Piston not firing, compression tests seem normal - 1975 Comet

Hi everyone:

I have gotten the 1975 Comet I just bought here in Dallas. I posted a bunch of pictures of the girl in the new guy section:
http://mmb.maverick.to/showthread.php?t=61087

She's got the straight 6-250 4.1L engine, and it's probably been sitting for a while (a year, maybe 2). Everything else for the most part seems to be in relatively good shape.

Please understand, I am a guy who likes working with his hands, and I catch on very quickly to mechanical repair stuff. I can fix moving lights, I have to believe I can fix this beautiful car.

So far, she runs - on 5 of 6 cylinders. Cylinder 2 will not fire. I have done the following, in order, so far to see if I could get it working:

1. found bad cylinder, took spark plug out, and it was oil-fouled badly (crusty and hard)
2. replaced spark plugs
3. looked down into the non-working cylinder - it has oil in it - coating the walls of the cylinder and the piston
4. replaced spark plug cables and distributor cap/rotor
5. checked the bad cylinder, still won't fire, and new plug had some oil on it already (which I cleaned off and re-installed the plug)
6. Seafoamed the engine, but did not see any white smoke
7. checked compression on the bad cylinder, it stayed solid at 90 PSI
8. put a spark plug non-fouler on the bad cylinder to see if that might work to get the cylinder firing
9. Checked the cylinder before and after the bad cylinder, pressure was 83-85 PSI

I have made sure that there is juice going to that plug, I have made sure the oil is at the correct level, and I have been reading the heck out of my Haynes guide. The guide suggests doing exactly what I did to check compression on the engine, and it also suggests that if you get zero pressure, add some engine oil to the cylinder. If the pressure improves, it is possibly a piston ring issue. If it does not, it could be a valve stem seal.

Since my engine immediately held pressure, but that specific cylinder is coated with oil and goo inside, could it be a piston ring? My wife and I have been researching this issue, and it obviously looks like a monster job. Can a guy who has a decent set of tools and a go-getter attitude even dream to fix this issue in his apartment garage?

The main problem I wanted to solve when I bought this car was to have means of getting around town, as my wife will be commuting and using our only vehicle. At this point, I want to make the car run well. I don't need to put the state of the art equipment in the engine at this point.

What do you think is the point when I keep searching to fix the car, or I sell the car and get something else? We don't want to sell it quite yet, but I am slightly nervous about such a big job, especially not really knowing what exactly is wrong with the engine. I am not scared of the task, just a little nervous because I have never done it before.

What do you think? What should I do?

I love this forum!
Jim

 

Kinda out there, but is that piston even moving? rotate the engine by hand and see if it is moving in the cylinder.

Just a long shot guess, but start there.

And you are seeing a spark on that plug when you turn the engine over?

Everything else sounds like you are doing the right thing.

 

Valve seals.

 

The reason I threw that long-shot out there is if that spark plug is firing, you should be fine. But if the piston is not moving (cap let loose or broken rod way down by the crank) it would not suck in much gas and wouldn't compress it, leaving behind all that gunk.

But first, verify that you have a spark on that plug.Then I will quickly go back and delete that 1st post and deny that I ever said anything that far out...

 

Did you check the spark for that cylinder? If you attach the plug wire to a spark plug, lay the plug on the engine (good ground) and crank the engine you should see a nice blue spark across the plug electrodes.

 

good idea - there is definitely a spark from the plug and the wire both (checked with just wire, checked with plug). I also turned her over once or twice by hand to see if that piston was moving, which it was.

weird, huh?

 

WOW. Talk about getting help and FAST. 3 posts in one minute!

Valve seals are a common problem on our old cars. They are still there, just in crunchy pieces down in the oil pan.

Cheap and easy fix, to boot!

You will need to use the compression tester's screw-in attached to an air compressor to compress the air in each cylinder, buy a cheap spring compressor from O'Reilly's, and pop off the springs and retainers, then slip on new seal, put spring and retainer back on, remove air hose, rotate until next cylinder has two closed valves, and repeat X6.

 

valve seals

I had suspected the valve seals a little after some research, but with my luck I assumed it was "to easy" of a diagnosis. The sarcasm starts when I say "but OBVIOUSLY I am a qualified mechanic..."

Are valve seals something that I could do in a weekend? If I do one, should I do all of them?

Something else that I kind of wondered about, mostly because this is my first foray into amateur mechanicdom - if that cylinder is fouled to bejeezus, could the lack of a clean surface cause it to never fire? What I mean is - can I somehow clean the cylinder out and maybe give it a better chance of working so that it can burn itself out?

I used one bottle of SeaFoam - 1/3 in the carb, 1/3 in the crankcase, 1/3 in the gas tank. Should I get another bottle, maybe try again?

 

Also, and please forgive my ignorance - but is it relatively easy to clean the pistons and valves when I have the valve cover off? Is this something that is way beyond my means? My assumption is that clean everything might make the engine happier, too!

 

Seafoam is crap. I have called it Snake Oil in previous threads.

Once it starts to fire, it will clean itself up in seconds.

Swapping valve seals will take about an hour.

Just make sure you have all the tools handy before you get started. Once you drop that valve into the cylinder, it will be very difficult to get it back out without taking off the head, which is a major job.

 

Scooper, you've got me really pumped about doing this!

 

look for one of these. Or I could mail you mine and let you borrow it, but it would cost as much to mail it back and forth as I paid for it. It is $8 on Summit, I think I paid $12 at O'Reilly.

I think I paid $16 for a set of V8 seals.

 

valve seals ordered! 12 of them at $2.29 each from O'Reilly. They'll be in tomorrow.

Scooper, what's that tool? Is that a spring compressor?

 

Yes.

You will need to take off the valve cover, rotate the engine until both valves are closed on cylinder #1, hook the air compressor up to the compression tester and screw it into the spark plug hole, put pressure on it to keep the valves pushed up. Use about 90psi.

Then use the compressor tool (shown above) to push the springs down, then tap the retainer until it pops down, and remove the 2 valve locks. Don't lose them.

Let off the spring compressor, take of retainer and spring, remove whatever is left of the old seal, put on new seal, put spring back on with retainer, compress it and put retainers back on.

Then turn engine so next cylinder has both valves closed and repeat for all the remaining cylinders.

You may find that the spring tool will force the valve to open causing your compressed air to come out. So just put the tool on the spring and apply moderate pressure and tap the top of the valve with a ball-peen hammer (lightly) until the retainers let loose, then the spring will compress without pushing the valve down.

 

Oh, yeah.

You will also need to drop the oil pan, remove the chunks of old retainer from your pan and oil pump pickup. Most likely replace the pickup tube and screen. That is where all of your old seals have ended up.

This is actually a harder job than swapping the seals. There may be steering components and engine braces in the way.