Bad Valves or Rings?

[BobN]

A compression test traced the cause of the cyl. 2 misfire on my 98 Outback
EJ25 to bad compression in that cylinder - it read 25lbs vs. 155lbs for cyl.
4. Since I cannot see or smell any oil burning, is it reasonable to
conclude that the problem is therefore valve-related rather than bad rings?

It will be a lot easier for me to re-do the head than to rebuild the entire
engine, so perhaps this is just wishful thinking.

Your informed, serious comments are much appreciated.

 

[Bob's Backfire Burrito]

A compression test traced the cause of the cyl. 2 misfire on my 98 Outback
EJ25 to bad compression in that cylinder - it read 25lbs vs. 155lbs for
cyl. 4. Since I cannot see or smell any oil burning, is it reasonable to
conclude that the problem is therefore valve-related rather than bad rings?

It will be a lot easier for me to re-do the head than to rebuild the
entire engine, so perhaps this is just wishful thinking.

Your informed, serious comments are much appreciated.

You need to do a "Leak Down" test. When you have pressure on the suspected
cylinder, listen by the oil filler, exhaust pipe and intake for flowing air.
Could be a burned exhaust valve...could be broken rings.....

 

[Dano58]

A compression test traced the cause of the cyl. 2 misfire on my 98 Outback
EJ25 to bad compression in that cylinder - it read 25lbs vs. 155lbs for cyl.
4. Since I cannot see or smell any oil burning, is it reasonable to
conclude that the problem is therefore valve-related rather than bad rings?

It will be a lot easier for me to re-do the head than to rebuild the entire
engine, so perhaps this is just wishful thinking.

Your informed, serious comments are much appreciated.

I assume you did only a 'dry' compression test...? Their are 2 more
tests you can do to narrow it down - do a 'wet' compression test,
where you squirt some oil into the suspect cylinder and re-do the
compression test. If it reads higher, it's the rings. If the same or
lower, it's probably the valves. You can also have a leak-down test
done, where compressed air is squirted into the cylinder, and the
source of the leakage is traced. You probably would need to take the
car to a shop for that one.

Dan D
formerly '99 Legacy L 30th (son's)
Central NJ USA

 

[johninKY]

Other possibilities are valves adjusted too tight and a leaking HG. HG
don't always leak between cylinders. But if I were a betting man, my
money is on a burnt exhaust valve.

 

[Carl 1 Lucky Texan]

I assume you did only a 'dry' compression test...? Their are 2 more
tests you can do to narrow it down - do a 'wet' compression test,
where you squirt some oil into the suspect cylinder and re-do the
compression test. If it reads higher, it's the rings. If the same or
lower, it's probably the valves. You can also have a leak-down test
done, where compressed air is squirted into the cylinder, and the
source of the leakage is traced. You probably would need to take the
car to a shop for that one.

Dan D
formerly '99 Legacy L 30th (son's)
Central NJ USA

I've often wondered how effective this test would be on a horizontal engine.

Carl