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Help CB250rs steering head bearing - seals?

Discussion in 'Honda 250cc Singles' started by Mike_T, Dec 2, 2019.

  1. Mike_T

    Mike_T Active Member

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    Hi all,

    quick bit of advice if possible:-

    I am about to replace the steering head bearings on my CB250rs, and the yokes as the top nut thread was very nasty on the old ones.
    I'll change to tapered bearings for longer life and easier fitting. I've done this job before on similar age bikes.

    The kit I got from a reliable UK supplier:
    https://www.davidsilverspares.co.uk/CB250RSA-1980/part_28287/

    Things seem to fit alright on the new yokes.
    However, on the lower bearing the original bearing has a dust seal on the cone, that will seal with the frame head lower.
    (Item 3 = dust seal that fits onto item 6 = cone):
    https://www.cmsnl.com/honda-cb250rs-1980-a-england_model16355/partslist/F06.html#.XePjatXgp9A

    But, my new set, has a washer to bring the lower bearing to the right height (as seen in link), but no seal. I can't use the old seal as it is directly on the cone.

    Anyone done this job? And do you just go with it and ignore the lack of a proper seal?
    The washer in the kit probably fills most of the bottom of the steering head, but I don't like the idea of it not having some sort of rubber seal.....
    any thoughts or advice? Ideally has anyone done the same job.....

    Thanks,
    Mike
     
  2. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    When doing a similar set up I fitted the seal under the bearing above the washer.
     
  3. Mike_T

    Mike_T Active Member

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    In case anyone else stumbles across this, a couple of notes / tips:
    I decided to buy another bearing set that came with seals, from Pyramid parts.

    Oddly the seal for the lower end was oversize and wouldn't fit in the frame. But I was able to use the top seal in the lower end, which was only slightly smaller than ideal. To make it sit well it had to go below the spacer washer so it didn't push hard on the bearings. (normally I'd agree with Murdo to put the seal above the washer).
    I was able to use the oversize seal at the top where it sits above the frame, but also isn't really needed.
    Overall, I think I should have questioned Pyramid as I'm not sure the oversize seal was the right one for the set - but I made it work OK. I now see in the UK "wemoto" have started selling an allballs set, if buying now I'd try that instead.

    Anyway, job is easy enough if you have the tools to drive the seals out / in, so conclusion is tapered bearings go into a cb250rs OK, but a couple of tips...

    -workshop manual tells you to disconnect all wiring and everything, but as many probably realise, after removing wheel and forks etc you can get away with disconnecting clutch cable and tacho from the head and then leave the rest connected. It's then possible to lay the whole handlebar/top yoke/headlight etc complete assembly on a table in front left of the bike and get full access.

    -With the new bearings and seals, the steering head top nut has castellations that press against the new bearing (or sealing washer) that probably would have slotted neatly into the original head race. The result is that the top yoke was sitting slightly higher up the yoke, just over a millimeter or so. I decided the upper yoke top nut wasn't getting enough threads on the yoke to trust - so changed to a thinner washer. An M22 A2 washer fits if you grind the hole very very slightly larger - the A2 is important, that means it's a thin (2mm) washer instead of the orginal 3mm+ washer (I have 19 spare out of the bag of 20 I had to buy if you need one...). Basically, the bearings were the correct size, but how other bits sit made the whole thing pull the yokes down very slightly so it needs common sense to check it's OK and solid.

    Hopefully the new bearings will last the bike it's next 40 years....
     
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