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Information Front Suspension Fork Oil Mod

mrbios

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At 43,000 miles on my 2012 NC700X I removed about 25cc using a plastic syringe and a roughly 24" length of 3/16" ID clear tubing? From each fork leg and added about a tablespoon of paint thinner to thin the existing fork oil which looked original and was dark brown. On a test ride around the block the forks are much more compliant and really take the edge off small bumps and if anyone worried about the suspension being too soft they could just add some fresh oil back in.
Also, when hopping up on a curb there was no bottoming out. In the future I will drain the oil and replace with a 5w or 0w and add about 30cc less than recommended and add oil as needed to reach desired firmness.

I ride fast enough in corners to regularly lightly touch the pegs and will update this post if the change in fork oil makes the bike unstable in corners or otherwise.

Key takeaways: (traditional forks - not inverted forks which I have never owned).
1. I think this is all I was looking for - a more mellow version of the stock fork. No plans for racing and if that changes I'll buy a "race bike".
2. Hard braking results in sudden dive same as stock - but not bouncy like you get from worn struts or or blown shock absorbers. Must be willing to tolerate some "mushyness".
3. Original 10 year old fork oil with 43K miles still providing an overly firm ride and NO LEAKS from the seals.
4. I have never changed fork oil except when rebuilding forks that are already leaking. I think the main benefit to changing oil is for off-road dirt bikes to reduce wear.
5. I will only change the fork oil and seals once the seals leak and at that time replace the two upper tubes which have rust bubbles from the original owner that never covered the bike and stored it outside for 7 years.
6. If you like your NCX but really want the very best then switch out the forks with compatible inverted forks.

UPDATE #1: 06-08-2022 ~ 250 miles
I have not yet noticed adverse handling issues such as a high or low speed wobble. I can still scrape pegs on both sides same as before and in one turn where the is a bump I feel the softer front fork action actually improves handling. The sketches part is just pumping the forks when squeezing the front brake lever because the fork compress SOOO much easier - so soft - but in actual driving things are fine including simulated hard "panic" braking. Also, if you try it and you don't like it it is easily reversed with bike on center stand remove caps and carefully add the same amount of oil that was removed. I'm considering removing more oil but don't want to overdue it or have forks that bottom out.

UPDATE #2: 06-21-2022 ~ 500 miles
Soft suspension and an inexpensive tire did not prevent me from Doin' the Boot Scootin' Boogie (not good)... the rider and bike pulled out of a very tricky situation.

UPDATE #3: 07-08-2022 ~ 700 miles
I can't imagine ever going back to the stock oil level with its harsh ride. Recently, on a back road at night I ran over some really rough pavement with no chance to prepare for the impact but thanks to the soft suspension it wasn't a big deal.

UPDATE #4: 07-12-2022 ~ 1000 miles
After doing about 250 miles with my club we road over some roads with broken pavement. The Harley's I was riding with have a short suspension stroke and had to limp along while the NC glided over the same pavement. Also, on long rides I would often get a headache from the bumps but this time I did not because of the softness of the forks.
 
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mzflorida

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4 weeks and a couple of hundred bucks late for me! Kidding aside, glad that worked for you. Others on advrider.com also have positive comments and say the forks really are improved through lighter oil; I don't recall any comments on adjusting the gap. Me personally, probably because of my lack of knowledge, would be a nervous wreck adding paint thinner to the fork fluid. Awesome quick fix!
 

670cc

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At 43,000 miles on my 2012 NC700X I removed about 25cc using a plastic syringe and a roughly 24" length of 3/16" ID clear tubing? From each fork leg and added about a tablespoon of paint thinner to thin the existing fork oil which looked original and was dark brown. On a test ride around the block the forks are much more compliant and really take the edge off small bumps and if anyone worried about the suspension being too soft they could just add some fresh oil back in.
Also, when hopping up on a curb there was no bottoming out. In the future I will drain the oil and replace with a 5w or 0w and add about 30cc less than recommended and add oil as needed to reach desired firmness.

I ride fast enough in corners to regularly lightly touch the pegs and will update this post if the change in fork oil makes the bike unstable in corners or otherwise.

Key takeaways: (traditional forks - not inverted forks which I have never owned).
1. I think this is all I was looking for - a more mellow version of the stock fork. No plans for racing and if that changes I'll buy a "race bike".
2. Hard braking results in sudden dive same as stock - but not bouncy like you get from worn struts or or blown shock absorbers. Must be willing to tolerate some "mushyness".
3. Original 10 year old fork oil with 43K miles still providing an overly firm ride and NO LEAKS from the seals.
4. I have never changed fork oil except when rebuilding forks that are already leaking. I think the main benefit to changing oil is for off-road dirt bikes to reduce wear.
5. I will only change the fork oil and seals once the seals leak and at that time replace the two upper tubes which have rust bubbles from the original owner that never covered the bike and stored it outside for 7 years.
6. If you like your NCX but really want the very best then switch out the forks with compatible inverted forks.
I have to slightly agree with your thoughts on the necessity (or lack thereof) of changing fork oil. The rear shock, obviously a budget model on the NC, is expected to go to end of like with no oil change, so why are we focused on fork oil changes? I guess because it can be changed, and some people like to do stuff to their bikes.

If fork oil changes are beneficial, I'd like to see a way to change shock oil, too.
 

dduelin

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"Different suspension stroke for different folks." The 2012-20 NC forks have very little rebound damping and upon release of the brakes after heavy braking the forks "pop" up and upset the suspension. Besides the harsh ride from too much high speed compression damping it is the other problem with the stock set up. Thinner oil makes the rebound damping worse so while it might help the harsh compression damping the trade-off is not something I want.

Changing the fork oil helps preserve the life of fork tubes, bushings, and seals and for the interested or inveterate tinkerers it is part of tuning the forks for a desired action or ride. The oil is ten bucks and spending even ten bucks is an issue for some owners and truthfully most motorcycles never accumulate the mileage where life of wear items becomes an issue but if you plan on keeping a bike for a long while changing the oil can pay off. Ten bucks is a fraction of the cost of seal and bushing kits. On the bikes where I've overhauled the forks at 70,000 or more miles the limited life of wear items is apparent. Degradation of the fork over time sneaks up on owners and they don't necesssarily notice the changes in ride and fork action.

Forks unlike rear shocks do not contain oil and/or gas under pressure and are safe and easy for DIY tuning or maintenance. If one has the specialized tools and knowledge then changing the valving and oil in a rear shock is easy but it's dangerous if you don't.
 
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mrbios

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"Different suspension stroke for different folks." The 2012-20 NC forks have very little rebound damping and upon release of the brakes after heavy braking the forks "pop" up and upset the suspension. Besides the harsh ride from too much high speed compression damping it is the other problem with the stock set up. Thinner oil makes the rebound damping worse so while it might help the harsh compression damping the trade-off is not something I want.

Changing the fork oil helps preserve the life of fork tubes, bushings, and seals and for the interested or inveterate tinkerers it is part of tuning the forks for a desired action or ride. The oil is ten bucks and spending even ten bucks is an issue for some owners and truthfully most motorcycles never accumulate the mileage where life of wear items becomes an issue but if you plan on keeping a bike for a long while changing the oil can pay off. Ten bucks is a fraction of the cost of seal and bushing kits. On the bikes where I've overhauled the forks at 70,000 or more miles the limited life of wear items is apparent. Degradation of the fork over time sneaks up on owners and they don't necesssarily notice the changes in ride and fork action.

Forks unlike rear shocks do not contain oil and/or gas under pressure and are safe and easy for DIY tuning or maintenance. If one has the specialized tools and knowledge then changing the valving and oil in a rear shock is easy but it's dangerous if you don't.
Gr8 info points and perspective gained from many years and miles. I must confess that I am tempted to change the oil now to clean things up.
 

mzflorida

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At 43,000 miles on my 2012 NC700X I removed about 25cc using a plastic syringe and a roughly 24" length of 3/16" ID clear tubing? From each fork leg and added about a tablespoon of paint thinner to thin the existing fork oil which looked original and was dark brown. On a test ride around the block the forks are much more compliant and really take the edge off small bumps and if anyone worried about the suspension being too soft they could just add some fresh oil back in.
Also, when hopping up on a curb there was no bottoming out. In the future I will drain the oil and replace with a 5w or 0w and add about 30cc less than recommended and add oil as needed to reach desired firmness.

I ride fast enough in corners to regularly lightly touch the pegs and will update this post if the change in fork oil makes the bike unstable in corners or otherwise.

Key takeaways: (traditional forks - not inverted forks which I have never owned).
1. I think this is all I was looking for - a more mellow version of the stock fork. No plans for racing and if that changes I'll buy a "race bike".
2. Hard braking results in sudden dive same as stock - but not bouncy like you get from worn struts or or blown shock absorbers. Must be willing to tolerate some "mushyness".
3. Original 10 year old fork oil with 43K miles still providing an overly firm ride and NO LEAKS from the seals.
4. I have never changed fork oil except when rebuilding forks that are already leaking. I think the main benefit to changing oil is for off-road dirt bikes to reduce wear.
5. I will only change the fork oil and seals once the seals leak and at that time replace the two upper tubes which have rust bubbles from the original owner that never covered the bike and stored it outside for 7 years.
6. If you like your NCX but really want the very best then switch out the forks with compatible inverted forks.

UPDATE: 06-08-2022 ~ 250 miles
I have not yet noticed adverse handling issues such as a high or low speed wobble. I can still scrape pegs on both sides same as before and in one turn where the is a bump I feel the softer front fork action actually improves handling. The sketches part is just pumping the forks when squeezing the front brake lever because the fork compress SOOO much easier - so soft - but in actual driving things are fine including simulated hard "panic" braking. Also, if you try it and you don't like it it is easily reversed with bike on center stand remove caps and carefully add the same amount of oil that was removed. I'm considering removing more oil but don't want to overdue it or have forks that bottom out.

Really interesting edit. I may experiment with a little heavier oil. I’m not experienced enough with suspension to comment on characteristics but rather only my observations. But if I do change it out, I’ll post here and see if it is decipherable! Thanks for the update!
 
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