No compression?

Tiny
STEVE ERRINGTON
  • MEMBER
  • 1970 MERCURY COUGAR
  • 5.8L
  • V8
  • 2WD
  • AUTOMATIC
  • 49,000 MILES
Just got the car listed above restored from a barn find. When I first started it there was a little smoke was sitting for 35 years. Smoke on driver side got progressively worse, I thought I might have stuck rings or bad gaskets has a full pan gasket did a compression test and 7 cylinders test at approximately 175 PSI, but 1 cylinder has a 0-3 PSI reading with the compression test. I then removed the head and inspected cylinder walls very smooth, and everything looked very good, and the head gasket also looks good. The valves seem to be seating nicely, I don't know why I have no compression.
Thursday, September 1st, 2022 AT 3:42 PM

26 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

If only one cylinder has low compression, have a helper crank the engine while the head is removed to confirm the piston in the affected cylinder is moving. If it is, then either we have a blown head gasket (which still should provide higher compression), worn rings (which would also provide more compression, or a valve stuck partially open. My first suspect is the valve. When you tested it, did you have the valve cover off to make sure both valves are moving fully?

Let me know.

Joe
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Thursday, September 1st, 2022 AT 8:53 PM
Tiny
STEVE ERRINGTON
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  • 16 POSTS
Hi Joe, thanks so much for your support. The valves and piston were moving well when we took the test. The head gasket also looked good. This morning I am going to remove the valves to check on the seats and pull the piston to check the rings to see if they are stuck. As far as I can tell this is all that can affect compression other than the gasket. Also, when I pulled the heads, they were full of coolant even though the radiator was drained some of the ports were nearly plugged in the heads but not in the block could the block be plugged inside where I can see and how can this be cleaned? Where we live, I cannot get help with this and really appreciate your support.
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Friday, September 2nd, 2022 AT 4:13 AM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi, just discovered that some of the gaskets are missing when someone before me worked on this motor please see gasket set ms96012 it is a metal pan with fabric on the heads the fabric parts are missing, and it seems that the exhaust manifolds are missing also. I have a lot of blow by so I'm still going to check the valves and rings.
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Friday, September 2nd, 2022 AT 6:22 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

If you had excessive blow-by, then first check the rings. You have already checked compression. Add about a tablespoon full of motor oil into the affected cylinder and recheck compression. If it is the rings, the pressure will increase. If it is a valve issue, there will be little to no change.

https://www.2carpros.com/articles/how-to-test-engine-compression

If a valve is sticking open, that isn't going to cause blow-by. It will simply allow the compressed air to leak past the valve. With an intake valve, usually you will hear a popping sound from the intake. If it is an exhaust valve, you likely won't hear it at all.

As far as the gasket set above, that won't have anything to do with compression. That is a valley gasket pan/gasket set. That sits under the intake and won't affect engine compression.

Let me know what you find or if there is anything I can do to help.

Take care,

Joe
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Friday, September 2nd, 2022 AT 8:30 PM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi, well, my piston is 1/2 gone the top ring is only 7/8 there big chunk about two inches long between the first ring slot and the third is completely gone. But not a scratch on the walls. I think someone just put everything back in place and sold the car. Also, no debris in the pan where would the chunks go? One other cylinder reads 150psi where all the rest are 175 so I'm thinking they switched this piston from the hole where this piston was. Are the pins that hole the piston head to the piston arm pressed fit. Its a 1970 351 Cleveland engine.
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Saturday, September 3rd, 2022 AT 10:57 AM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Also, thanks again for your support.
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Saturday, September 3rd, 2022 AT 11:03 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

Ugh, that isn't good. As far as how the connecting rod and piston are attached is simple. There will be a small circlip at each end of the pin holding the piston onto the connecting rod. Remove it and be careful not to lose it.

Once that is removed, gently tap the connector pin out in that direction.

Are you able to find a new piston and rings? Also, the broken parts should be in the oil pan unless someone has already removed them. Have you removed the oil pan?

Let me know.

Take care,

Joe
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Saturday, September 3rd, 2022 AT 10:42 PM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi,

There is no debris in the oil pan. Should have some replacement pistons from a Cleveland of the same year this week taking the other head off today where I think, this piston was originally located to see its condition. Is 175 PSI an okay compression for this motor it has 49,000 miles?
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Sunday, September 4th, 2022 AT 4:01 AM
Tiny
JACOBANDNICKOLAS
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Hi,

If there is nothing in the oil pan, someone took it apart and removed it. Also, I think it is a good idea to remove the heads as well.

Let me know what you find.

Joe
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Sunday, September 4th, 2022 AT 7:09 PM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi Joe, the head is off on the affected cylinder side. I removed the valves on that cylinder and there was approximately 1/16 pink build-up of dried clay stuff on the top of the intake valve. Don't know what this is from! Other than that, all valves and seats look good. To me, it is baffling not to find any further damage in the rest of the cylinder walls with a piston-like this coming out. But back in the late 80's a lot of weird stuff went on that was the last time this car ran. Have pistons from the same vintage motor hopefully coming so not to offset any weight or style issues Is 175 PSI for compression a good number? Thanks again for your support.
Steve
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Monday, September 5th, 2022 AT 5:42 AM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi Joe, one thing I forgot is the oil pan torqued.
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Monday, September 5th, 2022 AT 5:46 AM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi Joe,

Well, I removed the other head, and it looks like the cylinder sleeve has been replaced I can't take the piston out because of a residue build-up where the rings stop, I tried to hone it out but got worried that I might do more damage because this sleeve feels very thin compared to the others. We are moving across the country soon. So, I think I will just put it back together with the new piston and will have it looked at by professionals once there. Where we live now there is no one that does that here. My gaskets come tomorrow and my piston on Wednesday hope a goes well on the reassembly. Thanks again for your support.
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Monday, September 5th, 2022 AT 10:26 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

What you need to remove is a ridge reamer. It will cut the high spots so the piston can be removed. However, if it is bad enough that the piston won't come out, that may be a concern. As long as the compression was good on that cylinder, I would leave it alone.

Let me know. Also, have a safe trip.

Take care,

Joe
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Monday, September 5th, 2022 AT 7:53 PM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Hi, we actually don't move until mid-November I had a log staircase manufacturing business, and my shop is 16,000 sq ft full of stuff so as I am having actions, I want to get my car fixed so it is usable because we are selling everything, and I won't have these facilities when we leave. What's holding the piston in is a build-up of dark crust, all of the cylinders have it but you can see that this cylinder wall has been worked on and it feels weaker than the rest. I have only driven the car approximately 200 miles since I got it on the road and due to the buildup, I think it was used more than that in its broken piston condition because of the build-up. I don't think I would have built up in that short of time. Just worried that the rings might be stuck on that cylinder is there a solvent that breaks up that crusty stuff?
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Tuesday, September 6th, 2022 AT 3:33 AM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Sorry, auctions to sell stuff.
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Tuesday, September 6th, 2022 AT 3:34 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Steve,

If you want to clean build-up, brake cleaner is excellent. Just remember, it removes all oils as well, so make sure to put a film of oil on the cylinder walls because it will rust.

If you can, take a pic of the cylinder wall. I'm interested in seeing it.

Take care and good luck with the auctions. It sounds like you have your hands full.

Let me know if there is anything I can do to help.

Joe
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Tuesday, September 6th, 2022 AT 5:34 PM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
It looks like it was chamfered to slide the piston in, and the sleeve has a ridge at the top of where the piston ring stops on the changed sleeve or liner. The gaskets were put on wrong, so it did not get coolant from the second cylinder back. I was shown this on a YouTube video to be sure to put the gasket on correctly. So, this is most likely why this cylinder failed got overheated and melted.
So, this cylinder is not perfect but works to this point so I will connect back in the new piston is coming and will put everything back together. The shipper is overnighting the piston but where we live it takes 3 days LOL. Everything should be back together on Friday. I will have gaskets for the intake which should reduce the oil burn, a full piston should help reduce blow-by.
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Wednesday, September 7th, 2022 AT 7:07 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

Thanks for the update. I'm looking forward to Friday to seeing how things turn out for you.

Let me know. Also, I would rub some oil on the cylinder wall to prevent it from rusting.

Take care and I'll watch for your reply.

Joe
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Wednesday, September 7th, 2022 AT 6:48 PM
Tiny
STEVE ERRINGTON
  • MEMBER
  • 16 POSTS
Yes, me too. The red you see is mostly old coolant dye that was stuck in the heads and block after sitting stagnant for years because the gaskets were wrong.
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Thursday, September 8th, 2022 AT 4:22 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

It's Saturday and I've been wondering how things turned out for you. LOL

If you have a chance, let me know.

Take care,

Joe
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Saturday, September 10th, 2022 AT 7:10 PM

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