Posted to Technical Theory Forum on 8/14/2013
Hydraulic Lifter, Operation and Failure
I have mostly had experience with overhead cam engines so I
am not very familiar with hydraulic lifters / cam in block
engines and wanted to clarify some things about them.
Basically from what I understand the lifter rides on the cam
lobe and transfers the lifting motion of the cam to the
pushrod, and on to the valve. The two types of lifters I've
seen are solid (with manual clearance adjustment) and
hydraulic (which adjust clearance on the fly).
From what I understand the clearance in the valvetrain
changes because the block and head expand as the engine
warms up which causes the camshaft and rocker to get further
apart and would change the valve lift.
With solid lifters you would adjust the valves so there is
some clearance when they are cold that is taken up when the
engine warms. If adjusted too tightly, the valves could be
held open on the base circle of the cam and never close
completely, which is likely to cause misfiring due to lack
of compression, if adjusted too loosely, they are likely to
be very noisy because of the impact that occurs as the slack
is taken up, also with a loss of cam lift, and reduced
Am I correct on those points?
So with hydraulic lifters it seems that they run in lifter
bores which are fed by a common oil gallery which is toward
the end of the oiling system of the engine, so low oil
pressure or volume problems show up as lifter noise on these
The basic idea with the hydraulic lifters seems to be that
they have an oil feed hole that allows the gallery to
pressurize the body of the lifter and expand it when the
lifter is down, and then as the cam starts lifting it a
checkvalve closes and prevents the oil from draining out,
making the lifter turn "solid" as it works against valve
spring pressure to open the valve.
The clearance that increases as the engine warms up is taken
up filling the lifter more and more. The lifter also drains
down slowly as oil bleeds through the .0001 clearance
between the body and plunger, as the valve spring tries to
crush it down so if the vehicle is parked and left to cool
off overnight the valves adjust so the clearance is proper
for the cold engine start the next day.
That's how it works as I understand it, now on to
malfunction. Malfunctioning lifters are often noisy,
sometimes referred to as "collapsed", which I take to mean
the check valve is not working and the lifter is not holding
the oil or not filling. Maybe there is no oil pressure there
to fill it? If the lifter collapses isn't that the same as a
loosely adjusted valve? there will be a loss of cam lift?
Another failure referred to as a "stuck lifter" I think
means that the lifter plunger and body has seized together
and no longer adjusts to fill the slack correctly, so you
could have a lifter that is "pumped up" to the level of a
hot engine and stuck there which then holds a valve slightly
open when the engine cools off. Or if the lifter stuck at
the cold expansion then you would get that tapping noise
that doesn't go away after warming up and maybe a slight
loss of cam lift?
Another issue is with valve float - at high rpms with worn
out valve springs, the lifters could pump up too much
because the valve spring has weakened too much and can't
keep the lifter down - a competition between the oil
pressure trying to expand and take the clearance up and the
valve spring trying to keep the lifter against the cam.
If there was a lifter problem affecting the cylinder would
you definitely see it in the compression reading? I would
think that a cylinder would still seal properly but might
not pack as much air in with reduced valve lift?
Am I understanding this correctly or have I got a big
Ann Arbor, Michigan, USA
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