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Oh man - sorry to hear that. Your car has hydraulic lifters, right? Is it possible that two just didn't pump up, and maybe some simple cleaning will fix the problem?

I totally understand not wanting to go overboard, although I'm not qualified to give advice on how not to!

Been a frustrating year - hope your car is nicer to you next time you work on it!

Kevin,

What do you mean when you said "But 3 and 4 are not firing, despite the spark plugs working"?

Joe

Joe - I meant that I confirmed the spark plugs are receiving spark and that the spark plugs work (took them out and grounded them against the head while I turned the engine over). However, when the spark plugs are installed back in, pulling the wire off #3 and 4 causes no change to the running of the engine, whereas pulling the wire on the other cylinders causes a definite stumble. I should note the engine was stumbling during our testing yesterday....definitely feels like it's missing.

So I think that means that there is no detonation going on in those cylinders. That's what I meant by not firing.
Intake valves stuck closed? Exhaust valves stuck open?

Fuel and spark shouldn't be the issue, so that leaves air.

-Kevin

Good Morning...You might have a cracked distributor cap...or it may be warped so that the distance between the tip of the rotor and the tit on the distributor are not the correct distance apart...something around 25 thousanths is pretty normal...also, the two plug wires may not be fitting into the distributor cap properly...You are doing great work...Ernie in Arizona

Kevin,

The compression check you posted on 9/7 looked pretty good. You may want to re-check 3 and 4 to verify the compression to eliminate the possibility of a stuck valve(s). Good compression with the other 6 cylinders getting fuel would point to something electrical as Ernie pointed out. Is it possible that you might have a collapsed hydraulic lifter and the intake valve is not opening? That would be a new one on me!

Joe

Even a collapsed hydraulic lifter will still allow the valve to open and close sufficiently for the cylinder to function.

I plan on doing another compression test tonight when I get home to see what 3 and 4 show. My assumption is that they will show zero or very low. If so I'll see if I can figure out a leak-down test and see where it's going. I guess it's possible that I have a blown head gasket, but I don't think that would explain the loud tapping.

I pulled the cap and rotor when my friend and I were diagnosing on Monday. Didn't see any cracks in the cap, but it's not a new one. I don't know that it's an electrical issue because I confirmed that the plugs on 3 and 4 are indeed working.

Depending on what the new compression test shows me, I plan on getting the car back on my neighbor's lift and pulling the valve covers. He suggested running some Marvel Mystery Oil in the crankcase (drain a quart, add a quart of MMO) and run it up to operating temp and let it cool back down. Warm it up again a few times and see what happens. In his experience he's been able to loosen up stuck valves this way. Not sure how comfortable I am letting it warm up to operating temp with the loud tapping I'm hearing, plus I don't know that I trust my dash gauge.

-Kevin

Don't run it until you've determined the problem, especially the noise. Doing so may cause serious damage when it is likely something minor now.

Compression test:

1 - 150
2 - 135
3 - 0
4 - 135
5 - 135
6 - 132
7 - 135
8 - 145

Going to run a leak-down test on #3 after the battery charges. Went back to test #3 again and it sounds like I spent the battery. I left it hooked up the past couple of days on accident and I think I drained some of the power.

****EDIT - Leak down test shows intake valve as the problem. I couldn't tell where the cylinder was because with no compression in the cylinder I couldn't tell where the compression stroke was. So it's possible that it could be something else, but from what I tested all the air was coming out the carb.


-Kevin

OK, so #3 intake is stuck open; not even close to the end of the world. The rapping noise is the lifter coming up smacking it. The cure is starting the engine and letting it run on a high idle. I'd probably add a quart of oil to your tank of gas and turn it into the equivalent of two-stroke mix. There is an excellent chance after a while as the engine gets hot and with the lifter smacking it from the bottom the valve will let loose and come down. Just had this on a '53 I started that had not run since 1976.

#4 is not firing as it shares the intake port with #3 and the flow in and out of 3 is spoiling its mixture.