Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: nairb on January 13, 2025, 01:28:48 AM
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I have had this cb550k3 from new......... so know its history. The front end seems to be a bit spongy. So I looked up the free spring lengths on the fork springs. Then took one of the springs out and checked it.
The numbers for the spring length varied a bit from the various manuals. From 443.5mm or 425.
Mine turned out to be 470mm. Which was a surprise.
The spring :-
[attach=1]
Don't suppose anybody has checked their forks and has a spring length. Maybe a thicker fork oil might help??.
I just thought they were getting a bit old after 45k miles
Ta
Nairb
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Some owners, including me, have found out that the data concerning those springs in the Service Data section in the Honda Shop Manual are not correct. We have had several posts on this in the international forum. I would follow Honda's advice on fork oil though: 150-155cc of ATF. My springs have travelled 140.000lm and are still in excellent condition (and longer than in the Service Data).
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On my 500 K1 my front springs measured 445 mm in length, I looked at an old post where a service limit of 425 was mentioned, as you say hard to find reliable data.http://www.sohc.co.uk/index.php/topic,28909.0.html
Your 550 springs sound a good length at 470 mm, new oil of the correct volume might improve things without going for a heavier grade.
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Does it have a rebound spring fitted onto the damper rod?
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My K3 springs were 473mm
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Measurement clearly shows they are 480mm approx not 470mm. They are supposedly the same springs as the 550f2 and those off my 550f2 are 502mm long. There are some nos ones on eBay maybe ask them for a length check?
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Does it have a rebound spring fitted onto the damper rod?
Now I thought this was going to be a simple/quick job.... I did rebuild these forks ages ago to replace the fork seals. I dont remember now if they have "rebound springs" but if they do, they are cheap from DSS.
Some of the new springs on ebay suggest a spring length of 485mm.
I am going to take the forks off and pull apart to check both springs and check for rebound springs. I can then check all is correct.
It is winter, and it's the sort of thing we are supposed to be doing.
Can springs retain their length but become weaker??. Dunno.
I will report back
Nairb
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As regards keeping length yet becoming weaker in operation the manuals appear to indicate that there is a minimum length for service/replacement so there must be a connection between length & overall performance.
I would definitely look at replacement springs if there was vissible corrosion even if the length was within the service limits.
My 500 springs had been fitted with pre-load spacers, when I removed the spacers that I did not re-fit the spring length was still within limits.
On my 400 the front end felt much better after I carried out an oil change even though I used the standard grade fork oil. I did underfill the level by 25 ml due to not knowing the correct amount. One of my winter tasks when it's a tad warmer is to top them up though it's not as bad as overfilling I believe.
When you drain your fork oil it might be worth checking if the volume is the same on each side as well as the more obvious colour/condition of the old oil.
My Haynes Superdream manual shows ATF for the forks!
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Well, having pulled the r/h fork apart, all seems to be present and in-place. Including the rebound spring!. Will check the L/H one next and check the spring lengths in that one. Wonder if there will be a difference between legs.
The r/h set:
[attach=1]
At least I will make sure the oil levels are the same in each leg.
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Rebound springs? My 550F doesn't have rebound springs, is that just a K3 thing
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F2 got them Dom, F1 didn’t.
F2 and K3 share loads of parts.
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[...] The front end seems to be a bit spongy. [...]
I wish I had a bit of sponginess. ;) Mine have always been a bit spartan.
Bear in mind, that Honda marketed the K3 as the tourer version of the CB550s and that Americans want cushion in their ride.
BTW, what have you set your rear shocks at?
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Bear in mind, that Honda marketed the K3 as the tourer version of the CB550s
Well, it has been to the top of Italy a couple of times. And Paris 3 times and ..... Anyway, I suppose that makes it a tourer?. Great bikes.
All those years ago it seemed so easy. Chuck your lady on the back and off we went. Being 40 years younger might have helped.
Those rear shocks. I have had them to bits for cleaning and checking. I think they were set on one notch down from the max setting.
Great bike for pottering down the country lanes. Sponge or no sponge
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Conclusion:- Having checked both fork springs, I found 1 to be 5mm shorter than the other.(478mm vs 473mm).
I decided to re-use them but turned them the opposite way up - with the compressed part of the springs at the top of the forks. I was never sure which way they should go anyway?.
I used 145 cc of medium fork oil. Which is more oil that before. I didn't have enough ATF fluid.
They do seem to be better. Only a ride out in better weather will tell.
Thanks
Nairb
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What weight is medium? 5w 10w or 15w for instance. I wouldn't use ATF these days in forks, ok in the 70s but fork oil has progressed a lot since then. Personally I'd have put a set amount in one fork leg, measured the air gap and then used that to set the other, it makes sure they have the same amount of oil in each leg.
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What weight is medium? 5w 10w or 15w for instance. I wouldn't use ATF these days in forks, ok in the 70s but fork oil has progressed a lot since then. Personally I'd have put a set amount in one fork leg, measured the air gap and then used that to set the other, it makes sure they have the same amount of oil in each leg.
I used a modern fork oil in my 500 my build log says 160 ml of SAE15 in each leg.
That said Ken modern ATF's have also modernised since the 1970's with many ATF's now being fully synthetic, they also contain plasticisers to maintain seal life.
The problem I see with using an ATF is nowhere does the specification stipulate a universal understood grade/weight like 10W etc, my Superdream manual quotes ATF with no specific details such as Dexron2 etc.
Having only covered about 30 miles in 2024 I can't give honest feedback about how my forks feel except to say the clonk under braking they had before has gone. They felt okay when braking with the old noises gone. I plan to ride it more in 2025
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What weight is medium? 5w 10w or 15w
Here is a pic of the oil used.
[attach=1]
It would be nice to have a warm spring day to find out..... New spark plugs as well.
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You may find 10w a little light for damping on these old bikes, it depends a lot on the weight of the rider, I think the standard back in the day was 15w which is odd as most people riding them back then were light. I'd have put a little more in each leg as well, maybe 160cc.
First off, try it and see, if it doesn't feel right you can always alter the amount of oil.
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There was a recent post on here that showed that there is no standard fork oil weight between different manufacturers. If it says Medium on the bottle I would say that is fine to use.
I've used Silkolene 15w fork oil in my 400f and the fork action is ok for me. 👍
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Originally prescribed by Hondawas ATF, which is usually around 7w. I have had 10w fork oil in mine before but I like the 7,5w best.