Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: McCabe-Thiele (Ted) on January 01, 2023, 03:41:59 PM
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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?
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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
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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!
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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
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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?
(https://live.staticflickr.com/65535/52600271141_da34eb6934_o.jpg) (https://flic.kr/p/2o9793z)500 fork innards (https://flic.kr/p/2o9793z) by Macabe Thiele (https://www.flickr.com/photos/187487200@N03/), on Flickr
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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?
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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.
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I've got the O rings in stock Ted.
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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.
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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?
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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.
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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.
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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 ?
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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.
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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.
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Used in mtb forks currently, plastic spacers to make up length as required in either screw together or some types just clip.
[attachimg=1]
A possibility to help.
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I would need something 15mm thick with a 8mm hole with an outside diameter of 22 mm or so. Any links for these sort of items please?
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I would need something 15mm thick with a 8mm hole with an outside diameter of 22 mm or so. Any links for these sort of items please?
If that's what you plan to do Ted, why not cut one of the 30mm spacers you have in half to make 2 x 15mm.
Make sure they're cut square and both equal.
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I would need something 15mm thick with a 8mm hole with an outside diameter of 22 mm or so. Any links for these sort of items please?
If that's what you plan to do Ted, why not cut one of the 30mm spacers you have in half to make 2 x 15mm.
Make sure they're cut square and both equal.
The chromed thin tube that was used is IMHO mank. I had a big clear out about 3 years ago of old seat belt spacer fittings plus loads of old narrow wheel nuts - either would have done the job nicely. I know I will find something I can adapt to do a neater job.
Pretty sure I can find a pair of items that will do the job.
I have some bush inserts that were a part of a Polybush suspension kit somewhere in my garage just need to try to remember where I stored them.
I can always resort to some brass, alloy or SS stand off spacers if I can't find anything suitable in my garage.
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Just spent an hour removing one of the fork lock nuts - the nut will need replacing as it had been severely overtightened against the end of the thread to fit the pre-load spacers.
I'm certainly not using the old spacers - I'm in pause/thinking mode to decide if to return to standard or us a smaller spacer.
What thread is the shaft & nut supposed to be please it's an M8 but my M8 x1.25 dye is clearly the wrong pitch at first glance ?
I think it's M8 x 1.0 pitch??
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Just spent an hour removing one of the fork lock nuts - the nut will need replacing as it had been severely overtightened against the end of the thread to fit the pre-load spacers.
I'm certainly not using the old spacers - I'm in pause/thinking mode to decide if to return to standard or us a smaller spacer.
What thread is the shaft & nut supposed to be please it's an M8 but my M8 x1.25 dye is clearly the wrong pitch at first glance ?
I think it's M8 x 1.0 pitch??
If 10 threads measure 10mm then the pitch is 1.0. 👍
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Just spent an hour removing one of the fork lock nuts - the nut will need replacing as it had been severely overtightened against the end of the thread to fit the pre-load spacers.
I'm certainly not using the old spacers - I'm in pause/thinking mode to decide if to return to standard or us a smaller spacer.
What thread is the shaft & nut supposed to be please it's an M8 but my M8 x1.25 dye is clearly the wrong pitch at first glance ?
I think it's M8 x 1.0 pitch??
If 10 threads measure 10mm then the pitch is 1.0. 👍
Never thought of that - I'm thinking to myself that counting threads might be harder than it sounds - I have a little thread gauge tool but I can never decide if the bit of metal is sitting in the threads properly or not. (Need to go to Specsavers)
Sounds daft but my method is trying a nut on a bolt of known pitch - if it spins on by hand all is good. Trouble is the pitch isn't stamped on my nuts & I soon mix them all up in my bolt box. I confuse myself with great ease - with my Dad not being around like the old days I have no one to ask except here. (Note to self use different boxes for different pitches with label on box)
This opens up a new can of worms for me as I'm a bit old at 74 to be an Apprentice but in many ways I still am.
Back in the 1960's I was using my AVO meter almost daily - these days I only use it for the V bit A&O don't live in my brain any more.
I found myself re-learning lost skills when working on my 400 but I've been to bed a few times since then.
I realise now on the 500 not only is it a bit different but the learning curve has turned back into more of a dip!
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Stick with it Ted. There's always a few dips in the road on any journey. 👍😁
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I learn every day just reading the forum. Poor day when we stop learning Ted!🫢
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After looking at the thread damage on my fork lock nuts and one of the top threads on the long rod I have decided to not fit any pre-load spacers to the front forks - leaving it as standard as both spring legs are well within limits.
I've ordered a pair of new lock nuts from DS as there were a few other odds & ends I wanted from them - I will run a tap down the flattened thread to clean it up plus a die down one of the chromed fork top nuts on the same side.
I will fit the fork springs with the closer wound end at the bottom as this seems to be the consensus.
I also need to fit a couple of Helicoils in the right fork leg as the threads for the front fender fitting are not in great shape.
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Apologies Ted as I now think I didn't understand the status of components in original question, in that the spacers fitted are Honda's original equipment. I read that the other way now, is that correct ?
If so, then agree that fitting with just the springs is correct to assess what it's like.
To expand verification, preload is used to set "sag" if the spring rate is correct to carry the mass of vehicle and rider. Sag being how much the vehicle sits down into it's suspension expressed usually as % of total travel and with 20% being fairly normal.
This can be checked simply by sitting on the bike static and measuring how much it sits below maximum extension, often done with an O-ring pre fitted to one stanchion to let you see where it was after dismounting to have a look.
Purpose of sag is that any suspension sitting right at maximum extension in normal use has no capacity to cope with any quick extension due to road surface deformity. Usually set that way, the fork will "thunk" on minor road irregularities as it hits the top out provision and subsequently drive you nuts :) you want to try and avoid thunking definitely ;D
Progressive wound springs will work exactly the same either way up. Pedantic assessment will have them fitted with tightening coils at the top as best positioned with any extra weight then being on the sprung mass rather than adding to unsprung mass of the wheel assembly. In reality, although correct, it's highly unlikely anyone will be able to feel any difference as those grams have such a tiny additional contribution to wheel, brake, fork sliders etc.
The oil you use will control how quickly they respond to input. They seem to favour 5 viscosity or even 2.5 to let them move nicely on a road bike such that the fork can easily move in response to road riding (as opposed to someone that may want a more restricted control for higher pace applications) the 2.5 viscosity gives very good compliance for smooth ride in day to day riding. I like Motul fork oil as it gives that choice along with very good friction reduction to enhance that response by reducing stiction.
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Ted, instead of jumping straight in and using helicoils on the fork legs, it's worth trying a medium strength Loctite on the mudguard screws. Just nip them up lightly and let the Loctite take up any 'play' in the threads.
It'll hold them fine, unless the thread is virtually bare.
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Not sure what would happen with Locktite on the threads if I had to undo them in the future. One thread has a very short Helicoil in it already. The second thread is worn at the top but better part way down I've cleaned it out with a tap so the lower part of the thread should hold. I was going to leave it like that but it's a load of work if the mudguard shakes loose - I thought fix it once fix it right.
The spacers fitted are definitely not original.
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Use a medium strength threadlock, they are designed to be dismantled when necessary. No problem coming apart on a little screw like that.
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Purpose of sag is that any suspension sitting right at maximum extension in normal use has no capacity to cope with any quick extension due to road surface deformity. Usually set that way, the fork will "thunk" on minor road irregularities as it hits the top out provision and subsequently drive you nuts :) you want to try and avoid thunking definitely ;D
Progressive wound springs will work exactly the same either way up. Pedantic assessment will have them fitted with tightening coils at the top as best positioned with any extra weight then being on the sprung mass rather than adding to unsprung mass of the wheel assembly. In reality, although correct, it's highly unlikely anyone will be able to feel any difference as those grams have such a tiny additional contribution to wheel, brake, fork sliders etc.
Interestingly there was an odd clunk on the front suspension when I rode the bike before strip down - it felt like a metal on metal clunk as if the suspension was bottoming out - it was after hard braking - it was not a good sound - it sounded like just one side but hard to be sure.
So from what you are saying about un-sprung weight the tighter coils should strictly be at the top.
As you can see in the earlier photo the coils were well distorted even at rest due to the high pre-load .
Might it be worthwhile fitting a smaller spacers in the light of your comments about avoiding thunking or have I misunderstood you?
Fitting 10 mm spacers would be quite easy as would 5mm or none.
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Quite a few people complain about a clunking sound on the 500 suspension, seem to recall Philward was one. The 550 doesn’t seem to suffer from this problem but then the 550 doesn’t have that damper rod locked into the top nut.
It’s possible it could be the damper piston hitting the base of the damper chamber. In which case a heavier oil could stop it.
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Actually Ken I think you may have struck a cord with your post - when I drained the oil out of the legs there was not a lot on one side.
Also got me thinking that when I undid the chromed top nut on one side it was not connected to the rod. This might have just been as the lock nut was not locked - is it possible that it was not screwed into the shaft?
I'm thinking that due to the spacer compressing the spring that effectively might reduce total suspension travel.
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Yes, there's at least three potential causes of clunking right there.
1) damper rod disconnected will just shove it up and down because its effectively floating in the fork chamber, this until it clouts something to stop it.
2) lack of oil will not control the spring and load input such that it can just hit top or bottom of travel to knock.
3)you're right Ted, in that if you put too much preload onto a spring, then it risks going coil bound (coils hitting each other when compressed) before the suspension is through it's travel. This is viscous when it happens, and generally starts to break components.
Preload is only used as a trim in suspension. If there's alot of preload used then that suggests the wrong spring rate for the application, or someone's trying to use it outside its designed range.
Original spring is specified for median usage to support bike and reasonable range of rider weight. Significantly outside that (sidecar, very big rider, constant two passenger + luggage etc) would need that consideration rather than more preload.
I'd build it with everything correctly installed as original and go from there, adding small preload if needed then. Realistically, about 20mm additional preload on std springs is a practical maximum to work with. Any more points to the need for upping spring lb rate to get what's needed, but at the same length.
It shoukd work reasonably well just all standard Ted, or least of all give you a competent qualified baseline.
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I've sorted out the two damaged threads on the long rod with a thread file as my die did not seem to be the right thread.
Also a definitive answer on the spring it goes in with the tighter coils at the bottom, as this way up it sits properly on the bottom fitting - the end diameter is the right size this way up.
Just waiting for DS to send the lock nuts with some other bits I need.
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Seems like you're slowly getting the details pinned down Ted.
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Decided to assemble the front springs without any pre-load spacers. So back to original as the spring lengths are well within limits.
Nice new lock nuts from DS & the one poor top nut thread sorted.What looked like the right front fork seals that came with my 400 are the wrong size so new seals ordered from Pyramid.