Date: Thu, 8 Mar 2012 02:05:45 -0800
Reply-To: HotelWestfalia <zolo@FOXINTERNET.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: HotelWestfalia <zolo@FOXINTERNET.NET>
Subject: Re: How lifters work and Two turns to set valves?
In-Reply-To: <4f58447f.3221340a.3486.27ed@mx.google.com>
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David,
Thank you very much for the detailed explanation. Now it makes sense. This
is exactly what I needed to read.
Zoltan
----- Original Message -----
From: "David Beierl" <dbeierl@attglobal.net>
To: "HotelWestfalia" <zolo@FOXINTERNET.NET>
Cc: <vanagon@GERRY.VANAGON.COM>
Sent: Wednesday, March 07, 2012 9:32 PM
Subject: How lifters work and Two turns to set valves?
> At 09:10 PM 3/7/2012, HotelWestfalia wrote:
>>But how do I know, the valves open enough or they close fully? Somehow it
>>is foggy for me why to do two turns, or any for that matter.
>
> A hydraulic lifter has a piston in a very closely fitted cylinder. It is
> meant to have the space under the piston always full of oil. If it isn't,
> the lifter is soft and will not open its valve properly until it gets the
> air worked out.
>
> There's a weak spring under the piston, and if nothing stops it the spring
> pulls oil in through a check valve as it extends the piston fairly
> rapidly. However the only way to retract the piston is by applying strong
> steady pressure which forces oil very slowly out through the gap between
> piston and cylinder.
>
> Now think about the valve train. Camshaft pushes on the lifters, lifters
> push on the pushrods, pushrods push on the rocker arms which reverse the
> direction of motion and push on the valve stems, with strong resistance
> from the valve springs.
>
> The springs push back and are strong enough to slowly force the lifter
> piston back until the valve is closed. At this point the spring has no
> more travel so it can't push the piston back any farther. You adjust the
> rocker arm adjusters so that this point happens somewhere in the middle of
> the piston's possible travel.
>
> At that point, in theory, you're finished. The valves will maintain
> correct adjustment at all temperatures, operating and wear conditions for
> the life of the engine. Any time a clearance opens up in the valve train,
> the spring under the piston quickly extends it a little more, taking up
> the slack. *The amount that it can do this is the amount of the "preload"
> that you cranked in when you set things up originally. When that amount
> gets used up the lifter cannot extend itself any farther.*
>
> Any time the clearance becomes too tight and doesn't allow the valve to
> close fully, the valve spring shoves the piston slowly back into its bore
> until clearance is correct again. This action occurs as the engine warms
> up but also all the time, because any time a valve is opened its spring
> will be trying to force the piston into its bore, thus opening up the
> clearances. It can't do it much because the valve doesn't stay open long,
> but it does a little. This tiny clearance is taken up by the extending
> spring, and round and round we go. *If the piston bottoms out (too much
> "preload" then it can't allow the valve to close entirely.*
>
> As the valve train wears the parts become shorter and the correct position
> of the lifter piston gradually extends until the piston is fully extended.
> At that point it can no longer perform its function and it is now
> operating like an expensive and very slightly faulty solid lifter.
>
> The trouble we have with our WBX lifters is that (effectively) the valve
> springs aren't strong enough to keep them properly (and quickly enough)
> compressed, so they tend to not let the valves fully seat. That wrecks
> your compression.
>
> So you set the Type 4 lifters to .006 clearance cold, right? As the
> engine warms up that clearance decreases to somewhere near zero. Every n
> thousand miles you set them again because the clearances open up from wear
> and the valves start tapping.
>
> You can do the same thing with the hydraulic lifter. Treat it like a
> solid and give it .006 cold, and readjust on a similar schedule to the
> Type 4 engines.
>
> Or set it up touching, depending on the lifter to compress that .006 as
> the engine warms. You still have to adjust it as the clearances open from
> wear.
>
> Or at some reduced "preload" - but since the extending spring is not very
> strong, I frankly doubt if it makes any practical difference other than
> reducing the total amount of wear that the lifter can compensate for. I
> don't know that for certain, though.
>
> I would love to see someone take an engine that was losing compression
> because of the lifters and put stronger valve springs in it. I would
> *really* like to know what effect that has. But in the mean time,
> treating them like solid lifters works, at the expense of having
> to...treat them like solid lifters.
>
> Yours,
> David
>
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