxes should have drain plugs installed. Drain them every spring to get the water and oil out and refill with the 4 to 6 ounces of 90 weight oil for happy trails.

Comments welcomed.

Too many Diablos and parts to count.
Yamaha Apex (it outruns the Diablo for sure)
Yamaha 600 SX
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Schoobytwo (Bruce)
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