Fork Fluid

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Jul 24, 2007
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Going to rebuild the front forks on an 75MKIII and wondering what fork fluid to use. I've got access to amsoil Light and Medium grade, difference stating for a slower or faster rebound. Whats the word on the suspension for these bikes, i've never ridden it before. Thanks ~Gavin
I believe the consensus is that modern fork oils are superior to the motor oils and ATF that (necessarily) used to be used. Most riders seem to think 20 weight works best, although YMMV. - BrianK
It depends what condition your forks are in. After several rebuilds, new damper rods and caps etc. and adding a 'Covenant' kit I still had lots of topping with ATF. Last month after 9 yrs of putting up with it I changed the oil for 10-40 semi syn. No more topping and a slightly firmer ride. ATF seems to work well in some Roadholders and not in others. All depends on overall wear I guess. I'd go for a 10 weight to start.
I would think that the Amsoil light would be too light for the Norton forks, as it seems to be SAE 5 grade, the Amsoil medium may be OK as it appears to be SAE 10, but that could still be a bit light as the standard recommendation was for SAE 20 oil. Personally I prefer to use SAE 20 fork oil.
Just talked to another well advised amsoil dealer about running the medium #10 fork fluid, he said large heavy v-twin bikes such as harleys run 10W. He seemed quite surprised that this bike ran a 20W. Anyways, he strongly suggested the medium weight and i'm gonna run it and see what happens. I'll reply back and see if i need a "firmer" ride. ~Gavin
This talk of oil brings up all kinds of opinions. Run what feels good to you.

My take is this you need to change your fork oil at least two times a season. ATF F type wears enough to let you know it's time to dump it. The action starts to get harsh. More important than the fluid is the ease of dumping it and replacing it.
I can dump and re-fill in 20 minutes and the fresh oil makes much more difference than any kind of oil. It' got to be cheap and easy or ya won't do the changes and that kills the whole system. Having the rod wear into the cap because the oils dirty is just dumb. Dirty oil no matter how good is trash in your system. I have a test I do to bikes, I grab the front brake and I pump the the forks hard if I can make it top out or bottom out or if there is no noticeable increased dampening as I progress to the third and fourth pumps the front end is a joke. I will put my front ends against the best out there on the moderns no joke. It does not need to be stiff or bottom out,top out. With the right seals and internal parts and some drilled fork caps these things work. The info's been posted for years here and other places you have only to read it. Every person who has tested my bikes can't believe how good it can be. It's cheap and simple . I make so little on my kits that most of the pros don't think it can work they also always refuse to do a test ride and that's real sad.
Sorry about the preaching I guess I have been at this a while and hate to see people waste their time and money. As an entry fee you have to do the work yourself so I will see a lot more 10.00 a pint snake oil fixes before I am out a here.
GavinJuice said:
Just talked to another well advised amsoil dealer about running the medium #10 fork fluid, he said large heavy v-twin bikes such as harleys run 10W. He seemed quite surprised that this bike ran a 20W.

Maybe the Amsoil dealer is "well advised" about the lubrication requirements of relatively modern Harley (and other) fork types, but what needs to be taken into consideration is that the Roadholder fork dates back to 1947, when any kind of hydraulically damped telescopic fork would have been considered to be a relatively new idea, the damping oil viscosity required being rather more to do with the damper design and not really to do with the weight of the machine as I see it, and *motorcycle fork oil* would not have existed at that time, the only real choice for a commonly available fork oil would have been engine oil, the lightest type generally was SAE20 grade, so I expect that is why the Roadholder forks were designed to use SAE20, or light motor oil.

Oil specifically formulated for forks certainly didn't become commonly available (in the UK and probably many other countries) until around the late seventies, (ATF by that time being specified for some motorcycle forks) which, in any case would really have been too late for the Norton Company.
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