PCV valve rattle in 327 Chevy
Dogbite
vacuum line into the valve cover without the pcv to see if that eliminates
the noise?
Bob
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"Wayne" <nob...@nowhere.com> wrote in message
news:wpZ05.19$G3.170...@news.frii.net...
> Had the 327 rebuilt in my '67 Corvette. It is the L79 350HP engine. Went
> with an Isky split duration cam, 270 int 280 exh advertised duration, 221
> int/ 232 exh @ 0.050, 108 lobe centerline angle. Also went with zero gap
> rings.
>
> Engine runs well, but there is an infernal rattling sound from the PCV
> valve. Doesn't go away until you get above 2000RPM. Sometimes goes away
> after warm-up, but not always. Replaced the valve. No change. Both old
> valve and new seem to be functioning OK when given the shake test and the
> blows-only-one-way test. Have also turned idle up to 1000RPM with no
> change.
>
> I think the cause is reduced vacuum due to tight lobe centers coupled with
> very little blowby and therefore low crankcase pressure due to the zero
gap
> rings.
>
> Many of you would just run a breather cap, but I really want to keep the
> original valve covers which don't have breather holes. Any suggestions?
>
> - Wayne
>
>
Wayne
vacuum advance, which probably is not the best place to measure but was the
first spot I found with little time to do this. At idle, I measured 8-9
inches vacuum. At 1500RPM, measured 14 inches. This seems like it should
be OK, but the valve still rattles. It makes me think that maybe the
breather tube that connects from the air cleaner to the intake is not
working. There is some canister thing in the valley that I think is
connected with the PCV as well (forgive me, I didn't put this together
myself and don't know what everything is for).
The rattling of the valve is worse when driving around than when sitting
still. That is, 2000RPM going down the road is much noisier than 2000RPM
sitting still.
When I disconnected vacuum from the PCV and plugged the hose, the engine
wanted to die. Vacuum at the advance hose dropped to 5 inches and the
engine barely idled.
- Wayne
Dogbite <nos...@sasquatch.com> wrote in message
news:8i2onk$5rd$1...@news.sasquatch.com...
Dogbite
place. Try from the manifold, also, Where does the pcv plug into? Usually,
the pvc goes into the base of the carb or manifold right under the carb and
there may be another hose from the air cleaner to a valve cover. I'm not
really sure what came on a 67, but on a 65 that's what I had. The idea is
to have full engine vacuum to the pcv.
Bob
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"Wayne" <nob...@nowhere.com> wrote in message
news:vdh15.6$G3.170...@news.frii.net...
Wayne
vacuum advance does not use ported vacuum on a '67, so the readings I got
should be OK.
Another person suggested putting a restriction in the vacuum line to the PCV
on the theory that pulsating vacuum is the cause and this will dampen the
pulses as seen by the valve. I did notice the gauge needle moving when
measuring vacuum at idle.
- Wayne
Dogbite <nos...@sasquatch.com> wrote in message
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Rufus T Firefly
are not compatable?
PCV's have different opening points and allow diffrernt volumes of air to
pass through them depending on the engine they will be installed in. Try
something from a factory engine that has a much wilder cam than you have
now. A softer spring would keep the valve fully open at relatively low
manifold vacuum. One other thought is the breather should have slightly
more resrtiction than the PCV valve so a negative pressure can be maintained
in the crankcase. A wide open breather effectively breaks any vacuum the
PCV is capable of pulling. Valve covers without baffles and wide open
breathers don't work well with a PCV. I've been through this more than a
few times.
--
Mike ( Anti Spam Address )
"Opportunites are spawned from crisis"
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Dogbite
Hmmmm, I wonder if that's what's up with my van.....
Bob
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"Rufus T Firefly" <Ruf...@hknet.org> wrote in message
news:qcL15.26466$hp4.6...@newsread1.prod.itd.earthlink.net...
Wayne
the one I'm running (believe it was 254 at 0.050). Unfoturnately, the LT-1
PCV does not screw into a bung in the oil fill tube like the L79 PCV. So I
will have to make an adapter to try out this idea.
Considered trying to make an adapter out of the L79 PCV by drilling out the
valve, but I'm afraid the valve will just turn in the housing, or even if I
succeed in drilling there will be debris left behind.
There apparently were some early GM PCV's which were serviceable. They had
a case that screwed together, and you could remove the valve and the spring.
Never seen one.
- Wayne
Dogbite <nos...@sasquatch.com> wrote in message
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Dogbite
worked, so if everything is hooked up right in yours, I don't know why it
rattles. I had no idea there were different spring rates for different
motors. I thought they just came in different shapes.
Sorry I can't help you more.
Bob
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"Wayne" <nob...@nowhere.com> wrote in message
news:1wQ15.37$G3.187...@news.frii.net...
Jeremy Cusick
pcv valve checks as good, maybe it's just the nature of the beast and you'll
have to live with it. My $.02... -J
Phil Girlinghouse
Why is the vacuum gauge needle moving when you check vacuum at idle. The
gauge should read a steady amount, not fluctuate. If it fluctuates, you
may have an intake manifold vacuum leak that needs fixing first.
Fluctuating vacuum may be causing the PCV valve to be opening and
closing such that it is loud enough to hear. I would start by tracking
down the manifold vacuum leak.
As you appear to not know a lot about engines (no offense intended
whatsoever....and I could be full of it about this) you may want a buddy
to help you find and fix the leak. There are several methods and
everyone has their preference.
As for the "can" in the lifter valley.....is this the original engine?
If not, the early blocks ( '55 to ???) had the "can" as an oil baffle
that let fumes out and (tried to keep) oil in. This was a leftover from
the old "draft tube" used on early blocks and used a tube that ran from
the back of the engine, down along the passenger-side of the block, just
behind the bellhousing. A tab spot-welded on the tube used one of the
bellhousing bolts to secure it about half way down the length of the
tube. As air passed the bevel-cut tube, it drew fumes through the "can"
and out the tube......an early but crude crankcase ventillation system.
I had 4 or 5 early blocks (265s and 283s) in my '55 Chevy with this
setup. Don't recall exactly when this engine setup went away though.
Hope this helps and please post the cure when ya find it.
Phil
Wayne wrote:
>
> Hose plugs into the base of the carb at the back. Someone told me that the
> vacuum advance does not use ported vacuum on a '67, so the readings I got
> should be OK.
>
> Another person suggested putting a restriction in the vacuum line to the PCV
> on the theory that pulsating vacuum is the cause and this will dampen the
> pulses as seen by the valve. I did notice the gauge needle moving when
> measuring vacuum at idle.
>
> - Wayne
> Dogbite <nos...@sasquatch.com> wrote in message
> news:8i72ld$4cm$1...@news.sasquatch.com...
> > Yeah, the port for vacuum advance is generally timed so that's not the
> best
> > place. Try from the manifold, also, Where does the pcv plug into?
> Usually,
> > the pvc goes into the base of the carb or manifold right under the carb
> and
> > there may be another hose from the air cleaner to a valve cover. I'm not
> > really sure what came on a 67, but on a 65 that's what I had. The idea is
> > to have full engine vacuum to the pcv.
> > Bob
> >
> > --
> > "Bigger, Better, Faster, More!"
> >
> > To email, replace nospam with dogbite.
> > "Wayne" <nob...@nowhere.com> wrote in message
> > news:vdh15.6$G3.170...@news.frii.net...
> > > I did a vacuum measurement today. This is measured at the hose for the
> > > vacuum advance, which probably is not the best place to measure but was
> > the
> > > first spot I found with little time to do this. At idle, I measured 8-9
> > > inches vacuum. At 1500RPM, measured 14 inches. This seems like it
> should
> > > be OK, but the valve still rattles. It makes me think that maybe the
> > > breather tube that connects from the air cleaner to the intake is not
> > > working. There is some canister thing in the valley that I think is
> > > connected with the PCV as well (forgive me, I didn't put this together
> > > myself and don't know what everything is for).
> > >
> > > The rattling of the valve is worse when driving around than when sitting
> > > still. That is, 2000RPM going down the road is much noisier than
> 2000RPM
> > > sitting still.
> > >
> > > When I disconnected vacuum from the PCV and plugged the hose, the engine
> > > wanted to die. Vacuum at the advance hose dropped to 5 inches and the
> > > engine barely idled.
> > >
> > > - Wayne
> > >
> > > Dogbite <nos...@sasquatch.com> wrote in message
> > > news:8i2onk$5rd$1...@news.sasquatch.com...
> > > > What's your vacuum gauge doing at idle? Have you tried just plugging
> > the
> > > > vacuum line into the valve cover without the pcv to see if that
> > eliminates
> > > > the noise?
> > > > Bob
> > > >
> > > > --
> > > > "Bigger, Better, Faster, More!"
> > > >
> > > > To email, replace nospam with dogbite.
> > > > "Wayne" <nob...@nowhere.com> wrote in message
Charles
There is one isn't there . All the fumes you try to vacuum out through the
PCV have to be replaced somewhere. If you have a solid filler cap it needs
to be replaced with one that has a breather in it.
Charles
Phil Girlinghouse <rzt...@email.sps.mot.com> wrote in message
news:3951D501...@email.sps.mot.com...
Wayne
and seems to be working. Strangely, the rattle seems to come and go.
Either it's been better lately or I've gotten used to it.
When I pull the hose off the PCV, it sucks a lot of air and the engine
speeds up.
I kinda thought the pulsating vacuum was from the tight lobe separation on
the cam.
I've heard of spraying something like starting fluid around the edge of the
intake and listening for the idle to change to find a leak. I'm a little
reluctant to shoot flammable ether on a running engine. Any other
suggestions for a suitable, less dangerous fluid?
- Wayne
Charles <cwi...@pld.com> wrote in message
news:gzx45.178$LG1...@newsfeed.slurp.net...
John Laferriere
leaks. It'll cause a slight stumble when it penetrates the leak.
I've had good success in the past with this technique.
You are right, starting fluid sounds very, very bad!
Jim
sufficient for to notice the change in idle speed before it evaporates.
You can also use a piece of tubing like a stethoscope one end next to
your ear and the other as a probe, problem is sometimes valve action
noise will disquise or cover up the hissing sound a small vacuum leak
makes.
Jim