Flying with worn valve guide and/or worn rings?

[ConcernedOwner1]

So I think we’ve either got a bad valve guide or some worn piston rings on our O360. I can hear the engine hiss through the breather tube when pulling the prop through. Our oil usage has increased a little to around 5hrs a quart and it blackens quite quickly after an oil change. That aside, the compressions are still decently good, low 70’s average and it runs well.

Is there a risk of continuing to run an engine with a worn valve guide or ring if the compressions are still acceptable? Not quite ready to spend the money on an overhaul if it can go a bit longer. Advice? Thanks.

 

[455 Bravo Uniform]

You can’t have “worn rings” and “good compression” together. If the compression is good, then the rings and valves are sealing (at least during the test).

 

[Bell206]

Is there a risk of continuing to run an engine with a worn valve guide or ring if the compressions are still acceptable?

What was your mechanics take on your questions as he would be the one to ask. But, in general, based on the info you posted, I don't see any issues and even know some flying aircraft with higher consumption rates and lower compressions.

 

[flyingbrit]

Lycoming's limit for oil consumption is 0.006 x BHP x 4 ÷ 7.4 = Qt./Hr. They do not say whether BHP is the rated power or the operating power e.g. 65% of rated. So let us take the smaller number: .006 X 180 X 0.65 X 4 ÷ 7.4 = 0.38 Qt/hr. This is almost double your actual rate of 0.2 Qt/hr. FAA says minimum "compression" of 60/80 is OK. So according to both these standards you are good to go.

 

[Greg Bockelman]

Does the FAA actually say that or is it just generally accepted practice? I have heard less than 60/80 may be acceptable depending on other factors.

 

[Bell206]

Does the FAA actually say that or is it just generally accepted practice? I have heard less than 60/80 may be acceptable depending on other factors.

The FAA provides the 60/80 guidance in AC 43.13-1B which is similar to what Lycoming gives in their documentation. Continental use a different approach and sets the acceptable leakage rate based on the current ambient conditions via a master orifice which can be as low as 45/80 or even lower. It falls to the person performing the test to decide what is acceptable to them using whatever guidance they see fit.

 

[Dan Thomas]

Both Lycoming and Continental make an O-360. Which one is it?

And when was it last overhauled? Or had new cylinders on it?

 

[Greg Bockelman]

The FAA provides the 60/80 guidance in AC 43.13-1B which is similar to what Lycoming gives in their documentation. Continental use a different approach and sets the acceptable leakage rate based on the current ambient conditions via a master orifice which can be as low as 45/80 or even lower. It falls to the person performing the test to decide what is acceptable to them using whatever guidance they see fit.

Thank you. I didn’t know there was a difference between Lycoming and Continental.

 

[FORANE]

Stable oil consumption of 5 hours a quart doesn't sound too bad.

A sudden increase I had concerned me. I had 3 A&P's tell me I could continue to fly it. One cylinder had oily plugs. Here's what we found.

 

[unsafervguy]

You can’t have “worn rings” and “good compression” together. If the compression is good, then the rings and valves are sealing (at least during the test).

there are cases of a bad oil control ring with decent compression rings that will give you high oil consumption and good compression readings

 

[FORANE]

there are cases of a bad oil control ring with decent compression rings that will give you high oil consumption and good compression readings

Perfect example of that in pic above. We had good compression all around with that broken oil ring.

 

[flyingbrit]

FYI, the broken ring in the picture is the second compression ring, not the oil ring. However, it does act as an oil scraper and can have an effect on consumption as you noticed.

 

[BillTIZ]

FYI, the broken ring in the picture is the second compression ring, not the oil ring. However, it does act as an oil scraper and can have an effect on consumption as you noticed.

Were all of the parts accounted for to complete the ring? No missing metal down in the engine to cause other problems?

 

[FORANE]

Were all of the parts accounted for to complete the ring? No missing metal down in the engine to cause other problems?

Good question. I believe so. We've got about 200 hours on it since that pic.