Topic: Fork oil, using motor oil?

[Davidov]

I changed the fork oil on my 78 CB750F, what came out smelled like transmission fluid.
The old manual states "10w-30". So I used synthetic motor oil 5W-30.
Now I see everyone on SOHC4.net is saying ATF or specified Fork Oil.

Is there anything wrong with using synthetic motor oil?

[ekpent]

I just use trans fluid but different oils can be used to 'tune' the suspension.Seem like a straight weight oil  like a 20w though would give more of a consistent result than a multi that might change viscosity with temps ??

[MCRider]

To the question, no nothing wrong with any type of oil. Virtually everything has been recommended by someone at some time. Boils down to trial and error and what suits you. Some annuals say motor oil, others ATF, others specialized fork oil, etc.

ATF has some advantages, some additives to preserve and enhance seal life.

[KingCustomCycles.com]

I like snake oil but man, I hate extracting it from the little varmits.

[ekpent]

I like snake oil but man, I hate extracting it from the little varmits.

Just grab,squeeze and twist and it comes out the special drain hole at the back.

[Duke McDukiedook]

I changed the fork oil on my 78 CB750F, what came out smelled like transmission fluid.
The old manual states "10w-30". So I used synthetic motor oil 5W-30.
Now I see everyone on SOHC4.net is saying ATF or specified Fork Oil.

Is there anything wrong with using synthetic motor oil?

Some peoples say that using motor oil and not using ATF or Fork specific oil can cause problems with foaming.
They convinced me to use fork specific oil so I do, it's not that expensive.

[Tugboat]

Not that expensive?!? I just paid $15 for a quart of the stuff (Honda brand) at the local dealer. Now granted - it's enough to do at least 4 forks, but still.....

[TwoTired]

Not that expensive?!? I just paid $15 for a quart of the stuff (Honda brand) at the local dealer. Now granted - it's enough to do at least 4 forks, but still.....

If you are too cheap to invest $15 in your bike for proper function...  Well then...
Maybe spend $15 on a few beers and pee into your forks.  ($15 isn't even a full tank of gas anymore.)

I'd be concerned that 5w oil is a bit thin for proper damping action.  5W 30 is essentially 5W unless heated.  ATF has anti-foaming agents as well as seal "moisturizers" to help keep their resilience.  (Some motor oils do, too.) ATF viscosity seams the behave as 7 wt.

Fork oil has the anti foaming agents, seal "mosturizers" AND you get to select a viscosity that conforms to your ride requirements.
I like something between 10-15W.  !5W is great for mostly smooth highways. 10W seems better for bumpy roads, particualarly with a lighter bike like the  CB550.  For the 750 I prefer 15W.

The synthetic angle is a red herring.  The forks and seals don't care how the lube's molecules were made.   With synthetics, the size of the molecules are more uniform.

Cheers,

[Lostboy Steve]

Not that expensive?!? I just paid $15 for a quart of the stuff (Honda brand) at the local dealer. Now granted - it's enough to do at least 4 forks, but still.....

If you are too cheap to invest $15 in your bike for proper function...  Well then...
Maybe spend $15 on a few beers and pee into your forks.  ($15 isn't even a full tank of gas anymore.)

I'd be concerned that 5w oil is a bit thin for proper damping action.  5W 30 is essentially 5W unless heated.  ATF has anti-foaming agents as well as seal "moisturizers" to help keep their resilience.  (Some motor oils do, too.) ATF viscosity seams the behave as 7 wt.

Fork oil has the anti foaming agents, seal "mosturizers" AND you get to select a viscosity that conforms to your ride requirements.
I like something between 10-15W.  !5W is great for mostly smooth highways. 10W seems better for bumpy roads, particualarly with a lighter bike like the  CB550.  For the 750 I prefer 15W.

The synthetic angle is a red herring.  The forks and seals don't care how the lube's molecules were made.   With synthetics, the size of the molecules are more uniform.

Cheers,

As my friend would say "I just rofl'd in my pants". Which he uses as an expression meaning WOW! That was funny! Seriously, as any good cook knows adding a little corn starch to any liquid makes it slightly thicker. So before the urination occurs pour a good teaspoon of cornstarch into each tube. That should render about 5wt or so. FYI I use a good Maxim 10wt oil in mine. Which is what both my Buell takes and my brother in laws sportster.

[Lostboy Steve]

On a more serious note; Honda is good for using motor oil for everything. Most manual transmissions in their cars call for motor oil although I use synchromax. I could see 10wt motor oil in the fork but foaming could be an issue....

[cookindaddy]

I'm not sure which manual is being referred to.
My CB750 Honda Service manual calls for Honda ATF fluid in the forks.
That's what I used.
Expensive stuff and most of the bottle was left over as someone said.
Seems to work fine.

[MCRider]

My CLymer CB750 manual calls for 10W-30 motoroil OR ATF. OF course we woldn't use motor oil in auto trans, or ATF in the motor. Yet its OK for both in forks. Go figure. ITs just a different application.

Personally I prefer fish oil.   

[bjatwood]

I prefer Corn Oil, very handy for roadside meals when the need to feed comes up. But then again, I live in Nebraska and we have lots of Corn! 

[Terry in Australia]

There's more BS than science involved in folks predicting the best weight oil to use in bikes they're not familiar with, as the damping quality does not depend entirely just on the size of the holes in your damping rods.

Honda specified ATF because it worked well enough and there wasn't much in the way of specific weight fork oils available at the time. The Clymer manual specified engine oil to firm up the damping, as folks thought that the forks were under-damped, particularly when compare to European bikes of the era.

Bottom line is that while just about any oil will "work", you'll still need to personally experiment with your own bike, and depending on your weight and where it's distributed (i.e., whether you're a "Cafe Guy" and your weight is over the front of the bike clutching a pair of clubmans, or perhaps a "chopper guy" almost leaning backwards) and whether you've fitted firmer springs, or pre-tensioners, whether you've mounted a fairing and whether you're gonna haul luggage or fat chicks, will all need to be factored in. Cheers, Terry.

[ekpent]

Terry do I need 50w for a Fat Chick or will my ATF do ??     Guess it depends if she is on the front or back 

[Terry in Australia]

Terry do I need 50w for a Fat Chick or will my ATF do ??     Guess it depends if she is on the front or back 

Ha ha, well I'd go the 50W route Eric, you see, her massively fat body will push you further forwards (you'll probably be sitting on the tank, or thereabouts) so there'll be more weight over the front forks, not to mention what's a-happenin' down at the back........

[dave500]

i didnt like atf in the 500,im using 15/40 now,20/50 was too heavy for me,lighter dirt bikes are a different thing though,i always used a 2.5 weight in them.

[seanbarney41]

Terry do I need 50w for a Fat Chick or will my ATF do ??     Guess it depends if she is on the front or back 

he he.....he he....

[seanbarney41]

...he he he......

[Terry in Australia]

Those damn Harley guys get all the hot chicks! 

[Danno]

I have used both atf and 30 weight oil in my shock tubes if you want a softer ride use atf if you want a stiffer ride and less front end dive then us 30 weight  I will say that when you go to drain the fork oil and it is atf it will smell rancid also atf tends to weep more out the seal where as I have never seen a drop of 30 weight

[cookindaddy]

This is getting to be just like an oil thread....
Oh yah, it IS an oil thread!

[BobbyR]

Terry do I need 50w for a Fat Chick or will my ATF do ??     Guess it depends if she is on the front or back 

If she is that fat, you should have her run alongside for a few miles.

[Lostboy Steve]

Can we get a full size of those pics? I HAVE to read the captions..

[grasscutter]

Fill the fork tubes with Jack Daniels.  It won't be much volume, but if you break down... yup, you got a few nips to keep you level headed.