valve guides question

The 160 is the compression..did they also do a leakdown? This will pinpoint the problem and give you a percentage compared to the other 7 cylinders. If everything else is fine and you are purchasing the car knowing you will need valve guides and the price is right I would buy it. There is no way of knowing if it will get worse...drive it and enjoy. Do the valves on it's next service.

 

All this talk about compression tests and leakdown tests to determine if the valves need new guides... I don't understand how worn valve guides have anything to do with engine compression. The guides are outside of the compression chamber. In other words, theoretically you don't need any valve guides to have good compression!

This is my understanding of the symptoms of worn valve guides:
Worn valve guide allow oil and/or air to get into the intake and/or exhaust ports. This could lead to oil getting into the cylinder (oily plugs, high HCs, etc) or into the exhaust (oil into the cat, overheating cat, etc). A lot of oil passing through will show up as high oil consumption and black soot on the back of the car. If air gets past the guide on the intake side, that cylinder could run lean. The air leaking past the valve guides can also screw up the vacuum and makes the engine idle rough.

I think one cylinder with low compression is a sign that either the piston rings are not sealing properly against that cylinder wall, or the valves are not seating properly. A common way of determining which one is the culprit os to add a small amount of oil to the low cylinder and re-test. If the cylinder still reads low, its the valves.

Here is some more basic info on the subject:

http://www.valvoline.com/carcare/articleviewer.asp?pg=ccr20050801cc&print=true

All of this probably doesn't matter that much because once you take the heads off, you will probably want to get new guides and a valve job anyway. It's still going to cost you 10K. But if you want to continue to drive the car with badly worn guides, you risk premature failure of the valve (up to and including possible valve breakage) and possibly damaging some parts of your exhaust system. Could end up costing even more....

 

My (admittedly inexperienced) understanding is the guides get so worn, that the valves move around enough to have incomplete sealing when closed, THIS is what causes the low compression.

 

I suppose it's possible if they were really worn bad. You would be burning a lot of oil. Also, there would most likely be damage to the valves and valve seats.

 

They do, like a quart in 300 miles or less, and yes, valves and seats are often replaced too.