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Thread: Reasoning over Bentley's figures on m30 valve clearance

  1. #1
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    Default Reasoning over Bentley's figures on m30 valve clearance

    Bentley's manual tells the reader that greater valve clearance should be set to HOT engine - .35mm and lesser valve clearance should be set to COLD engine - .30mm...

    I find strangeness in these figures for the reason that everything expands in size with greater temperature - the camshaft becomes a bit wider, so do the rockers, and the eccentrics, and the valves, and everything else in nature...

    The reasoning tells that therefore, HOT engine must exhibit LESSER valve clearance for the reason of supplanted space by the mentioned parts since they are greater in size. That is:

    HOT - .30mm
    COLD - .35mm

  2. #2
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    http://member.rivernet.com.au/btaylo...vesM30E28.html
    this should help you out, but i believe you are right smaller clearances when cold is just stupid

    Germans: Why can't they make everything?

  3. #3
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    Drill a hole in a plate of steel. Heat the plate. Is the hole larger or smaller when it's hot?

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    Default Then i guess the bmw factory must be full of idiots too because they

    also state, .012 cold and .014 thousandths when the engine is warmed up...This motor also doesn't have tappets. It has rocker arms that ride directly on the cams...all this talk of cams expanding etc etc is wonderful except for the fact that the aluminum head that the rocker arm shafts,cams and valve are mounted in grows faster and more when heated than do the steel and cast components... so if you imagine the aluminum head expanding in all directions as it heats up that means the valve seat in the head is going to get closer to the the piston and the rocker shaft is going to get further away from the valve stem.... But rather than argue about what the factory determined a long time ago why don't you set the valves when cold as the factory specifies to .012 inches and then measure the clearance when the engine has warmed up... the factory spec states after the thermostat has opened.



    Quote Originally Posted by rob101
    no obviously someone hasn't had to seat a bearing before heat housing, housing gets bigger.
    Actually its because the cam expands and is on the other side of the pivot (the rocker) thus the gap closes on the follower and tappet side. i am used to working on cars with different rocker setups where the cam is the same side of the pivot as the tappet.


  5. #5
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    Quote Originally Posted by Rustam
    everything expands in size with greater temperature - the camshaft becomes a bit wider, so do the rockers, and the eccentrics, and the valves, and everything else in nature...

    FWIW ... Not ice, one important exception.

  6. #6
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    Quote Originally Posted by Bill R.
    also state, .012 cold and .014 thousandths when the engine is warmed up...This motor also doesn't have tappets. It has rocker arms that ride directly on the cams...all this talk of cams expanding etc etc is wonderful except for the fact that the aluminum head that the rocker arm shafts,cams and valve are mounted in grows faster and more when heated than do the steel and cast components... so if you imagine the aluminum head expanding in all directions as it heats up that means the valve seat in the head is going to get closer to the the piston and the rocker shaft is going to get further away from the valve stem.... But rather than argue about what the factory determined a long time ago why don't you set the valves when cold as the factory specifies to .012 inches and then measure the clearance when the engine has warmed up... the factory spec states after the thermostat has opened.
    I meant to correct myself bill, this was after looking at haynes and realising that 2 workshop manuals can't be wrong, The justification I gave was wrong too, but thats life sometimes your brain just stops working. So no i don't think the BMW factory is full of idiots, if I did I wouldn't be driving one would I? There are cars that have hot clearances that are smaller then cold clearances aren't there? I swear i've seen that somewhere before.

    PS: I have deleted that second post as it is a load of ****, I don't know what the hell was going on with my brain last night none of what i said makes sense lol.
    Last edited by rob101; 02-22-2006 at 01:56 PM.

    Germans: Why can't they make everything?

  7. #7
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    Question Bill R., should i set my valve clearances when the engine (M30 that is) is cold? I've read in a few places that this is the best for an aluminium head otherwise you get all different clearances as the head cools down too quick

    Germans: Why can't they make everything?

  8. #8
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    Quote Originally Posted by iNomis
    FWIW ... Not ice, one important exception.
    expansion of ice is not important in this topic. neither is it pertinent...

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    Quote Originally Posted by SRR2
    Drill a hole in a plate of steel. Heat the plate. Is the hole larger or smaller when it's hot?
    drilling a hole and heating is unnecessary - given that metal expands at higher temperature its quite obvious that the hole will be a bit smaller after heating...

  10. #10
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    Default bmw full of idiots???

    Quote Originally Posted by Bill R.
    also state, .012 cold and .014 thousandths when the engine is warmed up...
    At stake here is not quality of BMW engineers but the quality of Bentley's Mechanic reference for e34... I did find a couple of inconsistencies there.

    Now regarding various rates of expansion of aluminum and steel. The manual distinctly addresses the state of the engine as HOT it does not say "on the way of heating up". So the premise is of having an engine, warmed up to operational state - that is things are warm and expanded maximally. The issue of faster expansion of aluminum is irrelavant - its not what is addressed. Whats addressed now is the state of things after they have finished expanding - that is when the engine is hot.
    Last edited by Rustam; 02-22-2006 at 03:26 PM.

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