Front Fork Oil

[Kiwi_Roy]

I changed the oil in my forks

Dave, the guy in the local shop recommended transmission fluid which was cheaper than the fork oil he had in stock.

The manual says add 400mL (it doesn't actually say "In each leg") but I found the right fork seemed to be fairly full, just a couple of inches from top with no weight on, If I pushed the fork up it would run out. I spoke to Dave and he assured me 400 sounds about right for an inverted fork.

There is very little travel with a sudden stop and the ride seems a bit rough.

Also by the time I had spilt a bit and generally made a mess when I tipped the old oil back into the bottle I ended up with about 600mL total

I am tempted to suck some back out, is there a level I should have it at e.g. XX mm from top?

Can I do any harm by having the level a bit low?

 

Thanks

 

Roy

[Skeeve]

I changed the oil in my forks

Dave, the guy in the local shop recommended transmission fluid which was cheaper than the fork oil he had in stock....

I am tempted to suck some back out, is there a level I should have it at e.g. XX mm from top?

Can I do any harm by having the level a bit low?

 

ATF used to be the stuff for damper rod forks, back when fork oil was literally no different from straight wt. motor oil, and Japan, Inc. was trying to break into the motorcycle manufacturing world... ATF had all sorts of superior characteristics, so was a good choice for its time.

 

That time has passed.

 

Nowadays you can find actual fork fluids in "weights" that are more finely graduated than Dexron III's kinda-sorta 15wt equivalent, have superior seal lubricative qualities to reduce stiction, etc. etc. etc. Moreover, your forks were probably designed w/ a 5wt or 10wt fork fluid in mind, and the variable ATF viscosity [after all, it is intended to be used in a transmission that's probably running at about 100Fdeg rain or shine] is too high for your needs. As always, when in doubt, RTFM.

 

As for putting in too much/too little: oil height is critical to proper function! Why do you think that so much of the literature on modification/tuning of stock front suspension revolves around "change to this wt. fork oil, and adjust to this level from top when forks are fully compressed" - volume be d@mned?

 

Good luck w/ getting things sorted, & keep up the good questions!

[Buzzard]

While I have not, as yet, gotten into my Guzzi forks, I do service quite a few dirt bike forks. The basics are the same. The oil level for each leg is measured, with the fork leg out of the bike, level, spring out, suspension collapsed completely, from the top rim of the outer leg to the surface of the oil within. One must cycle the fork numerous times to fill the cartridge, and work any air out, or the level will not be correct. The distance is also referred to as "air chamber", because the air volume above the oil acts as a spring, resisting the further compression of the fork as it nears the limit of it's travel. This air chamber is a tunable item, often given a range of say, 130mm-100mm, with 100mm being the stiffer setting. The oil viscosity is a tunable item as well, one can try oils from 2.5wt to 15 or 20 wt. I personally like to use 2.5wt and 5wt oils, then use the adjusters to stiffen as needed. There is also an issue of lo and hi speed damping, the adjuster affecting the lo speed, but that gets pretty complex, and varies by fork design, and how many beers you've had.

 

Hope this helps.

[gstallons]

I changed the oil in my forks

Dave, the guy in the local shop recommended transmission fluid which was cheaper than the fork oil he had in stock.

The manual says add 400mL (it doesn't actually say "In each leg") but I found the right fork seemed to be fairly full, just a couple of inches from top with no weight on, If I pushed the fork up it would run out. I spoke to Dave and he assured me 400 sounds about right for an inverted fork.

There is very little travel with a sudden stop and the ride seems a bit rough.

Also by the time I had spilt a bit and generally made a mess when I tipped the old oil back into the bottle I ended up with about 600mL total

I am tempted to suck some back out, is there a level I should have it at e.g. XX mm from top?

Can I do any harm by having the level a bit low?

 

Thanks

 

Roy

 

Roy,

Purchase a tool from MotionPro to adjust the fluid level (for now) in eack fork leg. When it gets winter,remove the forks,disassemble them and get the ATF out & install a cartridge fork oil. Read Buzzard's post and memorize it. When you do put the forks together you can replenish with the correct wt. &volume of fluid.

BTW, aTF was the hot set-up in 1970 but things have changed in 40 yrs...........

[Kiwi_Roy]

Skeeve

I did RTFM, it said 400cc. that's obviously way too much. I agree level seems the best way to go, i was hoping someone would tell me, see below

 

Buzzard,

Thanks for the tips, I will set the air chamber at 100 mm as you suggest. If I find out later that it's wrong it will be easy enough to add a bit.

 

Gstallons,

Actually I think changing the oil is quite simple, once you take the wheel at you can unscrew the bolt that holds the internals and all the oil should drain.

 

Everyone,

I must admit I was a bit skeptical when Dave told me to use ATF because he had the more expensive oil right there. He runs what you would call an independent shop, not tied to any one brand.

I kind of trust him because he is a journeyman mechanic and used to own a Guzzi, so he can't be bad eh?

 

I'm off on a road trip tomorrow' I will take it easy until I find out how she feels

 

Thanks

 

Roy

[OldButNotDead]

I changed the oil in my forks

Dave, the guy in the local shop recommended transmission fluid which was cheaper than the fork oil he had in stock.

The manual says add 400mL (it doesn't actually say "In each leg") but I found the right fork seemed to be fairly full, just a couple of inches from top with no weight on, If I pushed the fork up it would run out. I spoke to Dave and he assured me 400 sounds about right for an inverted fork.

There is very little travel with a sudden stop and the ride seems a bit rough.

Also by the time I had spilt a bit and generally made a mess when I tipped the old oil back into the bottle I ended up with about 600mL total

I am tempted to suck some back out, is there a level I should have it at e.g. XX mm from top?

Can I do any harm by having the level a bit low?

 

Thanks

 

Roy

 

Just noticed that it's been 2 years since I changed my fork oil. Everyone's taste is different, but afte upgrading to 0.95 kg springs (I'm ~165lbs), I've been happiest using 7.5 wt oil and a 100mm air gap.

[Kiwi_Roy]

 

Just noticed that it's been 2 years since I changed my fork oil. Everyone's taste is different, but afte upgrading to 0.95 kg springs (I'm ~165lbs), I've been happiest using 7.5 wt oil and a 100mm air gap.

 

Ok, I went and sucked some out.

Jacked up on the hoist to take the weight off,

Slacked off on the top pinch bolts, They tighten the caps too.

Unscrewed the caps to end of thread

Lowered the bike slowly, the forks compressed pushing the caps up

Put a narrow tube down the gap (now heres the thing, about 3" down the tube strikes the end of the inner, I don't see how you can lower the oil lower than that or even measure for that matter

Syphoned out the oil until the syphon sucked air at 3".

So my oils down 75mm, the bike appreciates it, much smoother ride.

I also backed off on the damper screws 2 clicks, currently 6 clicks ccw, I can easily adjust that as I go

 

I will see how that goes

 

Off to Prince George in the morning, about 900 km

 

Thanks everyone.

 

Roy

[luhbo]

... he is a journeyman mechanic and used to own a Guzzi, so he can't be bad eh? ...

 

Wrong, this could be exactly the problem. Guzzis have changed even more than oils have done.

 

Hubert

[Kiwi_Roy]

While I have not, as yet, gotten into my Guzzi forks, I do service quite a few dirt bike forks. The basics are the same. The oil level for each leg is measured, with the fork leg out of the bike, level, spring out, suspension collapsed completely, from the top rim of the outer leg to the surface of the oil within. One must cycle the fork numerous times to fill the cartridge, and work any air out, or the level will not be correct. The distance is also referred to as "air chamber", because the air volume above the oil acts as a spring, resisting the further compression of the fork as it nears the limit of it's travel. This air chamber is a tunable item, often given a range of say, 130mm-100mm, with 100mm being the stiffer setting. The oil viscosity is a tunable item as well, one can try oils from 2.5wt to 15 or 20 wt. I personally like to use 2.5wt and 5wt oils, then use the adjusters to stiffen as needed. There is also an issue of lo and hi speed damping, the adjuster affecting the lo speed, but that gets pretty complex, and varies by fork design, and how many beers you've had.

 

Hope this helps.

I have been mulling over your post, you say spring out, can you be a bit more specific please. I won't get a chance to do it again before my trip but will do over the winter for sure.

Perhaps as a public service you could treat your Guzzi to an oil change and educate us all in the correct procedure.

The workshop and the owners manual both say 400 mL of fork oil but I don't think they are specific about weight. Perhaps if I had used something like a lab measuring cylinder I would have been right on, of course I didn't have one handy, the best I could do was use the scale on the side of oil container, shone a flashlight thru to get the level.

BTW, I don't expect to be leaping through the air so perhaps my settings are not as critical as a dirt bike

I collected the oil I drained out and poured back into the container, came to about 600 mL so either some had leaked out over the years or the PO had them serviced. The oil I drained looked OK but the ATF will match my K&N air filters at least when it leaks.

Cheers

Roy

[gstallons]

While I have not, as yet, gotten into my Guzzi forks, I do service quite a few dirt bike forks. The basics are the same. The oil level for each leg is measured, with the fork leg out of the bike, level, spring out, suspension collapsed completely, from the top rim of the outer leg to the surface of the oil within. One must cycle the fork numerous times to fill the cartridge, and work any air out, or the level will not be correct. The distance is also referred to as "air chamber", because the air volume above the oil acts as a spring, resisting the further compression of the fork as it nears the limit of it's travel. This air chamber is a tunable item, often given a range of say, 130mm-100mm, with 100mm being the stiffer setting. The oil viscosity is a tunable item as well, one can try oils from 2.5wt to 15 or 20 wt. I personally like to use 2.5wt and 5wt oils, then use the adjusters to stiffen as needed. There is also an issue of lo and hi speed damping, the adjuster affecting the lo speed, but that gets pretty complex, and varies by fork design, and how many beers you've had.

 

Hope this helps.

I have been mulling over your post, you say spring out, can you be a bit more specific please. I won't get a chance to do it again before my trip but will do over the winter for sure.

Perhaps as a public service you could treat your Guzzi to an oil change and educate us all in the correct procedure.

The workshop and the owners manual both say 400 mL of fork oil but I don't think they are specific about weight. Perhaps if I had used something like a lab measuring cylinder I would have been right on, of course I didn't have one handy, the best I could do was use the scale on the side of oil container, shone a flashlight thru to get the level.

BTW, I don't expect to be leaping through the air so perhaps my settings are not as critical as a dirt bike

I collected the oil I drained out and poured back into the container, came to about 600 mL so either some had leaked out over the years or the PO had them serviced. The oil I drained looked OK but the ATF will match my K&N air filters at least when it leaks.

Cheers

Roy

Roy,

I am using 125/150 GoldenSpectro Cartridge fork oil @120mm from the top of the (collapsed/no spring) fork tube. you really need to do this after a disassembly. Search this site for fork spring replacement or fork rebuild for help. If you need an exploded view of the forks we can provide them. The ? you can answer is: Do you feel up to it? I am not being terse but you are the only one who knows that. This is easy the 2nd,3rd,4th &more times you do it. After misreading the instructions & adding almost a qt. to each fork leg I know.

[Buzzard]

Roy, there is no way to accurately do the fork oil change with the fork legs in the bike. You need to remove the fender, wheel, brake calipers, and slide the legs out. It is a good idea to loosen the top cap while the leg is in the bike. With the fork leg out of the bike, and adequately supported, remove the top cap by unscrewing it from the cartridge rod top. The spring will then be easily removed. The cartridge rod will ease down, not to worry, you can lift it up, it won't disappear. (While this far apart, you can check and adjust spring preload if you please.) Now you can pour the old oil out, pumping the cartridge to help extract as much as you can.

 

I like to spread out some news papers to lay the springs and other parts on. Cleanliness is absolutely required, no dirt or debris allowed in the fork. As far as oil volumn and viscosity recommendations from the owner/shop manuals, they are to be considered as starting point. There are manuals on just the forks, and they go into the various aspects of tuning the fork. Everything is changable, to get a desired result. Spring rate, spring preload, oil viscosity, oil volumn, and the height of the forks in the triple clamps, are all things you can easily change. The actual valving of the forks, shim stacks and passage diameters, are more invoved changes, but doable by the home mechanic with some knowledge of what to do.

 

 

With the spring out of the leg, all the old oil out that you can get out, you may begin pouring in the new oil. By the way, cartridge fork oil is pretty special stuff. It is formulated to meet criteria such as lubricity, surface tension(which affects foaming, or lack of), compatability with other components(seals, wipers), viscosity retension under stress and temp changes, chemical stability over time and use, and so on. Buy a good brand of fork oil. Pour the oil in until you see it rising to about six inches below the top rim of the outer tube. Now exercise the cartridge quite a few times, until you cannot sense any air in it. Now carefully fill to the level you have chosen, say 110mm. I measure with a piece of hard wire, say a piece of coat hanger. I will mark the wire at 110mm, or bend it at 90 degrees with a 110mm leg, insert it into the fork, and watching with a flashlight, I can see when the wire reaches the fluid by making a dimple in the surface of the fluid. There are many expensive fork oil measuring devices to be bought, but if you aren't doing it for a living, don't bother. One tool I recommend is a large plastic syringe, with a piece of small plastic tubing attached to it, to remove any over fills. With the oil at the level you have opted for, you can now begin to reassemble the fork, put in the spring and spacer(the spacer is what provides spring preload), attach the top cap to the cartridge rod(caution here, in the middle of the cartridge rod is an extension tube that is acted on by the comp or rebound adjuster, it has to be correctly seated, look at it carefully when you remove it upon disassembly, get it back like it was originally.) It's a complicated job, but one that makes a lot more sense the second time you do it, and in a lot less time.

 

I do have new springs ordered for my Guzzi. When I get them, I will take some photos of the installation, and try to record the process.

[gstallons]

Roy,

Please consider the MotionPro tool. 08-0121 fork oil level tool. It is $23.99. Very cheap for perfection . I own one and would not part with it.

http://www.motionpro...artno/08-0121/.

[docc]

Good advice from Buzzard!

 

And now I know what is meant by "luftkammer" (air chamber)!

 

I use a 100mm air chamber to good effect. Maybe this change I'll try 110.

 

Fork oil viscosity varies wildly even within the same SAE "weight." A better measure is CentiStokes at a given temperature (usually hot, say 40C). Here is a great technical site to look at various brands: Peter Verdone Designs . I favor a 5wt in the lightest of the range (15 cSt).

 

I've thought of using an even lighter oil in the rebound side, but just haven't gotten it together to try that yet.

 

ATF is also highly detergent and should give your forks a loverly scrub out after some few miles.

 

Even more better is be certain you have the right springs (probably stiffer than stock) on reassembly.

[Tom M]

I just want to mention something that I and a few others here have seen when setting fork oil levels. After changing springs, spacers, and oil I rode for a week then went back in to take a little oil out because I wasn't getting full travel after riding some very rough roads fast. When I opened one leg (rebound side I think) I found the oil level was down a good 20mm from the other side. Even though I pumped the forks alot after filling them with oil there must have been some air left in the cartridge that only worked its way out after riding a bit.

 

FWIW I'm running a 110mm air gap with 5wt fork oil in the compression leg and 7.5wt on the rebound side with 1.05 kg/mm springs and 10mm of preload. The change to 5wt oil seemed to make the fork noticeably more supple and the stiffer springs are a huge improvement over stock for my 230lbs.

[Kiwi_Roy]

I just got back from my trip Vancouver - Prince George 1800 km in two days.

The bike was a dream to ride, just purred along.

As for the forks I had no complaint but I will pull the legs out again over winter and set them as per

Buzzard's detailed instructions. I will check out the Motion Pro tool also.

It sounds as though the 5 wt oil is the way to go.

Thanks again for all your input

 

Roy