Fork oil weights?!?!

[viclioce]

I was reading through my Ace 90/100 & 100 B manual tonight looking up fork oil volumes. I came across the old oil mix recommendations for the front forks.

It said, "mix 50% SAE 70W non-detergent motor oil & 50% SAE 30W non-detergent motor oil in a container and shake well to mix."

That's amazing! So what are most folks using these days for fork oil in an Ace or Super Rat for general use (i.e. Non-racing)? I've been putting synthetic 20 weight fork oil in the Road Toads but haven't ridden them yet. I want to advise my California friend correctly. Don't know if the Ace will be ridden by an adult or younger child. ; D Victor

[Bill2001]

I'm using BelRay 10w fork oil. I had the 10w on hand and I'm planning to do a couple of fill-ride a few miles-drain-refill cycles to flush out all the old yukky oil. The damping feels a tad soft, I may try some BelRay 20w. The big plus about fork oil is that it contains a seal-swell agent that cuts down on leaks. My forks "feel OK" so I won't rebuild til next year. This Winter I'm splitting cases and looking at the bottom end, clutch and tranny.

[viclioce]

I had an interesting discussion with Greg about the fork oils. He told me he tried the 20w fork oil on his Ace and found he only got about 80% of the travel capable in his forks with the 20w. Says when the bikes were built, there were no synthetic fork oils & the recommended use of a 50/50 mix of motor oil was all that was available. He also said he wouldn't recommend running 20w fork oil unless the rider was well over 140-150 lbs. So I'm going to leave the 20w in the Red Toad because my nephew is 6'5" and about 185 lbs.! If it still feels like he isn't getting full travel, I can reduce the fork oil to 15w and try again for near full travel. But for the younger grandsons I'll probably stick with 10w fork oil, when changing or rebuilding. Just some info to consider. ; D Victor

[dirty_rat]

I have never heard of that minor a difference in the oil weight causing the forks to not use their entire travel. I have seen this caused by the springs coil-binding (sometimes caused by too long of a pre-load spacer or the wrong springs), or by too much oil (thereby causing a hydraulic lock).

[taber hodaka]

I have seen the too much oil causing the problem, when I had the dealership in the 60's-----------Clarence

[Bill2001]

Exactly. This is a tuning parameter for forks. The oil volume determines the air space above the oil. This air space adds to the spring rate-- more air, more springiness, less air, less springiness. Snd you can mix different fork oil weights to get what you want. A 50:50 mix of 10w and 20w fork oil will result in a 15w oil (or close enough).

[Bullfrog]

The recipe I found in the Official Hodaka Workshop Manual (for the ACE 90) is 60% SAE 80 gear oil, with 40% SAE 30 non-detergent motor oil. The intent was to end up with 40 "weight" oil to provide proper damping. The previously mentioned for formula for a 50/50 mix of 70 gear oil and 30 motor oil would result in about 30 "weight" oil (according to current standards on gear and motor oils, hmmmm, mayhaps standards have changed in the last half century???) So far as I can see, the only reason to mix oils would be to achieve something "heavier" than can be bought off the shelf - so the intentions "behind" each of the formulas are striving to achieve "heavier oil"/increased damping when compared to using straight 30 weight motor oil.

My own experience with Hodaka steel slider forks from the Model 93 Super Rat thru the Road Toad model 02 suggests that ambient temperature is at least as "big" as rider weight and aggressiveness in determining the "proper" oil wt for the forks. (ALL of the previous sentence assumes using the proper volume of oil for the given forks.) I have found 10 weight oil to be exceedingly "light" on hot summer days, to the extent that fork extension/"topping out" was so forceful that I thought I'd get "bucked off" (approx. 100 degrees F ambient temp). Winter fork oil of 20wt (possibly 10) works for me. Summer time? Gotta be 30 or 40 (for me). Disclaimer: YOUR educated feel/opinion rules.

Ed
PS: 50/50 mix of 30 weight and 50 weight Aeroshell from the local airport will result in 40 weight.

[Bill2001]

Ed, it is my understanding that the "oil testing procedures" are different for motor oils and gear oils. A 70wt gear oil has the same "pourability" as a 30wt engine oil. So go by the "recipes" and not the numbers. In the '70's BMW used Aeroshell 4001 hydraulic oil in their forks.

The advantage of using real fork oil is that it has seal-swell and anti-foam agents that other types don't.

[socalhodaka]

Check your fork travel like this. Zip Ty travel inspector, a must for all travel inspections. Fool proof, comes I many colors beside black.

Attach then go on your favorite ride, self explanatory after that.

[Bullfrog]

Nice tip Kelly!

Bill - you are "on target" about different oils being tested differently - which is why I commented that mixing 70 weight gear oil and 30 weight motor oil in a 50:50 ratio results in, um, 30 weight oil (on the motor oil measuring scale) - somehow that doesn't seem all that useful. Using fork oil is a great idea . . . not sure you can find it anymore in 30 or 40 wts though.

Ed

[ossa95d]

PJ-1 still has 30 wt fork oil and I have it here. I haven't seen a source for 40 wt.

[dirty_rat]

Harley Davidson still sells a "Heavy Duty" 40 wt. racing fork oil.

[Bill2001]

Check your fork travel like this. Zip Ty travel inspector, a must for all travel inspections. Fool proof...

And that would be very handy for measuring spring sag (at least I guess that is measured on Hodie susp tuning).