Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Arch stanton on July 28, 2018, 09:37:20 PM
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Hello.
I have a 750f1 speedo apart for refurb, but it has no damping.
What substance should i use & where do i put it?
Obviously i dont want a bouncy needle on a rebuilt speedo.
I already have clock needles like windscreen wipers on my T500. Most annoying.
So your help would be appreciated.
Sean.
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Try contacting this Guy for advice:
https://www.cb750faces.com/cb750faces.nl/en/content/7-gauge-restoration-services
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Thank you for your willingness to respond.
I have taken your advice.
Sean.
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Never done a F1 only K0&K1 but you need 30,000cst silicone oil like this in the link below. Some people recommend higher viscosity but this worked fine for me. There will be a little pot underneath the top bridge below the needle, which will need refilling. On the 750K0/K1, I drilled this with a 2mm sharp drill bit and filled through the hole, from side top and then sealed it with aluminium filled epoxy. This meant that I didn't have to remove the top bridge, which is staked over and a bit tricky to remove. I used a small syringe fitted with a tiny bootlace ferrure that electricians use, which created a short injection needle.
https://www.ebay.co.uk/itm/Core-RC-100-Pure-Silicone-Oil-For-Diff-shocks-All-Grades-In-Stock-100-300-000/141159428673?ssPageName=STRK%3AMEBIDX%3AIT&var=440235905561&_trksid=p2057872.m2749.l2649
Select 30,000 cst
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Hello Ash.
I have looked at a few old threads on this subject.
There appears to be quite a difference between the K1 & F1
Speedo's in the damping pot dept.
The F1 has Very small bullet shaped pot that looks more like some sort of weight than anything else.
I cant think how the damping works.
There is no sign of a seal or joint.
I would post a pic but im a bit of a Dunce in the IT dept.
Sean.
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I think I have an F1 opened up speedo/tacho somewhere ... I will take a look.
If not kent400 on here (Peter Horton) will probably know.
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There are a couple of different damper designs used on the speedometer but they can be refilled is exactly the same way. The tachometer may have a different design that has a aluminium cap at the needle end but again can be refilled as Ash described. Where the speedo is concerned the mileage counter needs to be removed by carefully bending back the tabs that securing it to the mechanism frame. Whatever is used to seal the hole in the damper needs to be minimal otherwise it will touch the mileage counter as there is only a couple of millimetres clearance between them. No problem with the tacho of course. None of these have anything that could be described as a seal and leakage usually only take place if the gauges are stored face down.
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There are a couple of different damper designs used on the speedometer but they can be refilled is exactly the same way. The tachometer may have a different design that has a aluminium cap at the needle end but again can be refilled as Ash described. Where the speedo is concerned the mileage counter needs to be removed by carefully bending back the tabs that securing it to the mechanism frame. Whatever is used to seal the hole in the damper needs to be minimal otherwise it will touch the mileage counter as there is only a couple of millimetres clearance between them. No problem with the tacho of course. None of these have anything that could be described as a seal and leakage usually only take place if the gauges are stored face down.
Makes you wonder how Honda ship(ped) those parts as spares in the post to people without preventing them being upside down at some point Peter.
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I think it's only a problem if the gauge is left face down for an extended period. If you have ever seen an original box a gauge is supplied in it's marked with the instruction to store face upwards. What I don't quite understand is why some gauges of the same type loose their damping effect and others of the same age don't. Seiki gauges seem to worse as far as loss of damping is concerned. On the early Seiki ones it's only a question of removing the tiny nut under the needle, withdrawing the centre of the damper to re-fill.
Not so easy on ND ones of course.
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Hello again.
Can anyone explain to me.
How does the damper work?
It appears to me that there is a metal tank of oil with a continuous shaft running through it.
How can that work?
If the shaft rotated within the tank of oil, while the oil tank remaind stationary. Then i could understand it. Just as i could. If the tank was a solid mass & simply acted as a counter weight. But in that case. What is the purpose of the oil?
Sorry if I'm being a bit dense. But i simply dont get it!
You explanations are eagerly awaited.
Sean.
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There is a tube attached to the top, fixed bridge of the gauge. The upturned cup with viscous oil in it is attached to the shaft of the gauge and rotates. Therefore,as the cup rotates, there is drag between itself and the fixed tube,caused by the oil, which gives damping to the needle. Just really a classic 'spring & dashpot' damper arrangement but of the rotary variety.
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Hello Ash.
Thanks for your prompt response.
But there is no tube or upturned cup.
There is only what appears to be a solid cylindrical slug of steel which the needle shaft runs through. They are fixed together.
This is a ND F1 speedo.
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Hello Ash.
Thanks for your prompt response.
But there is no tube or upturned cup.
There is only what appears to be a solid cylindrical slug of steel which the needle shaft runs through. They are fixed together.
This is a ND F1 speedo.
Kent400 will know ...If not I do have an F1 gauge somewhere I can take look at but I bet the principle will be the same as the earlier gauges.
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Here is an F1 speedo showing the damper, I'm assuming the face i the same as you have with the km/h marking on the dial face. You can see the aluminium damper, you can see where I drilled it and subsequently re-filled it. The dark spot on it where the hole is sealed.
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Hello Kent.
Yes that is the same as my Speedo.
But what difference can the oil make if its in a cylinder
That moves with the needle shaft?
If the shaft moved through a fixed cylinder of oil, them there may be some resistance thus damping.
But surely. If the shaft +oil+cylinder all rotate in unison.
Then the result would be the same. Oil or not.
Wouldnt it?
Like i said. Sorry if i appear dense. But i dont get it.
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Brass tube is fixed to top bridge and doesn't rotate. Spindle passes through hole in brass tube. Needle attaches to top of spindle. Spindle has small alloy cup fixed to it, partially filled with oil. As top,small, alloy cup rotates there is drag between the inner wall of this alloy tube and the outer wall of the brass tube because of the viscous oil between the two tubes. Bottom (large) alloy cup rotates in the magnet.
[attachimg=1]
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Excellent description Ash and your previous post explained well.
Not all gauges need the damper re-filled. Easy to check, spin the drive with a match stick watching the needle if it drops immediately to zero as soon as the drive stops turning the damping is ineffective. If it slows down as it moves to zero there's a damping effect. If both gauges are off the bike compare with the tacho as it's a bit unlikely that both gauges would lose their damping. The damping effect of the two may vary slightly but the difference should be obvious.
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Right then. Its now making sense.
The confusion lay in the "Tube" I perceived the Brass tube to be a Bush.
When i seperated the 2 plates held together with the 2 brass press together things. I noticed some dried out clear substance. This was must have been the remnants of the oil.
Thankyou so much for your enlightenment.
Lastly. What did you use to reseal the hole you drilled?
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I used aluminium filled epoxy putty on my 750K0 to seal the hole but you have to make sure the hole and its surrounding are oil free...not an easy task. I used cotton buds and isopropanol (UPVC plastic window cleaner) to clean it, then abraded the outside surroundings of the hole with #600 wet and dry paper to give a key.
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Yes it was the oil contamination that had me wondering.
Things are a lot clearing things up.
Cheers Chaps.
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Hello again.
Just to say Thank you to you all for your patience, advice & explanations.
Following your advice i have successfully restored the damping on my clocks.
Cheers.
Sean.
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I use silicone oil 100,000 CTS. I inject that with a 1.2mm syringe from the top into the damper, after disassembling the damper. That oil is very thick and hard to get this into the damper. So I made a special tool to make it a bit easier (I restore 40-50 gauges each month).
My experience with thinner oil is that this will not last for many years. And the risk of oil leakage is higher.