Somebody suggested that Rotella can also be used as fork oil.

Any comments on this? Would 5W40 syn or 15w40 dino be better? I've got both. I might have some old Dextron laying around. I weigh 200 lbs, if that makes a difference. I deal with rough roads, and I'd like secure handling on the tarmac. One of my seals is blown (or full of dirt), for those who don't know.

Can using heavier oil increase the risk of blowing the seals, or is it the other way around? I read that Bill likes to say to use fork oil due to stiction, Is motor oil slicker than ATF in that regard?

Would it be a good idea to experiment with those thin Energy Star motor oils in the forks?

I wouldn't use a multi-viscosity oil for the forks. Damping rod forks already have undesirable characteristics, why further complicate this poor performance by introducing an oil that will change its performance during use?

If you are looking for an inexpensive fork oil you can use ATF Type F. But given that you'll probably change the fork oil once, why not use actual fork oil? We're only talking about a few dollars difference. There are probably other place to save money.

Gary_in_NJ wrote on 01/07/16 at 09:43:27:


Actually, multiviscosity oil should not change it's performance as much as a straight weight oil. Think varying temps and the purpose of multiviscosity oil.

cheapnewb24 wrote on 01/07/16 at 21:46:05:

Cheap is correct, multi vis oil does not actually change viscosity
It is 5, 10, 15, or 20 weight oil that changes viscosity less than single weight to the point where, at NOT, it's as thick as 30,40,or 50 weight oil would be at NOT
the idea that multi vis oil actuallt thickens as it gets hot is an understandable, but incorrect, idea
I'd still stick with ATF

oh, NOT is normal operating temperature (for an engine) just so there's no confusion

Both ATF and fork oil,.. are made to have consistent compression under pressure... at any temperature...

Use ATF... it's even cheaper than Rotella anyway... it's usually around 13wt... and that's real nice in forks...

I'm probably the only one here who does use engine oil in forks. I grew up on springer equipped bikes, and therefor have zero tolerance for fork dive while braking. ND30 or HD30 is alright at your body weight. I switched my forks to 60w, better, but still has noticeable dive while braking. I weigh 260 in full gear.

Next test round will be 75w or 85w gear oil. After that, if I still notice dive, the forks will scrapped in favor of a springer.

The braking torque on the lower arm pushes the arm up and it resists the weight that transfers when you apply the brake.

And in anticipation of your next question - springers don't handle better than modern forks, and they are heavy.

The epitome of a motorcycle is a UL/VL Big Twin. Factory rigid frame with well sprung seat. Factory drum brake springer fork. Flathead engine, proper generator, kick only, points ignition.

Too bad they went away in model year 1948.

That stated, the Savage/S40 platform can be built up to ride and handle like a proper motorcycle. Stiffer rear shocks. Heavier fork oil and more of it. Better tires run with the correct amount of air. I like around 40psi front and rear, which means no more 712F once the current one wears out. Narrower tires, 90/90-19 and 130/90-15 are as close to ideal as you'll find for stock rims.

You can seriously improve its running capability, but it costs cubic dump truck loads of cash. Proper 5 angle valve job. Hot cam. Overbore. Shave the head or deck the cylinder. Port match. Intake and exhaust runner clean up. Free flowing exhaust. Better flowing carburetor with a cable operated slide or preferably butterfly valve and no slide (think S&S for Harley Davidson Sportster or K Model). You are however stuck with a weak oil pump.

You can seriously improve the fit of the bike. Seat work, seat changes. Handlebar and riser swap. Grip swaps. Floorboards or forward controls.

You can seriously improve the aesthetics. 7 inch sidemounted headlight. Handlebar and risers. Seat. Tires. Fenders. Taillight. Turn signals.

It's your bike, your money, and your butt/back. Even with my lumbar surgeries, I'll take the ride/handling of a rigid/springer over an as issued modern "mush mobile" cruiser. Once my 4wd is back in service, my Savage is getting an irreversible full rigid frame conversion and a -2 springer.

Yeah, I bleed HD black and orange. Won't own one made after 1964 though.