Author Topic: Front end bouncy  (Read 1754 times)

Offline DomP

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Front end bouncy
« on: August 09, 2025, 08:23:06 PM »
The forks on my cb550 have a fairly horrible rhythmic bounce at around 40-45 mph, my initial suspicion was the front wheel being out of balance so removed it and balanced it as I'd not bothered doing it when I rebuilt it.  It was quite out so I thought I'd solved the problem, wheel back on and a ride out has shown I'm barking up the wrong tree.  Has any one got any thoughts or ideas as to what may be the issue?

 Forks have been fully refreshed with I believe 7.5 or 10wt fork oil and a small preloaded spacer added (tried removing spacers, no change) 
1975 XS650B
1976 CB550F1 current project
2012 Triumph Daytona 675

Offline Bryanj

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Re: Front end bouncy
« Reply #1 on: August 09, 2025, 08:28:23 PM »
Too much oil or too heavy oil

Offline DomP

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Re: Front end bouncy
« Reply #2 on: August 09, 2025, 08:40:39 PM »
Oh ok Bryan, I think it was probably 10 wt in reality, I put in the specified quality and measured the height but it was a while ago now.  Shall I drain it and refill with ATF?

Has anyone on here tried Yss Emulators in these forks?
1975 XS650B
1976 CB550F1 current project
2012 Triumph Daytona 675

Offline Murf

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Re: Front end bouncy
« Reply #3 on: August 10, 2025, 09:08:35 AM »
Is the tyre old, is the tyre fitted to the rim  evenly all the way around. Are the rear shocks ok. Has the tyre ever had that tyre slime stuff put in it.  Is the tyre a reasonable brand, do the sliders move up and down freely.  Is the inner tube new or old. Is there play in bushes in the sliders. Is the brake binding or disk warped.

Offline DomP

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Re: Front end bouncy
« Reply #4 on: August 10, 2025, 09:44:00 AM »
Its a  new Avon tyre, no brake binding and forks moving as they should. I will check the rim fitment today, its the only thing ive not thought to check
1975 XS650B
1976 CB550F1 current project
2012 Triumph Daytona 675

Offline Johnny4428

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Re: Front end bouncy
« Reply #5 on: August 10, 2025, 10:27:41 AM »
There was someone else on here had some issues with the front end, think it was OrcadeIan. Don’t think he ever resolved the issue!
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1
1978 Honda CB550K3
1999 ST1100 Pan European 50th Anniversary.
1975,1984,1986 Honda C90’s
1973 Honda CB750K3
1977 Honda CB550 (almost)

Offline DomP

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Re: Front end bouncy
« Reply #6 on: August 10, 2025, 11:03:06 AM »
Murf is onto something, its definitely not seated right which is my fault as I rebuilt the wheel myself.  If got it off, lubricated it with 50/50 washing up liquid and water but it just wont pop on the rim even if I over inflate.  Tge tyre is max 42psi so im not sure i should go any higher than 50 just to get it on.  Any thoughts?
1975 XS650B
1976 CB550F1 current project
2012 Triumph Daytona 675

Offline K2-K6

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Re: Front end bouncy
« Reply #7 on: August 10, 2025, 03:19:05 PM »
Think the "max" setting is recommended for usage and load rating.

You can usually go up to 70/80 psi to get them seated if necessary.

Lubricating the bead, I use silicone grease very, very, very sparingly smeared around entire tyre bead to do this. They'll usually pop on at about 25psi then.

Silicone is used as mould release in their manufacture.

Offline DomP

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Re: Front end bouncy
« Reply #8 on: August 10, 2025, 04:26:29 PM »
Ive had another go but its not quite right, disheartened so I decided to change the front tyre on my Daytona 675.   Breaking the bead was tough but mounting the new tyre was dead simple popped on the rim before videos even reached the standard tyre pressure.

I think the powdercoat on my cb550 rim might be just enough thickness to make it a tight fit, I'll try upping the psi a bit see if it goes on
1975 XS650B
1976 CB550F1 current project
2012 Triumph Daytona 675

Offline K2-K6

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Re: Front end bouncy
« Reply #9 on: August 10, 2025, 06:58:04 PM »
Yes, agree it could be powdercoat thickness contributing to that.

Had a spare alloy wheel refinished recently (my son's car) with a immaculate final finish, but quite substantial in comparison to factory finish and dimension.

Similar diameter to bikes at 18" but 245mm width though  .... used silicone grease to fit it without tyre levers at all to not damage the surface. Sat up on the bead at about 30 psi, although a whopping great BONG  :) its quite tight on there.

Plain soap doesn't seem to let them "creep" up over the J bead form as easily as silicone.

Offline Orcade-Ian

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Re: Front end bouncy
« Reply #10 on: August 10, 2025, 07:26:41 PM »
There was someone else on here had some issues with the front end, think it was OrcadeIan. Don’t think he ever resolved the issue!
Aye, twas me!  I tried new genuine Honda springs after lots of perms and coms with oil weight/capacity.  Brand new tyres both ends, sliders free, yokes straight, pinch bolt loose until down on its wheels.  Still not up to the standard of my 350/4, so as Johnny said, not really resolved.  I would describe it as 'patter'.  Forks go up and down as expected when pushed back and fore with front brake on and if you hit a large bump but hardly any movement on the road.  Not had the chance to swap bikes with Johnny to see what he thinks.

Ian

Offline DomP

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Re: Front end bouncy
« Reply #11 on: August 10, 2025, 08:08:00 PM »
Ive not had a chance to try it out since trying to reseat it, I'd definitely not describe it as patter, more shockingly bouncy😄

There's not that much of a raised seat on standard 550 rims is there,  spinning the wheel shows its true but the tyre definitely isnt quite
« Last Edit: August 10, 2025, 08:39:58 PM by DomP »
1975 XS650B
1976 CB550F1 current project
2012 Triumph Daytona 675