Intake or Exhaust Valve - Can I replace/Typical Cost

[Scout23]

Hey all,

1986 Tercel 3AC driving in cold weather started losing power/running rough and smoking white exhaust. After a head removal discovered a burnt valve on the second cylinder. I'm not sure if it's the intake or exhaust valve as I am just a beginner mechanic. I think it was caused by a loose exhaust piece which allowed super cold air (it was 10 degrees outside) into the manifold. Is the valve something I could replace without to much work or would I have to take to a machine shop? Can only the one valve be replaced by a machine shop fairly cheap or do they have to change them all? If I can replace it where can I source a replacement? I am at the point considering purchasing a new car and not wanting to put much more money into my Tercel. I included pictures to show the damaged valve. My Tercel has been good to me but now I'm driving 70 miles a day and it's a stretch for my Terc. If it's going to cost more than a hundred bucks I'm probably going to put her back together and sell for cheap. Thanks for any input it's much appreciated.

[Petros]

This was not cause by cold weather, it was casued by overhaeted exhasut valves from spark timing improperly set. This is an easy and fairly inexpensive fix now that you have the head off. how many miles on that engine? this happens occasionally on high miles cars. Replacing the exhaust valves is not costly at all.

I highly recommend replacing all the exhaust valves, and the valve stem seals. they do not cost much, and you will need a valve spring compressor that can be rented from an Autozone or other place that rents tools (Autozone is free rental, return the tool and get a full refund). You should be able to replace the exhaust valves and stems seals for about $30. (order on-line at a NAPA website for local deleivery and pick up, save 10 percent). If you pay a machine shop to do it they might charge you about $40 to install them if you bring them your head and the parts. they might want to charge you for other services, but it is not necessary to get it to run good again, so resist the temptation to have it crack checked, resurfaced, etc. A cleaning might be nice, but not necessary, you can do it yourself with a tub of solvent or paint thinner. You can decided when you check on the cost if you want to pay for other services.

follow my instructions on installing a new head gasket over in the repair guilds section. Very important if you want a durable and good running engine.

When you get it running reset your spark ignition at 10 deg BTDC (rather than the stock 5 deg), with the vac lines unplugged and capped off. This will reduce the temp of the exhaust and prevent this from happening again. Consider that you car likely has over 200k miles on it, and even with the 5 deg setting, it lasted that long (the other exhaust valves are not far behind from failure, they have all been heat damaged.). With the time set at 10 deg BTDC your exhaust will run cooler, saves the exhaust valves and you will get slight better fuel economy and a bit more hp too.

If you engine did not consume too much oil, it should give you many more years of low maintenance and trouble free service. the 5 deg setting was a bad idea and used to meet emissions standards, at the expense of extra hot exhaust gases that could damage the exhaust valves. it is important to make them last longer that you set the timing properly.

good luck.

[Scout23]

The engine has approximately 170,000. I replaced the head gasket not to long ago and followed your guidelines. Very helpful. Only thing I didn't do was put the extra holes in the gasket. Do you think this would have helped prevent this? When I set the timing last it was set to 10 almost 11 degrees. I was running at a fairly high speed when this happened but I don't think the timing belt jumped as it runs fine other than not firing on number two and I set the timing to 0 before pulling the head. All seemed in good condition. In order to pull the exhaust valves I should just follow the manual? I believe the previous owner said he had head work done and was thinking he had replaced the valves. Are there signs (color, shape) to look for heat damage to the valves? The first time I pulled the head it was super clean and there were no signs of damaged valves that I could see. The motor has used some oil. I was putting a quart in every few weeks but I actually think it was leaking more than burning it. I've since replaced some seals but didn't get to drive it much before this happened. Thanks again. Hope some can find this information useful.

[Petros]

that is definity heat damage to the valve, not likely they were replaced. they were more likely reground, which makes them thinner and more suspectiable to heat damage. Nothing else causes this kind of damage, it only occures when the exhasut valves get too hot.

Not putting the holes in the head gasket would not affect this, it only makes the head gasket more durable. the exhaust valves run at close to 1000 deg when set at the factory 5 deg BTDC at full throttle, at 10 it would drop it perhaps 200 deg (I have seen it in other engines that had exhaust temp meters). I would replace all the valves, if the valve stem seals are soft and pliable than I would reuse them. If they are brittle like hard candy, replace them.

[Scout23]

Didn't realize they ran at such hot temperatures. Your probably correct that the previous owner didn't replace them because there's a few other things like seals which are super inexpensive he didn't replace. I found the valves and valve stems at Orilleys cheaper than Napa. Will I have to have the new exhause valves ground? Do I have to readjust each valve that I replace to avoid engine damage?

[Petros]

the new valves can go right in, no grinding. the seats in the head, if in good condition, no large pits and the face is shinny, it is fine and can be used as is. if the face of the seat looks pitted and burned you can buy some lapping compound from the autoparts store (it is like really coarse tooth paste) and you CAREFULLY apply it to the face of the valve ONLY (do not get it on ANYTHING else!), insert the new valve and grind it into the seat. work it back and forth for 10 to 15 min, pull it out and wipe out the lapping paste with a clean rag and inspect the seat. this will polish it and remove any pitting. You may have to do this several times until the face is cleaned up. I have also put a low speed drill on the stem end and spun the valve against the seat, going both directions (not too fast). This will speed it up if badly pitted. when done clean everything off very carefully, you do not want any grinding paste to be left in the engine.

Usually this is not necessary, but it is a low cost way to resurface the valve seat in the head.

Once the head is all together, yes the valves have to be adjusted to factory spec because you replaced parts and the relationship with them will be different. I usually do this last after I have the head on the engine. DO NOT forget to do this step, it is very important. If adjustment is too tight that will also overheat the valves because it does not close all the way and it will not cool off.

[Scout23]

Put my order in for parts. Think I am going to give your advice a try and see how it goes. Parts won't be here for at least a week. I didn't find new valve springs or order new intake valves only exhaust valves. Have you typically had to replace the springs? I am probably just going to reuse the existing springs but are damaged springs common? Is the procedure similar for intake valves or is more work needed for them? Do you typically change the intake valves when changing exhaust valves? Thanks for all your help. Much appreciated.

[Petros]

intake valves and springs are very durable, I have never seen a broken, bent or damaged Toyota intake valve or valve spring, nor has anyone reported on it here. the Toyota stuff is very durable, it is only the exhaust valves than suffer this kind of damage, and it is more likely to fail after it is reground (it is now thinner and it is already heat fatigued for years of running).

the intake valves come out the same way the exhaust does, real easy (getting the keeper back in can be tricky, use grease and a magnet to help). You can remove the intakes and lap the seats for a better seal if necessary, but these run much cooler and seldom are they as pitted or worn as the exhaust. or you can just remove the intake valves, and if the seats look fine just replace the stem seal. If you wanted to go first class, you can have an automotive machine shop recut the faces on the intake valves, and the intake and exhaust valve seats. though if they are not bad looking it will not result in any noticeable benefit, only if they are really beat up. if the last owner had the seats reground they should not be too bad anyway.

Remember to keep clean up the lapping compound really good, wash off all the parts with solvent and compressed air. I run a bore brush (like a small bottle brush) up and down in the guild and than spray carb cleaner down it and blow it out. Instal the valve stem seals fisrt (very careful not to damage any of them, best to buy a few extras just in case). Put motor oil on the valve stems before you put it back in and use a dab of grease to hold the keeper in place while you release the valve spring compressor.

Also, keep the valves in the same order, so they go back into the same location. I number the valve heads with a felt pen right on the top. typically the seats and valve faces wear in together and you do not want to change it, unless you are replacing it with a new valve.