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Thread: 4BD1 Valve Clearance Adjustment Question

  1. 21st June 2010, 03:34 PM #1
    87County's Avatar
    87County
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    4BD1 Valve Clearance Adjustment Question

    Hi all,

    I've always assumed that the "rule of nine" was the easiest method for setting clearances on a 4 cyl engine with a 1432 firing order...(adjust rocker 1 when 8 is compresssed, then 2 when 7 goes down etc etc)...

    however

    The Isuzu manual describes rotating the motor to cyl 1 tdc, then setting valve nos 1, 2 3 & 6 (numbered from the front), then turn the motor through 360deg (1 turn) and adjust the balance of the rockers

    is there a reason for the method in the manual and what is the preference

    I ask because I think I am getting slightly diiffering clearances with each method ???
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  2. 21st June 2010, 03:54 PM #2
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    Blknight.aus
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    you should get the same clearances using all 3 methods of adjusting a 4 pot

    the rule of 5, which ever pistons valve set is on the rock subtract that from 5 and adjust that cylinder. IE 5-2=3 adjust cylinder 3s valves

    the rule of 9 which ever valve is fully open subtract that from 9 and adjust that valve IE 9-4=5 adjust valve 5.

    the loose valves. Set pot 1 to tdc and adjust all loose valves rotate the crank 360 degrees and adjust all loose valves.

    All should work on the 2.25,tdi and 4bd1 HOWEVER..... only the rule of 5 works for all 4 cylinder engine condfigurations if you try the all the loose valves or the rule of 9 you can wind up messed up on some multi valve or dual cam engines.

    the method in the book works because the phasing of the 4bd1 cam is in 90 degree segments (270 degrees of the cam is circular with no deviation from the given radius) so long as you are precisely on the rock at TDC then 1/2 the valves will be on an active segment of the cam so they will have no slack on them and the other half will be in an inactive section of the cam and will have play.
    Dave

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  3. 21st June 2010, 05:54 PM #3
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    87County
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    thanks Dave, that's a very useful summary of the methods
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