Slant Six Forum
https://slantsix.org/forum/

What would cause 0 compression on the Number 5 cylinder?
https://slantsix.org/forum/viewtopic.php?t=45706		 Page 1 of 2
Author:  blanc012 [ Sun Jul 24, 2011 12:27 pm ]
Post subject:  What would cause 0 compression on the Number 5 cylinder?
Hello all -

My 1970 dart runs okay. I did a compression test today and the results are as follows

1 - 120 psi
2 - 0 psi
3 - 110 psi
4 - 110 psi
5 - 110 psi
6 - 90 psi

I checked to see if the rockers are too tight on the number 5 cylinder and they seem okay. When the valves are supposed to be closed, the rockers will wiggle a little.

Does anyone know what my problem is?
Author:  blanc012 [ Sun Jul 24, 2011 12:30 pm ]
Post subject: 
I had the cylinder numbers mixed up.

Number 5 is the bad cylinder. That's the one that I checked the rockers on.

1 - 90 psi
2 - 110
3 - 110
4 - 110
5 - 0
6 - 120
Author:  nuttyprof [ Sun Jul 24, 2011 12:31 pm ]
Post subject: 
Could be a burnt valve or a hole in a piston.
Author:  blanc012 [ Sun Jul 24, 2011 4:42 pm ]
Post subject: 
Yikes. That doesn't sound good.
Author:  raPoM [ Sun Jul 24, 2011 4:55 pm ]
Post subject: 
Time to pull the head and have a look. My vote goes for burnt valve.
Author:  emsvitil [ Sun Jul 24, 2011 5:17 pm ]
Post subject: 
Broken rod.....
Author:  WagonsRcool [ Sun Jul 24, 2011 7:25 pm ]
Post subject: 
I usually see burned (exhaust) valves more often than piston problems- that said my last eng problem was I torched the ring lands on #6 piston.

You can do more tests but sounds like you have to do a teardown one way or another.
Author:  raPoM [ Sun Jul 24, 2011 7:34 pm ]
Post subject: 
Quote:
Broken rod.....
Only reason I would not agree is that he says that it runs "ok". Broken rod would cause an imbalance that you would notice.
Author:  blanc012 [ Mon Jul 25, 2011 6:20 am ]
Post subject: 
Thanks for the replies. At this time I will just continue to drive it. It doesn't smoke and runs well. I can only tell that it runs rough if I floor it.

I bought this car as a parts car several years ago. The previous owner was going to drop a 440 in it so he had never tried to start it. When I got it home I put a battery in it and it started with gas down the carb. I have put about 3000 miles on this car. It always got bad gas mileage (about 14 mpg) and didn't have good power. I thought it was just tired because it had 140,000 miles on it. I knew it had a miss but I thought it was the distributor.

Well last week I got a compression tester for my birthday. I checked the car and found the dead cylinder.

I have a slant from a 78 Aspen sitting in my garage. I will either use the head or put the entire engine in the car.

Thanks again for the information.
Author:  raPoM [ Mon Jul 25, 2011 7:23 am ]
Post subject: 
If its a burnt valve you can fix it for under 50 bux,and have a lot more power and get better gas mileage. All you will need is new intake/head gaskets,new valve,and some valve lapping compound.
Author:  USAJon [ Mon Jul 25, 2011 7:40 am ]
Post subject: 
how does it idle?

if it's a hole in the piston you would have blow bye say breather or dip stick tube

zero compression on a cylinder would have a poor'r idle

their a lot more easy to fix then non slant six peeps know.

the biggest issue i've had was exhaust flange bolts to exhaust pipe..they usually snap, and also the old bolts that connect the intake manifold to the exhaust manifold their a snapper too.

but these need not be challenged with removing the head only..
Author:  blanc012 [ Mon Jul 25, 2011 2:33 pm ]
Post subject: 
I really like the idea of replacing a burnt valve.

I also had not thought about leaving the manifolds in place. I thought that if I try to get the manifolds off, I would snap off one of those manifold bolts for sure. I'm going to try to leave the intake and exhaust on and replace a valve.

I thought about the hole in the piston. The car doesn't smoke at all. That's one of the things I like about driving it.

I will post again when I get the head off.
Author:  bigslant6fan [ Mon Jul 25, 2011 4:34 pm ]
Post subject:  .
Before removing the head,remove the valve cover,and rocker train. Then put a straight edge on the top of the valve tips,my vote is for a stuck valve.
Author:  kielbasa [ Mon Jul 25, 2011 4:41 pm ]
Post subject: 
LEAK DOWN TEST, that will show you where the compression is actually going.
Author:  madmax/6 [ Mon Jul 25, 2011 7:44 pm ]
Post subject: 
Broken rod is the dumbest thing I have ever read here.Ya got a burt valve,or really bad stuck rings.guzzi mark
Page 1 of 2 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/