ZERO compression on number 3

[tercle]

My Tercel started to run on three cylinders the other day.
The day before, it was smooth.

I did a compression check today and I have 0 compression on #3.

Is it possible to back off on the adjuster screws on the rocker arms enough so that they don't open the valves at all?
I was thinking of loosening them all the way and prying both number three valves all the way up.

My thinking is, if there's any compression then, it's definitely a sticking valve.

[xirdneh]

if it was a sticking valve I believe there would be a tapping noice too because the rockers would still move
i recently had a valve stuck open and it tapped
remove valve cover and wiggle the rockers
if one valve is stuck open the rocker will be flopping
burnt valve is more likely

[tercle]

It was tapping for weeks, but I don't hear the tapping anymore.
I took off the valve cover and none of the rocker arms have huge gaps when the engine is not running.
That surprised me.

Is there some diagnostic test that would confirm it is a valve - sticky or burnt - before I pull the head?

[timothygodden]

Pour some oil in #3 do the test again if you get compression then it's bad piston rings, if you get no compression it is a stuck or broken valve

[xirdneh]

Pour some oil in #3 do the test again if you get compression then it's bad piston rings, if you get compression it is a stuck or broken valve

That last line should say "if you get no compression it is a stuck"

[Petros]

no matter the cause, there is no way to fix it without pulling the head.

It is good to narrow it down, likely it is a burnt or damaged exhaust valve, before you do major work, but I can not think of anything that would cause zero compression in one cylinder that can be fixed without removing the head. And after the head is off you may find you have to pull the engine.

You might rotate the engine by hand so the #3 exhaust valve is fully open and than shine a strong flash light into the spark plug hole to see if you can get a look at the exhaust valve (you will have to put your head down low in the engine compartment next to the engine unless you can get a small mirror in there too).

Usually when a valve fails a pie shaped piece breaks off and goes out the exhaust system.

Good luck

[timothygodden]

Good catch xirdneh guess I wasn't fully awake yet, edited it

[tercle]

Squirted in some oil and tested again.
Still zero.

I saw on the Internet you can hold a piece of paper close but not touching the end of the exhaust pipe.
I stretched a piece of standard copy paper about a quarter of an inch away.
It definitely is momentarily sucking the paper in and the paper makes a popping sound on the end of the pipe and the pipe made little carbon circles on the paper.
I am told this test result indicates either a burnt or sticky valve.

So if it's burnt and/or a pie-shaped piece is broken off, how big is the danger of more pieces breaking off into the combustion chamber if I drive it?

[mrdance123]

As Petros said, you're going to have to take the head off,
unless there's something weird, the only other thing I can think of:
a weak or broken spring that can't lift the valve shut.
That you could fix from the top.
You can watch the valves open and shut (or not) while turning engine by hand.
I've run engines with the valve cover off to watch what happens,
but be careful not to splatter oil all over if you rev it up too much - stay at idle.

[Petros]

So if it's burnt and/or a pie-shaped piece is broken off, how big is the danger of more pieces breaking off into the combustion chamber if I drive it?

that cylinder does not get hot any more, so the exhaust valve will not get hot. Though if it is badly heat damaged, anything can happen. I drove mine for a few days on three cylyinders when it happened to me. Though it is likely a damaged valve, so who knows what can happen next.

I have seen 3ac engines completely "drop" a valve while it was running, the piston drove the valve stem all the way through the head, it also damaged the piston and bent the connecting rod. I do not know if it damaged the crank, which is possible it was bent, I scrapped the whole engine. I have also seen 3ac engines that had the whole valve head break off and embed within the piston top, it too badly damaged the head, piston and connecting rod. I was able to salvage the block on that one.

Not worth the risk, all of the valves are just as old and likely about to also fail, driving on 3 cylinders only puts more load on the remaining cylinders. Do not drive it any more than necessary, get the head off, replace ALL of the exhaust valves (the others are not too far from failing either...I learned that the hard way). the exhasut valves do not cost much, and all are likely heat damaged, the #3 just failed first. put in all new valve stem seals while you are at it. the intakes are okay to reuse, they do not get nearly as hot and usually last the life of the engine.

It would be ideal if you can have the valve seats resurfaced too, though you can likely just hand lap them with the new valves to get a decent enough seal.

You will also need a new head gasket while you are at it. follow my procedure over in the repair guides section and you will get it together in one day, and will be good for another 100k plus miles.

To prevent this in the future, always set your spark timing to 10 or 12 deg btdc (not the 5 deg per the FSM). Late timing was done for emissions purposes, the fuel does not burn all the way during the power cycle, reducing emissions, but also reducing efficient. Unfortunately it results in much hotter exhaust (the fuel is still burning when the exhaust valve opens), causing the heat damage to the valves. The most efficient engine, and the coolest exhaust temps come when you have it set at the most spark advance you can get without ping or detonation.

It is hard to believe that by wastefully burning more fuel to travel the same distance that you will reduce environmental impacts. Particularly if you consider the retarded timing results in premature severer engine damage.

[tercle]

Thanks all!
Petros, you called it. When this valve damage is in its early stages, can it make a clicking sound?

Because that clicking sound is gone now.
Replaced the exhaust valves and stem seals, hand-lapped and gave the cylinder head a mild Petros treatment (it was already flat).

[Petros]

looks like the broken off piece was rattling around in there for a bit, likely the source of the clicking sound. You can see there is some pitting damage to the cylinder head on the flat surfaces. fortunately it does not appear the piece was big enough to cause too much damage. you probably had some matching dimples in the piston crown. you are very lucky it was not a much larger piece of valve.

No matter, it is fixed now and likely will never be an issue. Some day if you ever remove the catalytic converter you can retrieve the lost piece of valve.