Fork Oil Change

Is 20W50 engine oil (non-synthetic) OK for the forks?

Why not use proper fork oil ….

Happy to go get some, if necessary, but is it?

Mart UK said:

Is 20W50 engine oil (non-synthetic) OK for the forks?

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I can testify straight 30W will hammer at 50F.
20-50 solved it.

I would probably get 20W as per the manual. I expect that's what is in there and the ride is good, but not changed since 2014. Plus I have had the forks stick a bit when on the sidestand, bars pointed to the left, still does it after releasing the axle pinch bolts and pumping then re-tightening. So, thought I would try new oil. But not looking o change the damping rate on the road.

I have plenty of fresh 20W50, so that would be a little win, if it is fine to use?

Change it each year I would say is more important than which oil. You might be surprised how it gets particles in it along with
water. I take the legs right off. Silt often is in the bottom.

Mart UK said:

I would probably get 20W as per the manual. I expect that's what is in there and the ride is good, but not changed since 2014. Plus I have had the forks stick a bit when on the sidestand, bars pointed to the left, still does it after releasing the axle pinch bolts and pumping then re-tightening. So, thought I would try new oil. But not looking o change the damping rate on the road.

I have plenty of fresh 20W50, so that would be a little win, if it is fine to use?

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I've not been able to find 20W for years in the USA so I use 30W. I also weight much more than normal - 30W feels good to me. I've always thought that the viscosity changing additives in multi-weight oil were not good for forks since the manuals all seem to specify single weight oils.

Sticking forks can mean that they are no parallel with each other. Unless you corrected it the last time the front end was loose, you can bet that they are no parallel. It can take more than the axel pinch bolts to fix that.

marshg246 said:

I've not been able to find 20W for years in the USA so I use 30W. I also weight much more than normal - 30W feels good to me. I've always thought that the viscosity changing additives in multi-weight oil were not good for forks since the manuals all seem to specify single weight oils.

Sticking forks can mean that they are no parallel with each other. Unless you corrected it the last time the front end was loose, you can bet that they are no parallel. It can take more than the axel pinch bolts to fix that.

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10w30 and 20w50 are specified in the mk3 manual I have, along with SAE20. But always 150cc.

I may have to delve deeper to sort the sticking problem. Fork oil is the 1st step. Oddly, it only happens on the sidestand, I only notice it when I lift it off and straighten the bars. I can't reproduce it off the sidestand.

Mart UK said:

I may have to delve deeper to sort the sticking problem. Fork oil is the 1st step. Oddly, it only happens on the sidestand, I only notice it when I lift it off and straighten the bars.

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I thought they all did that! My Commando's forks do the same presumably because the weight of the bike is still on the forks with the bike leaning over so I'm doubtful a change of oil will cure it.

Mart UK said:

Oddly, it only happens on the sidestand, I only notice it when I lift it off and straighten the bars. I can't reproduce it off the sidestand.

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Just thinking out loud: I wonder why the forks are compressing when put on the side stand (assuming you mean they stick coming up). You would think that would extend on the side stand.

marshg246 said:

Just thinking out loud: I wonder why the forks are compressing when put on the side stand (assuming you mean they stick coming up). You would think that would extend on the side stand.

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My forks extend slightly when on the stand. When pushing the bike down off the center stand I get a slight "clung" sound as they spring back to riding position and the full weight becomes seated on the suspension. Using Bel-Ray 15 which may not be "flowing" or moving readily enough, not sure yet.

This chart might be helpful.

I'm currently using ATF as 20weight oil was giving little to no fork movement..

How much damping you get is a function of the clearance between rod and the damper top and the valve to damper body plus the viscosity of the oil. If you have refurbished the forks and got these clearances tight then you need a thin oil, old unrefurbished forks with factory wide clearances need thicker oils. Regardless of the viscosity with internal springs which rust you need to change the oil annually.

kommando said:

How much damping you get is a function of the clearance between rod and the damper top and the valve to damper body plus the viscosity of the oil. If you have refurbished the forks and got these clearances tight then you need a thin oil, old unrefurbished forks with factory wide clearances need thicker oils. Regardless of the viscosity with internal springs which rust you need to change the oil annually.

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Exactly why I'm getting no fork movement i spent a fair amount of time tightening up all the clearances. lifting & reducing drilling in the damper tube etc...im hoping once the clearances have improved ill get some movement

olympus said:

Exactly why I'm getting no fork movement i spent a fair amount of time tightening up all the clearances. lifting & reducing drilling in the damper tube etc...im hoping once the clearances have improved ill get some movement

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If it does not loosen up then go for thinner oil, use @Lineslinger 's link to Peter Verdone's oil comparison to find an oil that is really thinner as at modern fork oil viscosities there seems to be no carry over from one range to another.

olympus said:

Exactly why I'm getting no fork movement i spent a fair amount of time tightening up all the clearances. lifting & reducing drilling in the damper tube etc...im hoping once the clearances have improved ill get some movement

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I did the same ended up using 5w oil to soften things up , but very happy with the results

Forks give oil a surprisingly hard time, heat and use cause the oil to break down over time, different forks / oils / use will break down differently of course.
But in real life fork oil is often neglected. I’d go as far as to say that most bikes out there are running with broken down fork oil.
Proper fork oil is designed for the task at hand, so is always a good idea IMHO. But ANY oil, changed regularly, is good !

L.A.B. said:

I thought they all did that! My Commando's forks do the same presumably because the weight of the bike is still on the forks with the bike leaning over so I'm doubtful a change of oil will cure it.

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Don't follow. The weight of the bike is on the forks when I stand it up, off the sidestand, too?

What I'm experiencing is:
- I usually stand up, still on the bike, have the front brake on while I fish around for the sidestand and then push it out beyond the spring retraction.
- Handlebars left, then get off the bike.
I would say, in that process, at some point the bike has it's own weight and some of mine, compressing the forks a little.

- Bike sitting on sidestand, I lift it upright. Fine. When I turn the bars to straight, the front rises up a little on the forks, before I put any of my weight on the bike.
- If I bounce it up and down with the brake on, the fork movement is smooth and nicely damped, regardless of the direction of the bars.

It's possible it did, but I dont recall it happening before the tyres were changed. I use a local garage to remove the wheel and swap tubes and tyres. So possible they didn't properly set up the axle, or over tightened, but would that bend the forks, or cause these symptoms? Unfortunately, changing the tyres was the first thing I did, before riding it, so can't be sure. But loosening the axle pinch bolts and pumping made no difference.

The fork oil is due for changing, regardless. I was unable to find any 20 weight locally this afternoon, so will have to buy on-line.

Hi Mart UK

I started a thread on grade of oil for fork oil used by members of AccessNorton
and got some useful information. Click on "Fork oil grade" below :

Fork Oil Grade

Might be worth reading so that posters do not have to repeat themselves.

Best wishes to all for a good New Year

Is it necessary to square up the forks?

Seen this done on other bikes by loosening mudguard brackets, lower yoke pinch clamps and axle clamps, bouncing front end while on center stand and carefully re-tightening everything without disturbing fork positions?