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Help Adjusting valves - gb250 /cbx250rs

Discussion in 'Maintenance' started by nixon, Jul 24, 2018.

  1. nixon

    nixon Active Member Premium Member

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    hi ppl

    giving my mates gb250 a tune. I downloaded the manual to get specs and instructions.

    pretty vague.

    it states to check both intake/exhausr on T..on compression stroke?

    Wouldnt it be either int OR exh to be measured.... then rotate to T and, piston down, measure other?

    hope that makes sense!

    also , what do ppl use besides the square 2.5mm looking tool to adjust?
     
  2. Wozza

    Wozza Active Member

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    yeah its done on compression stroke,this is so both valves are closed and the cams/rockers are in the right position....
    I used a set of pc micro tools to adjust..supercheap auto do the correct tool but its a special order..failing that a bit of suitable ID alloy/copper tube smacked square with hammer will work..good luck with getting them right 0.05mm and 0.08mm is paper thin and a pig to get spot on..also give the cams lobes a good looking at, these can be pooched if the servicing has been lacking...
     
    Last edited: Jul 24, 2018
  3. nixon

    nixon Active Member Premium Member

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    Appreciate your response!! thanks

    Ended up using needle nose type vice grips - work great. The exhaust are super tight.. havent done yet but it should run much much better.. guy was complaining it ran bad after 15 min.. he doesnt know anything about bikes, asked him about valves.."whats that.."
     
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  4. nixon

    nixon Active Member Premium Member

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    Well still confused

    its on the "T" crankshaft.. piston I believe at top. The intake valve set .05 no issues, one was a little tight

    But - the exhaust cam has the rockers fully pushed- even complety removing the adjuster - no clearance.

    Shouldnt i be doing exhaust on "T" on down stroke? when its compreession you cant measure exh valves..they closed??


    (ps on those annoying crankcase cap with big slot.. used an impact driver with wood hole bit modified , woked great!)
     
  5. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    It sound's like you might be 180 degree's out? eg it's on the exhaust stroke not the compression stroke
    The valve's should be closed, eg all the way up

    I would back off the intake valve adjuster's and try turning the engine over 1 full revolution by hand so the T is at the top again, then see if any valve's are open

    Even post up a picture if you can, we might be able to explain it for you
     
    Last edited: Jul 25, 2018
  6. Wozza

    Wozza Active Member

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    yeah as above turn the motor over till you see the inlet valves open and close then keep turning till you see the T..I put a drink straw or something the wont damage the bore or piston down the plug hole, so you can see the piston come up on TDC..also there are 2 letter marks, 1st an F for checking timing then the 2nd mark is the T for TDC

    Edit ..correction there are 3 sets of marks, there is also a set of timing advanced marks
    Doh!
     
    Last edited: Jul 25, 2018
  7. nixon

    nixon Active Member Premium Member

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    kinda funny. struggling with this more than my dohc 16v fireblade shims! on that theres marks on cam /cranckshaft.

    I keep checking on T - always fully closed exhaust. im missing something hmm.. im rotating counterclockwise.. plug out. The "t is very vague..like a tan colour?

    i guess what profile should the two cams be in their ideal spot? ie if 12 oclock is upright..6 oclock down

    cam exh.jpg
     
  8. nixon

    nixon Active Member Premium Member

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    thanks..in from shed but are those other marks just holes? i couldnt see anything else!

    cant wait till i figure out what im doing wrong... i thought id be finished by now!
     
  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Cant see much in your picture sorry.

    It's the same thing you had to do to check the clearance's on number 1 cylinder on your DOHC Fireblade.

    Try putting your finger in the spark plug hole and turn the engine over by hand,
    once it start's pushing air out past your finger it's almost at tdc on the compression stroke,
    keep turning it over till the T line's up with the mark in the casing, then set the valve clearance's

    Post a pic up of the T, it may just have a line there ?
     
  10. Wozza

    Wozza Active Member

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    Yeah the T is hard to see.....I had to use a torch and look up towards the top of the rotor to see it,Plus the F and I I advance marks can look like the T mark, the reason I use something in the plug hole as a visual cue...working on old bike I tend not to trust the factory marks.....
    Honestly it wasn't that hard, pretty much the same on all motors Ive done..I just missed the T a few times..once that was lined up both rocker rattled around easily...adjusted gaps and around a few times recheck and done..if your still having issues maybe time to start looking at other possible issue..cam timing out of wack..valve/seat regression ect ect....

    Clipboard01.jpg
     
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    Last edited: Jul 26, 2018
  11. nixon

    nixon Active Member Premium Member

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    Yeah, those above instructions just dont seem to work - the T- always has exhaust cam lobe at maximum.

    I gave up, just rotated each cam lobe to top and set.
     
  12. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Turn the engine over 1 full turn and it would be closed then ?
    There should be another timing mark on the cam gear's you line up as well
     
  13. Wozza

    Wozza Active Member

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    So long as it works :) glad its sorted..if its still flaky when hot try replacing the coil...I just used a generic xr250 one,
    made a huge difference in startup and running...
     
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  14. nixon

    nixon Active Member Premium Member

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    yeah i would have thought that another mark on cam gear! but no mention..ive already put together and changing front tyre. hopefully its all good
     
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  15. Wozza

    Wozza Active Member

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    Sorry been away sulking :)
    There are marks on the cam gears both have straight lines with EX on one side and IN on the other, these lines line up level with the top lip of the head when the T is lined up...well they should if installed correctly and timing chain is in spec
     
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