Jeff York wrote:
Wanted some advice on my cylinders. I pulled my heads on my ĢPAS 2180 VW to have them done. Had
one cylinder that seems low on compression and needed to help coil one
so why not have them rebuilt. Lots of carbon on the heads and a few of
the cylinders give me the impression the cylinders have been over washed
from running too rich. <<
I think it boils down to what's more important to you, your time or your
money? And maybe also, how much of a hurry are you in? I'm not sure
what you mean by "washed over" or "coil one", but those cylinders are
reusable, and when the engine's turning 3000 RPM, those scratches will
not be a factor. But ersonally, if I have the heads off of a VW or
Corvair, I either hone the cylinders and re-ring them, or more usually,
simply replace them, as cheap as VW cylinders are.
And I wouldn't trust anybody to do a valve job on a VW (or anything
else). I've told this story before on my web page, but I'll tell it
again. I first met Jim Hill at a KR Gathering, and found he was from my
local area. I visited him at his hangar, where he complained that it
took forever for his "rings to seat" in his KR2. It seems his 2180 ran
like a 3.5 cylinder for the first 50 hours, then smoothed out, but at
100 hours it became a 3 cylinder. He went thru this 3 times, each time
getting a "valve job" from a reputable engine builder, GPASC. I
insisted he let me look at his heads before he sent them off again.
First thing I noticed was that one valve had a lot of slop, with the
seat quite eroded valve guide wallowed out, so I knocked out the guide,
and went to the freezer and got a new valve guide to drive in it's place
(yes, I keep a box of VW guides in my freezer at all times). When I
started grinding the seat, the stone only ground one side, sort of
crescent shaped like my example above! Hmmm.
It became obvious that the valve guide was not coaxial with the seat
when the head was manufactured. I ground the crap out of it until it
sealed, but I couldn't help but wonder what mechanic bozo would do a
"valve job" and not even bother to blue it and lap the valve, which
would have graphically shown the total lack of seal between valve and seat.
What was happening was the valve wouldn't seal, but the side forces on
the valve would eventually elongate the bore in the guide until it did
seat, and it would start running better, usually after about 50 hours.
But then that slop in the seat would allow it to wobble around and wear
the valve face and seat excessively until it needed another valve job at
100 hours. Happened three times, just like clock work.
This was the first time I'd ever seen this phenomenon on a head straight
from the factory, but somebody else had THREE opportunities to notice it
before I did. This is just one of the many reasons nobody touches any of
my cars but me, but don't get me started on the subject of paying
"professionals" to do something for you! The mind-blowing thing about
this is that GPASC would simply replace valve and guide and not re cut
the seat, and send the head back to him for a repeat performance.
I visited Steve's house when I bought N891JF, and his basement shop was
pretty basic. I got the impression that he farmed out all the engine
rebuild work to some local place....at least that's what I'd like to
think. Whoever did that work either had no conscience, or no clue how to
properly rebuild a head. I don't trust any part of my engine to anybody
else, and no, I'm not "open for business" to rebuild heads. Heads are
pretty cheap too, in the grand scheme of things, but I do use top notch
exhaust valves, for a good reason. Wide open airplane usage is hell on
them. A sucked valve will kill an engine in less than a second. Been
there, done that at 7500', got lucky and didn't do much damage to the
plane in the corn field landing.
As Mike Stirewalt mentioned, see some of the many Corvair engine
rebuilds I've done on the Corvair (which are VERY similar to VW's), and
on most of my engines, I run VW pistons and cylinders. See
http://www.n56ml.com/corvair/valvejob.html for a LOT more on this
subject. I could go on forever about this kind of stuff, but I'll spare
you and quit here.....
Mark Langford
m...@n56ml.com
http://www.n56ml.com
Huntsville, AL
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