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Date:         Tue, 1 Feb 2000 00:03:59 -0600
Reply-To:     John Rodgers <inua@HIWAAY.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Rodgers <inua@HIWAAY.NET>
Subject:      Re: 6 mils of lash...
Comments: To: David Beierl <dbeierl@IBM.NET>
Content-Type: text/plain; charset=us-ascii

David, from what I know about hydraulic valve lifters, you are pretty much right own. Most of my experience is with aircraft engines and they work the same way. I'm not so sure I agree with all the rhetoric about some engines having lifter problems and some not however. I know there are thousands of horizontally opposed piston aircraft engines out there all running hydraulic lifters. If I recall correctly...and its been a long time since I went through this....there is a basic "lash" setup clearance for engines that have had the valve ttrain worked on or had lifters replaced. Once that clearance is set, proper operation of the lifter piston inside is all that is needed for the valve train clearance to adjust itself to zero clearance.

As for horizontal operation being a problem, I wonder. Witness the horizontal aircraft engine. They don't have air entrapment problems with the lifters.

John Rodgers 88 GL Driver

David Beierl wrote:

> At 02:45 PM 1/31/2000 -0800, Mike Miller wrote: > >Please keep this on the list. I don't understand hydraulic lifters after > >years of thinking that I did. I hoping to learn something from these > >exchanges. > > The "barrel type" hydraulic lifter as used in the Vanagon has four basic > parts: A cylinder, a springloaded piston, a check valve, and a pushrod > socket. It has the obvious major function of transmitting motion from the > cam to the pushrod; it also supplies oil to the hollow pushrod to lubricate > and/or cool the valve stem and valve train. It is designed to (fairly) > rapidly elongate if there is any slack in the valve train, and to very > slowly shorten if the valves aren't closing fully. > > Here's how: The cylinder is the outer body of the lifter. It's solid at > the bottom, open at the top (toward the pushrod) and has a hole and > machined ring in the side that lets pressurised oil from the gallery into > the inside of the lifter at all travel positions. > > The piston is is inside, sitting atop a spring. It has two peculiarities: > there is a ball check valve in the top which allows oil to get into the > bottom of the lifter but not out; and it is very precisely fitted to the > cylinder so that oil can *very slowly* leak out around the sides. > > Resting atop the piston is the pushrod seat, and there's a circlip to keep > the whole assembly together. The seat has a hole in the middle which > matches the hole in the end of the pushrod, and pressurised oil constantly > flows through this into the head, and then back through the pushrod tubes > to the sump. > > If you leave a lifter alone the spring will extend and shove the piston up, > in turn shoving the pushrod seat up until it hits the circlip and has to > stop. If the lifter is immersed in oil at this time, oil will be sucked > through the check valve into the chamber below the piston, and be trapped > there. If you now try to push the piston down again, it acts roughly like > a solid bar; the oil trapped under the piston prevents it from > descending. If you continue pushing strongly, the piston will very very > slowly descend as oil leaks out around the sides. When you're assembling > lifters in the shop you use a cutoff piece of pushrod and a vise to slowly > collapse the assembly far enough to get the circlip in. > > In the engine, again assuming that the gallery is full of oil, the lifter > will expand and suck in oil until it takes up all the clearance btw lifter, > pushrod, rocker, and valve. It will push against the valve with the > strength of the internal spring, and the valve will push back with the > strength of the valve spring. The valve spring should be strong enough to > overpower the lifter spring, and the valve will remain closed. > > When you operate the engine, if any slack develops in the valve train, the > lifter expands to take it up. Or, if the clearances change so that the > valve is not quite closing, the valve spring pressure will slowly collapse > the lifter until once again the valve closes completely. > > So you see that in the ordinary way of installing a lifter, you place it in > the engine in the fully extended state, then you take up the slack in the > sysem and then continue to close the adjustment a specified amount. This > forces the valve open, but it gradually closes again and leaves the system > able to adjust itself either longer or shorter as needed. After that you > go away and forget about it forever. It takes care of itself. Whenever > you stop the engine at least one of the valves will be open which will > gradually collapse that lifter, but it will pump up again as soon as you > run the engine. Because of the horizontal position of our lifters they > have trouble purging air bubbles, which is why it's important to use an oil > filter that prevents oil from draining back out of the galleries -- you > want that oil available instantly to fill whatever lifter collapsed overnight. > > That's how it 'sposed to work. If a lifter gets dirty, of course, it will > stick and not adjust itself properly -- but some Vgon engines with new > everything in the valve train are not working properly. You have to adjust > them so the lifters are really fully extended, or they kill the > compression. Nobody so far has jumped up with a precise explanation, but > the fact is demonstrable. Come to Providence if you want to see it > happen. I have my theories about this, but they're not proved (or > disproved) yet. > > Does that help? > david > David Beierl - Providence, RI > http://pws.prserv.net/synergy/Vanagon/ > '84 Westy "Dutiful Passage" > '85 GL "Poor Relation"


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