Fork Oil - SAE to Weight Conversion

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Bob_FLA - 10/26/08 at 11:54am

My service manual specifies 5 ounces of SAE 20 oil for the front forks.
My choices of "Weight" at the store are:
Bell Ray 5, 7, 10, 15
Maxima 5,10,15,20
Are there any differences SAE vs Weight from oils back in the day to the oils they have now?
The fork oil will be for a Wombat 94 - 180 lb rider in Florida (mostly hot weather)
Thanks Bob

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Bullfrog - 10/26/08 at 12:59pm

While I can't comment on the technical details of SAE viscosity ratings and "weight", I am confident in recommending the Maxima 20 weight fork oil.
The Wombat forks were manufactured back in the days when fork oil was available in 10, 20, 30 and 40 wt. You'll want at least the 20. Being in Florida, you may want 30 wt or even 40 wt.
You can pick up 30 wt non-detergent oil at your local NAPA store. So that would take care of the "30".
For 40wt, mix the 30wt "half and half" with 50wt non-detergent motor oil obtained at your local airport fixed base operator (aviation engine oil - about $5.00 quart the last time I checked). Note that a lubrication engineer has opined that mixing 30wt and 50wt in equal parts does indeed result in 40wt.
Ed

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Bob_FLA - 10/26/08 at 1:48pm

Ed
I'll probably just go with the 20.
I also just noticed that my forks do not have a drain plug at the bottom of the fork. Do you just turn the bike upside down - or is that cheating.
Bob

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Bullfrog - 10/26/08 at 4:00pm

Bob:
Since the '70's I've maintained that I like to work on motorcycles more than working on cars . . . partly because, if there is something I can't reach - I can just lay the motorcycle on it's side or turn it upside down! But in the case of the Wombat 94 forks and draining oil, that shouldn't be necessary. I think you have just missed seeing the drain screws. They can be found in the bottom of the sliders between the slider and the axle - so the front wheel does have to come off to drain the oil. But you don't have to turn the bike upside down.
The 20 weight seems like a very logical place to start . . . and you may find it is "just right" for you. But keep in mind that you have options for adjusting the damping.
Ed

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Bob_FLA - 10/26/08 at 7:15pm

Ed - your right I do see it now. In the diagram it is shown offset, and obvious. Mine is right on the bottom flat part VERY, close to the axle. Thanks. - Bob

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