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Crazy valve clearances

Discussion in 'XJ Technical Chat' started by 82750maxim, Mar 12, 2019.

  1. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    My advice still stands.

    26,000 miles is only the fifth valve clearance check for an airhead, and it shouldn't be loose by 2mm at all...ever.
    The valve clearances tighten up as the valves beat the seats into the head.

    Also, the cams lobes can't wear anywhere near that fast. They are harder than the shims. They can get scratched up by turning the cams over with a shim out of the bucket, but that's becasue of the higher surface pressure from the smaller contact area, and the sharp edge of the bucket lip.
     
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  2. 82750maxim

    82750maxim New Member

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    The lobes are slightly blued. I was wondering if a lifter spring could be rusted, or just super junked up not allowing a proper return.

    I appreciate the fix.
    I let the bike sit for more than 24 hours before performing this check. The clearances all are about the same. They have a .2 mm difference across the board, but the clearances are 2.083 for each exhaust, and the intakes varied, very slightly, but stuck around the 2.2 area. It was difficult to get an exact measurement.

    The bike was fired up twice. Once when I met the PO, and once when I got it home. I honestly thought it was pilot jet related due to the way it revs when it starts dead cold. I thought I’d start off simple and check the clearances, that’s when the can of worms opened.

    There is definitely a rust issue.
     
  3. 82750maxim

    82750maxim New Member

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    If the valves are severely bent or not seated properly, that would throw off the clearances correct?
     
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  4. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    Seems if its revving like that, there's not going to be a lack of compression......but a compression test is definitely in order, like K-Moe said.

    Let us know what you find. First we need to find out if valves are sticking open or not. If any valve is sticking open and you don't know it, but setting the clearance correctly, you'll end up open the valve even farther, and THEN you could run into valve/piston contact issues. DONT ADJUST CLEARANCE TIL WE KNOW THAT ALL VALVES ARE CLOSING ALL THE WAY
     
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  5. 82750maxim

    82750maxim New Member

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    I haven’t adjusted anything. All I have been doing so far is investigating. I know somethings screwed up here, so I want to diagnose the problem before doing anything. I will do a compression test, but I’m still certain I need to pull the head. Again, if anyone has seen/made a tutorial videos it would be a nice aid with the service manual. I’ll be starting that process probably Saturday since I have Sunday off work.

    I will report back, thanks again.
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    102.PNG .102

    sorry :(but first I have to ask if you are reading your feelers correctly

    how did you measure the 2 mm gap?


    2.083 mm clearance with a 275 shim cannot be fixed with a shim.

    2 mm across the board is not a natural thing to happen to all the valves
     
    Last edited: Mar 14, 2019
  7. 82750maxim

    82750maxim New Member

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    Xj550h yes. I am aware that this is not fixable with a shim, which is why I’m here. It’s definitely weird. I’m using my feelers correct. I measured the gap using multiple feelers and adding them up. The valves I believe aren’t seated properly amongst other things. Won’t know for sure until I pull the head this weekend.
     
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  8. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    You will know if you just do a compression test
     
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  9. Ryengoth

    Ryengoth Active Member Premium Member

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    Btw what is a good compression reading on the air blocks? On the 550 block I got around 180psi on each except 4 which was 175. The service manual does not state an acceptable psi range, unless I missed something.
     
  10. 82750maxim

    82750maxim New Member

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    One other thing, the cam chain tower is super loose, has play back and forth underneath the tight chain. I can almost push it out from under the tight chain, can I adjust this? Or is this possibly a broken spring of some sort
     
  11. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    The compression specs are in the factory manual, and on this website.
    The Information Overload Hour
     
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  12. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    What part are you calling the cam chain tower?
    Are you referring to the top cam chain guide?
    Pics would be of help.
    Your machine has an automatic cam chain tensioner, but it is possible for them to get stuck (rarely, but possible).
    When you spin the engine do you notice a link on the cam chain that looks different from the others? (there should not be, but that would indicate that the chain had been replaced at some point).


    Pulling the head on the YICS engines is not something that should just be done without thoroughly diagnosing the problem. There is some additional cost involved due to the YICS port o-rings, and a bit more effort involved due to the additional clamping studs on the inderside of the head.

    Save yourself several hours of work and do the compression and leakdown tests before pulling the head. You could be doing all that work for no reason. You might have to do it anyway, but diagnosis should lead the way.
     
    Last edited: Mar 14, 2019
  13. 82750maxim

    82750maxim New Member

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    Appreciate the feed back, my buddy has the same bike just an 83. I just helped him do his valves last night. Tower probably isn’t the right term, the chain isn’t super loose but the guide between the two visible sprockets has side to side play underneath the chain. His was solid, which is why I was worried, I’m at work and won’t be able to take pictures until tonight
     
  14. Ryengoth

    Ryengoth Active Member Premium Member

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    My 82 550 support tower had side-to-side play but it contacted the chain and you could not move the chain downward between the timing sprockets.
     
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  15. k-moe

    k-moe Pie, Bacon, Burbon. Moderator Premium Member

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    The upper guide just sits loosley in place. The only thing holding it is chain tension, and the guide does need to move a bit to allow the chain to track the sprockets as the cams move.
     
  16. bensalf

    bensalf Active Member

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    yeh, my top chain guide also moves from side to side, tho mines a 600
    stu
     
  17. 82750maxim

    82750maxim New Member

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    One less thing to worry about! thanks.
     
  18. XJ550H

    XJ550H Well-Known Member Premium Member

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    measure your cam lobes
    camlobes.PNG
     
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  19. XJ550H

    XJ550H Well-Known Member Premium Member

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    edit ;)
     
    Last edited: Mar 17, 2019
  20. Ryengoth

    Ryengoth Active Member Premium Member

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    Well maybe I read it wrong. I will be testing again with the new head installed.
     

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