Topic: Ever measured the fork oil height?

[Frostyboy]

I have always felt the front forks on my 550 are a bit harsh. The 750 club I'm in had a workshop day the other week & a member there asked if I'd ever measured the fork oil height. I've only ever added the recommended quantity of oil to the forks, but now I've learned that too much oil may result in a harsh ride.
I'd be interested to hear if anyone has a clue as to what height the oil should be. I believe it's measured with the spring out and the bike resting on the forks when bottomed out.
I'm thinking about measuring mine where it stands now & start lowering it 5mm at a time to see if the ride improves. Any thoughts?

[dave500]

i actually run more than the specified amount by say 20ml,some people like to make work for themselves i think?these do have a somewhat harsh front end for stabilty at speed,use lighter oil if you want it softer without all the bull #$%*.

did he give you a specification?

[Deltarider]

Interesting. Has any of you ever checked with a torchlight if there's an upper mark inside the tube? I know some other models have such a mark, but I forgot which.
Viscosity can be a personal matter. Because of my lenght I sit a bit further towards the rear. Next time I'll experiment with ATF. Isn't that around 7,5?

[dave500]

i thought it was more like 5 wieght?depends how finiky you want to get?if you can detect how a few mm of oil height affects the feel your a better man than me gunga din!

[Frostyboy]

I might get you to take mine for a ride next time we get together Dave you can tell me if it rides different to yours. I've just rolled over 62 this month so maybe I'm just getting a bit fragile. 
Eric mentioned 120mm measured from the top of the tube, but I'm not sure that that spec would be universal.

[Untold]

I've had the same issues with my 550, and have been playing around a bit. I started with 5 1/2" from the top. Then lowered it to 6" from the top and it feels pretty good.
I used a spray bottle nozzle, and measured 6" from the bottom of the straw and marked it with a piece of tape. Then stick the straw into the fork tube and line up the tape with the top of the fork tube and start spraying out any excess oil. When oil stops coming out, then you know it's at 6", where the straw can no longer reach.

[Frostyboy]

I've had the same issues with my 550, and have been playing around a bit. I started with 5 1/2" from the top. Then lowered it to 6" from the top and it feels pretty good.
I used a spray bottle nozzle, and measured 6" from the bottom of the straw and marked it with a piece of tape. Then stick the straw into the fork tube and line up the tape with the top of the fork tube and start spraying out any excess oil. When oil stops coming out, then you know it's at 6", where the straw can no longer reach.

6" is 152.4 mm. Was that with the fork compressed or with the wheel off the ground Untold? It's nice to hear someone on the same path.

Redneck method.
http://www.youtube.com/embed/lLm5cLwKzl8

[Steve_K]

I like to measure fork level, too.  One thing to check on oil level is to be sure the damper is covered with oil.  If not the oil could could froth and lose damping.  Oil level can help with compression damping, too.  More oil, less air to compress, stiffer compression damping. 
Fun things to try!
Steve

[Harsh]

I have always measured the height of fork oil.  This is what I start out with and adjust if necessary.  I set it fairly close to the amount of travel that the forks have.  Most street bikes have 4.5 - 5 inches of travel, (about 115 - 130mm) so an oil level in that range works for most bikes.  Some bikes work best with the stock level, some benefit from less, others are better with more.

[tlbranth]

I think a harsh ride might be due to fork 'stiction' more than oil type or amount. That was the case for me. Randack has a pretty good technique for fixing it on a naked Goldwing. Same thing applies to sohc bikes.

http://www.randakksblog.com/removing-stiction-from-gl1000-front-forks/

[Powderman]

Where would one go to see what the correct level is suppose to be? I have to replace the oil in both my CB400f and the CBR600f1.

[Untold]

I've had the same issues with my 550, and have been playing around a bit. I started with 5 1/2" from the top. Then lowered it to 6" from the top and it feels pretty good.
I used a spray bottle nozzle, and measured 6" from the bottom of the straw and marked it with a piece of tape. Then stick the straw into the fork tube and line up the tape with the top of the fork tube and start spraying out any excess oil. When oil stops coming out, then you know it's at 6", where the straw can no longer reach.

6" is 152.4 mm. Was that with the fork compressed or with the wheel off the ground Untold? It's nice to hear someone on the same path.

Redneck method.
http://www.youtube.com/embed/lLm5cLwKzl8

That was with the forks bottomed out, springs out. 

[grcamna2]

I believe Racetech has a chart when replacing fork springs & bushings or using their oil(they have good synthetic fork oil & teflon coated bushings also)which gives measurements for ea. individual bike for the fork oil level.
They have good tech also.

[MCRider]

The go-fast guys do it that way. But not on the bike. You'll play heck keeping the bike stable and such lowering it to bottom out. The tubes/legs come off and you measure like untold says.  But that's not the end all. YOu can still adjust by using a syringe type affair to draw out the same amt from each side, and road testing it.

Such a tool is available from Motion_Pro and the like.

[Untold]

I do it on the bike. It's easy with a center stand.

[MCRider]

I do it on the bike. It's easy with a center stand.

You let the front collapse to the bottom? I'd think it would roll forward off the stand? I guess not?

[HotCarl73]

I do it on the bike. It's easy with a center stand.

You let the front collapse to the bottom? I'd think it would roll forward off the stand? I guess not?

i just did my 750 k3 today. i replaced springs and oil. put a jack under the engine with bike on centerstand.  i was gonna measure the oil height with spring out and forks collapsed. i bungy corded the centerstand forward. let the jack down and forks collapsed as expected. what i wasn't expecting was the jack didn't roll smoothly and came off the piece of wood i had under the engine. the centerstand tried to fold but the bungies held it from going all the way back. handlebars were off too, so i had nothing to grab. i got very lucky and was able to stabilize it and throw 6 ozs of oil in each leg and get it back together without dumping the bike. i think the manual calls for 5.5 ozs, but i didn't have time to screw around looking it up. i'll get a better system worked out and try it again next time. be careful.

[MCRider]

I do it on the bike. It's easy with a center stand.

You let the front collapse to the bottom? I'd think it would roll forward off the stand? I guess not?

i just did my 750 k3 today. i replaced springs and oil. put a jack under the engine with bike on centerstand.  i was gonna measure the oil height with spring out and forks collapsed. i bungy corded the centerstand forward. let the jack down and forks collapsed as expected. what i wasn't expecting was the jack didn't roll smoothly and came off the piece of wood i had under the engine. the centerstand tried to fold but the bungies held it from going all the way back. handlebars were off too, so i had nothing to grab. i got very lucky and was able to stabilize it and throw 6 ozs of oil in each leg and get it back together without dumping the bike. i think the manual calls for 5.5 ozs, but i didn't have time to screw around looking it up. i'll get a better system worked out and try it again next time. be careful.

Doable I see, but clumsy and possible disaster.

[bwaller]

I think we all need to spend more time on our suspension. About the only way to attempt some change is to measure the oil level from the top. By just removing the springs ("unscrew" them on the way out and most of the oil will wind down the spring) and gently lowering the front you can add or remove oil and measure exactly the level to keep notes. Plus measure total travel while you're at it. Knowing this will help determine oil level no matter what bike because oil level will affect the amount of travel too.

It's not complicated but suspension tuning is rewarding work especially if your back is vintage too!   

[splitt]

On my CB750, I set the fluid level at 6". (springs out, forks collapsed)

I strapped my bike to my motorcycle jack and raised it off the ground. Placed something under the front wheel and slowly let the bike down until the front suspension starts to bottom out. I just use a turkey baster that I picked up at the dollar store that I mark the dimensions on with a permanent marker. Add fork oil, then suck out the excess with the turkey baster at the desired level. Repeat on the other fork.

[scottly]

The last time I changed fork oil I checked the level with a dip-stick. After adding 6.25 oz of ATF to my K7 750 forks, the level was about 14 5/8" below the top of the tubes, with the springs in place and the forks extended. It was still a bit harsh, and travel was about 2" or less when applying the front brake aggressively. I drained some oil until the reading was about 16" below the top of the fork tube, and the front end gained an inch of travel under heavy braking, and feels more compliant in general. I might drain a tiny bit more to see how it feels... 

[dave500]

the old 40 year old springs will be sagged aswell owen,remove one and check its free length,a spring works can reset them.

[PeWe]

Progressive fork springs have an instruction about oil level here: http://www.progressivesuspension.com/pdfs/forkSprings/3055.pdf

Might be useful as a std guideline.

Fork oil level/volume should be checked according to the steps outlined in your authorized shop manual. Measurement of your fork oil by level is the preferred method. However, some manuals only specify a volume measurement. Due to the design of a progressive wound fork spring it will displace more oil thus requiring a maximum oil level of 5.5" (140mm).

Caution: This is not a recommendation, it is only a precautionary statement. If your manual specifies an oil level higher than 5.5" (140mm) set the oil level at 5.5 (140mm).
(Oil level is the distance from the top of the fork tube to the top of the oil with the fork completely collapsed and the fork spring removed see figure 1.) This measurement can be made by using either one of the Progressive Suspension Fork Oil Level Adjusters (FOL-1 or FOL-2)

I'll check this method this week on my CB750-K6 that is in the assembly phase. New fork sealers mounted last weekend. It has progressive springs too. I'll measure the volume of oil needed to reach 140mm as long it's below max 220-230cc(ml) as the HONDA manual say.

[Frostyboy]

Thanks everyone for the feedback. Some great advice to follow for sure. The Progressive pdf was really interesting thanks PeWe.
I won't have a chance to follow it all through for a couple of days, but my shoulder blades are feeling better already. I'll do my best not to let the bike fall over during the process.
Cheers. 

[Harsh]

I can't see getting an accurate measurement if you leave the fork tubes on the bike.  The measurement needs to be taken with the tubes vertical and not at an angle (like they would be if they are still on the bike).

[Untold]

When I drop mine down, they are pretty much exactly vertical while still on the bike. I'm surprised to read about people
having difficulty. Takes me 5 minutes.

[Clyde]

It is usual in modern bikes to use the level to set up forks. Normally done off the bike with no spring and the tube fully down in the slider.

With my Z1B- Kawasaki published a bulletin back in  August 1974 recommending people use the level method rather than the volume method. They gave a figure 422mm with the spring in and forks extended to the max.
I made a level tube tool and checked the Z1. I found that there was about 8mm difference in height between left and right forks.
I was having problems with the handling and felt it was a bit harsh over small bumps, so changed from 15 to 10W but raised the level by 15mm. Definitely worked.

I did a few tests on the Kawasaki and it did not make more than 1mm difference if the fork was on an angle as you insert the tube down through the centre of the spring.
On modern Showa (43mm) forks with no spring to centre the tube, it would be significant but as they have to be done off the bike it is not a problem.

It would be worth trying to get some good data as to heights with Honda's as I have found it a much better way to set up forks.

Clyde

[MCRider]

When I drop mine down, they are pretty much exactly vertical while still on the bike. I'm surprised to read about people
having difficulty. Takes me 5 minutes.

550 may be easier than a 750?

[Untold]

When I drop mine down, they are pretty much exactly vertical while still on the bike. I'm surprised to read about people
having difficulty. Takes me 5 minutes.

550 may be easier than a 750?

Yeah, that could be the case.  I also put a 2" board under my center stand, so the angle of the forks ends up slightly more vertical when dropped down.

[HotCarl73]

this would all be a lot less perilous if i could find a forks extended (front tire lifted off the ground), springs out fork oil level for my k3 750. i guess it can't be done that way or else i would have found it by now. seems like it would make the process a lot simpler and safer. went for a ride with my 6 ozs per leg and it seems fine and better than it was. i'd still recommend doing it properly, though.

[lucky]

You need to get a shop manual and measure the amount of fluid like the book says.

[scottly]

this would all be a lot less perilous if i could find a forks extended (front tire lifted off the ground), springs out fork oil level for my k3 750. i guess it can't be done that way or else i would have found it by now. seems like it would make the process a lot simpler and safer.

That's why I measured the oil level with a dip-stick after I had filled the forks with the "recommended" measure of oil, with the forks extended and the springs installed: that gave me a baseline. I found that a very small volume of fluid had a VERY drastic change in the level, as measured with the dip-stick.

[dave500]

i rang king springs here the other day owen and they will only reset coil springs lower not higher,because of work place health and safety what ever that has got to do with stretching a hot spring longer?

[PeWe]

I did my fork today. Collapsed and filled with oil, max from top 140mm according to the progressive fork spring description. (I have progressive springs)
I measured the oil. One tube 190cc, the other ~200cc to reach 140mm level. Not that much difference. 1cl and 2-3cl less than HONDA manual recommendation.

I used a syringe with hose. Hose length from syringe bottom 140mm. Filled the fork tube a little bit too much and could suck it back in the syringe and got rather exact 140mm below the top of the tube.

This time no additional distance tube for the spring preload when it get 15mm preload with the fork top plugs.