Compression Test ... Am I Interpreting Correctly?

[john]

Could use some input. My other car, 1995 Honda Odyssey (I know, it's not a toyota, but an engine is an engine and the Honda forum stinks) with approx. 220,000 miles on a 2.2 liter 4 cyl engine. Failed smog; high HC and Nox. Good spark and fuel.

Compression check: #1 145lbs #2 138 lbs #3 0 lbs #4 147 lbs. Test was done with all spark plugs removed; cranked engine about 5 seconds for each cylinder. Engine was warm.

put 2 tablespoons oil into #3 cylinder and compression rose to 15lbs. Installed spark plugs in other cylinders and tried compression test again on #3 and compression rose to 45lbs. I left the gauge on for approx 5 minutes and the pressure held at 45lbs and did not leak away.

I'm interpreting this as faulty rings in #3. The pressure did rise slightly with the oil added and did not fade away. If the valves or head gasket were at fault, I'm guessing that the pressure would not have held, but would have leaked past the valves. Does this sound correct?

I would like to rebuild or replace this engine, but I do not think I could do it. The engine is actually removed from under the car. I would have to raise the car really high. Really would need a lift. Also, difficult to get to stuff since it is mounted sideways. Really makes me appreciate my Tercel.

I replaced the rod and main bearings years ago by dropping the pan while the engine was still in the car. I also replaced the head gasket a few years ago. I can separate the head from the block with the engine in the car.

If you guys agree that my problem is the piston rings on #3, I will attempt to replace them with the engine still in the car.

thank you for any advice.
john

[Petros]

It is pretty rare that rings in one cylinder will fail. Worn rings are usually low across all cylinders, and yours are actually pretty low. Most likely cause is bad exhaust valves. YOu just have to pull the head, and have all the valves reground, new seals, etc.

However, if you intend to keep the car, it is not that much more work to drop the pan after you have the head off, and than you can slide the pistons out and replace the rings. makes sure you lightly hone the bores, and clean them good, and than install the pistons with the new rings. Be very careful with the ring compressor, it is easy to damage the new rings when installing the pistons. Make sure the bearing caps get installed correctly, and you will be good as new.

I do not care for the transverse engine install at all, but Hondas are one of the worst cars for access, everything is so tight you can hardly get your hand into the engine compartment without removing everything. Honda has always been that way.

[dlb]

while rare, i had an '89 tercel coupe that had the rings on one cylinder give up. it had low compression on that cylinder when i bought it and after many years of faithful service, the rings on that cylinder finally gave up the ghost.

regardless, i agree with petros' approach. while you have it all apart you might as well do both jobs while you're in there, especially if the engine is such a PITA to access.

[john]

Thank you both for your replies. I would like to have the valves serviced, except that when I opened up this engine last time, I was only able to raise the head about 2 inches. That was enough clearance for me to swap my head gasket. I'm hoping this time to have 3 inches of space so I can raise the piston enough to access the rings. Removing the head completely might not be an option. There is so much stuff in the way, including the intake manifold which is crammed next to and under the firewall. It would be really difficult to get to the manifold bolts.

I have looked around the internet and used engines are available. Average price seems to be about $700. I believe I would probably have to have someone install it for me.

Will have to mull this over.

- If the valves are the problem, would the cylinder have held pressure with the compression gauge in place for several minutes.

- Thinking about it, if my rings are bad, would pressure have leaked past them too during the compression test?

Is there any sure way to determine if the problem is just the rings? or just the valves?

thank you, john

[Petros]

classic leak down test is to put a pressure fitting into the spark plug hole and put a compressed air hose on it. Than you listen to the crank case, the exhaust pipe, and the intake manifold. you will hear where it is leaking, or perhaps all places.

You can likely get access to remove the head if you just unbolt the cross member/front suspention and allow it to drop down 3 or 4 inches. You usually an do that without removing everything. I am not familiar with the Oddessy, but perhaps you should peak at the FSM and see if they require removing the engine just to remove the head (might be, but not usually likely). You also might invest in a few more socket extensions and u-joints for the socket wrench set. IF you systematically remove the ducts, plastic covers and heat shields first, it is not so bad.

Good luck.

[john]

Did the leak-down test today. 80% leakage on #3. I listened to the tailpipe, valve cover, dipstick holder, intake, and checked the radiator.

At first I thought I was hearing air; I was listening through a piece of pvc sprinkler pipe. I then realized that I heard the same sound even when I pointed the pipe away from the car. I then did my best to hold my ear next to those openings. Lot's of fun with my ear on a hot exhaust pipe. I actually heard air at the exhaust pipe and realized that I was on the exhaust stroke and not the compression stroke. Once on the compression stroke I could not hear any air leaking anywhere. The stupid harbor freight gauge quit reading, so I completed my testing with the air compressor hooked directly to the spark plug hole.

I went by the machine shop and quizzed them. He felt that if it was just rings, compression would have come up higher with the wet test.

I also realized that when I did my compression tests, the meter holds the result until you purge the air from the gauge. I had been thinking that the air from the compression test was being held at pressure by the cylinder. It sometimes takes me awhile to figure stuff out.

I did notice that when I turned the crankshaft with my wrench to reach top-dead-center that some whisps of smoke came out of the dipstick tube. My guess is that this was some of the blow by that is going past the rings on #3.

Will think about what to do. I may attempt to remove the head and have the valves serviced, and replace all rings... have to buy the whole set anyway.

than you again for any thoughts. I'm a photographer, not a mechanic, but I try my best.
john

[Petros]

Sounds like it could be the valves, it is a lot of extra work, but you can drop the oil pan and remove the pistons when the head is off. Than you can put new rings on the pistons without removing the engine. Though I suspect 90 percent of the problem will be fixed when you have a valve job done.

use this procedure to replace the head when you get it back from the machine shop:

https://tercel4wd.com/forums/viewtopic.php?f=7&t=6059

[john]

Amazing info! Thankyou very much!
john

[john]

Petros, you nailed it. Pulled the head this morning. Two exhaust valves on #3 were burned and slightly cracked at the edge. I was actually happy to see the problem! No more mystery. Head is at the machine shop and will be ready to install this weekend. I actually had a beautiful 70 degree day to work on it. Some nice cool weather out of Washington! Beats the 100+ we will have soon.
Than you again!
john

[Petros]

have the machine shop install all new exhaust valves, they get heat damaged. And after one goes, the others are not far behind. The intakes can be reground without problems, they run much cooler.

After you get it back together, from now on set the spark timing at 10 deg BTDC instead of the factory 5 deg. It will allow the exhaust valves to run cooler (more of the fuel is burned before the exhaust valve opens), but you will have to set it back at 5 deg for your annual smog inspection. The 5 deg setting was an emissions accommodation, but it is bad for the exhaust valves, and for efficiency as well.

Good luck

[dlb]

have the machine shop install all new exhaust valves, they get heat damaged. And after one goes, the others are not far behind. The intakes can be reground without problems, they run much cooler.

After you get it back together, from now on set the spark timing at 10 deg BTDC instead of the factory 5 deg. It will allow the exhaust valves to run cooler (more of the fuel is burned before the exhaust valve opens), but you will have to set it back at 5 deg for your annual smog inspection. The 5 deg setting was an emissions accommodation, but it is bad for the exhaust valves, and for efficiency as well.

Good luck

i think he's still talking about his honda odyssey, petros. sounds like you're giving tercel-specific info. maybe not though!

[john]

Passed smog with the Honda Odyssey today! I had the head off in 4 hours. I followed your advice Petros and just went at it one part at a time. Lots of stuff to remove. Really do appreciate my tercel!

The machine shop serviced the valves and replaced the burned ones and surfaced the head. I installed it in about 8 hours. Went slow and tried not to screw-up. The emissions were still over the limit and a new cat cleaned them up.

Thank you again for the encouragement!
john