No Compression

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67/6barracuda

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Hello,
I have been trying to get a slant six that has not started in 13yrs from last time registered 99' it has spark and fuel but no compression. I got O readings from three out of the four cylinders and 30 psi out of #6 stop checking after that. So my question is if its not reading anything it must be that the head gasket is gone right? I would think that piston rings wouldn't be worn that bad what do you guys think?

denis
 
So i guess I should pull the valve cover and see whats going on in there? this is my first project so not really sure. would the motor still turn over with valves stuck? What should I look for? when I pull the cover
 
Hello,
I have been trying to get a slant six that has not started in 13yrs from last time registered 99' it has spark and fuel but no compression. I got O readings from three out of the four cylinders and 30 psi out of #6 stop checking after that. So my question is if its not reading anything it must be that the head gasket is gone right? I would think that piston rings wouldn't be worn that bad what do you guys think?

denis
I think stuck valves also. On my slant, there was a bit of fuel that dripped into the manifold and onto the valves. The gas got old and hard and froze the valves. I had to use a hammer to get them out even after I had pulled the head. One thing that will work to loosen them is model airplane dope thinner available at good hobby shops. Either Pactra, or Brodak.
 
Could be a lot of things, you know "why it was parked?"

Could indeed be head/ gasket problems

Could be stuck bent or burnt valves

Could be rust in the cylinders / rings/ valves AKA a combination of problems.

Very first thing I'd try is to squirt a little oil down each plug hole and re-test compression

MAKE SURE your compression tester is not leaking. If it's a "hold in by hand" deal, I'd find a screw in one, not that hard to find at garage sales, CL, or even new, not that expensive

Looking at the valves, just use some logic. If there is slack in some rockers and not others --then those are stuck open.

If you have a compressor, "rig" a fitting to inject air in the cylinders. You need to do this at TDC for a given cylinder, and look and listen for air out the carb throat (intake valve) out the exhaust (exhaust valve) or bubbles in the coolant with the cap off

N' yah. some sort of aggessive solvent, a couple cans of spray carb cleaner, paint thinner, etc, would probably be helpful. Do NOT turn the engine over very much with stuff like that in there. Add oil to lube the rings first.
 
Rings stuck in piston lands. They may not be able to be freed, but try several squirts of Marvel Mystery oil thru each spark plug hole and let them sit for a few days. Then see if it will start. Heat from running them may eventually free them.

Good luck!
 
Pulled the valve cover and I was able to push down on the rockers on most of the valves. Except the ones fully opened. I was surprised that of how clean everything looked. I will try putting some oil down the cylinder to see what happens. This sucks because I was told it was the timing chain was the reason it was parked and replaced it to find out there is now compression.
 
Me too I aligned the dots and had the rotor facing number six. That's how it was facing when I pulled the original chain. So there is a possibility that I had messed it up but I should still be getting a reading from the compression tester I would assume. Thanks a lot for the input guys.
 
Well put some ultra lube in all the cylinders and didn't make any difference in compression. Reading 0psi on all cylinders except #6 it was 32 psi. As I turned it over all valves and lifters look to be operating quite nice. How would I know if it was the head gasket there is a lot of crud on and around the head it self. I have some vacation time coming I think I might do the head gasket next. What do you guys think? Is it hard or even worth it?
 
If the rings are gummed up really bad no amount of oil will seal them. Sounds like it's time to tear it down.
 
If you have a air source

you could remove the rocker shaft

so, that you know the valves are closed

air the cylinder at the spark plug hole and listen for escaping air

to determine if it's a intake/exhaust valve or the rings

The auto parts place may have a leak down tester
 
i would put two or three table spoons of ATF in each cylinder. let it sit for a couple of days and try to turn it over by hand. go a full revolution and then put another 2 or three in.

pull the valve cover and tap the rockers on the valve side to see if they move... should bounce with the old tired springs.
 
He's already said he could open the valves that were not opened by the cam. If the timing chain was installed wrong, he would have different compression readings. The way I read it, he says he has zero on 5 cylinders and 32 PSI on one cylinder. That means 5 cylinders have to have something in common. I bet that don't all 5 have holes in the top so stuck rings is what I am banking on.
 
Get the Harbor Freight compression gage set like I have, cost ~$15 on sale. You can use the hose in the kit to connect to an air compressor (standard air fitting). Use that as a poor man's leak-down checker. With each piston at TDC compression, listen & feel w/ tissue for air flow from the PCV valve hole (w/ oil fill hole plugged). That would be bad rings. The only other places to leak are to intake or exhaust, other than to outside via a bad head gasket. It seems inconceivable that a bad head gasket could take out 5 cylinders.

The timing dots don't usually line up at TDC #1. It was TDC #6 on my small block. I forgot about slants, but you can read up here. I can't recall a way to put a timing set on wrong and still have the dots line up.

Before I started tearing the engine apart, I would try to run it. Even before that, I would turn it over by hand. If you feel 3 strong "air springs" in 2 crank revs, the engine is good and your compression testing method is bad. You can turn most slants over by tugging on the alternator belt.
 
Guys motor does turn freely and valve train from what i can tell is in good working order. I would think based on the wealth of all your knowledge that its either stuck rings or head gasket. I assumed by adding that ultra lube that's about as thick as honey it would bump compression a bit and it did for #6 from 30psi to 32psi but still 0 psi on all the other cylinders. This motor I had cranked over about 50 times trying to start it so I would hope these rings would be unstuck by now. Who knows? Probably right on needing a rebuild.
 

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Guys motor does turn freely and valve train from what i can tell is in good working order. I would think based on the wealth of all your knowledge that its either stuck rings or head gasket. I assumed by adding that ultra lube that's about as thick as honey it would bump compression a bit and it did for #6 from 30psi to 32psi but still 0 psi on all the other cylinders. This motor I had cranked over about 50 times trying to start it so I would hope these rings would be unstuck by now. Who knows? Probably right on needing a rebuild.

the rings wont just unstick... and thankfully you put something in the cylinders before cranking it that many times or you could kiss your cylinders good bye... the ATF will eat what ever is causing the rings to stick (rust, carbon, etc) and free them so you can get it started and then get it warmed up... i would have recommended changing the oil at the beginning and then after you get it up to temp but to late for that...
 
That's what i was thinking how in the world would it read 0 psi under any condition i would have thought it would at least build up a little pressure and leak out. So I am mind boggled right know no obvious signs of damage other than the built up oil/sludge all over the bottom of block but the valve cover was extremely loose also.
 
That's what i was thinking how in the world would it read 0 psi under any condition i would have thought it would at least build up a little pressure and leak out. So I am mind boggled right know no obvious signs of damage other than the built up oil/sludge all over the bottom of block but the valve cover was extremely loose also.

it happens... really i cant explain it as the rings have outward tension but they do stick in the lands and will cause no compression...
 
You could always pour marvel mystery oil down each of the cylinders as well. I've had super stuck rings only freed by marvel and nothing else. There is other underlying issues I can almost bet but lack of compression in that many cylinders seems like a timing chain issue to me. That or a seriously blown head gasket
 
You could always pour marvel mystery oil down each of the cylinders as well. I've had super stuck rings only freed by marvel and nothing else. There is other underlying issues I can almost bet but lack of compression in that many cylinders seems like a timing chain issue to me. That or a seriously blown head gasket

if it jumped a tooth than yes the timing chain could cause some issues... not ZERO though...

here is my deal with oil... oil has a little bit of detergent in it, good for a clean engine and keeping it clean. ATF is cleaners and eats anything... goes after carbon like nobodies business...

once he gets it running and hot then he can pour down the carb and get the carbon off the valves and piston tops
 
I don't understand the timing chain as it relates to the compression sure the timing could be off but there is dots and dowels used to but the timing set on. I guess i don't understand. That's why I am here you guys probably forgot more about Mopars than ill ever know.
 
I don't understand the timing chain as it relates to the compression sure the timing could be off but there is dots and dowels used to but the timing set on. I guess i don't understand. That's why I am here you guys probably forgot more about Mopars than ill ever know.

ok as the cam spins it opens and closes the valves in order to fire. the cam is installed on a centerline so that the valve events (open and closing events) are correct for that engine (lots of factors).

so when you have a timing set wear out and jump a tooth or more then the events are all wrong and when a valve should be closed it is now open = no compression
 
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