Not understanding 500 front suspension 🤔

[McCabe-Thiele (Ted)]

I suspect I will feel daft to ask this question as soon as I post it but here goes.🤔🤔🤔.

Lying in bed trying to get to sleep had me wondering what stopped the front fork legs from falling out when the front wheel is raised.
The upper fork legs are clamped to the steering column. The long spring / plunger is bolted to the bottom of the fork legs so what acts as the travel stop when the forks are fully extended?

[Orcade-Ian]

Happy New Year Ted,
The internal damper tube is bolted to the bottom of the slider and has a collar on the top - which won't pass right through the bottom of the stanchion.  So sleep easy, the wheel can't fall off, except in extremis!

Ian

[philward]

On the early 500 (upto K2), they use the 450 forks that has a threaded rod that runs from the damper in the lower fork and screws into the top chrome nut that screws into the top of the stantion - thats the set up on your early 500 I think Ted

Sorry for duplicate, Ian answered while I was typing!

[Orcade-Ian]

Sorry Phil and Ted,
I forgot it was 500 - of which I know 4/5 of bugger all, I was thinking 350/4,400/4 and my latest acquisition, the 550/4. 500 is like old Brit Iron then? Except it works!

Ian

[McCabe-Thiele (Ted)]

On the early 500 (upto K2), they use the 450 forks that has a threaded rod that runs from the damper in the lower fork and screws into the top chrome nut that screws into the top of the stantion - thats the set up on your early 500 I think Ted
Sorry 0
Sorry for duplicate, Ian answered while I was typing!

The penny still has not dropped - there is a thread in the chrome top nut but this would lock the long bar solid between top & bottom if used ?
The long spring passes up the slider tubes so no stop there. Surely the fork gaiters do not act as a stop?

Or is the bar in the photo not solid but is the springy bit?
I can't seem to be able to press it down by hand - so I'm either a weak nerd or it takes some force?

500 fork innards by Macabe Thiele, on Flickr

[Oddjob]

The large alloy bit at the bottom is the damper chamber. The allen key bolt which goes in the bottom of the fork slider anchors this to the slider so it can't travel up. The top hat on the end of it is to spread the load at the bottom so it doesn't punch through the bottom of the slider. The large rod is the damper rod, on the 500 this screws into the top nut. The stanchions are shorter than the combined length of the spring and damper, hence why when you insert them into the slider they can move up and down and the spring protrudes from the end when it's inserted. The rod has a small piston attached at the bottom, this is what allows the damping to happen, the spring is there to return it. So as the damper rod moves down the piston travels down the damper chamber and small holes in the piston allow oil to pass through, the bigger the holes the less damping occurs and vice versa. The damper rod is trapped inside the damper chamber so it's this which anchors the whole thing together, it can come apart but I've never had to dissemble one.

The spring acts as the return, the more the spring is compressed the faster it returns the forks to full extension, so fitting washers on the top of the spring for instance helps the rebound, modern forks have what's called preload adjusters on them, which essentially are small spring compressors, the more they are wound in the harder the spring action is. On modern forks there is also a way to adjust the damping externally.

That help?

[McCabe-Thiele (Ted)]

Kerching the Penny has dropped -  having read Kens explaination it now makes sense in my head.
I decided to use a block of wood on the floor & one held in my hand & the bottom rod moves it's not one piece - all makes sense.

Next issue will be the correct order of assembly & adding the oil - my manual is lacking the detail I'm looking for so I will need to hunt for any posts here on how to do it or find a U tube video.

I am thinking that the thread on the top of the rod will need to be fully screwed into the top bolt before screwing it into the slider - the bottom bolt & washer fitted but not tightened fully to allow the top bolt to screw into the slider - nip up the bottom bolt - fluid in before fitting the main fork seal & circlip not forgetting to fit the drain bolt  am I close ?

I have the main oil seals etc but will need to get the right O rings for the top chromed  nuts as Phillpots took them off when they did the hard chroming.

[Nurse Julie]

I've got the O rings in stock Ted.

[Oddjob]

On the sohc bikes the seal can go into the slider before they are assembled, if a seal blows all you need to is to remove the bottom bolt, slide off the slider, replace the seal and reassembled. Only need to remove the top nut to put the oil back in.

Thread the topnut onto the rod as far as it can go, nip up the locknut and the pull up the stanchion after putting in 160cc of oil, fit the locknut into the stanchion and job’s done.

[McCabe-Thiele (Ted)]

I've looked in the parts book & the washer at the top of the spring & the short steel tube below the top lock nut are not shown (see photo posted earlier).

If I screw down the large chromed top nut pretty well as far as it will easily go then the lock nut will need to move upwards by about 4mm - this will take some of the tension out of the spring as the tube spacer at the top will be pushed  upwards by the spring - is this okay?

Does the fitting look original as the Haynes Manual & Honda Parts book does not show the tube or washer ?

Should I measure the uncompressed spring to see if its within the right limits?

[Oddjob]

The washer and tube look like an attempt to get more spring preload Ted. I'd remove them and measure the springs free length as they are known not to be the best springs in the world, a little too bouncy was the general opinion at the time.

I'm not 100% sure but I seem to recall the tight end of the spring goes to the bottom not the top.

You can drive the new fork seals in with a large socket Ted, saves buying a seal driver. The clips can also be replaced with stainless ones to avoid them rusting. I'd also advise filling the underside of the seal with silicon grease, it helps to stop the spring getting rusty and failing, which is surprising as it should get covered in oil but it doesn't seem to as I've found the bottom of the seals just covered in rust off the spring. Same with the upper spring if it's exposed to the elements.

Myself and Roo bought some fork caps that you can adjust the preload on along with an air valve so you can have air assisted forks, they reckon a bit of air (around 5-10psi) in the forks helps to stop the fork oil foaming.

https://www.ebay.co.uk/itm/362877892416

https://www.ebay.co.uk/itm/314092799547?hash=item492163c63b:g:-sIAAOSwg81i6JUh Those are for the CB450/500T but it's the same seller, if interested just send them a message. Roo has fitted his and found they are too high and hit the bars unless you wind down the preload till it's got 10mm of preload or 2 rings left showing. If your springs are tired that may be just what you need anyway.

[McCabe-Thiele (Ted)]

If the original springs gave a bouncy ride it might be worth leaving it as it is - I did not ride the 500 any great distance but the ride & front suspension seemed oaky to me for my Sunday afternoon riding style.

I'll check the spring length first if I can work out how to get the nut undone as the shaft just rotates - I can undo the lock nut partly by using a pair of nuts on the thread to hold the shaft but then it refuses to come undone any further due to the remaining spring load - I will see if I can get a tool I have to hold the bar to stop it from rotating.

Not keen on returning it to standard if they were not great in the first place - clearly someone has modified it to cure a short coming.
I'm thinking some replacement better springs will be either expensive or no longer obtainable.

[McCabe-Thiele (Ted)]

I've managed to undo the lock bolt with an odd tool I have without damaging anything now the Genie is out of the bottle.

The free spring is 445 mm in length - not looking forwards to putting it back in place even without the tube spacer!

The Haynes Manual talks about the servicable spring limit being being 425 mm so the spring length is good.

Any observations or comments welcome ?

I'm minded to put the springs back without the tube spacer.
The spacer is 28 mm long plus a 2 mm washer making it 30 mm in all.
The closer wound coils are at the top end - not sure if that is the right way up - the photo in my manual appears to show the closer coils at the bottom. I
f it ends up too bouncy/soft  maybe tinkering with the fork oil might compensate ?

[K2-K6]

I've managed to undo the lock bolt with an odd tool I have without damaging anything now the Genie is out of the bottle.

The free spring is 445 mm in length - not looking forwards to putting it back in place even without the tube spacer!

The Haynes Manual talks about the servicable spring limit being being 425 mm so the spring length is good.

Any observations or comments welcome ?

I'm minded to put the springs back without the tube spacer.
The spacer is 28 mm long plus a 2 mm washer making it 30 mm in all.
The closer wound coils are at the top end - not sure if that is the right way up - the photo in my manual appears to show the closer coils at the bottom. I
f it ends up too bouncy/soft  maybe tinkering with the fork oil might compensate ?

Easiest to seperate function to make spring decision Ted.

Spring rate (poundage) has to be set to support machine and rider and should be more or less correct as is.
Preload (squashing it static) sets the ride height of the vehicle, too little and it'll just sit too low in it's travel before you even need the suspension.
Damping (oil viscosity, flow internally etc) just controls the spring and kinetic input thats acted apon it from riding. It won't compensate for the spring as it can only speed up the mass movement or slow it to give control in pace over the forces acting then.

Broadly, without good reason it's wise to put it back as it was.

For fork caps under pressure I let them go to full length (maximum space for spring) then push the cap down with a socket and non ratchet breaker bar, turn it backward until you hear the thread lead drop into place (picks up the first point at which the threads can engage) and while still pushing on it start turning it clockwise to begin tightening. This usually picks up the threads no problem and allows fairly easy installation.

[McCabe-Thiele (Ted)]

I like the idea of the fork springs being as they were - the spacer tube is not even cut  square as I would like it to be.

My current thinking is to find a 15 mm spacer in place of the existing 30 mm tube & washer arrangement. That would give me a bit more pre-load than standard but not so much that the coil was put so far of shape when at rest.