half the compression

Bought the 64 Valiant 3 years ago, and it has/had run great. The previous owner had the original motor rebuilt. Last year I did a compression check just to see what it had. It had a 144psi average, so above stock. Well over the last few months the car has been driven 500 miles a week. I was riding to work with my brother, but he sitched to another shift.*
So I noticed the the gas milage has been dropping. So I did a tune up, but not much help. Over the last couple weeks the power and mpg have dropped. Did a compression check this morning and had a 70psi average with #2 cylinder reading 0. Didn't have time today, but will do a leak down test tomorrow.*
Never seen all cylinders drop like that at the same time. Anyone else have this happen? My first guess is valve seats had enough. I see a lot of people putting money in the block and going cheap on the head. Secon guess cheap cast rings. I've put 30,000 plus miles on it. Not sure how many the previous owner put on it. Th oil and coolant look great, so thinking head gasket may be ok.
Did set the valves about 4,000 miles ago, started to run ruff. All were set pretty close. But #2 exhuast i did have lto back off a bit. That's why I am leaning toward the seats.Seen quite a few heads with exhaust valves sucked in the head.

Yup sounds like seats. You can put air in each cylinder with the valves closed and verify. Air escaping through the tail pipe would verify exhaust valves are not seating.......for whatever reason.

Or a valve adjustment gone tight, possibly due to valve seat recession, but could also have just been set too tight.

Try doing a wet and dry compression test, that will help determine if it's in the cylinder wall or valves...

exhaust seats my guess 30000miles is the magic number from my experience , with people not using harden seats ,unless your carb is way lean then sooner,

AJ/FormS said:

Or a valve adjustment gone tight, possibly due to valve seat recession, but could also have just been set too tight.

Click to expand...

Yeah if it already isn't too late...........