SOHC.co.uk Forums > CB500/550

Fork irregularities

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Orcade-Ian:
When I first put the 550 F1 on the road, I had put Putoline 7.5 weight oil in the forks (cos I had some!) but hadn't stripped them at that stage.  Front end didn't feel right on the road - as if the forks weren't even working even though they went up and down when stationary and rocking back and forth with the brake on.  Nowhere near as comfortable and compliant as my 350/4 and 400/4.  The innards are pretty much the same on all 3 bikes.  Anyway, I bit the bullet and pulled the front end apart and completely stripped and cleaned the legs, fitted new seals and new head bearings while I was at it, which were a bit notchy.  As per old 70's stuff I used ATF (160cc/leg) which is 10 weight.  It's still crap and leaning down to touch the slider at 40mph over a rough road (don't try this at home!!), it seems as if they are solid on the move, yet go up and down when stationary. Tightened the spindle clamp on the free side only after bouncing the forks to prevent misalignment as always.
Surely they shouldn't feel so different from the 350 and 400, even accounting for the weight difference?


Any clues?

Ian

K2-K6:
Some others (previous experience on here) have tried and like a thinner oil.

Specifically Motul 2.5 viscosity to improve compression damping acceptance, helping to bring subtlety into the fork.

I like their oil in forks across different makes, it's not a magical solution but you may find a decent improvement when judging it for your circumstances.

Notionally ( and a very sweeping statement) damping system are grouped around 5 viscosity for damping rates, with the valving holes being targeted to use in this  range, and with 10 often giving slow response on "hit, stutter" input, reducing that demand appears to move the fork away from "bobbing" the bike's mass over those ripple type bumps.

I generally like the Motul performance for stiction reduction too, seems to reduce this to help free the slide movement against initial reluctance.

As already mentioned, performance seems good with it but no magic just a very competent product with a lower viscosity range than many produce.

Orcade-Ian:
That's a good shout,
Many thanks - our local excellent bike shop - Dr D's Bike Surgery has Putoline 2.5 but not sure about Motul - I will ask!  The proprietor, David Henning is into Crossers - we have a very healthy Orkney Motocross Club and he has quite an array of stuff available.  If anyone is visiting these wonderful Islands and needs any help - he is your man.
I remember feeling pleased that the stanchions slid smoothly into the yokes but can't remember if I tried rotating them in the yokes to check for possible bend - it won't take me long to check but not stripping them completely to roll on a big surface plate until Winter layup - if another lighter oil (no, not lighter oil!) doesn't improve things, it could be a Phillpots job when it goes into hibernation.  Otherwise, the bike is going well after years of inaction.
Ian

K2-K6:
Putololine a respectable brand too, used it in Moto-X as well quite some time ago now  :)

Currently work on MTB forks (a number with 40mm stanchions) where stiction recievs high criticism, hence my favouring Motul, but dont have anything in the way of comparison to Putoline to assist here.

The viscosity should be reasonably very close in range to make it worth evaluation if easily available locally.

Assuming the stanchions check out with a in situ evaluation, then likely it'll at least tell you something.

Something I also do, if you feel the dive under braking application is too fast when using this viscosity, then additional oil in 5 or 10 ml increments (don't think you'd want to go over 185ml at a guess) will shift the air gap volume above the oil to make a little more spring support as the pressure rises more quickly, it can just give a little more spring cushion  effect to help in slowing the movement toward end of travel.

Orcade-Ian:
Thanks again and I will drop it to 2.5 and keep the volume at about 150 for now (it will only be an overnight drain, not a strip) and add more if it feels needed.
I'll check the truth of the stanchions before I do anything else - I can't believe I wouldn't have done that before when they were apart - but I could have forgotten!

I'll report back when I get the chance but I have a trip to Lochcarron planned on the new Forza next week.

Ian

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