Fork Oil When to Change and Why

hotroadking · Dec 29, 2004

Been having some discussion on the fork oil, when should you change it on a heavy cruiser like a heritage or road king, and what is the reason, does the oil really deteriorate in 10 to 15K it's not like it is running through a motor and getting hot to 250 degrees.

Thanks

XS650 · Dec 29, 2004

Fork oil can get pretty gross looking. It would be a good idea to change it at the recommended interval or soonerthe first time and then adjust based on how the oil looks. MC forks are diabolical devices and have a lot of high force internal rubbing because of the relatively short overlap between the slider and tube and the effects of braking forces on that interface. Sometimes you get a lot of metal and bushing particles in the oil.

It would also be an opportunity to go to a premium brand of fork oil. Forks need all the help they can get.

msparks · Dec 29, 2004

quote:

Originally posted by hotroadking:
Been having some discussion on the fork oil, when should you change it on a heavy cruiser like a heritage or road king, and what is the reason, does the oil really deteriorate in 10 to 15K it's not like it is running through a motor and getting hot to 250 degrees.

Thanks

Reason to change the OEM stuff is crap. Go with a quality synthetic and be sure there is the correct amount. It will be the world of difference. Especially if you ride in cold weather or very hot weather.

The other reason is that moisture and dirt can contaminate the forks. Fresh oil will keep the seals clean and help them last longer.

I have a buddy that just put the Amsoil Shock therapy in his 2002 Yamaha FJR, he say's it's like night and day. Especially on a cold morning.

Another reason to change the oil is if you want to go lighter or heavier to change the characterists of the forks. I did this on my Triumph ST I wanted a heavier oil to help slow the rebound (more dampining) as I was getting the pogo effect going around corners. Some folks like it lighter to get a fast rebound.

drive it forever · Dec 29, 2004

Your fork seals will last longer, and you will get better suspension action. I change the fluid after about 4-5 off-road rides on my suzuki dr350se dual-sport. Dirt bikes are finicky about changing fork oil and you know the difference riding between fresh and old/shot fluid. Its very common to change fork oil several times a season for a dirtbike and I guess its overdue on a street bike at 15k.

KW · Dec 30, 2004

You guys ain't going to like this but, I have had great success with type F transmission fluid in my bikes.

Fork oil can be some nasty, smelly, gross stuff after a couple of years.

cos · Dec 30, 2004

KW,

I see nothing wrong with ATF. One of my bikes is an old Honda 250 (that never get's ridden) and the manual specifies ATF for the forks. On my other bikes I use either Amsoil or Redline fork oil. Redline has quite a nice selection of weights that can be mixed if ya want to get a custom weight. I "made up" a batch 17.5W for my Suzuki. Why? I read a bunch of different posts, some recommending 15W and others 20W. I split the difference and the front end feels much better than stock.

SKUNKY · Dec 30, 2004

I change it once a year...usually 8-10k...I use Spectro 15 wt ...on a dresser

XS650 · Dec 30, 2004

quote:

Originally posted by KW:
You guys ain't going to like this but, I have had great success with type F transmission fluid in my bikes.

Hydraulic oil with good anti-wear properties seems reasonable for forks

Way back in the olden daze of the 1960s and early 1970s, Curnutt recommended ATF thinned with bit of diesel for the offroad MC rear shocks he built.

SKUNKY · Dec 30, 2004

PS...change break fluid at same time...

tom slick · Dec 30, 2004

the only problem i forsee with ATF is you don't know exactly what viscosity you are getting. is it a 10, 20, 10w-20 etc? with fork oil you know what visc. you are buying.

srivett · Dec 30, 2004

I change it every year and use proper fork oil. When I was using non-detergent Castrol 30 it would turn into water after a season! Flush the forks out with kerosene while you're at it. My oil comes out black, even after a good flushing.

You know those horse things in playgrounds mounted on a spring? That's how a motorcycle with bad fork oil and rear shocks will handle.

Steve

tmorris1 · Dec 30, 2004

quote:

Originally posted by srivett:
I change it every year and use proper fork oil. When I was using non-detergent Castrol 30 it would turn into water after a season! Flush the forks out with kerosene while you're at it. My oil comes out black, even after a good flushing.

You know those horse things in playgrounds mounted on a spring? That's how a motorcycle with bad fork oil and rear shocks will handle.

Steve

That bike must have stiff forks if you are using a 30Wt oil. Usually my dirtbikes get a 5W or 10W

Lugosi · Dec 30, 2004

Generally, when a bike manufacturer specs ATF for fork oil, it is ~7.5w. PJ1 sells "ATF" weight fork oil, as a weight between their 5w and 10w. Honda specifies ATF quite alot.

satterfi · Dec 30, 2004

quote:

Originally posted by tom slick:
the only problem i forsee with ATF is you don't know exactly what viscosity you are getting. is it a 10, 20, 10w-20 etc? with fork oil you know what visc. you are buying.

Even knowing the weight, eg. 5w, 10w, you don't know exactly what you're getting.

Here's a couple of charts I've used when experimenting.

suspension fluids

Spectro, Bel Ray, others,Comparison

Viscosity index, Spectro, Bel ray, others

Shaman · Jan 12, 2005

can anyone specify a brand to use?

satterfi · Jan 13, 2005

quote:

Originally posted by Shaman:
can anyone specify a brand to use?

I don’t think it makes much difference. Bel-Ray, Spectro, Maxima are usually easy to get.

Getting the viscosity right is more important than the brand, especially if you don’t have fully adjustable forks. I don’t have a compression damping adjuster so I have to mix weights to get compression the way I like it.

Don’t assume the manufacturer spec’s the right oil. Honda must have had a watercraft engineer spec the oil and spring rates for the VTR1000.

Like srivett, I also use kerosene to flush and rinse the black crud out.

Mackelroy · Jan 17, 2005

quote:

Originally posted by hotroadking:
Been having some discussion on the fork oil, when should you change it on a heavy cruiser like a heritage or road king, and what is the reason, does the oil really deteriorate in 10 to 15K it's not like it is running through a motor and getting hot to 250 degrees.

Thanks

Can't say specifically on your Harley. Offroad forks should come apart after first ride or so. The oil that's in them is not necessarily bad. It's usually either Kayaba 01 or Show 5 weight which aren't crap oil, new forks and the breakend just contaminates with a new bike. So everyone says it's crap oil when they see the result.

Street bikes 10 or 15 k would work. Your not going to cantamiate oil as quickly versus off road, and if upside down forks they'll probably have a seal leak by that time anyway. I recently replace the oil in some very high end performance forks(nothing Harley related) but with 15 k on them and was very surprised at how good of condition the oil was in. Cartridge forks are sensitive to contamination so the oil changes are good to flush.

But when you change it IMO, it should only be mildly discolored or you going too long.

[ January 17, 2005, 11:35 PM: Message edited by: Mackelroy ]

jagabom · Jan 23, 2005

In my Clymer's book for the 79 Honda 750 it says to change the fork oil every 6k miles or each year.
Use Dexron ATF or fork oil. Does not specify which type of fork oil. Also think about changing those front springs. A Honda mechanic said that this was why my tires were wearing funny. He said they do wear out.

Jim
79 Honda

Mackelroy · Jan 30, 2005

((((((when a bike manufacturer specs ATF for fork oil, it is ~7.5w)))))))

My testing using ATV is much thicker than a true fork oil in 7.5 weight

Could be bad or good, I liked the compression, but I didn't have rebound adjustment to correct the slow rebound. So the ATV was short lived

wileyE · Jan 30, 2005

I'd use whatever HD advises and change it at HD interval. It's just a cruiser and probably only has 2" of travel if the bikes been lowered (like most road kings). It's not like a sportbike or dirtbike that is stroking a lot of fluid through the valving where viscosity would relly show a difference. I'd also think HD put decent oil in it at the factory, not like the old fish oil stuff that went in some of the old *** bikes. Unless you want to spend the time experimenting with cause and effect of different fluids and fluid levels you might just search on some HD forums and see what everyone else is using? Nice bike BTW, would be my choice in HD's.

Fork Oil When to Change and Why

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