Author Topic: Fork oil level vs. volume  (Read 1287 times)

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jhark37

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on: March 18, 2020, 11:21:31 pm
Doing a number of tinkering tasks today that involved removing wheels to get new tires, and installing new front pads from Hitchcocks.  While at it, thought I would change the fork oil to a lower viscosity in attempt to 'soften' the front end.

Service manual calls for 430 ml/14.54 oz oil per fork tube.  When I put that amount in, oil was 3" from top of tube, vs. 8" before draining.  So either the manual is wrong or the original fill was wrong.

I know this reduces the amount of air in the tube and may lead to harshness, exactly what I am trying to reduce.  Think I'll test it out and can
always suck some oil out if need be.  Should be interesting.

Any reactions?

John


George 350

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Reply #1 on: March 18, 2020, 11:37:26 pm
Hmmm. If the oil is just 3" from the top I would expect you will be close to hydraulic lock on full compression. 
After the fill did you 'bounce' the forks to see if the level dropped?
Personally I would leave the top nuts off and raise the front wheel up to see how high up the oil comes.
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EnfieldGuy

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Reply #2 on: March 19, 2020, 08:20:28 am
Doing a number of tinkering tasks today that involved removing wheels to get new tires, and installing new front pads from Hitchcocks.  While at it, thought I would change the fork oil to a lower viscosity in attempt to 'soften' the front end.

Service manual calls for 430 ml/14.54 oz oil per fork tube.  When I put that amount in, oil was 3" from top of tube, vs. 8" before draining.  So either the manual is wrong or the original fill was wrong.

I know this reduces the amount of air in the tube and may lead to harshness, exactly what I am trying to reduce.  Think I'll test it out and can
always suck some oil out if need be.  Should be interesting.

Any reactions?

John

Interesting to know how you get on with the change in viscosity.

Just as a matter of interest, when I fitted harder springs the oil level as from the factory was more like 8" from the top on my bike as well. I also noticed a discrepancy between the service manual and owners manual for the fork oil capacity, the owners manual calls for 473ml / fork which I assumed was a misprint.


jhark37

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Reply #3 on: March 19, 2020, 12:48:33 pm
After "sleeping on it". I've concluded the manuals must be wrong, that 8" from top of tube must be correct.  Soon as I get a chance, I'll syphon out enough oil to get it back down to 8".  Now if my new tires would come in, I could test it out!

John


Richard230

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Reply #4 on: March 19, 2020, 01:43:33 pm
Most factory repair manuals list fork oil quantities for a fork that is new and completely clean of any residual oil. That can cause trouble for refills of a previously well-oiled fork tube.  ;)
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olhogrider

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Reply #5 on: March 19, 2020, 11:09:37 pm
After "sleeping on it". I've concluded the manuals must be wrong, that 8" from top of tube must be correct.  Soon as I get a chance, I'll syphon out enough oil to get it back down to 8".  Now if my new tires would come in, I could test it out!

John

Is that with the spring in place?


jhark37

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Reply #6 on: March 20, 2020, 01:13:14 am
Is that with the spring in place?

Yes.


Richard230

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Reply #7 on: March 20, 2020, 01:15:22 pm
Yes.

All of the service manuals that I have seen provide an oil level that is measured with the springs removed and the fork fully collapsed. That is the way I set the oil level when changing the oil in the forks of my 2012 Bullet and that worked great.
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jhark37

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Reply #8 on: March 20, 2020, 10:49:30 pm
All of the service manuals that I have seen provide an oil level that is measured with the springs removed and the fork fully collapsed. That is the way I set the oil level when changing the oil in the forks of my 2012 Bullet and that worked great.

The service manual I have for the Royal Enfield INT650 specifies 430 ml of fluid.  No reference to dimensions.  And it's obviously incorrect.

John


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Reply #9 on: March 20, 2020, 11:54:58 pm


Couchy

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Reply #10 on: July 14, 2020, 07:04:57 pm
Stripped my forks today to install stiffer springs.
With stock springs out and fork compressed the air gap was 140mm. I drained the oil and there was 410ml that came out. I didn’t strip damper rods so there would be a tiny bit left. That isn’t far from the manual spec.
The replacement 9.0 linear springs are SV650 fitment and are 100mm longer than the stock springs meaning the preload spacers needed cutting down to 80mm.
Filled back up with 10w oil to the same 140mm air gap. Once back on bike set sag and had a bounce. May need to go to 15w oil but I’ll take a ride out first and see.


Starpeve

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Reply #11 on: July 15, 2020, 12:42:22 am
Stripped my forks today to install stiffer springs.
With stock springs out and fork compressed the air gap was 140mm. I drained the oil and there was 410ml that came out. I didn’t strip damper rods so there would be a tiny bit left. That isn’t far from the manual spec.
The replacement 9.0 linear springs are SV650 fitment and are 100mm longer than the stock springs meaning the preload spacers needed cutting down to 80mm.
Filled back up with 10w oil to the same 140mm air gap. Once back on bike set sag and had a bounce. May need to go to 15w oil but I’ll take a ride out first and see.
Thanks mate- you’re doing all my experimenting for me! Nice to see levels and measures stated with such accuracy, Particularly the air gap,
also interesting that you suspect 15 weight oil is the go. Do you think you’ll stick with the stock volumes?
Cheers, Steve👍
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Couchy

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Reply #12 on: July 15, 2020, 09:13:49 am
Thanks mate- you’re doing all my experimenting for me! Nice to see levels and measures stated with such accuracy, Particularly the air gap,
also interesting that you suspect 15 weight oil is the go. Do you think you’ll stick with the stock volumes?
Cheers, Steve👍

I’ll ride the bike later and see. Rebound feels a bit quick with the 10w in but a ride will tell me more. My new shocks arrive today so once they are bolted in I’ll go out. For pure road use I didnt really have an issue with the front but I’ll do a few Trackdays on mine with race tyres on so I’d like them a bit better for that. I also like to tinker in the garage 🤣👍


Starpeve

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Reply #13 on: July 15, 2020, 10:20:57 am
I’ll ride the bike later and see. Rebound feels a bit quick with the 10w in but a ride will tell me more. My new shocks arrive today so once they are bolted in I’ll go out. For pure road use I didnt really have an issue with the front but I’ll do a few Trackdays on mine with race tyres on so I’d like them a bit better for that. I also like to tinker in the garage 🤣👍
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Baz

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Reply #14 on: July 15, 2020, 05:42:31 pm
Were you guys taking the forks out to drain them, or sucking it out using a tube? I've done it the second way before and just ignored the quoted volume and refilled them to the exact same level, seemed to work.
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