: 425 Missing..Need advice



lacville78
03-30-11, 12:48 AM
Hey,

The 425 in my 78 Sedan is missing on 2 Cylinders on the left bank.
I compression tested the engine and all the cylinders are averaging 80psi
Except for the left bank where I have 2 Dead cylinders.
I'm thinking the head gasket is allowing compression to leak between the 2 cylinders.

I know this engine is worn out. But does anyone think it would be worth it for me to only pull one head and fix the 2 dead cylinders?

I'm using the car as a daily and other than the miss engine seems to run good.
Due to the miss I have to change the oil about every month.
I'm just wondering if I could buy some time before a rebuild.

csbuckn
03-30-11, 01:25 AM
You can try that stuff at auto parts stores that garuantee to fix your head gaskets before you take it apart. I've never used it nor do I know what the overall damage to you motor will be using it but it may be worth a shot. Other wise, do both head gaskets.

lacville78
03-30-11, 02:14 AM
You can try that stuff at auto parts stores that garuantee to fix your head gaskets before you take it apart. I've never used it nor do I know what the overall damage to you motor will be using it but it may be worth a shot. Other wise, do both head gaskets.

I almost bought some of that stuff. But I noticed my oil isn't getting coolant in it and the tailpipe isn't smoking.

The stuff works by getting into the water jackets and sealing them up. But I was wondering how would it work if that part of the head gasket isn't leaking.


I might pull the other head while I am at it.

Thanks for the help!

deVille33
03-30-11, 09:35 AM
You have to do more investigating to determine the cause of your low compression. By your description it sounds as if the fuel is going past the rings. You could send your waste oil out for an analysis. NAPA has a kit. You send your sample of the drained oil to their lab and they send you back a desciptive analysis of your oil condition.
You can also test your cylinder sealing by running a sealing test.
You need 1. - Compession tester leader hose with a fitting which you can plug your air compessor line to.
2. - A means to shut off or turn on the air
3. - Regulated air set @ or about 30 #
Remove the spark plug and thread the leader hose into the spark plug hole.
Turn the engine until the engine is on the compession stroke - both intake and exhaust valves closed.
Introduce the air to the cylinder.
Once the cylinder fills, it should hold the air.
If you can hear it escaping, find where it is coming from.
If it is going into the crankcase, your rings aren't sealing.
Going out the tail pipe, you exhaust valve is the culprit.
Coming out the carb, Intake Valve.
Bubbles in the radiator neck, head gasket.
These engines are virtually trouble free and have great longevity. I have only seen wear problems after abuse or after very massive amounts of mileage applied to them.
Does your drain oil smell like fuel? It is possible ( but I doubt it ) that someone ran it in a state of poor tune and burned a hole through the pistons, or that worn valve stems have allowed a carbon build up in the cylinder to compremise the pistons ring lands.
If you don't have the equiptment or doubt your mechanical skills, it's time to take it to your trusted Cadillac technician to have it diagnosed.
You didn't fill out your profile, so I don't know where you are located.


With both valves closed, introdu

lacville78
03-30-11, 11:23 PM
Thanks for the info,
Im located near houston.

The oil is getting dilluted by gas.
I'm going to redo the compression test. And this time I will write everything down and post it. I will also put oil in the cylinders and test them again.
My dad told me about the air method. Basically it is just rotate the engine until the valves close then shoot it with a rubber tipped air gun. And have an assistant listen to the exhaust and carb.

But I don't imagine that would really be worth the effort because if I pull the head the problem will be apparent.

I remember last time I compression tested it the cylinders were low except for the 2 dead ones next to each other on the passenger side bank.

My dad told me the engine could have gotten hot. As there is some evidence that happened. I can see some rust stains where maybe a hose blew at one point.
Anyways he said the engine could have got hot and burned up a ring. I'm wondering wouldnt they all burn evenly?? I know they are supposed to wear evenly.

My whole thing is, I know this is not an ideal situation. To patch this worn out 425.

But, Im suspecting that there is a bad head gasket or burned valves that is causing those 2 cylinders to be dead.

I'm just wondering if I could just fix that issue and drive the car with the worn out engine for some time (without a miss)

That would let me save some money for a 500 build.

I'm thinking before this 425 fiasco is over I'll be out about $200 or so plus my labor.

But the 500 install would cost me around 1,000 to 1,500
Plus id want to rebuild the 400 while I was at it.


So what I would be doing is just buying time.
But you guys are the experts!
I just want to know if what I am proposing is even a viable option