Re: Noisy hydraulic tappet? (me too)

["Fred Munro" <munrof@isys.ca>]

-----Original Message-----
From: Matt Howe <ismhowe@state.me.us>
Date: Monday, February 02, 1998 1:27 PM
Subject: Re: Noisy hydraulic tappet? (me too)



>I've noticed a "ticking" coming from my valve cover that may be this, but
it
>does not go away at all, (at least I haven't noticed, I can't hear the
sound
>with the hood down) Any ideas as to what this might be?
>
>-Matt
>


Matt;

    As the engine heats up, the components in the valve train (particularly
the valve stems) expand. In the "old days" of solid lifters, the expansion
was compensated by setting an adjustable clearance between the lifter and
the cam lobe or the lifter and the valve stem. Hydraulic lifters solved the
adjustment problem. They are collapsed at rest and expand against the valve
train components as the oil pressure comes up. The lifters are designed to
maintain a zero clearance against the cam lobes at design oil pressure. As
the components heat up, the lifters shrink a bit in height while continuing
to run at zero clearance against the cam lobe. This, of course, makes for a
quieter engine.
    If a lifter can't expand completely (dirty or worn internals, clogged
oil passage, low oil pressure, etc.) there is clearance between the cam lobe
and the lifter and you hear the characteristic tapping sound.
    The ticking sound you hear may be a bad lifter.

HTH

Fred Munro
'91 200q  245k km