No compression on two cylinders

[al chernoff]

Wow... seems you found a symtom, but the cause is what we all want to know. I
don't know enough to tell you how to proceed, but before you do come down,
maybe a call to Jum Statkus might help. He is very good at giving you
suggestions and offering advise.
Keep us informed.
al

> From: "Walter "
> To: gmcmotorhome
> Subject: Zero compression
> Date: Sat, Apr 15, 2000, 3:41 PM
>
> About three weeks ago I reported a hesitation under load. Emery and I have
> chased this down. We replaced vacuum hoses, put is a new module, new pick
> up coil, substituted his spare coil, cap and rotor for mine. Disconnected
> the EKE knock sensor, replaced the fuel pump, adjusted the timing, switched
> from main to auxiliary tank. Then today I pulled all the plugs and checked
> the compression. 5 cylinders at 120, #5 at 100 and 6 and 8 at zero. I
> reinstalled the plugs one at a time in 6 and 8 and still no compression.
> The #6 plug was fouled (wet and black) when I changed the plugs in CA about
> 1200 miles ago. The new plug is still wet and black. Looks oily. We feel
> that the head gasket must be blown between the two cylinders.
>
> Any suggestions before I drive my six cylinder GMC 70 miles to Albuquerque
> to try out Jim Statkus, who comes highly recommended by Al Chernoff. My
> concern is that we (Emery and I) pull the head and then find it is not a
> head problem
> and we are 70 miles from help. I guess I could have it towed.
>
> Puzzled in Santa Fe, but enjoying the good company and insights of Emery.
>
> Any help or suggestions greatly appreciated.
>
> Walter
> 78 Royale 455

 

[hawk ii]

From: "Walter "
To: gmcmotorhome
Subject: Zero compression
Date: Sat, Apr 15, 2000, 3:41 PM

....today I pulled all the
plugs and checked
the compression. 5 cylinders at 120, #5 at 100 and 6
and 8 at
zero. I
reinstalled the plugs one at a time in 6 and 8 and
still no
compression.
The #6 plug was fouled (wet and black) when I changed
the
plugs in CA about
1200 miles ago. The new plug is still wet and black.
Looks
oily. ......
Puzzled in Santa Fe, but enjoying the good company and

insights of Emery.

Any help or suggestions greatly appreciated.

Perhaps this may shed some light on the problem.

#1. remove #6 and #8 plug
#2. remove plug to the hei cap and coil
so that the HEI does not fire when engine
is cranked
#3. remove dist cap
#4. turn engine over until the rotor points to the
cylinder you wish to check. (just look at how the
dist. would seat to get an idea where that plug
wire would be)
#5 this will assure you that the cylinder is near
TDC and that both values are fully closed
#6 use a air hose and blow into the cylinder spark
plug hole.

results
A. if you hear air out the carb (intake valve
problem - (unlikely - this causes the
engine to backfire or spit out the carb

B. if you hear air out the exhaust(most likely)
- then you need to check if the exhaust
valve is hung by looking for a lot of
(rocker / value stem movement) -
do this by shaking the rocker arm). If not
hung - them most likely burned. (it does
take much of a missing edge to give 0
readings

C. You MAY be able to pickup a blown head
gasket by pressurizing the cylinder at TDC
and listening to the other cylinder hole
with a rudder tube.

P.S. unfortunately I believe you will have to
remove the A/C bracket to remove the even
cylinder valve cover

IT is amazing how are 455's can run fairly well on
less
than 8 cylinders. -

=====
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. ___________ (MY TOYS) (904)672-0571
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[gene]

mine was similar, I was burning oil, ran well , did not smoke, everyone
was sure it was a head and valve problem. I took it to Mondello for new
heads,

us shot is two cyl with broken rings, heads off, now what ?? cost as much
to put them back on as to finish the rebuild. Once the heads are off
there are not many options. I had to buy a new engine,

I recommend taking to Albq... if there are a lot of miles on the engine,
there will be other things to do.
timing chain
water pump
lifters
valve job
etc,etc

gene

>From: "Walter "
>To: gmcmotorhome
>Subject: Zero compression
>Date: Sat, Apr 15, 2000, 3:41 PM
>
>
>About three weeks ago I reported a hesitation under load. Emery and I have
>chased this down. We replaced vacuum hoses, put is a new module, new pick
>up coil, substituted his spare coil, cap and rotor for mine. Disconnected
>the EKE knock sensor, replaced the fuel pump, adjusted the timing, switched
>from main to auxiliary tank. Then today I pulled all the plugs and checked
>the compression. 5 cylinders at 120, #5 at 100 and 6 and 8 at zero. I
>reinstalled the plugs one at a time in 6 and 8 and still no compression.
>The #6 plug was fouled (wet and black) when I changed the plugs in CA about
>1200 miles ago. The new plug is still wet and black. Looks oily. We feel
>that the head gasket must be blown between the two cylinders.
>
>Any suggestions before I drive my six cylinder GMC 70 miles to Albuquerque
>to try out Jim Statkus, who comes highly recommended by Al Chernoff. My
>concern is that we (Emery and I) pull the head and then find it is not a
>head problem
>and we are 70 miles from help. I guess I could have it towed.
>
>Puzzled in Santa Fe, but enjoying the good company and insights of Emery.
>
>Any help or suggestions greatly appreciated.
>
>Walter
>78 Royale 455
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/

 

[scott shean]

Walter, I'm way behind on mail, and you have probably
already received other responses.

Before you go too far with your repairs, remove the valve
cover and check the valve train. It may be something
external to the cylinders. It's a long shot, but it doesn't
take much effort to check it out.

BTW, if you drive over hills with only six cylinders, you
should expect quite a bit of extra heat load on your cooling
system, so watch your temperature gauge.

Scott Shean
Baton Rouge, LA
78 Royale

>-----Original Message-----
>From: owner-gmcmotorhome
>[mailtowner-gmcmotorhome]On Behalf Of
>EMERYSTORA
>Sent: Saturday, April 15, 2000 8:28 PM
>To: gmcmotorhome
>Subject: GMC: No compression on two cylinders
>
>
>From: "Walter "
>To: gmcmotorhome
>Subject: Zero compression
>Date: Sat, Apr 15, 2000, 3:41 PM
>
>
>About three weeks ago I reported a hesitation
>under load. Emery and I have
>chased this down. We replaced vacuum hoses, put
>is a new module, new pick
>up coil, substituted his spare coil, cap and rotor
>for mine. Disconnected
>the EKE knock sensor, replaced the fuel pump,
>adjusted the timing, switched
>from main to auxiliary tank. Then today I pulled
>all the plugs and checked
>the compression. 5 cylinders at 120, #5 at 100 and
>6 and 8 at zero. I
>reinstalled the plugs one at a time in 6 and 8 and
>still no compression.
>The #6 plug was fouled (wet and black) when I
>changed the plugs in CA about
>1200 miles ago. The new plug is still wet and
>black. Looks oily. We feel
>that the head gasket must be blown between the two
>cylinders.
>
>Any suggestions before I drive my six cylinder GMC
>70 miles to Albuquerque
>to try out Jim Statkus, who comes highly
>recommended by Al Chernoff. My
>concern is that we (Emery and I) pull the head
>and then find it is not a
>head problem
>and we are 70 miles from help. I guess I could
>have it towed.
>
>Puzzled in Santa Fe, but enjoying the good company
>and insights of Emery.
>
>Any help or suggestions greatly appreciated.
>
>Walter
>78 Royale 455
>