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Valve clearance...info on motor

Discussion in 'Engine & Transmission' started by Ian and Shelley, May 18, 2019.

  1. Ian and Shelley

    Ian and Shelley Active Member

    Messages:
    143
    Location:
    Umina Beach
    Hi again...

    Been poking around the engine and noticed the info sticker on the fan housing ( Not sure how I haven't taken notice of it before) ..

    Is has a 0.006 valve clearance for inlet and 0.008 for exhaust..


    I have always read elsewhere inlet and exhaust to be the same....

    What should I follow?
    Can anyone confirm these valve settings are good?

    Thanks

    Ian
     

    Attached Files:

  2. tintop

    tintop Well-Known Member

    Messages:
    401
    Location:
    Canberra
    Hi Ian, your 1.8 litre engine came out with sodium filled exhaust valves and were set at 0.2mm (.008) instead of 0.15mm (.006).

    you may or may not still have the sodium filled exhaust valves.

    even without the sodium valves, I always give the exhausts a bit more gap anyway

    Patrick
     
  3. oldman

    oldman Super Moderator Staff Member

    Messages:
    8,293
    Location:
    Avalon Beach NSW
    X 2 regarding exhaust clearance.
    I’ve always run with 6 thou. inlet and 8 thou. exhaust.
    This was on the advice of the engine builder........he knows a LOT more than me, so I listen to him ;)
    I’m running a stock 2 ltr.
    Cheers,
    Mark
     
  4. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,750
    Location:
    Penna, Hobart
    A very loose bit of background on the valve clearance gap as I understand it.

    In theory at operating temperature the gap should be close to 0 thou, but in reality it should have a little give to allow for a slight over heat situation.
    The main reason is to allow the valve to sit on the seat for the maximum period to allow the most heat to dissipate into the seat and head .

    If the gap is too large it reduces the open time and reduces the fuel air mixture (for the intake valve on the intake stroke) and increases the amount residual burnt gases left (on the exhaust valve and exhaust stroke) reducing the efficiency of the engine.

    Too small a gap decreases seat contact time and once the engine warms up the valve may not close fully at all, leaking burnt or still burning fuel, increasing the temp on the edges of the seat and causing them to deteriorate resulting in a burnt valve.

    All up a little loose is better that a little tight, and for the minor bit of efficiency/power loss by setting the exhaust valves(which obviously runs hotter) at the larger gap, regardless of the valve construction, may help to reduce the likely hood a burnt valve. The intake set at the recommended .006 thou.


    Adrian
     
  5. cbus

    cbus Well-Known Member

    Messages:
    11,532
    Location:
    sunshine coast
    Adding to that from a timing perspective.
    Ensuring enough advance to reduce heat on exhaust valve while gasses are rushing past it.
     
    Mr Beckstar likes this.

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