fork oil

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87m6chris
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fork oil

Post by 87m6chris »

1970 T500,
I'm tearing down the forks at the moment and the service manual says new oil should be 220cc
of straight 30 weight oil.
Just wondering if that is still the best recommendation or has a different oil has been found to be better?
Thanks,
Chris
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Re: fork oil

Post by Coyote »

30wt oil is way too heavy. After market Belray at 15wt would be a good choice, or you can do like a lot of us do and use ATF (automatic transmission fluid). That's what I am using in both my bikes.
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Re: fork oil

Post by GreenMachine »

Is 30wt too heavy even for fuller-figured units like myself? That's what I planned on using...
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87m6chris
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Re: fork oil

Post by 87m6chris »

But there were lighter weight oils when these shocks were designed, wouldn't the engineers
have taken that into account with the size valves?
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Re: fork oil

Post by H2RICK »

But there were lighter weight oils when these shocks were designed
I think you're missing the point here, Chris. Certainly the base CRUDE was "lighter" (composed of lighter fractions than modern "heavier" crudes) but refined oils that are stated as being SAE30 or whatever each fall in clearly defined viscosity ranges. The Society of Automotive Engineers set up the viscosity rating standards donkey's years ago so that no matter where the crude feedstock comes from or what its original viscosity is, the refined SAE30 end product is the same viscosity no matter whose name is on the can or what refinery it came from.
Straight 30 weight is a very viscous oil and would be almost impossible to pump through the tiny orifices in the forks of these bikes. It would be almost like having a solid front end.
IF you lived in a really hot place with average daytime temps around 110*F (say, maybe, the Sahara Desert) then you MIGHT need a fork oil as heavy as a 30 weight IF you weighed 250+# and IF you were racing the bike in a 6 hour endurance contest. :wink:
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GreenMachine
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Re: fork oil

Post by GreenMachine »

H2RICK wrote:
But there were lighter weight oils when these shocks were designed
I think you're missing the point here, Chris. Certainly the base CRUDE was "lighter" (composed of lighter fractions than modern "heavier" crudes) but refined oils that are stated as being SAE30 or whatever each fall in clearly defined viscosity ranges. The Society of Automotive Engineers set up the viscosity rating standards donkey's years ago so that no matter where the crude feedstock comes from or what its original viscosity is, the refined SAE30 end product is the same viscosity no matter whose name is on the can or what refinery it came from.
Straight 30 weight is a very viscous oil and would be almost impossible to pump through the tiny orifices in the forks of these bikes. It would be almost like having a solid front end.
IF you lived in a really hot place with average daytime temps around 110*F (say, maybe, the Sahara Desert) then you MIGHT need a fork oil as heavy as a 30 weight IF you weighed 250+# and IF you were racing the bike in a 6 hour endurance contest. :wink:
It is pretty hot here today (mid 90's) and I did have a big lunch, but I take your point. So you're using straight ATF? I have a 15 litre drum of ATF in the shed (what can I say - I own a Ford pickup!), would be handy if that works.
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Re: fork oil

Post by oldjapanesebikes »

Like others who have already chimed in, I've run ATF in the forks for a while. No complaints. 8)
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Re: fork oil

Post by Rustygt550 »

Chris, I used SAE 30 oil in my T500 forks, I have yet to try it yet.

Dont forget the T500 has crude damping compared to the GT's & does not have the same internals. The T500 workshop Manual states that SAE 30 oil is to be used but the Owners handbook states 10-30.
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Re: fork oil

Post by 87m6chris »

Makes sense, ATF it is then.
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Re: fork oil

Post by Buffalo-guy »

One benefit of using ATF, outside the price, is the fact that it has additives that keep the seals flexible and supple,extending their service life. SAE motor oil does not. I can't remember when I didn't use ATF. Cheers.
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Re: fork oil

Post by Suzsmokeyallan »

I dont like using ATF in forks as its sort of 'edgy' when you run it between your fingers compared to oil. I also prefer something a bit more slippery since most of these old forks dont carry slider bushings.
I use a dedicated fork oil of either the Bel Ray or Maxima brand. For the GT750 or RE5 I use a 15 weight and for the T500 a 20 weight as those forks are pretty pathetic when it comes to their internal dampening design.
For what its worth,,,ATF is not recommended in motocross front forks.
Two strokes, its just that simple.

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Re: fork oil

Post by H2RICK »

Allan +1....and another reason NOT to use ATF is the viscosity.
Nowhere on a can/bottle of ATF do you see a viscosity listed.
"Why is that ??" you say.
Well, it's because the SAE doesn't really have a hard and fast regulation about the viscosity of ATF.....or for most other stuff to do with ATF, for that matter.
When pressed, most refiners will say "It's around 20 weight.".....but that can (and does) turn out to be anything from 15 weight to 25 weight depending on which transmission manufacturer's spec the ATF meets i.e. GM Hydramatic (Dexron), Ford (2 different specs depending on which tranny you have), etc etc.
Sooooo....you pays yer money and you takes yer chances....with ATF.
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Re: fork oil

Post by oldjapanesebikes »

H2RICK wrote:....and another reason NOT to use ATF is the viscosity.....
Well - yes and no. :shock: As with all things there are many sides to the discussion and I'll leave it to the experts to battle it out as that would exclude me, but perhaps these charts (yes - the top one is an eye test) can help. You may actually want to download it so you can more easily zoom in to see it. What you are interested in are the two left columns where it lists make and then the ISO viscosity in cSt. To convert that ISO viscosity to SAE, you can use the chart that I've included below it and reference the column for SAE engine oil and the left side column for viscosity in cSt at 40C. What you will find is that several brands of ATF land in the midst of the specialty fork oils as far as viscosity is concerned, and often it is the ISO spec that is listed for ATF oils. For example, Shell Dexron has a 40C cSt of 34.35 which if you look at the lower chart means is has an SAE engine oil weight of about 15. 8)

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Or - you can just use what you like using :D
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Re: fork oil

Post by parksie »

I also agree with Allan, as far as the T500 I always use 30 weight (when I can obtain it), they are notoriusly oversprung and underdamped
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Re: fork oil

Post by H2RICK »

Thank you for that, Ian.
It's interesting to note that Mobil Synthetic ATF (apparently the only ATF on the list) is at the lower end or is just a little lighter than SAE20 weight when measured at 40*C......and then its viscosity increases as the temp rises to 100*C where the viscosity is in the mid to upper range of SAE20 weight....but still in the 20 weight band. Interesting phenomenon and something to keep in mind. Obviously great strides have been made by some refiners in their viscosity improvers. A lot of the mineral oils get a LOT thicker at higher temps.

And to all the Titan owners my deepest sympathies for owning a set of forks with such primitive internals that require such a viscous fluid to be able to work even close to properly. :wink: :P :mrgreen:
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