No compression in one cylinder.. anything I can do before pulling head?

It has been suggested before , you need to pressurize your cylinder with 120 lbs or air.
Get a fitting or modify what you have, I knocked out the center out of the spark plug and welded a air chuck that fit my hose.
Fill the radiator flush to the top...If you have a leak to the water passage you will see bubbles.
Valves have to be closed when testing.
 
Econoline, I didn't see anything out of the valves or crankcase with the rockers off, but I also didn't see anything with the rockers back on, and I still had no compression. So I'm thinking pushrods are fine, and valves appear to be fine too.

drag-200stang, I'll try to get a hold of a leak down tester so I can pressurize the cylinder. With the gurgling I heard when I was pumping smoke into the cylinder though, I'm pretty sure I'll see bubbles in the coolant when I do that.

I guess the big question is whether a new head gasket fixes the problem, or if I have a crack somewhere...
 
Ok well I feel kinda dumb, I didn't realize that the check valve in the end of the compression tester hose can just unscrew out... so did that, blew air in through the hose and even at only 40 or so psi I could hear air rushing out somewhere. Just to make sure I had the engine turned enough, I pulled the rockers off again, and same thing.

I used a stethoscope and could hear air flowing through the headers, and then I could feel it coming out of the tailpipe. No bubbles in the coolant.

So yeah, I guess head gasket was sealed fine and it's a bad exhaust valve or seat? I guess the head is coming off this weekend. Is there anything basic I can try to repair myself? Or am I better off just bringing the head back to the machinist and have it looked over again?
 
I do not think that you will know till you take the head off and look at it .
Let us know what you find .
 
Ok, got the head off tonight. Honestly, nothing stands out to me.. Attached are a few pics of cylinder #5. The head gasket didn't look like anything blew out or was burnt up.

I'll probably bring it back to the machine shop tomorrow and have them look it over.
 

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that's not the wrong sidea da head 2 look @?
 
Well I stopped by the machine shop today, and he showed me that the back of the valve had a thick coating of film on it, and starting to go up the stem. He said it was caused by bad gas and this was preventing it from closing all the way. He also saw evidence of it building up on some of the other valves too, but not as bad.

The gas was only about a year old, and I usually keep a bit of stabil in it too, but he said he's seeing this more and more every year with gas getting worse and recommended I clean out the fuel tank and blow out all of the fuel lines. He said once the old gas hits the heat of the combustion chamber it gets a consistency almost like Permatex #2.

He's going to give the head a good cleaning, reassemble it, and pressure test it before giving it back, but he seemed pretty confident that was the problem. Luckily I had only idled it for maybe 5-10 minutes, so it wasn't long enough to start burning up the valve, so it's looking like no parts need to be replaced.

What do you guys think? Is the shelf life of new gas really only less than a year now for these engines?
 
"...shelf life of new gas really only less than a year..."
was it ever?
I'd say U get some probs in under/close to 3 mo.

I usta leave my bronk out doors, run it Oct- March every yr w/o problems (6, 7 mo of gas souring in the bowl'n tank) & she'd still start w/a lill tromp to the floor (set the carb linkage on the choke finger - linkage) and a few sec of "key hold-over".

Around Y2K (with the noticeable climate crisis round here) the gas here got more'n more alcohol init. Required same w/either a spry of starter fluid or a drizzle of a few teaspoons of gas in the throat.

I think I C 'that residue' in ur pic. Surprised that's the problem.
 
I think your machinist screwed up & the head has too little clearance in the valve to valve guides.
I would tell him to let you look at the head dissembled & take some photos in the suspected areas.
 
It's been a while, but just wanted to check back in. Fnally got enough put back together to test compression again, and it looks good across all the cylinders! Still not sure if it really was the gas or just needed another cleaning/reassemble, but that was a huge relief. I'm going to drain the gas tank, rebuild the carb, and blow out all the fuel lines, and should be ready to try to run it again.

Thanks again for all the help, I learned a lot on this one...
 
"...learned a lot ..."
but wuz it abt the orig problem?
Important 2 C what it wuz 2 avoid a 2nd time...
Good Luck, hope membership here is useful...
(y)
 
That's fair, in the end I didn't really learn what the problem was other than it seems like it was bad gas... that's an easy thing to avoid. It was certainly a single stuck exhaust valve though that had nothing to do with the rockers/pushrods/etc. What I did learn was a bunch of new tricks for isolating that, which is a huge help for someone who's learning to work on engines as he goes.
 
"...It was certainly a single stuck exhaust valve..."
if ur confident that was "it", then its all that can be hoped for, no?

Forgot now, how far did U got in the 'break in' process?
Motor wuz in vehicle? Ran 20 min?

"...a huge help for someone..."
the rewards of ur willingness get repaid, congrats, keep goin mate!
 
Engine was in the car. It had about 3k on it since the full rebuild. I pulled the head to have a crack in the intake repaired, and while it was out they also cleaned it up, milled it down a bit, and reassembled it. It probably ran for about 20 minutes (like a tractor) while I messed with the timing and carb adjustments before I realized this wasn't going to get fixed by tuning. That's when I shut it down and started trying to track down what the problem was and noticed the lack of compression.

I have everything mostly back together now and plan to rebuild the carb this weekend and then try to start it up running off of a gas can with fresh gas. If that works out, then I'll deal with draining the gas tank and cleaning out the lines.
 
"...the 'break in' process? ..."
tryin to figure out where U R. If it needs the above.
I'm lost here...best to stay out, sorry
:oops:
 
Oh, well the engine was broken in after I had it rebuilt a few years ago.. but I guess that brings up a good question - is there anything special I need to do after this recent head rebuild? I always thought break-ins were just for the piston rings and the cam/lifters which are all in the block in this case.
 
yup, all the rotating prts (inc valves, cam, crank, all of it if it moves).
These were broke in already? nonea dem have been changed or put in w/o 'break in"?

I'm just thinkin "B4 he starts it up..."
If "all set" U can say: "Jump ina lake, Chad."
All I B membah is U sayin U started it up'n shut it dwn quickly cuz -0- compression in #5...
 
I feel your machine shop is at fault.
Too tight of valve guide clearance & possible valve seals that are starving the top end of oiling.
No one can convince me it is fuel related.
 
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