Dead cylinder

zenwalk · Post by **zenwalk** » Sun Jul 31, 2005 9:48 pm

I have an '85 4WD, 3A that suddenly lost power going up a hill. Changed the plugs, wires, cap, rotor and all that...cylinder is definitely getting spark so I performed a compression test...#1-200, #2-200, #3-200, #4-25!

I added oil through the spark plug hole and the compression did not improve so I'm told it's not a piston ring problem. I checked the valve clearances and they were all to spec.

Might this be a burned valve? I'm about to remove the cylinder head to inspect it but I don't really know what a burned valve looks like or what I'm really looking for.

Any thoughts or an alternate diagnosis?

clbolt · Post by **clbolt** » Sun Jul 31, 2005 9:52 pm

It does sound like a burned valve, and it should be easy to spot. The edge of the valve will be deformed so that it isn't round at that spot anymore.

zenwalk · Post by **zenwalk** » Sun Jul 31, 2005 10:09 pm

Thanks for that speedy reply CLBOLT.

My manual says to remove the distributor completely when removing the head. It doesn't appear to be necessary, is it?

The less I do that may disturb the timing, the better.

clbolt · Post by **clbolt** » Sun Jul 31, 2005 10:25 pm

I wouldn't remove it to remove the head, but if you're going to replace the burned valve and have a valve job done, you'll end up having to do it anyway.

GTSSportCoupe · Post by **GTSSportCoupe** » Tue Aug 02, 2005 2:31 pm

zenwalk wrote: I have an '85 4WD, 3A that suddenly lost power going up a hill. Changed the plugs, wires, cap, rotor and all that...cylinder is definitely getting spark so I performed a compression test...#1-200, #2-200, #3-200, #4-25!

I added oil through the spark plug hole and the compression did not improve so I'm told it's not a piston ring problem. I checked the valve clearances and they were all to spec.

Might this be a burned valve? I'm about to remove the cylinder head to inspect it but I don't really know what a burned valve looks like or what I'm really looking for.

Any thoughts or an alternate diagnosis?

You don't suddenly burn a valve. It sounds more like a stuck valve or ring, or most likely a blown head gasket. Run some seafoam or something through it to see if it makes a difference (will for a stuck valve/ring).

Check your oil/coolant to make sure they are not mixing. Also check to see if you are burning coolant or oil from that cylinder. Check the plug for signs of this.

Good luck.

clbolt · Post by **clbolt** » Tue Aug 02, 2005 7:42 pm

You absolutely can suddenly burn a valve, and it'll happen while the engine is operating under load. I burned the hell out of one in my 73 Mustang convertible street racing back in 1985. I also burned one in a Honda Civic while climbing through the mountains.

All it takes is a valve which was cut too thin (as was the case with my Mustang), or a combination of a wayward piece of carbon, a worn valve, and a load.

GTSSportCoupe · Post by **GTSSportCoupe** » Tue Aug 02, 2005 11:12 pm

clbolt wrote: You absolutely can suddenly burn a valve, and it'll happen while the engine is operating under load. I burned the hell out of one in my 73 Mustang convertible street racing back in 1985. I also burned one in a Honda Civic while climbing through the mountains.

All it takes is a valve which was cut too thin (as was the case with my Mustang), or a combination of a wayward piece of carbon, a worn valve, and a load.

Interesting! I actually did not know that. I thought it happened over a long period of time from too lean a mixture or something to that effect. In all my years spent on Toyota forums, a burnt valve is something I've actually never heard of. I think it is very rare to happen in a Toyota engine; Toyota must make good valves.

clbolt · Post by **clbolt** » Tue Aug 02, 2005 11:40 pm

GTSSportCoupe wrote: Interesting! I actually did not know that. I thought it happened over a long period of time from too lean a mixture or something to that effect. In all my years spent on Toyota forums, a burnt valve is something I've actually never heard of. I think it is very rare to happen in a Toyota engine; Toyota must make good valves.

Toyota made almost everything good on the old Tercels.

3A-C Power · Post by **3A-C Power** » Wed Aug 03, 2005 7:18 am

Almost everything - notable exceptions are the 2nd and 3rd syncronizer rings

Lateer · Post by **Lateer** » Wed Aug 03, 2005 6:25 pm

Agreed.

There's a job I'm not looking forward to in the near future...

hornett22 · Post by **hornett22** » Thu Aug 04, 2005 12:27 am

burnt valves are common in toyotas actually.it's from vacuum leaks,exhaust leaks,and valves too tight.

xirdneh · Post by **xirdneh** » Thu Aug 04, 2005 4:50 pm

if you get a compression checker (cheap ones around 20.00)
you can pull a plug & insert compression checker and crank over the engine
if the gauge does not build up much pressure or is very low on one cylinder only it could very well be a burnt valve. if one cyliner is low squirt some oil in cylinder and try checking compression again. if pressure increases it is not a burnt valve. pressure should be near 180 on good engine. lower readings are not bad as long as all cylinders are within 10 of each other.

pulling the head requires pullin cam shaft which will mess up timing anyway
so go ahead and yank the distributer but i would recomend getting the number one piston at top of stroke and pulling distributer cap to see where rotor is pointing (looking straight on at distributer the rotor should be pointing nearly northwest) the timing mark on crank pully will be at zero also.
when you reassemble duplicate this