Why adjust the valves?

Discussion in 'Engine & Transmission' started by saabman, Dec 28, 2016.

?

when you check your valves has the gap opened up or closed

  1. Increased gap the - need to tighten up

    50.0%
  2. Reduced gap - need to open up

    50.0%
  1. saabman

    saabman Well-Known Member

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    Goulburn
    Ok here we go...

    I was looking at nats beetle today and thinking about things that need doing to it and the thought of the regular check the valves line popped into my head and I started wondering why do we need to check the valves.

    This is not in the sense that the valve clearance needs to be correct for optimum performance and prevent burnt valves but why does the valve clearance go out in the first place?

    I will ASSUME that the last time the valves were touched they were correctly set.

    My thinking is going like this..

    1. Check the valves and the clearance is correct - no problem
    2. Check the valves and the clearance is too small - what cause the gap to close up?
    Some things I can think of are
    • the valve seat is being bashed into the head (very Bad?)
    • the valve stem is being stretched (Bad?)
    3. Check the valves and find the gap has increased
    • worn cam
    • worn/bent pushrod
    • worn cam follower

    My thinking on the issue is that if the clearance is reducing we have a major problem occurring replace the heads/ valves and all is well? Leaving the clearance too small will speed the problem up causing burnt valves.

    If the clearance is increasing this is not a serious failure - unless a pushrod is bent. failure to recitfy this situation possibly would not cause any more grief than an engine running porely due to reduced valve opening times and excess noise.

    please note this post is my musings and questions for discussion and not concrete answers.

    I wish to be enlightened by those that know :)
     
    Last edited: Dec 28, 2016
    David H and oldman like this.
  2. Barry

    Barry Well-Known Member

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    Basically all the reasons that modern cars got rid of and went to chain drive
    In addition is the fact we are air cooled and heat control is almost non existent

    Air Cooled and push rods are soooooooo old skool

    Heat is the main culprit and the points you list are at the top

    Your musings are perfect
     
  3. Blunderbus

    Blunderbus Active Member

    Messages:
    542
    Location:
    St Helena, Melbourne .
    Most engines use hydraulic lifters which essentially adjust themselves , solid/ mechanical or roller lifters don't so need to be adjusted to allow for valve seat wear and recession and expansion.
    My diesel Land Rover has roller lifters and I check the tappets every 20k.
     
  4. Blunderbus

    Blunderbus Active Member

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    Location:
    St Helena, Melbourne .
    And nothing to do with timing belt or chain , just another method for the same result.
     
  5. oldman

    oldman Super Moderator Staff Member

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    Nothing wrong with valid musings Bernie ;).
    The best answer I can come up with, without delving into my limited mechanical knowledge is.......because....:rolleyes:
    Cheers,
    Mark
     
  6. Alpal

    Alpal Moderator Staff Member

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    And its such fun!
     
  7. David H

    David H Well-Known Member

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    Okay Saabman,
    My 2 bobs worth so they've got a target to hit or respond to!;).
    Any variation from the known is worth exploring.
    Firstly I love your musings. Sorta where my head can go on a good/bad day!
    Secondly....for me.....it's about metal & how it's made & it's not made on the same day so even tho' it fulfills certain tech specs doesn't mean it's the same as his mates in your engine. So same steels made on different days at different temperatures react differently to the changing heat in their environment (your engine). Expansion/contraction over time affects each structure differently.
    Tell me how old you are & are you getting shorter or taller!!:( Seems your life is just a pushrod & how well you were made.:)
    Fantastic Musings by you & thanks for posting.
    My uncle (ex vietnam vet) once asked me why he lost weight overnight. My response was " if you turn the engine off you won't but even at idle you use some fuel".
    Cheers,
    David H:rolleyes:
     
    Last edited: Dec 29, 2016
  8. saabman

    saabman Well-Known Member

    Messages:
    4,717
    Location:
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    Thanks for the feedback :)

    The metallurgy one I had discounted as I figured after a period of time the metal structure would either settle and give no effect or you would get random changes ie sometimes loose and and sometimes tight. but Im no Metallurgist so Might need to look into that a bit more.



    Ive added a poll to the thread may be a bit belatedly but it would be interesting to see what you all experience.
     
  9. Grantus

    Grantus Well-Known Member

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    I like polls, and encourage the use at KC......and was going to vote, but missing the 3rd option:

    "Never done this, so no idea.":(

    So I'll refrain from voting, for result accuracy. ;)
     
  10. David H

    David H Well-Known Member

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    So what would account for the "sometimes loose sometimes tight"?

    Unlikely any metallurgical structure would ever 'settle' & be stable for the heat/ no heat environment it lives in!o_OOtherwise it would last forever & not wear!

    See comments in 76 Fuel injection. Non f/i engines have more heat variance. yeah..get hotter by so much more.

    No need to 'run down' after fast run in F/i. In non f/i hard run leads to over CHT & if no 'idle down' energy goes to Cylinder head which absorb heat & then 'rapid cooling' (cos you turned it off in winter/autumn) cracks head going from really hot to really cold as an alloy:rolleyes:structure.

    The valve that needs adjusting is "the one that's stretching & the one that's getting shorter is the one getting more brittle by heat (slowly turning to ash:)& shrinking)".

    Guess which is the hotter cylinder? Heat reduces height!:D;)
    Speed increases height & lengthens !The other 2 cylinders!


    In short you can absolutely 'flogg' a F/i motor & you'll never crack a head!!
    You will need to adjust the valves after you've 'flogged it' because rear of engine is hotter & that effects the small bits of metal in your engine that go fast!;) You will never crack a head no matter how you treat a F/i.
    Done several in non f/i even given due care.
    Temperatures!
    Cheers,
    David H
     
    Last edited: Jan 2, 2017
  11. David H

    David H Well-Known Member

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    By that poll it looks like I'm 50%. Half closed up & half had to be loosened.
    Was there an option that mechanic charged me for adjusting valves & they were all okay?
     
  12. saabman

    saabman Well-Known Member

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    You need to get your hands dirty Grant :)

    David why does the non FI lead to higher CHT temp after fast run - I would have thought that would be due to poor tuning - wrong main jet.

    whats with all these insomniacs :0

    I had a quick google of the issue last night and found a thread on a BMW bike forum discussing the same issue and one poster commented that you could get a situation where the embedding of the seat or streatching of the valve was offset by the wear of the cam/follows etc. so no change of valve clearance but the engine was slowly destructing
     
    Grantus likes this.
  13. cbus

    cbus Well-Known Member

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    Not relevent to type 4 motors but going back to 50s n 60s type engines , they were very poor materials in head and valve to the point that valve grinds were a common periodic service.

    One point that may add to our engine variations in gaps may be the numerous heavily facetted adjusting screws.
    These must surely cause issues with adjustments and holding settings.

    Buy new / quality ones folks.
     
    oldman likes this.
  14. David H

    David H Well-Known Member

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    Carb Kombis throw in a less precise fuel/air mixture & thus they burn hotter. My carb 2lts did 120,k before low compression. My F/i does 240,k before I get sick of oil leaks.:) I put the less mileage between overhauls down to the bore getting 'washed' a bit more by fuel/air mixture.
     
    Last edited: Jan 4, 2017
  15. saabman

    saabman Well-Known Member

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    I might be mistaken but I thought the EFi engines ended up with more trouble due to leaner mixtures causing higher temperatures.

    I could be totally wrong there. My current kombi build WILL be EFi

    Col yes I also had wondered about the adjusting screws been a problem .
     
  16. David H

    David H Well-Known Member

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    Hi Saabman,
    Not my experience. In fact quite the opposite. Never lean, plugs look perfect on every service (over 100 of them) but I do think it always comes down to a good Air Flow Meter to inform the computer making the injection decisions & of course clean injectors.
    With any air /fuel mixture it's best to have them burn at the optimum. Too much fuel burns hot & 'washes' the bore of lubricating oil....too lean burns exhaust valves because combustion is too hot. Both those excess temps move up into the head where it has to cope. http://forums.kombiclub.com/threads/fuel-injection-sopru-camper-76.54501/
    Cheers,
    David H
     
    Last edited: Jan 4, 2017
  17. Grantus

    Grantus Well-Known Member

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    Why would I want to do that, when I pay a very skilled mechanic, (who unlike me, actually knows what he is doing), to get his hands dirty instead? :rolleyes:

    I don't bark at strangers either, if I have a dog to bark for me.....;)

    :p
     
  18. Wayne murray

    Wayne murray Well-Known Member

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    You have left the door wide open on that Grantus o_O but I won't say anymore!
     
  19. cbus

    cbus Well-Known Member

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    [QUOTE="Grantus, post: 597683, member: 2180"
    I don't bark at strangers either, if I have a dog to bark for me.....;)
    :p[/QUOTE]

    I dont bark either.
    But not adverse to a warning shot . proximity variable :)
     
  20. Grantus

    Grantus Well-Known Member

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    Location:
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    Now I'm confused Wayne? :confused:

    I admit, I've never adjusted valves..........:rolleyes:
     

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