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valve question...

Discussion in 'Engine & Transmission' started by 77panel, Aug 5, 2021.

  1. 77panel

    77panel Member

    Messages:
    64
    Location:
    Coffs Harbour
    The short story, just short of home my 2 ltr suddenly started making a noisy tapping so I parked it up , then in the morning checked the valves to find the exhaust valve on No.3 was way out (maybe 1.5 turns) but everything visually appeared to be ok. After adjustment it ran as good as it usually does (?) drove it up and down the road, no problem (?) Today however on my short trip to work, it started huffing and puffing and upon checking, sure enough that valve was over tightened. I've backed it off and again it seems ok... but what is going on?
     
  2. rstucke

    rstucke Well-Known Member

    Messages:
    1,854
    Location:
    Wamberal NSW AUS
    loose valve seat?
    something caught between the valve and seat?
    Rocker stud slowly pulling out of the head?
     
  3. grumble

    grumble Well-Known Member

    Messages:
    1,361
    Location:
    Taree
    Does it have hydraulic lifters? If not it mat be a loose valve seat or a loose valve guide. I don't think a rocker stud pulling out because the valve tightened up the next day.
     
  4. 1500king

    1500king Well-Known Member

    Messages:
    1,649
    Location:
    Adelaide, SA
    Couple of scenarios..

    1) It gobbled up an accelerator pump nozzle that fell out of the carb, chewed it up and now it spat it out.

    2) Loose valve seat-Do a leak down test(hot).
     
    grumble and Mordred like this.
  5. 77panel

    77panel Member

    Messages:
    64
    Location:
    Coffs Harbour
    Thanks to everyone who replied... I will do the leak down test (looking to borrow a test unit) and let you know the result. Cheers
     
  6. splitbus

    splitbus Well-Known Member

    Messages:
    3,341
    Location:
    Brisbane
    Loose valve seat, time to pull motor
     
  7. 77panel

    77panel Member

    Messages:
    64
    Location:
    Coffs Harbour
    yep...., d'oh!

    2021-09-01_144154.jpg 2021-09-01_144414.jpg
     
    Wayne murray and Barry like this.
  8. rstucke

    rstucke Well-Known Member

    Messages:
    1,854
    Location:
    Wamberal NSW AUS
    check out the crack in the head
     
    oldman, Wiz and Barry like this.
  9. Wiz

    Wiz Well-Known Member

    Messages:
    434
    Location:
    Near Ballarat
    From your experience would the crack have occurred first causing the seats to drop?
    PR
     
  10. rstucke

    rstucke Well-Known Member

    Messages:
    1,854
    Location:
    Wamberal NSW AUS
    I think the crack caused the seat to drop, but what caused the crack?
    Could have been when the seat was put in but unlikely as the crack usually appears between the valves (weakest Point)
    That crack looks to be in a fairly thick bit of casting
    Overheating the engine around the heads usually just expands the aluminium around the seat and they drop but could also cause cracks
    Detonation is another cause, but affects the pistons more
    Compression ratio to high (after rebuild) and incorrect timing are a recipe for disaster too.
    and then there's fatigue from old age.
    Short answer, don't know what caused the crack
     
  11. rstucke

    rstucke Well-Known Member

    Messages:
    1,854
    Location:
    Wamberal NSW AUS
    Just had a look at a spare head in my workshop.
    That crack is in line with the exhaust port on the other side
    And specifically inline with the exhaust stud nearest the crack.
    if the surface of the exhaust pipes on the heater box section of the exhaust system aren't in line (level when a straight edge is held across them) then maybe that stud may have been over tightened to seal the system properly, stressing the area.
     
    Last edited: Sep 2, 2021
    David H, Wiz and Grantus like this.
  12. 77panel

    77panel Member

    Messages:
    64
    Location:
    Coffs Harbour
    Here's a straight edge across the exhaust ports...
    exhaustports.jpg

    And for reference, images showing cracks in the same location, on other heads from other motors....
    crack1.jpg crack3.jpg crack4.jpg

    This motor has run flawlessly for the 20 (??) years that I've had the kombi, so maybe just it's just old age. (?)
     
  13. rstucke

    rstucke Well-Known Member

    Messages:
    1,854
    Location:
    Wamberal NSW AUS
    definitely not your heater boxes, maybe old age like you say.
     
    oldman likes this.
  14. David H

    David H Well-Known Member

    Messages:
    6,612
    Location:
    newcastle
    I had 2 crack in the same spot after I'd driven the bus real hard (ah...my youth:() & it had gotten hot & then I shut it down before it had a chance to cool down. T'was a 76 2ltr carb that the mechanic at the time used to like the mixture on the rich side.
    Cheers
     

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