Roadholder fork oil change

"Unscrew the large filler plug on top of each fork leg and 'pull up' the front wheel to expose the springs. Place a block of wood under the wheel to hold the springs clear. Using two spanners, unscrew the filler plug nuts from the top of the damper rods. Remove the block and allow the forks to move to full extnesion. Four in 142ccs of grade 20 oil in each leg." All straight from the Norton Maintenance Manual and Instruction Book. In many ways better than a Haynes manual. You should buy a copy. Gordon.

SAE 20 oil is the recommended fluid from back in the day, and the quantity is 5 fl oz. These days a lot of riders use automatic transmission fluid in their forks, maybe because straight 20 oil is not so easy to find?

SAE 20 fork oil is readily available. Try Demon Tweeks, 1 litre is about £10, free postage, and they have a very quick service.

Cheers

Alan

Previously wrote:

SAE 20 fork oil is readily available. Try Demon Tweeks, 1 litre is about £10, free postage, and they have a very quick service.

Cheers

Alan

Hiya, Just a word of warning, make sure you have a substantial block or box under the front of the frame to take the weight of the bike when you unscrew the two big nuts on top of the forks. I did this job on a H*nda cb750 four when I was a mere callow yoof ! and didnt realise what would happen when I undid the second nut. I undid one nut and nothing happened apart from a slight boing! as the first spring came loose, Ok to proceed then, thought I, commencing to undo the second one. as soon as the last of the screw thread cleared, the front end collapsed like the bike had been shot. both springs hanging out the top of the fork legs and manky oil everywhere. The bike fell forward off the centre stand and fell flat on its side. How I larfed at myself and my lack of forethought.

Cheers Alan, Shenstone branch

Previously wrote:

SAE 20 oil is the recommended fluid from back in the day, and the quantity is 5 fl oz. These days a lot of riders use automatic transmission fluid in their forks, maybe because straight 20 oil is not so easy to find?

I seem to remember that 5fl oz as listed by Norton isn't actually the right or best quantity. I think there's a technical article somewhere that says they function better with a little more oil.I'm going on holiday again soon but if I get the time I'll try and find it.

Cheers, Lionel

I too became fed up with the wait for the oil to spiral downwards, made worse by trying to do two at once and regularly becoming confused over which measure I had poured into each leg.

The answer is to bore out a couple of old fork nuts and weld a decent length of tube to them. It's then possible to fill each tube with the correct amount and walk away and leave it for an hour.

[IMG]http://i248.photobucket.com/albums/gg164/commando16h/NOC/Fork%20Tool_zpsxnmjzfhq.jpg[/IMG]

20w/50 works as it stays at 20 as there is no engine heat, neat solution from Richard or you can get a cheap syringe off ebay and inject it, the graduations show how much is going in. I do one side at a time so the suspension does not collapse

Good tip on ensuring the frame is supported. I did wonder and probably would have, but then...

Regarding getting the oil to fill more quickly, the Commando factory manual advises extending the forks, to draw the oil down. Don't know if Commandos Roadholders are essentially the same as the heavy twins, but might be worth trying, before getting the drill out.

Reminds me to post that ATF is generally 5 to 10wt so will reduce damping over the 20wt, if you have refurbed the forks recently and sized the damper valves to the damper tube and the rod bush is a good fit then ATF will work but for old worn forks 20wt is the way to go.

I find  that the weight of panniers and  use of centerstand  keeps the bike stable.  I pump the forks to expell  all  fluid  before  putting on the stand.  A small  batten under the tyre releaves the tension on the top nuts  to ease undoing . A good pull up on the guard  and kick a  bigger timber wedge under the tyre .   I read an article on fork oil  and it was clear that  there is  a wide variance in quality and  accuracy in the  numbers.  Might have been on Access Norton site. 

I've just modified a pair of spare top nuts to help aid fork oil replacment - drill and tap two holes in each at 6mm (sorry !) with countersunk tops and then add stainless screws to fit.

Once the old oil is drained and bottom screws replaced - with the top nut 6mm screws removed, use one to pour in the oil using a small funnel and tube and the other to allow the air to escape.

I've not actually put them on the bike and tried them, as I only completed the work the other day, but the theory is sound. 

Regards - Paul.

Take care before choosing multi grade oil. SAE 20 matches the viscosity of 20W-50 at minus 20°C.  By the time you reach plus 20°C, a 20W-50 is far closer to SAE 40 than to SAE20.

 But as others have said, products sold as "fork oil" don't necessarily have numbers with the same meaning. Allegedly.

From what you say David , it seems that 20/50 is not really suitable for a primary case  as its likely to be more 50 than 20 once warmed up.  Back to  ATF I think. Works in forks too.

I found this. Make of it what you wish! If the lines for 20 and 50 are correct  then the 20-50 line on here doesn't meet 20 grade at -20 degrees as far as I can see.