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  1. #1
    Frank.de.Kleuver's Avatar
    Frank.de.Kleuver is offline Tyre Kicker
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    Pumped up lifters due to (for example) high revving

    Hi Guys,

    I'm in the process of learning things regarding valve to piston clearance measurements when using hydraulic lifters.

    As I understand one should measure the clearance by using a solid lifter and adjust for zero lash (when possible) or to using a solid lifter with your actual lifter pre-load correction.

    Either way one should regard a clearance of approx .100" for the inlet valve. Some say an absolute minimum of .050" could be ok to.

    This clearance is for: expanding components due to heat, valve bounce and pump up action when revving the engine to high.

    I hope I'm correct up to now.

    But the following thing is bothering me because I don't understand this. How does a lifter looks like in a pumped up state due to high revving on the end of the opening movement of the inlet valve (maximum lift)?

    This in three situations:
    1- Standard lifter
    2- High revving lifter
    3- Roads Bleed down lifter

    In case of lifter C one should take into account a additional clearance of not 1.6 (rocker ration) times the pre-load but als times the pre-load with .030" for the small plunger in the middle.

    I made a drawing to explain things.

    Many thanks for your help

    Frank

    Pumped up lifters.jpg
    Don't drive faster than your angle can fly - See more links of my engine buidling at http://www.flickr.com/photos/roverv8/sets/

  2. #2
    russell_ram2 is offline Chief Bottle Washer and Tea Boy
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    Frank,

    not sure quite what your point is, but you are correct, your lifter can only 'pump up' until it uses up it's pre-load (0.040 in your picture). Valve will close up to piston clearance by this times rocker ratio. However, as you also say, this is complicated by expansion of the hot engine components. In the Rover case, of course, the aluminium block & heads expand at twice the rate of the steel valves and pushrods: the valves though are probably 5 times the temp of the rest of the engine so it's all a bit tricky.

    Of course, if your lifters do pump up, then they hold the valve open slightly giving you a self imposed rev limiting effect.

    Russ

  3. #3
    Frank.de.Kleuver's Avatar
    Frank.de.Kleuver is offline Tyre Kicker
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    Hi Russ,

    So you say Liffter setup B?

    If the lifters keep the valves from closing completely during pump up due to high revving the pre load is used up and why are these valve not closing? Is this because of the additional length of the hot valves?

    I'm try to find out why one should maintain such a high clearance .100" when the totall expantion due to heat is not that high. I don't know what lash is used when using solid lifters.

    What are your thought about a safe valve-piston clearance of < .100" ?

    Kind regards,

    Frank
    Don't drive faster than your angle can fly - See more links of my engine buidling at http://www.flickr.com/photos/roverv8/sets/

  4. #4
    wilf's Avatar
    wilf is offline Banned for owning a STAG!!! Pit Babe Magnet
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    A "pumped up" lifter would be "C" in your diagrams. That is what Russell was saying.

    It is not just thermal expansion you have to take account of for valve - piston clearance. Conrods stretch at high rpms.............
    Crendon has left the building................bright yellow Stag has landed.

  5. #5
    Frank.de.Kleuver's Avatar
    Frank.de.Kleuver is offline Tyre Kicker
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    If it would be lifter C than that would mean the pushrod would be pushed up 1 + 0.8 mm (preload + middle pluncher movement)? That's a lot.

    Frank
    Don't drive faster than your angle can fly - See more links of my engine buidling at http://www.flickr.com/photos/roverv8/sets/

  6. #6
    wilf's Avatar
    wilf is offline Banned for owning a STAG!!! Pit Babe Magnet
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    It can only "Pump up" by the 40 thou preload, as Russell said.
    Crendon has left the building................bright yellow Stag has landed.

  7. #7
    russell_ram2 is offline Chief Bottle Washer and Tea Boy
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    Frank / Wilf,

    I think picture B is correct. The 'small plunger' in the middle Frank refers to (and has moved upwards) in picture C is merely a cup that allows the same lifter to be used for different rod diameters by only chamging that small part - I don't belive it is part of the operating mechanism as such.

    "If the lifters keep the valves from closing completely during pump up due to high revving the pre load is used up and why are these valve not closing? Is this because of the additional length of the hot valves?"

    The (cylinder head) valves are closed when the valvetrain i sat rest with 40 thou pre-load in the lifter. If the lifter expands by 40 thou due to pump up then the valve train is now 40thou too long and so must hold the (head) valve open independent of/excluding expansion effects.


    "What are your thought about a safe valve-piston clearance of < .100" ?"

    I think you'll find that this is the unversal number theat everyone uses and I'm pretty sure it's just an empirical number that has been proven to work/be safe over the years. Even then, valves will hit pistons at extremes of revs when springs/lifters ect fail to restrain the motion of the valves in the manner which the camshaft tries to prescribe. I'm sure you could run closer than that for individual builds if you had sufficient data on which to base your revised clearance.

  8. #8
    russell_ram2 is offline Chief Bottle Washer and Tea Boy
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    ps. Don't waste your money on Rhoads bleed downs - you'll be stripping the engine to fix the idle rattle soon after.

  9. #9
    Frank.de.Kleuver's Avatar
    Frank.de.Kleuver is offline Tyre Kicker
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    I know a engine builder who gave me an absolute minimum of 40 thou for p-v clearance for a road/track day kind of car with a relative mild cam (crower 50232).

    PS I run roads lifters in both my Super Seven and RAM Cobra and I can't here the rattling noise because I have the exhausts to my left and right in the open car I think they do a good job in my lightweight seven (700kg). The Cobra pulls a bit better from standstill. But maybe my hearings is gone
    Don't drive faster than your angle can fly - See more links of my engine buidling at http://www.flickr.com/photos/roverv8/sets/

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