Date: Thu, 17 Jun 2010 19:51:49 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: Last gasp: low compression exhaust valve can't pass smog
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Hi Roland,
Even if you can get it through a smog check or get a waver, it's not very
good to drive it like that.
It wastes fuel, and in general helps increase wear on the engine some.
what I would do is a nice solid valve job and new headgaskets on that one
side.
You're right, AMC heads have lower quality valves. 'The Really Cool/Good'
head job with new heads is AMC heads with better valves than the come with.
I'd figure on new exhaust valves at least on that head.
some of my experiences/thoughts on waterboxer heads :
Some say the original VW ones tend to crack. I have seen a few cracked
ones, but nothing chronic.
I prefer the VW heads with a fresh valve job and they fit better too.....
I have seen several AMC heads that pinch the outer water gasket, causing
them to leak, or blow out easily with an overheating incident. It's
important to check that gap there .....put head on engine block without the
rubber gasket, measure that gap ...make sure it's the same all the way
around ( I have one AMC head that fits very tilted, pinching the gasket
badly on one end ) ...
And I go for half a millimeter compression on the rubber gasket ,
something like that. I'd have to check my notes. I just measure the
thickness of the rubber gasket, then check the distance between head and
block and see if it makes sense or seems right. Seems that half a mm
compression was about right.
on that gap -
too little and it won't be squeezed enough to seal well, too tight and it
will pinch and split sooner than it ever should. Most people and shops just
slap on the head as far as I know ...
Meticulous workmanship pays off.
there really isn't a lot of penalty in doing one side at a time ....some
labor on the exhaust system might be repeated doing one side, then months
later the other , but not badly.
adjusting the bottom of the heads for that gap is difficult. If the gap is
too small, then it's easy to mill a little off the bottom of the
head....however there is still a problem for most machine shops.
Machine shops reference off the top of the head when resurfacing the bottom
of it,
but for a waterboxer that is not the reference point..............it's where
the heads sit on top of the barrels...in the combustion chambers ....machine
shops do not normally have a way to reference from there ....their machining
needs to be parallel to the combustion chamber metal ring places..
and the right distance from there. So tricky to do if it's not in the
ballpark of what is right about compressing that outer rubber gasket. I
trust VW heads much more than AMC heads in that regard - that rubber gasket
fitment/compression.
Scott
www.turbovans.com
----- Original Message -----
From: "Roland" <syncronicity1@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, June 17, 2010 4:33 PM
Subject: Last gasp: low compression exhaust valve can't pass smog
> Ok,
>
> So, again trudged to the smog station after various lower cost attempts
> (California).
> - High HC at idle, 270 PPM and more. The max allowed is 120.
> - HC at 2500 RPM is fine (because of course the compression happens at
> that
> speed).
>
> Apparent root cause: exhaust valve, cylinder #4
> - compression is in the 85 lb range, vs the others in the 130-145 lb
> range.
> - leakdown test said "84% out of exhaust".
> - I can see / feel/ hear an occasional miss at idle (I think).
> - So it seems pretty clear that lower compression / miss will cause high
> HC.
> - It runs fine, last weekend just did a 270 mile trip.
> - Root cause of bad valve? Don't really know, the engine has AMC heads,
> vehicle has over 200K miles, so obviously the heads were redone at some
> point. About 4 years ago I blew the water pump on the freeway, didn't
> turn
> it off right away, but also passed smog after that event. Maybe just more
> time caused the valve to go bad. But I believe I've also read that the
> valves in AMC head go bad faster than expected. Also, the upper bolt is
> missing from where the exhaust manifold / header attaches to #4, but I
> can't
> feel any air/exhaust flow -- maybe the lower bolt is holding the gasket.
>
> Potential paths:
> - get the left side head replaced, not sure I am willing to do it myself,
> tough to get at, seems like many peculiarities on this one, I may screw
> something up. ( I would if I still had my Austin Healey). The 2 shops I
> spoke with would use a new head, from their estimates it must be many
> hours
> of labor.
> - go to the California Carb appeals to the referee. I have the papework,
> I
> think I've spent enough $ that they may give me a 1 time waiver. (i.e.
> delay facing the problem, but I am planning some trips, I don't want this
> engine to go bad this summer.).
> - get both heads replaced while we are at it? (I don't have all the
> records, but the bottom end probably has 200K + miles on it.)
> - costs just go up from there.
>
> Anybody have any ideas at all high I could get past the smog test without
> replacing the head?
>
> Thanks!
> Roland
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