Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: zebedee85 on August 23, 2017, 09:08:32 AM
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Hi folks - seeing some conflicting information on this question. I need to change fork seals on my CB750F1. I am expecting to drain the forks, removal wheel and accoutrements, mudguard, spring etc. Then dust cap and circlip, then work the lower fork leg off the stanchion. one at a time of course with a jack under the front of the engine.
My question is, do I need to loosen or even remove the bolt which holds the damper in the lower fork leg (the bolt that goes direct up into the lower fork leg)? I don't really see how loosening it affects the lower fork leg's ability to be removed, yet I see some disassembly videos recommend this.
any thoughts?
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Yes you do, as that Allen bolt is what holds the lower leg to the damper, you need to remove it completely, then the lower leg will drop off so you can replace the seal. Use genuine Honda seals or you'll be doing the job again soon!
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You also need to detach the mudguard and caliper to get the leg off, don't disturb the fluid pipe on the caliper, just undo the two large bolts joining the caliper halves together.
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Good advice, thanks. Can I not remove the old seal by removing the circlip and working the lower leg up and down in situ until it pops out? Then I can remove the entire assembly from the yoke, whip the old seal off from the top and slide the new one down the stanchion on and tap into place using a punch and the old seal? Then I can replace the circlip and put the whole leg back into the yoke?
This would only work the bottom of the stanchion can come up far enough to push the old seal out?
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Probably not, the seals are generally quite tight in the lower leg. It is far quicker and easier in the long run to separate the lower leg from the stanchion (chromed part) and gently lever the old seal out of the lower leg. DO NOT use a screwdriver or sharp object, if the scratch the soft alloy of the area the seal fits in it will almost certainly leak, use something blunt like a bicycle tyre lever, even the handle of an old fork or spoon! Another way some people have used is a couple of self tapping screws in the old seal from the top, then pull on them with mole grips.
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ok I'll have a go and report back
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ok I'll have a go and report back
Can't remember which Honda forks but on some of them you loosen that hex head screw and the whole thing it screws into moves...so I shove a wooden dowel down the leg and push down hard on it so that the friction stops the assembly from turning. I seem to remember a broom handle but that's maybe too large dia., depending on the forks concerned.
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That's F1 forks you're thinking of Ash, easiest way is to leave the spring in under tension, then remove the Allen bolt with an air or electric impact wrench. Always worked for me!
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I use a ratchet strap to put some tension on the leg.
Never had any problems getting the bolt out doing it this way :)
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Early 750 forks had bushes so you could take the circlip out and work the seal out but later ones like yours don't have the bushes so the slider has to come off, workshop way of undoing the allen bolt is a windy gun and long 3/8 drive allen key but putting the spring under tension usually works as well.
N.B
You need a long series allen key
BE CAREFULL removing the old seal as if you scratch/gouge the inside of the leg where the outer of the seal fits it will forever leak
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I had a problem with that bolt on my F1, it just kept turning on me, so I removed the top bolt put a socket in and replaced the bolt, it still laughed at me. So in the end I had to put a bigger (longer) socket under the top bolt, put the fork leg in the vice and jammed the top nut against the wall, tightened the vice, gave the bolt a few sharp taps and hey presto out it came. So if you do use the broom handle method you may have to vary the length.
Cheers
Denis
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I now use an impact driver with a hex bit. So far has never let me down, (need some wood to touch).
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Got it - broom handles are popular. I don't have an impact gun, just the old fashioned one which requires physical violence. I'm sure I'll understand when the fork is apart but do I take that the broom handle goes down the stanchion?
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Yes, with the spring removed.
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see http://forums.sohc4.net/index.php?topic=19797.0
or search
https://www.google.com/search?hl=en&as_q=broom+handle&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=sohc4.net&as_occt=any&safe=images&as_filetype=&as_rights=
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Got it - broom handles are popular. I don't have an impact gun, just the old fashioned one which requires physical violence. I'm sure I'll understand when the fork is apart but do I take that the broom handle goes down the stanchion?
If I still lived in that area, I could get them out in less than a minute. Holland engineering are just the other side of Buckingham to you, they can get them out.
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If you still have the springs compressed, i.e. You haven't taken the top caps off there should be enough friction to allow you to undo the bolts, it needs a sharp "crack" to get them to released rather than steady pressure, so get the Allen tool in there apply gentle hand pressure to take up any slack and the turn in a fast sharp motion, or whack the tommy bar with a hammer or ratchet with the palm of you hand, it a sharp shock that you need to deliver to the Allen screw.
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Don't matter how much you crack it, if some sod has used a stainless bolt, you will never get it shifted. Had a pair last year, took the heads off with the air gun and then it was time for some drilling >:(
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Or if someone has drastically over tightened them, I'm doing my CBR1000F on Saturday, left seal has gone, fingers crossed that no Neanderthal has been around it in the past!.
Actually the previous owner (I'm the second owner from new)was a Neanderthal, he tried to free off the front brakes with a bar and bent a disc, tried to remove the rear brake dust seal with a screwdriver and damaged the calliper casting, the main fuse was loose in its sockets so he put a u shaped steel plate in its place , it would have blown at about 2000 amps 😄, so many bodges, luckily I got decent replacement parts cheaply but it's the last time I buy a bike sight unseen.
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On my 350F no amount of tension or clamping would stop the inner damper section revolving and I ended up having to drill the Allen screw out. Fortunately I managed it without damaging the slider. It appeared to have been fitted with thread lock.
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Honda uses threadlock on those Allen bolts, and recommend using it on re assembly.
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Honda uses threadlock on those Allen bolts, and recommend using it on re assembly.
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That is correct, that is why they are hard to remove without the assistance of air ;)
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Honda uses threadlock on those Allen bolts, and recommend using it on re assembly.
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That is correct, that is why they are hard to remove without the assistance of air ;)
Everything is hard to do without the assistance of air Trig ! 😄
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Well with all your help and the Messrs Haynes I have removed the forks and the old seals. It felt a bit easy to get all the bits off, I know it was maintained by a mechanic (allegedly) but it hasn't done more than 1500 miles since 2007. Maybe it was well stored, and well maintained, who knows.
Anyway - old fork oil was disgusting, and the seal area of the problematic fork leg was gouged with screwdriver marks. It'll be a case of living with this if it weeps again. the butt of a 17mm spanner had just about enough length and strength to lever the old seals out, which I used to tap down the new ones with a mallet.
I have refilled them, but they are not on the bike yet, that's Monday's job. So far, so good.
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Oh and following the manual on the damper bolt was fine, just leave the spring in situ and turn, both came out first time using this method. Thread locker on the way back in, job done.
Next time, my theory on the gouged inner surface is that a little gasket sealant might just be ok. It's crude and horrid, but lower fork legs are not easy to come by.
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Good job, mine was straight fwd too, apart from when I dropped the slotted top retaining washer, which immediately vanished through a portal into another world, only to reappear 30 mins later and 15feet from where I dropped it, I didn't bother with threadlock , instead I put a small block of rubber in each recess so that the screw can't unwind, if I ever have to strip them again it will be easy to undo the screws,...surprising how much nicer they ride with oil in both legs!.
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Perhaps all those washers and fixings we drop travel the place all the socks that go missing from the wash do. Fork oil is probably a good idea. Im a bit puzzled by the damping spring on the part fiche though, i couldnt see anything taking the stanchion out. They are almost certainly not on the garage floor, so im hoping they are still in place, wherever they are. Ill report back and post some pics when ive got everything back together again
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They are inside the stanchion, under the top of the damper rod, which if you left the damper rod inside the stanchion, they will still be in place.
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I did! Thanks, that puts my mind at ease
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If you look in the Haynes manual at the damper rod/ piston, the thin end is where the Allen bolts you removed screw into. The small rebound spring you were worried about slides on the thin end inside the stanchion, and abuts against the bottom of the piston head. When the forks are fully extended, it cushions the impact between the piston/rod and the slider. Hope that makes sense to you.
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Well - the operation was a success, though now I'm getting some stiction. I was a bit over zealous with the fork oil quantity so letting them drain a bit might fix it. No weeping though.
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Too much fork oil - removing approx 10cl both sides fixed stiction.
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When you use the drain bolt, it will still leave oil in the tube so, keep a eye on the measurements ;)