Help , 0 compression in #5
Thread Starter
Pro
Joined: Dec 1999
Posts: 673
Likes: 0
From: Venetia,Pa,USA
Help , 0 compression in #5
Any ideas. Rockers go up and down , push rods appear OK also. All other cylinders are 185 PSI.
It's a new ZZ4 short block. Less that 15 miles. Has run poorly since installation. 0 PSI compression in #5 cylinder. Holed piston????
What do you think. Not looking forward in pulling out engine again. #$%^&*()(*&^&*()*&^&*(
You can just post answer or E Mail me directly at orawiecs33@comcast.net
It's a new ZZ4 short block. Less that 15 miles. Has run poorly since installation. 0 PSI compression in #5 cylinder. Holed piston????
What do you think. Not looking forward in pulling out engine again. #$%^&*()(*&^&*()*&^&*(
You can just post answer or E Mail me directly at orawiecs33@comcast.net
Racer
Joined: Aug 2010
Posts: 297
Likes: 9
From: Holiday Shores IL
You can do a leak down test to determine if its a valve or piston related issue.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
Instructor
Joined: May 2012
Posts: 201
Likes: 0
From: co
You can do a leak down test to determine if its a valve or piston related issue.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
that is if there is a piston and rings in the bore
did it back fire and pop when you ran it????
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
You can do a leak down test to determine if its a valve or piston related issue.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
First thing to look for is a valve stuck open. If it's stuck too far open, it may have snapped off or cracked. Reset valve lash on that lung, run your compression test again. If it's zero, off with the head.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
You can do a leak down test to determine if its a valve or piston related issue.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
I suppose in your situation, just connect an air line to the spark plug hole and listen for where the air comes out. Make sure both valves are closed either by backing off the rockers or rotating the engine. You won't need much pressure.
Good luck. Hope it's something simple.
first Suspicion would be tight (bottomed) lifters.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
If the engine backfires out the intake, the intake valve is open, if it afterfires out the tailpipe, the exhaust valve is open If it blows out both ways, well, you know.
IF this is a new engine (15 miles) then redo the valve adjustment while running. Place enough towels or rags around the engine to catch the oil, keep the engine at idle, and adjust them This way,
back off each rocker one at a time till it clacks, then tighten till the clacking stops. tighten to 1/2 turn after the clacking stops. Then go to the next one. Adjust them hot.
IF this is a new engine (15 miles) then redo the valve adjustment while running. Place enough towels or rags around the engine to catch the oil, keep the engine at idle, and adjust them This way,
back off each rocker one at a time till it clacks, then tighten till the clacking stops. tighten to 1/2 turn after the clacking stops. Then go to the next one. Adjust them hot.
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
<snicker> been there done that! Live and learn 
I'd check the valves/rockers as many have mentioned. I've seen more that once where someone adjusts the rockers and then goes back through them again. Problem is, the lifters will bleed down from the initial lash setting which makes them seem loose. So they tighten them a bit more. Then they fire the engine which fully pumps up the lifters and now the rockers are so tight they're holding the valve open.
I'd check the valves/rockers as many have mentioned. I've seen more that once where someone adjusts the rockers and then goes back through them again. Problem is, the lifters will bleed down from the initial lash setting which makes them seem loose. So they tighten them a bit more. Then they fire the engine which fully pumps up the lifters and now the rockers are so tight they're holding the valve open.
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Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Now my policy is: hot and running. Period.
It helps to take some old valve covers and cut out a slot to get to the adjusting nuts (or whatever you have). Or maybe something like this:
Thread Starter
Pro
Joined: Dec 1999
Posts: 673
Likes: 0
From: Venetia,Pa,USA
I loosed the rocker arms so I would be sure that the valves would be seated by the springs. I put 50 PSI air pressure thru the spark plug hole. The air came out of the area where the push rods go thru. First thought would be it was coming from crankcase. However the reason I bought the short block was that I had the EXACT same problem on #2 cylinder. It was 75 PSI while the other cylinders were 185. I assumed the problem was a cracked ring and had 7 racing years on the engine. I had the heads checked. Pressure and vaccum tested. I didn't pay attention to placing the heads back on the side they came from and can't tell because I cleaned the other head before installation. Now I'm wondering if the head isn't the one that had the problem before and it only shows up when torqued. I know on this side of the engine the problem should have been on cylinder #7 if I switched heads. I'm wondering if removing and retorquing if the defect/crack has caused the new problem. ANY THOUGHTS.
I'll be removing the the head and have it checked for cracks. I thought it would have shown up ; but maybe the defect/crack only shows on head being torqued in place.
A little distressing having invested almost $3500 and having a similar problem. $%^&*&^&*(*&*()
I'll be removing the the head and have it checked for cracks. I thought it would have shown up ; but maybe the defect/crack only shows on head being torqued in place.
A little distressing having invested almost $3500 and having a similar problem. $%^&*&^&*(*&*()
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
I loosed the rocker arms so I would be sure that the valves would be seated by the springs. I put 50 PSI air pressure thru the spark plug hole. The air came out of the area where the push rods go thru. First thought would be it was coming from crankcase. However the reason I bought the short block was that I had the EXACT same problem on #2 cylinder. It was 75 PSI while the other cylinders were 185. I assumed the problem was a cracked ring and had 7 racing years on the engine. I had the heads checked. Pressure and vaccum tested. I didn't pay attention to placing the heads back on the side they came from and can't tell because I cleaned the other head before installation. Now I'm wondering if the head isn't the one that had the problem before and it only shows up when torqued. I know on this side of the engine the problem should have been on cylinder #7 if I switched heads. I'm wondering if removing and retorquing if the defect/crack has caused the new problem. ANY THOUGHTS.
I'll be removing the the head and have it checked for cracks. I thought it would have shown up ; but maybe the defect/crack only shows on head being torqued in place.
A little distressing having invested almost $3500 and having a similar problem. $%^&*&^&*(*&*()
I'll be removing the the head and have it checked for cracks. I thought it would have shown up ; but maybe the defect/crack only shows on head being torqued in place.
A little distressing having invested almost $3500 and having a similar problem. $%^&*&^&*(*&*()
Even if a head is cracked, it won't give the symptoms you're describing....there will be *some* compression. If the head is badly warped, you'll have a pan full of coolant.
If the valves aren't closing all the way, you should be able to visibly see a height difference. You can also compare the valve stem height to other valves.
got to see where this goes. all basic engine build or repair.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
I loosed the rocker arms so I would be sure that the valves would be seated by the springs. I put 50 PSI air pressure thru the spark plug hole. The air came out of the area where the push rods go thru. First thought would be it was coming from crankcase. However the reason I bought the short block was that I had the EXACT same problem on #2 cylinder. It was 75 PSI while the other cylinders were 185. I assumed the problem was a cracked ring and had 7 racing years on the engine. I had the heads checked. Pressure and vaccum tested. I didn't pay attention to placing the heads back on the side they came from and can't tell because I cleaned the other head before installation. Now I'm wondering if the head isn't the one that had the problem before and it only shows up when torqued. I know on this side of the engine the problem should have been on cylinder #7 if I switched heads. I'm wondering if removing and retorquing if the defect/crack has caused the new problem. ANY THOUGHTS.
I'll be removing the the head and have it checked for cracks. I thought it would have shown up ; but maybe the defect/crack only shows on head being torqued in place.
A little distressing having invested almost $3500 and having a similar problem. $%^&*&^&*(*&*()
I'll be removing the the head and have it checked for cracks. I thought it would have shown up ; but maybe the defect/crack only shows on head being torqued in place.
A little distressing having invested almost $3500 and having a similar problem. $%^&*&^&*(*&*()
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Installed (and removed) this pan with the engine in the car several times...
No oil pan...
Oil pan...
Last edited by 96GS#007; Nov 15, 2012 at 08:40 PM. Reason: added pics
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
Yours is the first then. Plenty of us have 7qt pans (I ran a Canton 15-240T pan, some have Champ, others Morroso, etc) that have been removed with the engine in the car. Pop the motor mount bolts loose and you can jack the engine to give yourself plenty of room.
Installed (and removed) this pan with the engine in the car several times...
Installed (and removed) this pan with the engine in the car several times...
Raise it just far enough for the pan to clear....no need to unhook everything and lift it out of the car. It's possible that lung wasn't hone correctly (or at all) as well. Get #5 slug out and see what's going on inside.
Thread Starter
Pro
Joined: Dec 1999
Posts: 673
Likes: 0
From: Venetia,Pa,USA
I'll give it a try starting next week. At 71 I don't have the drive/energy I once had.
I'll keep everyone posted.
Thanks again for comments. If anyone thinks of anything else please chime in.
I'll keep everyone posted.
Thanks again for comments. If anyone thinks of anything else please chime in.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
At 71; your doing pretty good!
Hang in there. The simple fact that two blocks are giving the same symptoms is really Suspicious! The common demoninator here is the heads, unless I mis-understood your 7:28 AM post. This trail is still leading toward a head problem...but how?
I know what I would do..
Hang in there. The simple fact that two blocks are giving the same symptoms is really Suspicious! The common demoninator here is the heads, unless I mis-understood your 7:28 AM post. This trail is still leading toward a head problem...but how?
I know what I would do..
Racer
Joined: Aug 2010
Posts: 297
Likes: 9
From: Holiday Shores IL
Well, you can try this:
Pull the head and have it looked at.
While that is going on, get a piece of 1/4" plexiglass and cut it into a square a bit larger than the cylinder.
Drill a hole in it for your air nozzle.
Clean off the surface of the block and put a bit of petroleum jelly around the cylinder and lay the plexiglass piece on top. Hold it down and put some air in there and see if it just blows past the piston.
If it does, I'd be suspecting missing rings or something worse.
Of course take a look at the cylinder walls while you are there.
If you see abnormal looking markings, pull the block.
If you make the plexiglass piece, save it and cc your heads.
Use a graduated burette or large syringe with accurate markings.
Just something to do.
Pull the head and have it looked at.
While that is going on, get a piece of 1/4" plexiglass and cut it into a square a bit larger than the cylinder.
Drill a hole in it for your air nozzle.
Clean off the surface of the block and put a bit of petroleum jelly around the cylinder and lay the plexiglass piece on top. Hold it down and put some air in there and see if it just blows past the piston.
If it does, I'd be suspecting missing rings or something worse.
Of course take a look at the cylinder walls while you are there.
If you see abnormal looking markings, pull the block.
If you make the plexiglass piece, save it and cc your heads.
Use a graduated burette or large syringe with accurate markings.
Just something to do.
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
