VANAGON archives -- January 2002, week 4 (#437)

Date: Sat, 26 Jan 2002 17:54:40 -0500 Reply-To: "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM> Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com> From: "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM> Organization: Bulley-Hewlett Subject: Re: Aircooled lifter noise In-Reply-To: <20020126.124244.-329675.9.wilden1@juno.com> Content-Type: text/plain; charset="US-ASCII"

Perhaps you have confused my assertion.

Jake has asserted that un-adjusted valves are a cause of valve seat failure because the valve "slams against the seat".

I am saying that (while valve seats are a common cause of problems) slack valves that clatter are NOT slamming on the seats, the rocker arms are (fairly harmlessly) clattering against the valve tips.

There is no such thing as the seats "hammering back" into the heads or "slamming" on the seats. When you observe the seat declined into the intake or exhaust port, it is due exclusively to overheating, not to slack in the valve train. Most loosened seats are due to the same reason.

The valves transfer their resident heat to the heads primarily through the seat (secondarily through the valve guide). When you overheat an air cooled motor, the failure almost un-failingly entails exceeding the heat-sink capacity of the alloy surrounding the valve seat. If the alloy in that area can't shed heat fast enough, it softens, and the valve springs pull the valve and seat into the port as the cam lobe recedes.

Then, during the "valve closed" cycle, more heat is transferred, further softening the alloy, and the spring pulls the seat deeper on successive closings of the valve. It happens rather silently, since the valve is coming to rest as it normally would, until the seat recedes far enough that the valve can no longer seat, and exhaust gas spills around the valve, super-heating the port until the compression drops to the point that combustion cannot continue in that cylinder.

Exhaust valve seats are more prone to failure n this way because they are in the business of transferring more heat than intake valves.

Even if there is slack in the valve train when the eccentric portion of the cam has the valves at rest, there is no "slamming" the valves on closure. During the period that cam moves to closes the valve, all slack in the valve train is removed due to spring tension, and the valve closes normally, though perhaps earlier than it should. Any shock action (clatter) in the valve train takes place as the eccentric portion of the cam rotates to OPEN the valve, suddenly closing the slack space between the rocker arm tip and the valve tip. Does this make sense now?

For those who are interested in more than anecdotal folk-motor wisdom from necromancing your way through the entrails of failed motors, there is a fantastic book you *might* find at your local library that details EVERYTHING you might want to know about your engine.

It covers every aspect of every type of internal combustion engine, including air-cooled engines which were apparently much more pervasive then than now. Complex problems at the close of each chapter test your learning. It was a 4th year primer for M.E. students, but has some good "on the street" knowledge, if you are willing to wade through the engineering school stuff.

From historic, walkable Mount Olive, NC,

G. Matthew Bulley Bulley-Hewlett Corporate Communications Business: www.bulley-hewlett.com Alliance: www.ntara.com Home: www.MountOliveNC.info

-----Original Message----- From: Stan Wilder [mailto:wilden1@juno.com] Sent: Saturday, January 26, 2002 1:43 PM To: gmbulley@BULLEY-HEWLETT.COM Cc: vanagon@GERRY.VANAGON.COM Subject: Re: Aircooled lifter noise

G. Matthew Bulley wrote: Jake Raby and I have a difference of opinion on this matter of un-adjusted valve clatter, and I think I should point that out. It is his assertion that valve clatter is (at least in part) the sound of the valve slamming closed against the seat, and this in turn is partly to blame for valve seat destruction or loosening. I disagree. ----------------------------- Stan Wilder replies: After restoring several Westfalia and building many engines I have to agree with Jake. After you've done the homegrown cleaning procedures and adjusted the lifters and not gotten the desired silence. Its best to do a compression test or cylinder leak down test. In almost every situation where the homegrown cleaning and simple adjustment procedures failed to silence the valve noise I found bad seats. Not necessarily dropped but loose or getting ready to drop. In rare situations I've gotten the lifters to quieten by removing and reinstalling the rock arm assemblies (removed for inspection of adjusting screws and valve stem contact areas.) I've had and run engines with loose seats that just occasionally lost enough compression to make the engine hard to start. Some of them have run as much as 10K with this near fatal condition. Ultimately the seat either dropped enough to keep the valve open also denting the piston top, worst still I've had loose seats and the seats have hammered back into the head leaving the seat floating in the port. I've seen intake and exhaust valves with this condition. (pictures by request). If your intakes drop out or hammer back I'd blame that on poor rebuilding. If you Exhaust seats drop I'd blame that on long use and overheating. Cracks are caused by a several problems with the foremost being heat then poor welding repairs. I've gotten 140 K out of both VW OEM heads and AMC (made in Spain) heads so the valve dropping problem can be attributed mostly to abuse of overheating. Its not as common as most of us are led to believe.

Stan Wilder

On Sat, 26 Jan 2002 11:25:28 -0500 "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM> > I propose that valve clatter is produced solely as the slack in the > valve train is eliminated by the lobe of the cam coming around and > slamming the rocker arm tip against the tip of the valve. Having > slack > in the distance between the rocker arm tip and the valve does NOT > slam > the valve CLOSED (as Jake asserts), because the entire valve train > is > under spring load as the cam lobe retreats, and therefore there is > no > sudden slam, jus the normal valve closing. Think about it. > > Either way, well-adjusted valves are important to longevity and > efficiency for your motor, so let's get them right. > > If your valves are still noisy after a few miles on the road, I'd > suggest a chemical treatment to free up the sticky lifters PRIOR to > messing with the adjustment. Sometimes crud fouls the hydraulic > lifters. > I wrote a LENGTHY description of how to do this back in 1998 or > thereabouts, and I am sure you can find it in the archive. > > In essence, you are going to swap your oil out for a 50/50 mix of > 10-w30 > and ATF transmission fluid and a new filter; high-idle it in the > driveway for 30 minutes (do NOT drive it). You could also include > an > entire quart of MMO don't overfill. > > During the high idle, the clatter will go away, and you will smile, > but > keep it at high-idle for a full :30 minutes to continue the clean > up. > Swap the filter and oil to whatever you normally use. Drive it for > 100-300 miles. Change oil and filter again. > > *IF* the clatter doesn't go away, readjust the valves. As for the > great > "preload" debate, I've used 2 turns, 1 turn, 1/2 turn, and no > preload. I > have no opinion other than to say that 2 turns is (IMHO) excessive. > > Last note, some say that MANN or VW OEM filters are best to solve > this > issue, particularly for WATER cooled flat fours, as they have > better > flow characteristics. I won't even go there. They may be right, but > I > can't justify the $6.00 cost. I don't share the philosophy that oil > has > to be sanitized to be clean enough to prevent wear, and I don't > believe > that *some* cheaper filters are just fine if you keep your oil > changed > regularly. > > I use Fram PH8A, which is a MUCH larger filter than the OEM, and > has > been my filter of choice for type 4's since the mid eighties. Buy > the > "extra guard" if your FLAPS has it. > > Telling you this though is like telling the Mother's Against Drunk > Driving list that I put bourbon in my kid's night-time feeding so > that > they will sleep well. Flame all you want, you won't get me to > switch. > (from the bourbon, or the Fram) > > Happy motoring. > > From historic, walkable Mount Olive, NC, > > G. Matthew Bulley > Bulley-Hewlett > Corporate Communications > Business: www.bulley-hewlett.com > Alliance: www.ntara.com > Home: www.MountOliveNC.info > ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/.

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