#4 Cylinder intake valve stuck open Options

[gnomefabtech]

So I'm trying to resurrect this 76 (or is it a 75?) that I just bought and it doesn't have compression on the #4 (rear right) cylinder. After some tests with compressed air it's clear that the intake valve isn't closing. I pulled the valve cover and the rockers move OK but that valve does not close all the way. Everything else looks good.

I have a lift but was wondering if I could pull that head without dropping the engine. It looks like there is room but I'm not sure about the engine tin etc. Seems like either the valve is bent or somehow stuck and maybe I can just fix the one thing there.

Anyone pull heads while the engine is still in the car?

[gnomefabtech]

Thanks for the reply. I'll pull off the intake and maybe be able to see if the seat is dropped. No idea if it ever ran in this condition. I never ran it.

Are dropped seats a common thing on these? The motor looks like it's never been opened and is totally stock.

[VaccaRabite]

Thanks for the reply. I'll pull off the intake and maybe be able to see if the seat is dropped. No idea if it ever ran in this condition. I never ran it.

Are dropped seats a common thing on these? The motor looks like it's never been opened and is totally stock.

So, yes an no.
I re-read your first post this morning with a non-sleepy head and there are some things we should confirm.

You describe #4 as "Rear right." That would be Cylinder 3.
#4 is passenger side forward - the one that is deep in the cooling tins.
Cylinder 1 is Driver rear (shallow)
Cylinder 2 is Driver Front (deep)
Cylinder 3 is Passenger rear (shallow)
Cylinder 4 is Passenger front (deep)

For all the cylinders, the intake valve is the inside valve, and the exhaust valve is the outside valve (when viewing the cylinder bank as a paired set).

Cylinder 3 exhaust the most common valve to fail, followed by cylinder 3 intake. This is because Cylinder 3 is the hottest of all the cylinders due to the airflow under the tins, and the exhaust valves run hotter then the intake valves as the intakes are getting cooled by fuel.

I guess the first thing you should do is make sure the valve is not set super tight and the adjuster isn't holding the valve open. This may likely to be the problem, but it is easy to check, and you need to check valve clearance anyway. AND!!! A overly tight valve is often a sign of a failing valve seat. Or its possible whoever did the last valve check just really buggered up the job - but all things given I think that this is not likely.

I'm also assuming that the engine spins free by hand. If you tested compression and the engine did not lock up or make very bad sounds, that's promising. Another indication that the seat is failing but has not failed.

So the prognosis is better then it was last night when I was posting from bed, but still not great. But there is hope the last person to set valve clearance was just ham handed and got over tight.

Obviously if the valve pops, it will lock up the engine, or damage the piston, or damage the rod, or all three. This is something you want to be SURE about before starting the engine.

Zach