Dead hole. What’s the next step

-
69moredoor

69moredoor

Well-Known Member
Joined
May 5, 2019
Messages
506
Reaction score
597
Location
VA
So a few months ago I got a 318/904 cheap. It had sat for a looong time In A 72 valiant supposedly after the owner had passed. I got it home and fabbed up a run stand. All seemed ok (fluids, had some compression in all holes (didn’t write down numbers but all were over 100), clean under valve covers)so I proceeded to getting it running. This was my textbook. I always used pertronix and sucked at timing and carbs so this was it. I’m going to learn and get good.
I rejoiced when she lit and ran well...I’ve been playing with timing and enrichment etc. got her going real well today but she was “shaky” and I couldn’t get past 14-15 on the vacuum gauge when running.since she was running well and I figured the rings weren’t stuck by now....let’s do a dry and wet compression check before posting here..

mall were 120-130 except for cylinder 2.
60.....I tried multiple times and with oil. Got one outlier of 90 but every other time 50-60.
I pulled the valve cover and checked to make sure the valves weren’t stuck. They were still moving
Pulled rocket shaft and checked the pushrods to make sure they were both straight. They were. No cracks in valve springs seen. Rockers back on. Rechecked compression. 0...nothing. Zero!
Checked 4,6,8. Still fine.

so teachers of mopar...what do I do next/check?
Air in cylinder? And see if goes to pan or?
Valve seat check?
 
Make sure both valves on that cylinder are closed. Put air in the cylinder. If you hear it coming out of the carburetor, burned intake valve. Coming out the exhaust, burned exhaust valve. Coming out of the valve cover area, hole in the piston. It will be one of those three.
 
Last edited:
Thanks guys. Next day off is Friday. I will :
1)Put air in cylinder and check for bubbles in coolant/radiator
2)check for air as listed above
3) check oil fill/dipstick tube
4) put borescope in a see what I see
 
Take the rocker gear off the side with the low-compression cylinder. pressurize a Known good cylinder to 80 psi, but stand clear of the fan when you do, because the pressure will blast the piston to the bottom of the cylinder.
Ok now with a mallet, give each valve a lil bop, right on the end of the stem, and straight down; and listen very carefully to the sound it makes. Repeat it several times to burn it in your brain. Also, take note of how it feels when you bop it. The air pressure in the good hole will drive the valve and mallet right back at you, making a beautiful loud popping sound.
Ok now go do the same on the bad cylinder. and note the difference. Keep bopping them until the sound changes. Then continue on the one that is changing.
Why?
Well, in my experience, RUST, or carbon loosened by time, can form on the sealing parts of the valve or the seat, thus keeping the valve from sealing. If this happens in a running engine, already installed, the cure used to be to go out and blow the carbon out of it by a high-speed run, which would usually cure it. But not always, and so , then you were stuck lifting the heavy head over the fender.
But you, having been smart, already found this problem, before ever installing it. So bopping the valve stems is a quick and easy way to let the valve springs crush whatever is in there, and the air pressure will blow it out, and inform you when the job is done. Or not,lol
There is still a chance , as others have said, that there is other damage, But you will find that out in a few minutes once you get to bopping..
BTW using this method with the rocker gear removed, puts the piston at the bottom, so you cannot bend a valve during the bopping. But should the air pressure fail to drive the piston down, you better do it manually by turning the damper; just make sure to not have any air hooked up, while you are doing that, so you don't get maimed.. Furthermore, don't wail on the stems!, just bopping them a few to several thousands of an inch should get it done, if it's gonna get done.
Be advised that any time you shut an engine off, there are always some valves open, and the most open one will have a twin halfway around in the firing order. With a F.O. of 1843/6572 , just count of 4 cylinders and go and check your compression test results, for a low number on that one. If you find that, then it's probably prudent to bop that one too. So to be clear, if you have a bad #8, go check #5. If #2, then check #3. etc
 
Last edited:
Quick update as I ran out to the shed since it’s bothering me:
(Aj. Thanks. Will do that. Saw your post when I came back in)
No visible damage to top of piston no foreign material with borescope
Put air to cylinder. Fan moved a little bit confused me
Air came out of carb. Said oh **** but realized valve wasn’t completely closed
Removed rocker shaft to ensure no pressure
I could hear air in the cylinder. Face to carb nothing
Removed exhaust pipe/muffler Hand over exhaust manifold. Nothing felt
Pulled dipstick. Nothing felt
Pulled breather. Nothing felt
Popped rad cap. No bubbles.
I’ll try aj’s tip. Then I’ll take video to show the air sound in engine/cylinder on friday
**I did not note what air pressure the line was at. Will make sure it’s at 80 Friday

stay tuned. And MANY thanks
 
69moredoor said:
Face to carb nothing
Click to expand...
If carb not at WOT;
Not good enough; air could be transferring to another cylinder, under a closed throttle valve, and exiting somewhere else.

69moredoor said:
Pulled dipstick. Nothing felt
Pulled breather. Nothing felt
Click to expand...
Almost good enough, air could be exiting into the intake up the PCV circuit. You gotta plug all exits from the CC and I use a low-pressure gauge on the dipstick tube; but in times gone by, I would stick a hose on the dipstick tube and put the other end in my mouth

69moredoor said:
Popped rad cap. No bubbles.
Click to expand...
Since the stat is closed, you might have to wait a long time for bubbles. Instead watch for any movement in the liquid, especially a rising liquid level, as, if air is entering the cooling system, it will push the coolant backwards thru the system, displacing it ever higher in the rad, and forcing it to overflow the open filler opening.

69moredoor said:
Removed exhaust pipe/muffler Hand over exhaust manifold. Nothing felt
Click to expand...
probably overkill, but should be accurate. And a really good sign
 
Noted, and will check I owe you a beer. (Several)
 
As usual, this has been made WAY to complex. Good luck. I hope you find it.
 
This is exactly why I love a leak down tester. If the fan moved and the belts are on, it's because the air forced the piston down in the cylinder and turned the crank.
 
RammerJammer75 said:
This is exactly why I love a leak down tester. If the fan moved and the belts are on, it's because the air forced the piston down in the cylinder and turned the crank.
Click to expand...

yeah. I’ll pick one up at China freight
 
Probably carbon or something trapped between the valve and seat. Tapping on the end of the valve like AJ mentioned might do it. You can also try spinning the valve. You can usually do it by hand with a little inward pressure against the spring. If it was a broken ring or hole in the piston, you would have noticed quite a bit of oil smoke coming out of the exhaust, so, I doubt that's the problem. If the oil pressure was good (at full operating temp), and everything was quiet, you should be good. Since the engine is out, I think I'd still pull the pan and take a look at the bearings and timing chain. A fresh re-seal and new freeze plugs will save you grief down the road.
 
cudamark said:
Probably carbon or something trapped between the valve and seat. Tapping on the end of the valve like AJ mentioned might do it. You can also try spinning the valve. You can usually do it by hand with a little inward pressure against the spring. If it was a broken ring or hole in the piston, you would have noticed quite a bit of oil smoke coming out of the exhaust, so, I doubt that's the problem. If the oil pressure was good (at full operating temp), and everything was quiet, you should be good. Since the engine is out, I think I'd still pull the pan and take a look at the bearings and timing chain. A fresh re-seal and new freeze plugs will save you grief down the road.
Click to expand...
Two weeks ago after running it I had a slight weep at the timing chain cover. I replaced water pump and did the timing chain gasket. Chain was fine. Was a steel gear double roller chain. Did oil pan too. Cleaned out the pan. I did t check bearings but for what it’s worth I did try and jiggle the rods with no movement. I did the six lower freeze plugs as there was a lot of gunk antifreeze and man there was a lot of crap in there. Then she got painted and all that was left was to tune it/get good with carbs
 
Pic just because

DC9C5B42-FCB0-4ACF-A841-1248B09752BA.jpeg
 
Well, China freight was out of leak down testers so I amazoned one. I’ll do the test when it gets here ....BUT ...I have a lead. Bear with me
Rockers still removed
did the bongo test. #4 bongo’d so as to learn the sound. And fan spun.
Moved onto #2. Same EXACT sounds as #4. The fan also spun just as much as #4
I also spun the valves before and after bongo test
Next test
made sure throttle was open pressure at 90#
No air out of carb
Coolant level did not move
No air out of exhaust manifold
I cut fingers off a rubber glove, taped them over dipstick, breather, and pcv. They did not inflate at all.
Now remember back to when I said I did the compression test and got 60....then removed rockers to check the pushrods. Then reinstalled and got 0?...

could this cause it. Could this lifter be cause of the exhaust valve to stay open enough?
see pic below
 
A5BD0884-585A-4F10-872A-9C2D532F7E25.jpeg

You can see the plunger is cockeyed and appears to be slipping out. Could it have been starting to eject itself? Then when I checked pushrods it moved out more to where it is?

plausible? Next to check ?
 
69moredoor said:
View attachment 1715697644
You can see the plunger is cockeyed and appears to be slipping out. Could it have been starting to eject itself? Then when I checked pushrods it moved out more to where it is?

plausible? Next to check ?
Click to expand...

If the exhaust valve was staying open, you would have heard air escaping through the exhaust. Did you?
 
RustyRatRod said:
If the exhaust valve was staying open, you would have heard air escaping through the exhaust. Did you?
Click to expand...
I didn’t think so but...I definitely didn’t with the rockers removed. Reinstall and see/double check? I don’t risk any damage doing that do I?(if it comes apart)
 
69moredoor said:
I didn’t think so but...I definitely didn’t with the rockers removed. Reinstall and see/double check? I don’t risk any damage doing that do I?(if it comes apart)
Click to expand...

No, you need the valves closed. You're going in too many directions because the usual suspects have come in and complicated it all to hell and back. The last thing you needed was a leak down tester. That in no way will help you find a DEAD cylinder. You can find it SO much faster with conventional methods. A leak down tester is a tool whose purpose is is to determine the percentage of cylinder leakage. Since you have a dead cylinder and I ASSUME you've gone down every other avenue, such as spark plug, plug wires and the like, your cylinder leak down is 100%.......you don't need a leak down tester to determine THAT.

But you chose who you wanted to listen to, so good luck!
 
Last edited:
I always say start simple. dead cylinder absolutely could mean a dead miss, which could be spark related or electrical. Or loss of compression of course. If something is "broke" Inside the engine it is true you don't need a leak down tester, just hook up a shop hose through a compression tester lead and listen for where the air is hissing out. Either the exhaust, carb, or in the crank case. Doesn't get any simpler or cheaper. I also want to add, a burnt non sealing valve or valvetrain problems will be evident by popping and backfire out the carb or exhaust because the compression is leaking out when the explosion happens when the valves should be closed. Rings? usually pressurize the crankcase, oil blowing out the dipstick tube and what not, if popping through the carb I instinctively pull a valve cover and watch what the rockers are doing. An engine will/should have compression with a worn round cam lobe, but will run like a "dead cylinder". There is alot you can figure out without guages and testers. A basic knowledge of the four strokes of a four stroke engine and mechanical timing etc gets ya started. When you have developed a solid "hunch" then break out the guages and testers. You sometimes will know when the engine has to come apart with out testers.
 
Dartswinger70 said:
I always say start simple. dead cylinder absolutely could mean a dead miss, which could be spark related or electrical. Or loss of compression of course. If something is "broke" Inside the engine it is true you don't need a leak down tester, just hook up a shop hose through a compression tester lead and listen for where the air is hissing out. Either the exhaust, carb, or in the crank case. Doesn't get any simpler or cheaper. I also want to add, a burnt non sealing valve or valvetrain problems will be evident by popping and backfire out the carb or exhaust because the compression is leaking out when the explosion happens when the valves should be closed. Rings? usually pressurize the crankcase, oil blowing out the dipstick tube and what not, if popping through the carb I instinctively pull a valve cover and watch what the rockers are doing. An engine will/should have compression with a worn round cam lobe, but will run like a "dead cylinder". There is alot you can figure out without guages and testers. A basic knowledge of the four strokes of a four stroke engine and mechanical timing etc gets ya started. When you have developed a solid "hunch" then break out the guages and testers. You sometimes will know when the engine has to come apart with out testers.
Click to expand...

That's me. Cheapest and simplest first. Out of necessity. lol I don't own a leak down tester. Never had one. Used one a time or three. I'll never have use for one, because I'll never be in a position where I'll need one. If anything I own starts to exhibit signs of bad ring seal, bad seating valves, or skipping, I'll just fix it. Were I a racer and raced a lot, I would get one. I don't really consider it a diagnostic tool. It's more a measuring device to determine percentage of cylinder leakage and seal. Yeah, I guess you could use it as a diagnostic tool, but as such, it's time consuming and complicated. No line mechanic in the WORLD in their right mind would use one to diagnose a skip. Talk about wasting flag time. LOL
 
Rusty, you’re right. I kept it simple and tried again. If I put me ear over the dipstick tube. Like almost putting my ear in, I can hear air coming out. Guess it’s rings. Ok was hoping not since the fan moved when I first pressurized it, but If I put my ear in the breather hole I can faintly hear it too. Dang

thanks for the help all
 
That lifter in the pic, in it’s current state....... is an issue.

You may be able to maneuver it out of the motor without pulling the manifold.

I’d try and get it out and see if you can figure out how it ended up like that.
 
Good that you figured it out. And like RRR said you were looking for a leak, the leak down tester tells you how much of a leak, you didn't need to know that, you just needed to know "yeah its leaking when it shouldn't be" Its like a "go no go" test. Also like PRH says you take not of any "visual" indicators of what is "broke" . remember think "inexpensive and easy" things first... or KISS method. we all ran out and bought parts when we were starting out, but it gets expensive. have you ever bought a starter only to find out its the battery or a bad cable? Also dont be afraid to tear that thing down. Its fun and you'll learn something :)
 
Last edited:
You must log in or register to reply here.
-

Back
Top