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1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
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Author:  squighound [ Thu Sep 23, 2021 9:58 am ]
Post subject:  1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Hi,

My wife recently inherited a 1965 Dodge Polara (2 door coupe) with a 225 slant 6 (apparently a rare Canada-only engine option). The car was fully restored about 20 years ago, only has 47k original miles, and is in fantastic condition in general. However, cylinders 4 and 6 are not firing. Compression test shows 0psi on both cylinders (the other cylinders are all around 120psi). Lots of blue smoke. Plugs are good. Checked the valve lashing and other than a couple minor adjustments, it was good (and made no difference). What are my next steps? I'm guessing the car sat quite a bit of the past few years, so am I looking at a couple seized piston rings? Dried out and leaking head gasket? Thanks in advance.
Author:  mcnoople [ Thu Sep 23, 2021 11:05 am ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Pull the spark plugs squirt some oil down the holes (not the tubes the actual threaded holes) into the cylinders. If you can get it to run and get warm the rings might unstick on their own. It won't be a head gasket. I got my 65 2dr valiant about 22 years ago and it had sat for 18 years when I got it. It had no compression on ANY cylinder, some solvent, some time, and some oil got it all working again.
Author:  Rick Covalt [ Fri Sep 24, 2021 9:36 am ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Valves could be stuck in their guides also?
Author:  squighound [ Mon Sep 27, 2021 4:31 pm ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Quote:
Pull the spark plugs squirt some oil down the holes (not the tubes the actual threaded holes) into the cylinders. If you can get it to run and get warm the rings might unstick on their own. It won't be a head gasket. I got my 65 2dr valiant about 22 years ago and it had sat for 18 years when I got it. It had no compression on ANY cylinder, some solvent, some time, and some oil got it all working again.

Thanks - I've been trying this (seafoam intake cleaner, oil, even tried some diesel). No dice so far. When I put liquid into the cylinder through the spark plug holes, I can hear it just dripping through into the oil pan...

A couple more things: The car will run and get up to temp idling, but if I try to drive it, within a mile it will blow the oil breather cap and the pcv valve. It blew the oil cap hard enough to put a dent into the hood from the underside. :(.

Also, I bought a boroscope camera this weekend and took a peek down the affected cylinders. Couldn't see much due to the angle, but I've attached a couple pics of what I was able to see.

Thanks!

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Author:  Jase [ Mon Sep 27, 2021 4:46 pm ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Quote:
Quote:
Pull the spark plugs squirt some oil down the holes (not the tubes the actual threaded holes) into the cylinders. If you can get it to run and get warm the rings might unstick on their own. It won't be a head gasket. I got my 65 2dr valiant about 22 years ago and it had sat for 18 years when I got it. It had no compression on ANY cylinder, some solvent, some time, and some oil got it all working again.

Thanks - I've been trying this (seafoam intake cleaner, oil, even tried some diesel). No dice so far. When I put liquid into the cylinder through the spark plug holes, I can hear it just dripping through into the oil pan...

A couple more things: The car will run and get up to temp idling, but if I try to drive it, within a mile it will blow the oil breather cap and the pcv valve. It blew the oil cap hard enough to put a dent into the hood from the underside. :(.

Also, I bought a boroscope camera this weekend and took a peek down the affected cylinders. Couldn't see much due to the angle, but I've attached a couple pics of what I was able to see.

Thanks!
Uh-oh.. that does not look promising..

I am far from the most experienced here on the forum, but it looks to me like your second picture shows the top of the piston missing, and the piston ring is showing...

If that is the case, then I am guessing long term heavy detonation killed your pistons, but that is just a guess.. and it is a wild guess, so it could be wildly wrong..

My second guess is that gas is making its way past both of your dead pistons, and accumulating in the crank case until the vapors ignite and that is what is blowing your oil cap off.. If you smell the oil on the dipstick It will likely smell strongly of gasoline.
Author:  Daddiojoe [ Mon Sep 27, 2021 6:07 pm ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
I broke a piston in my slant six and pushing oil out the breather cap/blowing the breathing cap out was a symptom. Since you are sure that the valves are opening and closing and the lash is not different from the other valves it looks like you are going to have to get into the block and see about pistons and rings.

Best of luck.
Author:  DadTruck [ Mon Sep 27, 2021 7:39 pm ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Agree, that second photo looks to be a burnt piston.
The only fix is an engine tear down and re build.
Did the slant have any performance work done to it?
Asking as it is very rare for a stock slant to hurt a piston like that.
If you don’t know what may have been done to the engine, be sure to measure piston recession and cc the combustion chambers and take a good look at the cam to see if it is stock or not. Also check the piston ring end gaps.
One more thing, can you post a photo of the car. Those mid 60’s big Dodges were awesome cars.
Author:  squighound [ Tue Sep 28, 2021 8:46 am ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Yeah, that's what I was afraid of. Looks like I'll need to pull the head and get a closer look at the valves and the pistons, then go from there. Might have a winter rebuild project on my hands....

As far as I know the engine is stock. It's a 1965 Dodge Polara 440, but came with a 225 slant 6. Apparently it's a Canada-only option. It was my wife's great-grandmothers, then went to her son (my wife's great uncle) after she passed, and now my wife has inherited it. Restored about 20 years ago, and only about 47,000 original miles. Other than this engine problem it's in great shape.

Thanks for the help, guys.

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Author:  DadTruck [ Tue Sep 28, 2021 9:04 am ]
Post subject:  Re: 1965 225 Slant 6 - 0psi compression in cylinders 4 and 6
Nice Car!
You had mentioned a dented hood from the oil fill cap popping off.
Just an idea, may want to check with on of those hail damage-paint less dent repair shops,
Perhaps they could remedy that.

And is that car also 727 push button tranny and an 8.75 rear?
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