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#469512 - 02/07/05 05:11 AM Motor Oil for fork oil?
Shaman Offline

Registered: 07/27/04
Posts: 2358
Loc: Frankfort, Kentucky
A few people on the ZX6E board have stated that they have used 30 wt. motor oil for their forks. Can anyone give a reason why this would not work, aside from it is not recommended from the factory.

#469513 - 02/07/05 05:27 AM Re: Motor Oil for fork oil?
Marlin Offline

Registered: 11/13/04
Posts: 189
Loc: Raleigh, NC
If I remember correct fork oil is like a 10wt in Honda crusiers, so 30wt sounds thick?

But SOME have used ATF fluid like M1 atf. Cheaper and supposed to hold up much better.

#469514 - 02/07/05 06:41 AM Re: Motor Oil for fork oil?
wileyE Offline

Registered: 11/18/04
Posts: 1967
Loc: Kitsap, WA
Subject: Oil Viscosities
Regarding the discussion of oil weight for front forks, I saved the
following post from the observed trials list because it addresses this very
question, and because I thought it was kind of cool that someone cared
enough to sit at his workbench with a stopwatch and run thickness tests on
all kinds of oils. You'll see there's a big difference in different kinds of

Jim Winterer
St. Paul, Minnesota

Date: 16-Feb-1999 06:19pm CST

This is a reissue of previous info with some additions. The below is
valuable in evaluating what oil to use in forks (to set dampening speed)
and what oil to use in 2-cycle motor gearboxes (to affect clutch
performance), or just plain interesting to technonerds.

I wrote an e-mail some months ago describing my home made viscosity
meter, consisting of 50cc of oil passed through a vented plastic
container with a .140" orifice at bottom. Time to drain being the output
of the test. I was at the time measuring oil viscosity for gearbox use
to find a thin oil to eliminate drag with my Scorpa/Rotax clutch. Dexron
II ATF did just that.

My method is rough and not standard. The units are not Centisokes, but
seconds to empty with home-made set-up, similar in concept to standard
viscosity meters. My method is a handy comparative tool for determining
comparative oil viscosity at room temperature. I also do not care about
high temperature viscosity, or even viscosity index (which considers the
difference between high and low temp viscosities. Most two stroke gear
box and fork applications are relatively low temp, so one number is

The bottom line is you simply cannot trust SAE weight range numbers as a
way to compare oil thickness. The SAE system is NOT a measure of
viscosity, but rather a range of viscosities. We are being robbed of
important information by oil re sellers, particularly suspension in oils,
by their not showing their actual viscosities. Sure makes it hard to
tune suspension or alter clutch characteristics! The SAE way of looking
at things allows sale of a 2.5 weight oil that is thicker than a 5 weight
oil! But who cares. That fellow who puts in Bel-Ray High Perf. Fork Oil
7 weight oil after taking out his Bel-Ray High Perf. Fork Oil 10 weight
oil will swear up and down his forks move quicker because it "says so
right there on the bottle!" Also, that fellow will also swear up and
down that his clutch drags less with motor oil instead of gear oil
because "them there numbers on the bottle is smaller." Well, gear oils
use a different SAE scale. Now that's really intuitive!

My results. Shorter time means thinner viscosity. There are some
surprises in there.

Gear Related:
Stihl Chainsaw Bar Oil 2006 97s
Valvoline 85W140 Gear Oil 83s

Valvoline 10W40 Motor Oil 57s
Unilube Synthetic 75W-90 Gear Lube 50s
Belray Gear Saver 80 weight 50s
Citgo Chrysler Spec 7176 ATF 41s
Valvoline Dexron III ATF 26s (a great option for
eliminating clutch
drag in trials bikes)

Bel-Ray High Perf. Fork Oil 10 weight 21s (same oil as 7 weight)
Bel-Ray High Perf. Fork Oil 7 weight 21s (same oil as 10 weight)
PJ1 Fork Tuner H.V.I. 5 wt. 16s
Bel-Ray High Perf. Fork Oil 5 weight 14s
Golden Spectro 85/150 2.5 wt. Very Light 13s (a petroleum/synthetic
cartridge fork oil)
Stock Paioli Fork Oil from Factory, Used 12s
Honda/Showa SS7 shock oil 5 weight 12s
Fox Racing Oil 5 weight J26 12s
Maxima Zero-Fade Light Shock Fluid 5 wt. 11s (white bottle)
Maxima High-Perf. Light Shock Fluid 5 wt. 11s (black bottle)
Stock oil out of a Boge shock 11s

Isopropyl Rubbing Alcohol 9s
Justice for Corrupt Powerful Politicians 11.76 Gigaseconds

Note how the 10 and 7-weight Bel-Ray fork oil is the exact same oil,
while the 5 weight is not. That's right, the exact same oil! Cheating?
Not exactly. The weight of an oil is not the viscocity but rather the
SAE viscocity RANGE, so you can have overlap in the ranges, and
legitimately can sell two different weight oils of the same viscocity,
though this is misleading. Because oil is highly a subjective
experience, like spark plugs and the myths surrounding them, there will
be fellows who will swear their forks move faster with that 7 weight
verses 10, even though it's the exact same oil! Too bad the actual
viscocity numbers of oils are hardly ever listed on the bottles. On rare
occasion you will get the SAE weight expressed as the lower and higher
viscocity numbers. Case in point: Golden Spectro Synthetic/Petroleum
Cartridge Fork Fluid. They say on the bottle:

85/150 is equivalent to 2.5 (light) fork fluid for SHOWA forks.
125/150 is equivalent to 7.5 (medium) fork fluid for KAYABA forks.

Thus you see in the above statements the association of viscocity numbers
with their corresponding ranges. Note how the upper limit of 2.5 weight
is the same as the 7.5 weight? Confusing, isn't it! Perhaps I should
buy only Golden Spectro, as they at least are up front with what's in the

Note also how the higher gear lube weight is thinner than the motor oil
of a lower weight number. That's because motor and gear lubes use a
different scale, though they are still called "weights". It is also why
motor oil can cause more clutch drag than a "heavier" gear lube. To
those on the 650 list: Obseved Trials riders use their clutches almost
like an automatic transmission, especially when stopped or barely moving.
Clutch drag is thus a bad thing, as it tends to make you want to roll
forward when you don't want to. It upsets contol while balanced and
makes shifting while stopped and balanced very hard and notchy.

Back to the forks. Conclusion. I used 300cc of the Maxima shock oil in
the rebound side, as the viscocity was the closest of the available oils
I had. It turned out to be right upon riding the bike later in the day.
Shock oils, however, get sticky when they dry out. Hopefully that won't
have any bad effect on the fork seals. It should not, as I have long
used shock oils in forks with no harmful effects. For years I used Showa
(now Honda) 5 weight shock oils in forks. Shock oils tend to be very
light, therefore conducive to most trials bikes with their fast
suspension speeds. Shock oils also tend to be of higher quality as the
application is much more severe than that of forks.

Have fun digesting this info.

Chris Johnson, Engineering Director,
College Park Industries, Inc.

#469515 - 02/19/05 05:28 AM Re: Motor Oil for fork oil?
drive it forever Offline

Registered: 09/03/04
Posts: 843
Loc: Grove City, OH
I use valvoline atf+3 in my 96 suzuki dr350 dual-sport forks. It's like a 7wt oil with anti foam adds in it. Its the only valvoline product I use for anything.

#469516 - 02/20/05 02:14 AM Re: Motor Oil for fork oil?
Silk Offline

Registered: 07/26/03
Posts: 3851
Loc: New Zealand
A lot of the older bikes,before they got all sophisticated,used engine oil in the forks,my old XS1 for instance.In my twin shock trials bike I use either 5 weight fork oil or ATF...depending on what I have around at the time,no other reason,I can change my rear shock oil on this bike too.ATF in my XT600E,10 weight fork oil in the XLV750 I just sold.

#469517 - 02/20/05 07:53 PM Re: Motor Oil for fork oil?
tmorris1 Offline

Registered: 07/15/03
Posts: 2219
Loc: MN
I think 30Wt oil would give a pretty harsh ride.

#469518 - 02/23/05 08:04 AM Re: Motor Oil for fork oil?
MIDLF Offline

Registered: 02/21/05
Posts: 1
Loc: SE Wi
I would say a harsh ride would depend on the fork. I have an 89 FLHS Harley with RaceTech cartridge emulators. RaceTech calls for a heavier oil than HD stock. If I remember correctly 20 weight. I run Mobil 1 15W-50 and it works great. For fork use the 15 is the working number. I figured if the forks did start to heat up the multi-weight would hold the damping force constant. I would imagine if the forks needed a 5 weight and 30 weight was put in, the ride would be harsh.