Fork oil weight??

..I have an '83 Honda VT750C and I'm currently using 20wt. The forks seem a
little stiff in sub freezing temperatues, and a little soft in the hot
weather.

I was thinking of using a 10/30 wt oil, but the only multi-grade oil I can
find is engine oil.

Does anyone make a multi-grade fork oil?
Would this caue a problem using multi-grade engine oil in the forks?

Thanks!

 

It's my understanding that fork oil wieghts don't
really translate well to engine oil weights. I think
I'd stick with a fork oil. 20wt seems a little heavy
also.

 

I'd have thought it was too heavy an oil at any time, actually.

Not to my knowledge. Multigrades only 'change' from one grade to another
(as it were) at temperatures far, far higher than you'll ever get in a
fork.

No, but it would be a complete waste of time because, in practice, it
would only ever operate at the lower end of the multigrade scale.

 

Ummm, do you have to ride so fast on cold mornings?

Can't you avoid riding over frost heaves and sharp-edged bumps, or
maybe just sit back go slow and relax and don't put a lot of weight on
your wrists? That *is* a cruiser model, yannow...

It would be nice if there was a simple solution, like multi-grade fork
oil that worked as well in the winter as it does in the summer.
Suspension tuners have tried everything from fish oil to automatic
transmission fluid, trying to solve the problem of harsh damping due
to crude damper rod oil flow control.

Sorry, but your forks do have crude damper rods inside them with a few
small holes drilled in them to control rebound damping.

Since the damping due oil flow through those holes is *very* sensitive
to stroking velocity, you can get into a situation where the fork oil
cannot flow rapidly through the holes and you get a very harsh action
as the fork compresses. (1)

Riders of sport bikes lean forward over the short handlebars and
really notice the jackhammer effect of restricted oil flow at high
stroking velocities because they put more weight on the handlebars.

20 weight fork oil is a little heavy, but it's what I use during the
summer riding season in California.

I tried 30 weight oil, but it was too thick for vigorous riding during
the winter months. The heavy oil caused too much compression damping
and the front tire chattered over small bumps and the whole motorcycle
wobbled.

(1) Race Tech, a California company that makes parts for forks has a
part called a Gold Valve Emulator. It's an adjustable oil pressure
blow off valve that sits on top of the damper rod and blows off excess
compression pressure.

I dunno if Race Tech has any GVE kits especially intended for the
VT750 Shadow, but if you knew what the internal diameter of the fork
tubes was, maybe Race Tech could advise you as to which GVE would fit
in your fork tubes.

 

I can't remember the reason, but I read somewhere that engine oil is
not a good idea for shocks, it should be a so-called 'hydraulic'
fluid, even automatic transmission fluid, aren't there multi-weights
for those?


Also, I thought viscousity numbers are specific to fluid type, eg., 90
weight gear oil is about the same viscousity as 40 weight
lubricating oil. Is 20 weight fork oil the same viscousity as 20
weight engine oil?

 

ATF is fine in forks, yes. Even recommended for some bikes.

See my posting about multigrade oils and operating temperatures. Off the
top of my head, I think that in a 10/40 oil, the viscosity is the same
at ambient temperature and at 100 degrees C, but Google or Wiki and you
should get chapter & verse.

Either way, there is *no way* that a road rider will get a Honda cruiser
fork up to the higher figure.

 

<snip>

In other words, you have failed to answer the OP's questions
*completely*.

 

Piss off, Piggy.

 

I've met more than a few people with that misapprehension. From one
of many references: http://en.wikipedia.org/wiki/Gear_oil

"API viscosity ratings for gear oils are not directly comparable with
those for motor oil, and they are thinner than the figures suggest.
For example, many modern gearboxes use a 75W90 gear oil, which is
actually of equivalent viscosity to a 10W40 motor oil."

 

Go on, then. You say you're the guy who tries to dispense good technical
advice to newbies.

 

I ought to point out the twin idiocies in this paragraph.

First, what is a "short handlebar"? Some cruisers have "short
handlebars". The length or width of a handlebar has *nothing* to do with
the effect of damping oil.

Secondly, if there is more weight put on the front end, then you might
actually *need* a heavier damping oil.

Tell me, do you actually know anything about motorcycles?

 

Have another glass of claret and go outside and argue with the lamp
post, Piggy.

 

No, come on, seriously. You say you're the newbie's friend. Why didn't
you answer this guy begging for assistance?

 

You're the dude who's begging for assistance, Piggy.

Sorry, but I won't let you blow me...

 

Color me "misaprehended"! ;-)
Have always thought that the 90W didn't look or feel THAT much different
than 40W and now I know why. Not a big fan of Wiki as a definitive source
but that page linked to some that ARE......and I think from those charts,
that it would be more properly characterized as equivalent to 50W motor oil.
Thanks for the correction. Learn something new every day.

 

straight Weight oils are comparable to one another. So a 40 weight is
thinner than a 90 weight. On the other hand, multiviscosiy oils ARE NOT
COMPARABLE to straight weight viscosities, nor technically other brands
viscosities, or even the same brand.

The first number is the cold "flow" characteristic, and the second is
the hot "flow" characteristic. It has nothing to do with straight weight
viscosity comparisons.

Clay

 

According to these guys, engine oils, gear oils and hydraulic
oils each have their own rating system and are not comparable
by oil weights.

http://www.maximausa.com/technical/lubenews/spring98.pdf

 

Yeah I didn't explain that as well as I should have. I should have said
engine oils, or motor oils. Specifically I was referring to straight
weights versus multi viscosity oils of LIKE type.

The sus, or ssu weights are standard viscosities and are always what
they are. That scale is used quite often in industrial gearboxes and
hydraulic systems. You know when you buy 250 ssu oil, no matter where
you get it it's the same at the measured temperature.

Clay

 

Yeah I didn't explain that as well as I should have. I should have said
engine oils, or motor oils. Specifically I was referring to straight
weights versus multi viscosity oils of LIKE type.

The sus, or ssu weights are standard viscosities and are always what
they are. That scale is used quite often in industrial gearboxes and
hydraulic systems. You know when you buy 250 ssu oil, no matter where
you get it it's the same at the measured temperature.

Clay

 

Listen up, Fudge-oli and learn something. (1)

The Saybolt Viscosity is determined by flowing 50cc of oil *very
slowly* through a
calibrated orifice.

So a SSU 220 oil takes 220,000 seconds to flow through the orifice at
a certain temperature.

What we need to do here, is flow 500cc's of *cold* oil through three
orifices that are about 1.0 ~ 1.5 mm in diameter in a matter of
*milliseconds*!!!!

If you double the stroking speed in mm/sec or cm/sec, the flow
resistance *quadruples*!!!!

At some point, a suitable oil that works at a reasonable stroking
speed won't be able to pass through the orifices at all.

That's why Race Tech invented the Gold Valve Emulator to blow off
excess pressure at high stroking speeds.







(1) **** you, Piggy. Don't answer this post.