Burnt valve?

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SirFoxx
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My tercel:: 1981 Toyota Tercel w/ 7age

Burnt valve?

Post by SirFoxx »

It seems like I can never catch a break with this car. I recently noticed that my tercel started sounding a bit different while driving, almost like it was not running on all 4 cylinders. I sequentially pulled the plug wires until I found that cylinder #3 isnt firing at idle, or while its revved up. I swapped the plugs and plug wires and nothing changed. Previous to this, while on my way to work, my thermostat got stuck most of the way shut, and the temp gauge got rather close to the red. Could this have caused damage to the valve? I know the exhaust valves are prone to burning, and I have read on here that a few memebers have had the #3 cylinder valve burn.

Also, while checking the spark on #3, I noticed that my spark is an orangeish-purple, as opposed to the bright blue I'm used to seeing. I replaced the dizzy cap a few months ago, and just replaced the rotor and coil today, and the color didnt change. What else should I check? I'm going to clean the connector that feeds power to the dizzy, but am unsure what else to check.
1988 DLX 4wd Tercel Wagon w/ weber (RIP)
1985 4wd Tercel SR5 (RIP)
1986 Base 2dr Hatch (RIP / PARTS)
1986 DLX 4wd Tercel Wagon with ???
1985 DLX 2dr Tercel Hatch w/manual swap
1981 2dr Toyota Tercel w/7age (RIP)
1981 3dr hatch Toyota Tercel w/Turbo 4AGE
1981 3dr hatch Toyota Tercel SR-5
xirdneh
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My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Re: Burnt valve?

Post by xirdneh »

Compression check the cylinders. If one is very low it could be a burnt valve. If two cylinders side by side are low that would be head gasket blown between cylinders.
If burnt valve is suspected squirt motor oil in cyl and check compression again. If pressure does not increase it is a valve.
Love those Tercell 4x4 wagons but they sure suffer from road noise.
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Petros
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Re: Burnt valve?

Post by Petros »

agree with Xirdneh, do a compression check. also, make sure the big vacuum hose that goes to the brake booster is good, once I had a massive leak in it and it caused the #3 cylinder to have no power because it was too lean, per power drop test (pulling plug wire one at a time). I almost pulled the head thinking it was head gasekt, but thought I should do the compression test just to confirm it. It was not the head gasket, and found the cause, saved me a lot of extra work.

running hot would not likely cause the valve to burn, it is usually caused by factory spark timing setting (too low) causes much hotter exhaust gases (fuel is still burning when the valve opens, causing it to overheat).
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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SirFoxx
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My tercel:: 1981 Toyota Tercel w/ 7age

Re: Burnt valve?

Post by SirFoxx »

So I just did a compression test. From 1 - 4 (rad to firewall), they were: 90, 85, 20, 75. Thoughts?

I also checked the timing recently. My first question is: What line, and which way, is the check valve supposed to go on? I noticed that if it was blocking the vacuum, it was ~3* at idle, and if it let vacuum through, it jumped it all the way up to like 20* at idle. I flipped it so it was blocking the vacuum and reset the timing to 10*.

edit: I checked the fsm, apparently the recommended psi is supposed to be 178, and minimum 128. I think this engine is a bit tired. Regardless of that, I think I still have an issue with #3.
1988 DLX 4wd Tercel Wagon w/ weber (RIP)
1985 4wd Tercel SR5 (RIP)
1986 Base 2dr Hatch (RIP / PARTS)
1986 DLX 4wd Tercel Wagon with ???
1985 DLX 2dr Tercel Hatch w/manual swap
1981 2dr Toyota Tercel w/7age (RIP)
1981 3dr hatch Toyota Tercel w/Turbo 4AGE
1981 3dr hatch Toyota Tercel SR-5
xirdneh
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Joined: Thu Aug 04, 2005 11:38 am
My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Re: Burnt valve?

Post by xirdneh »

Check valve, air flow direction, air is being pulled from dist so the valve would be open to that direction of flow. Take it out and suck on each end to determine how it will be installed.
Love those Tercell 4x4 wagons but they sure suffer from road noise.
xirdneh
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Posts: 2121
Joined: Thu Aug 04, 2005 11:38 am
My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Re: Burnt valve?

Post by xirdneh »

Your supposed to disconnect both vac hoses to dist and plug the ends when you set timing
Love those Tercell 4x4 wagons but they sure suffer from road noise.
xirdneh
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Posts: 2121
Joined: Thu Aug 04, 2005 11:38 am
My tercel:: 87 tercel 4x4 wagon w/reringed engine, 83 tercel 4x4 wagon w/salvaged engine and 4.1 Diff's
Location: seabeck, washington, USA

Re: Burnt valve?

Post by xirdneh »

Those are some pretty low readings on pressure, might go up if engine is warm.
If you squirt oil in the three with highest pressure and pressure in them goes up that is supposed to mean rings are worn. Are you going thru a lot of oil?
Love those Tercell 4x4 wagons but they sure suffer from road noise.
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SirFoxx
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My tercel:: 1981 Toyota Tercel w/ 7age

Re: Burnt valve?

Post by SirFoxx »

xirdneh wrote:Those are some pretty low readings on pressure, might go up if engine is warm.
If you squirt oil in the three with highest pressure and pressure in them goes up that is supposed to mean rings are worn. Are you going thru a lot of oil?
I am going through a lot of oil. And I did remove all and plugged the lines when I set the timing as well. It's not surprise to me that the rings are worn.
1988 DLX 4wd Tercel Wagon w/ weber (RIP)
1985 4wd Tercel SR5 (RIP)
1986 Base 2dr Hatch (RIP / PARTS)
1986 DLX 4wd Tercel Wagon with ???
1985 DLX 2dr Tercel Hatch w/manual swap
1981 2dr Toyota Tercel w/7age (RIP)
1981 3dr hatch Toyota Tercel w/Turbo 4AGE
1981 3dr hatch Toyota Tercel SR-5
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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Burnt valve?

Post by Petros »

try the compression test with some motor oil squirted into the cylinders and take the readings again. If #3 does not go up much, likely it is a burnt exhaust valve. if it does go up, along with all the others, looks like it could use a re-ring job. But before you do that you might try a Seafoam oil treatment, than add a can of "Restore" and drive it for a day. If the compession is not improved than it is time to rebuild it.

good luck
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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SirFoxx
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Posts: 335
Joined: Sun Feb 05, 2017 5:42 pm
My tercel:: 1981 Toyota Tercel w/ 7age

Re: Burnt valve?

Post by SirFoxx »

Petros wrote:try the compression test with some motor oil squirted into the cylinders and take the readings again. If #3 does not go up much, likely it is a burnt exhaust valve. if it does go up, along with all the others, looks like it could use a re-ring job. But before you do that you might try a Seafoam oil treatment, than add a can of "Restore" and drive it for a day. If the compession is not improved than it is time to rebuild it.

good luck
So far I've done 2 seafoam treatments. Not much improvement with oil consumption. I did try adding oil to #3 and the reading did not go up. There is a machine shop in KC that specializes in heads, so I will call them to see how much itll cost to get a valve job done and to check to see if the head is still true. While it is at the shop, I suppose I will check to see if I can rering with std rings, or if it needs to get bored out.
1988 DLX 4wd Tercel Wagon w/ weber (RIP)
1985 4wd Tercel SR5 (RIP)
1986 Base 2dr Hatch (RIP / PARTS)
1986 DLX 4wd Tercel Wagon with ???
1985 DLX 2dr Tercel Hatch w/manual swap
1981 2dr Toyota Tercel w/7age (RIP)
1981 3dr hatch Toyota Tercel w/Turbo 4AGE
1981 3dr hatch Toyota Tercel SR-5
User avatar
Petros
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Posts: 11930
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Burnt valve?

Post by Petros »

you can rebuild the head without replacing the rings, but with compression so low it will be down on power. though no harm will come from driving it with worn rings, other than high oil consumption.

the machine shop should be able to resurface the head, I highly recommend replacing all four exhaust valves. When one goes the others may not be far behind (they do not cost much as I recall). You can regrind the intake valves no problem. you should also have new valve stem seals installed, and if they need it, replace the valve guides as well (the machine shop should be able to measure guide wear).
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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SirFoxx
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Posts: 335
Joined: Sun Feb 05, 2017 5:42 pm
My tercel:: 1981 Toyota Tercel w/ 7age

Re: Burnt valve?

Post by SirFoxx »

Just as an update, took the head off, and here is what I found. Totally cant see why it has a dead cylinder.

Image
1988 DLX 4wd Tercel Wagon w/ weber (RIP)
1985 4wd Tercel SR5 (RIP)
1986 Base 2dr Hatch (RIP / PARTS)
1986 DLX 4wd Tercel Wagon with ???
1985 DLX 2dr Tercel Hatch w/manual swap
1981 2dr Toyota Tercel w/7age (RIP)
1981 3dr hatch Toyota Tercel w/Turbo 4AGE
1981 3dr hatch Toyota Tercel SR-5
User avatar
Petros
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Posts: 11930
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Burnt valve?

Post by Petros »

not surprising. VERY IMPORTANT: replace all four exhaust valves. they are all the same age and will soon suffer the same fate (I discovered that the hard way once).

You are fortunate it was a small piece, I have seen several times, a large piece break off into the cylinder and do very severe damage to the engine, in once case it punctured the head, danged the piston, bent the connecting rod and even put a bend in the crankshaft. Basically, it trashed the whole engine: so it is not worth trying to reuse the old exhaust valves at all. they are cheap compared to engine damage.

The intake valves can be reground, they run cool and should not suffer the heat damage the exhaust valves do. have the machine shop check the valve guides for wear, and of course they should install new valve stem seals.

Now, what do do about your rings: they should also be replaced. if the wear in the cylinders is not bad (within spec), than you can replace the old rings with standard size ones. I have found however that is rarely the case, and the block should be rebored oversized, and install oversized pistons and valves. this is a major operation, worth doing but it is costly and takes time. so you might just go for standard rings and live with it for now.

Good luck
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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