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By windmill john
I’m going to change Gupta’s fork oil. Just wondered if anyone has used 5 weight? Is it too thin? Can the seals cope?

Reason for asking... I’m out of ATF and I have loads of BMW Aeroshell 4. It’s a bit secret what the viscosity of this is :roll:
I’m reasonably sure it’s 5 or 7.5W

I don’t think our hosts will be upset with this question, it’s not as if I’m buying elsewhere; they’re currently sending me a tyre.
By jawa-enfield
I have 2 bullets and both have very different front fork springs/behaviour.
The oil helps to dampen it.
Are the springs too stiff and want them more 'alive' use thin oil or mineral ATF, and vice versa..
User avatar
By windmill john
I'm going to run with the Aeroshell-4. Read their tech spec and quite interesting what the viscosity is at different temperatures.
Looks like leaking shouldn't be an issue and it will be fine re temp.
Doing this tomorrow and fitting a new front tyre.
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By stinkwheel
Sounds like a good plan. I've started using multigrade fork oil in all my bikes since having trouble with single weight stuff going far too thin when it gets hot after prolonged abuse.
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By windmill john
I don’t normally look at stats in this depth, but the viscosity figures at different temp decided it for me.

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By zonggong
ATF is typically around 35 cSt at 40 C and 7.0 - 7.5 cSt at 100 C so Aeroshell 4 is about half as light at 40 C. I assume that the operating temp won't be much higher then this. The Aeroshell will work fine as it is a hydraulic oil but you may find the forks a little more springy.
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By windmill john
Well just done them. One had 200ml, one had 150....... at least they match now!

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