Date: Fri, 4 Jul 2003 09:01:58 -0500
Reply-To: John Rodgers <j_rodgers@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <j_rodgers@CHARTER.NET>
Subject: Re: Bad intake valve @ 30,000 miles????
Content-Type: text/plain; charset=us-ascii; format=flowed
Dennis,
Speaking of lapping the valve to the seat, I don't think there are but a
handful of shops that go to that trouble. That's to bad, too. It is time
consuming, but it is the ONLY way to get that final perfect fit. I was
taught in Aircraft Mechanic school, and also practiced the procedure in
engine overhaul work later, to grind the valves per spec, then using a
special lapping tool - basicly a straight stick with a suction cup on
the end, apply valve grinding compound to the valve face, drop into the
valve guide so the valve vace met the seat, stick the lapping tool to
the face of the valve, then rotate the lapping tool back and forth, lift
the valve and rotate it 120 degrees, drop it back to the seat then work
the tool back and forth again. If the seat and the valve face were well
mated in the grinding process, the lapping process would leave a
non-shiny band in the center of the valve face and the center of the
seat. You could tell immediately if the grinding needed to be redone or
the valve and/or seat needed to be replaced. The lapping would be first
done with a coarse grit, then finished with a very fine grit. When done,
the whole thing was washed off with a solvent, the valve dropped into
the guide with only the weight of the valve holding against the valve
seat. The cylinder/head was then filled with gasoline. If the gasoline
did not leak out, then the fit was acceptable. If it leaked, the more
lapping with the fine grit was required. Doing it this way is the
ultimate in producing the highest quality work .....and performance. It
is something I think builders of high performance machinery do all the
time, but I don't beleive to be common shop practice in ordinary
garages. I know it is done on the high horspower racing aircraft that
use the 1000 plus horsepower big piston engines as a power source.
Regards,
John Rodgers
88 GL Driver
Dennis Haynes wrote:
>Yes, this happens. I doubt VW replaces the valves in the so called new
>heads. The failure may also be caused by improperly machined valve seats
>and not lapping to he valves to the seat.
>
>Dennis
>
>
>-----Original Message-----
>From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf
>Of Sam Payne
>Sent: Thursday, July 03, 2003 10:40 PM
>To: vanagon@GERRY.VANAGON.COM
>Subject: Bad intake valve @ 30,000 miles????
>
>Good Men and Good Women of The List:
>
> I went today to look at a 2.1 for sale, leftover from a conversion.
>It's a VW factory rebuilt engine with 30,000 miles on it, (it's out of
>the
>vehicle, so it was tested cold). The engine looked its age, the seller
>is
>a really nice guy (and a List member!) but the leakdown test showed 10%,
>10%, 7% and 35%. I did the test twice on all cylinders, valves closed @
>TDC etc. and got the same values. I retested the 35% cylinder 4 times
>(really liked the engine), the last time with a tablespoon of 20w-50 oil
>in the cylinder; still 35%. On the low cylinder only I heard obvious
>leakage at the intake manifold. So the leak is through the intake valve.
>I
>tried to backflush possible debris out of the valve with compressed air
>when it was open, but no luck.
> Questions: Neither the seller nor I could understand why the
>INTAKE
>valve would fail after 30,000 miles only. The heads are AMC but the VW
>factory would replace the Spanish valves with German ones, right?
>Wouldn't
>they? Any ideas?
> Also, crankshaft endplay *seemed* excessive (I didn't have a dial
>indicator). Bentley specifies 6 thousandths max, but I could see a tiny
>bit of play and hear a clunk when I pulled. It *felt* more like 10-15
>thou. If it's sloppy I'm not worried about shimming the flywheel but am
>concerned about damage done. ???....
>
> Thanks in advance for the help!
> Sam
>
>
>
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