1. Dismiss Notice
  2. Hey Facebook people... We've created a group for XS400.com members to connect. Check it out!
    Dismiss Notice
  3. Want an XS400.com t-shirt? Go to the store to order. Limited sizes and quantities available.
    Dismiss Notice

Valve Adjustment SOHC ?'s

Discussion in 'The Garage' started by kindest, Oct 7, 2013.

  1. kindest

    kindest XS400 Addict

    ok so I am trying to adjust my valves cause they never have been in 30 years and for the life of me I get them right and I will manually turn the engine a bunch of times and then they are off. I know I am tightening the nut right as well as holding the adjusting screw so nothing moves. What I think the issue is when I turn it to the mark LT it won't stay there. If I let up pressure it moves closer to LR. Am I supposed to try to hold it at LT while adjusting or let it naturally move once I go to that line?

    :banghead:
     

    Attached Files:

    Last edited: Oct 8, 2013
  2. Yamaguy55

    Yamaguy55 XS400 Addict

    146
    3
    16
    PA
    Even simpler version is to pull both plugs.
    - Bring the engine up to TDC on the side you're doing, (I stick a dowel or a #3 Phillips down the hole and rotate the engine to be sure it is at TDC) then be sure there is slack in both the intake and exhaust rockers. That way you know you're on the top of the compression stroke, not the exhaust stroke.
    - Next: back off the adjuster and carefully look at the top of the valve stem itself. If there is a divot there made by the adjuster screw, you'll never get accurate adjustment. But you can guess and snug up the adjuster slightly from where the feeler gauge says you're on and hope for the best.
    - If it were me, I'd completely remove each adjuster and look at the end that contacts the valve. These are similar if not the same as those that are/were used on lots of Yamahas, from the XS650 to others. They are hard coated on the valve end, and after the coating wears through, the surface flakes off/pits and that causes endless adjustment problems. If any are pitted, replace all four.
    - Usually, the adjusters are pitted and there's a divot on the valve, but unless the valve divot is really deep, setting the clearance to the minimum is usually fine. The valves on this era engine tend to close up as the valves beat themselves into the head.

    - Another thing that causes continuously variable valve timing on these is worn rocker shafts. With the adjuster out, see if you can feel any slop. It is hard, but "twisting" the rocker, for lack of a better term, tends to allow it to show up. There is of course some play, but not sloppy slam-bang loose.

    Good luck. If I had to guess, I'd say your tappet screws are pitted, and that's the problem.
     
  3. kindest

    kindest XS400 Addict

    well they look pitted but only a smart part is pitted. it would seem the feeler gauge would cover way more area thereby negating the pits?
    I am more worried about finding TDC when I turn it to LT isn't it supposed to stay on the line the second I let go it moves and appears the piston goes down every so smally. Should bungee the wrench so it won't move?
     
  4. Yamaguy55

    Yamaguy55 XS400 Addict

    146
    3
    16
    PA
    Yes, it needs to stay at the top. There are multiple reasons why it moves, but it really does need to be at TDC to set the valves. The rocker is on the base circle of the cam, which is the cylinder part, not the lobe. If it moves off of TDC, one of the rockers will be on the beginning of the lobe and will give a false reading. I take the accuracy of the marks with a shovel of salt. Most are correct, but not all. If you're a real stickler, use a dial gauge.

    The pits will affect more than you think.
     
    buztabuzt likes this.
  5. kindest

    kindest XS400 Addict

    as usual i am an idiot and was trying to adjust them on the exhaust stroke. I think I am golden now. lol
     
    buztabuzt likes this.
  6. Yamaguy55

    Yamaguy55 XS400 Addict

    146
    3
    16
    PA
    That would certainly cause problems. If the tapper screws are pitted, get a set before next valve adjust. If you store bike in winter (I know, your weather isn't that bad) then oil change, valve adj, then store. I like to do my big projects/heavy maintenance when I put the bike away. Then it is ready to go in Spring. If you're going to sync the carbs, do so right after new plugs and valve check, it affects it.

    Glad it worked out.
     
    buztabuzt likes this.
  7. kindest

    kindest XS400 Addict

    thanks for the help dude. I got a spare engine so I might have good spares of everything. Yes be jealous of our weather here :) Even tho In our super mild winter's I am too much of a baby to ride. lol
     
  8. Yamaguy55

    Yamaguy55 XS400 Addict

    146
    3
    16
    PA
    I'm not jealous. Lived across the bay in the early 60s. Corp HQ down in silicon valley. I like it here just fine. Freeway moves all day, every day.
    But thanks for asking!:bike:
     

Share This Page