Cylinder #7 down on compression

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Inertia said:
I'm just passing on 40 yrs experience working then owning a large auto repair center in our Capital city.
I had an outstanding mentor, and I trained 3 apprentices.
If one of my mechanics showed me that piston, compared to others, I'd want to know why, and certainly warn the customer that something was awry.
I come here to share my knowledge and experience, while "hunting" on a different site .

And miss the juicy stuff from those on ignore, rofl
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I understand where you are coming from. I am going to stop by Advanced Auto on my way home from work and I will do a wet leak down and see what happens. What should I use for the test? Paint Thinner? I don't see myself pulling the engine and doing a complete rebuild at this point in my life. I have a wife who hates that I spend so much time in the garage, a son in his first year of college and I just found out the subframe on my 08 Police package Charger has a bad subframe so money is not easy to come by. I am going to clean up the pistons the best I can and hope and pray that whatever you don't like about #5, I think that's the piston you're referring to is from a previous problem. I'll keep you all posted.
 
gtgto said:
I understand where you are coming from. I am going to stop by Advanced Auto on my way home from work and I will do a wet leak down and see what happens. What should I use for the test? Paint Thinner? I don't see myself pulling the engine and doing a complete rebuild at this point in my life. I have a wife who hates that I spend so much time in the garage, a son in his first year of college and I just found out the subframe on my 08 Police package Charger has a bad subframe so money is not easy to come by. I am going to clean up the pistons the best I can and hope and pray that whatever you don't like about #5, I think that's the piston you're referring to is from a previous problem. I'll keep you all posted.
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Hey, look at the bright side, you might wet test it, and they all hold fluid evenly, lol, then you can come back here and tell everyone my asshole is sucking wind, and I guess I would deserve it.
Should be able to get cleaning solvent, or varsol at the parts store, kerosene.
If nec, I would just slap the repaired heads on, totally understandable, but you at least know that plug will likely foul, put another plug in carry on.
Done that to many vehicles too, including my own, lol
What were the old plugs like, are they around?
Good luck .
 
Inertia said:
Hey, look at the bright side, you might wet test it, and they all hold fluid evenly, lol, then you can come back here and tell everyone my asshole is sucking wind, and I guess I would deserve it.
Should be able to get cleaning solvent, or varsol at the parts store, kerosene.
If nec, I would just slap the repaired heads on, totally understandable, but you at least know that plug will likely foul, put another plug in carry on.
Done that to many vehicles too, including my own, lol
What were the old plugs like, are they around?
Good luck .
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Post 15 of this thread has a couple of pics of the plugs I pulled out. #5 seems to be the one being talked about.
 
gtgto said:
Post 15 of this thread has a couple of pics of the plugs I pulled out. #5 seems to be the one being talked about.
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I kinda look at it as if you walked down a rack of servers, and one was different, looked funny, maybe discolored by heat, label melted, or some such.
You have a choice, report it, or ignore it, this is kinda your choice.
 
Can you give us the specific spark plug number. It’s on the plug.

Not really sure the point in cleaning off the pistons. If you insist, do the grease thing like mentioned earlier.

I’m always amazed when people are surprised that their 55 year old motor doesn’t have original parts in it. Nearly all piston replacements in the late 70s, 70s and 90s were low compression due to available gas.

If it blows 150 psi when you are done, it’s probably because it has a replacement cam too.

Consider a shim head gasket for installation.
 
BSB67 said:
Can you give us the specific spark plug number. It’s on the plug.

Not really sure the point in cleaning off the pistons. If you insist, do the grease thing like mentioned earlier.

I’m always amazed when people are surprised that their 55 year old motor doesn’t have original parts in it. Nearly all piston replacements in the late 70s, 70s and 90s were low compression due to available gas.

If it blows 150 psi when you are done, it’s probably because it has a replacement cam too.

Consider a shim head gasket for installation.
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BSB67 said:
Can you give us the specific spark plug number. It’s on the plug.

Not really sure the point in cleaning off the pistons. If you insist, do the grease thing like mentioned earlier.

I’m always amazed when people are surprised that their 55 year old motor doesn’t have original parts in it. Nearly all piston replacements in the late 70s, 70s and 90s were low compression due to available gas.

If it blows 150 psi when you are done, it’s probably because it has a replacement cam too.

Consider a shim head gasket for installation.
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Look how much better that looks. The head gasket I took out was a Permatex 8553 I think. The plugs are NGK V-Power GR4

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Happy to report i did a wet leakdown test on a few cylinders and they all held fluid overnight. #5 being one of them.I've had the car for more than 8 years and know now the engine is .30 over with cylinder walls that look like they were machined a week ago. Both heads are now at a local machine shop and I even took my manifolds to be sandblasted and powder coated. It was recommended to me to go with thinner head gaskets. The ones that were on my car , Felpro 8553' are like $14 a piece. Cometic .27 are $98 a piece....Thats a **** ton of a difference. Would it be worth it?
 
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1971 CY Dodge Dart said:
While they may be the 72-73 8.5:1 compression pistons, that doesn’t necessarily mean that’s what your compression will be. Those look like the pistons I have but my compression comes in at 9.0:1.
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That's opposite of what factory engines normally come in. Normally, the 72-73 low compression 340s come in at under 8.5. I've measured a few early and late ones and none were close to what they were rated for. I wonder if yours has aftermarket pistons?
 
gtgto said:
Happy to report i did a wet leakdown test on a few cylinders and they all held fluid overnight. #5 being one of them.I've had the car for more than 8 years and know now the engine is .30 over with cylinder walls that look like they were machined a week ago. Both heads are now at a local machine shop and I even took my manifolds o be sandblasted and powder coated. It was recommended to me to go with thinner head gaskets. The ones that were on my car , Felpro 8553' are like $14 a piece. Cometic .27 are $98 a piece....Thats a **** ton of a difference. Would it be worth it?
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Nope. You'll never know the difference.
 
RustyRatRod said:
That's opposite of what factory engines normally come in. Normally, the 72-73 low compression 340s come in at under 8.5. I've measured a few early and late ones and none were close to what they were rated for. I wonder if yours has aftermarket pistons?
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They do, Sealed Power.
 
gtgto said:
I understand where you are coming from. I am going to stop by Advanced Auto on my way home from work and I will do a wet leak down and see what happens. What should I use for the test? Paint Thinner? I don't see myself pulling the engine and doing a complete rebuild at this point in my life. I have a wife who hates that I spend so much time in the garage, a son in his first year of college and I just found out the subframe on my 08 Police package Charger has a bad subframe so money is not easy to come by. I am going to clean up the pistons the best I can and hope and pray that whatever you don't like about #5, I think that's the piston you're referring to is from a previous problem. I'll keep you all posted.
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How can you do a leakdown test with the heads off?
 
Killer6 said:
It was a fluid leak test, kinda like checking valve seats with parts wash fluid, not an actual leakdown test.
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That will tell him absolutely ZERO regarding ring seal since they have gaps. They are not made to HOLD fluid or pressure for any length of time past the explosion of combustion. The results will mean not one thing.
 
RustyRatRod said:
That will tell him absolutely ZERO regarding ring seal since they have gaps. They are not made to HOLD fluid or pressure for any length of time past the explosion of combustion. The results will mean not one thing.
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Look at the bright side, at the very least it may have dissolved some gummy deposits & freed the rings up a bit, lol...
 
Killer6 said:
Look at the bright side, at the very least it may have dissolved some gummy deposits & freed the rings up a bit, lol...
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Now that's entirely possible.
 
These areas don’t look great. They usually push the gasket into the valley, but no milkshake oil. I always re-torque the Felpro gaskets. The fasteners always turn a bit more after sitting overnight.

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furrystump said:
These areas don’t look great. They usually push the gasket into the valley, but no milkshake oil. I always re-torque the Felpro gaskets. The fasteners always turn a bit more after sitting overnight.

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I’m going through a motor that had weeping 8553pt gaskets. When I pulled the heads the headbolts broke loose very very easily. Made me wonder if they didn’t even torque them…

So since you mention this, when I put the heads back on (felpro 1008 this time) I might let it sit overnight and retorque.
Do you just go retorque them or do you loosen then retorque?
 
For what it's worth, I run the engine through break in, 2 or 3 heat cycles. Then retorque the heads. Felpro #1008's. Yes, it's a pain, you have to pull the exhaust manifolds or headers back. Started doing this after I had my block square decked and new trick flow heads. Made the mistake of using orange antifreeze, both heads leaked. Getting rid of the orange antifreeze and retorquing fixed the issue. Had the same issue of leaking with Fram kinda green looking antifreeze. Use straight good old 3 year green antifreeze.
Several will argue, but that's okay. Just saying what has worked, or not worked for me with 2 cars.
 
It is such a PITA to run it, then re-torque. That I just let it sit overnight. Then in sequence back each one off a 1/4 turn and re-torque. They all turn more. Never had an issue doing it that way. Have pushed the gasket into the valley if I didn’t don’t re-torque. Now I run Cometic, they do not turn farther when re-torquing so I don’t re-torque them.
 
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