1 Million Gallons of Oil on m'Belly!

[moosepileit]

Is there any benefit to direct compression baselining? The single recording gauge on one cylinder while the others are sparkplugs removed, powered by the starter.

Measures the entire stroke, not just TDC.

Will a ring issue show up more clearly than a differential test at TDC?

[Paul 5r4]

My numbers for #1-3-4 were 76 or better over 80. #2 was 65/80. My local FBO friend helped me, (A&P). Although he didn't get down and put an ear to the exhaust etc, said he did say he didn't hear any hissing/leaking. As far as the increased oil on the bottom... I never noticed when it actually started. I've just noticed more than the first several years it's been flying recently an increase in oil. I can't say it was a sudden increase... I just don't know. Also I've been watching the oil levels closely and it doesn't seem to need anymore that usual. My usual is maybe a third to half quart in maybe in 10 hours.

[lr172]

Originally Posted by moosepileit

Is there any benefit to direct compression baselining? The single recording gauge on one cylinder while the others are sparkplugs removed, powered by the starter.

Measures the entire stroke, not just TDC.

Will a ring issue show up more clearly than a differential test at TDC?

I am a believer that traditional compression tests are generally more valuable than leak down tests (what they call compression tests in the avaiation world). However, there is a place for leak down tests. The combination of both provides the greatest diagnostic benefit.

I think both tests should show a cracked ring. A cracked ring can be a bit tough to catch, as two rings are used and one cracked ring won't change the compression as much as most would expect.

Larry

[DanH]

Originally Posted by Paul 5r4

My numbers for #1-3-4 were 76 or better over 80. #2 was 65/80. My local FBO friend helped me, (A&P). Although he didn't get down and put an ear to the exhaust etc, said he did say he didn't hear any hissing/leaking.

Darn, right in the marginal range.

There is definitely some hissing/leaking, even with the 76 psi cylinders; that's why they were not 80/80. The question is where and how much.

Four ways for air to escape:

1. Ring leakage
2. Valve seat leakage
3. Spark plug seat leakage
4. Cracked head

The rings always leak a little unless submerged in oil, so you should expect some crankcase hiss. I try to ignore it, instead checking the other three items first. They are fairly critical, while ring leakage is not.

Opinions vary, but I think the best way to check valve leakage is to drop the pipes, intake and exhaust. That puts your ear right there at the open ports. You may be able to feel blowing air with your hand. You can even slap a sealed cover plate on the port. It's not hard to fabricate. If the leakdown value jumps up, well, there you go....a sure diagnosis. Intake valve leakage isn't good, but it's not nearly as critical as exhaust valve leakage. If the exhaust can't sit in good contact on its seat, it will overheat and melt eventually.



Plug seat problems are best found with a bottle of Mr. Bubble.

Don't discount a cracked head. The worst ones leave black oil tracks on the outside of the head, so a visual inspection is a good start. Peer between every fin, in particular the crown and cylinder thread areas. If suspect, bring out Mr. Bubble again.

This is an O-200 cylinder. With it pulled and on the bench, it's easy to seal the base with a plate and a sheet of rubber, and do all kinds of checks. Here the problem was pretty obvious (see the gooey black oil tracks?), but I wanted to see how evident the hiss might be, and I already had the base plate from my A-65 days.





If process of elimination doesn't net a culprit, it is a ring problem. Lycoming and Continental have very different ideas about static vs dynamic ring seal. Read the referenced service information.

[Paul 5r4]

Thanks for your response Dan! To make sure I understand, those black streaks on that cylinder are without fail a sign of some sort of cracking of the cylinder???

[DanH]

Originally Posted by Paul 5r4

Thanks for your response Dan! To make sure I understand, those black streaks on that cylinder are without fail a sign of some sort of cracking of the cylinder???

Yes, although to be the cause of your year-old leakdown result, they would probably be more than a streak.

The location in the above photo says the crack is at threaded connection which ties the steel cylinder to the aluminum head.

[Paul 5r4]

Your expert advice is always appreciated! Thanks Dan! When I get back from Sun and Fun, (driving this year), I'm going to have another look at my number 2 cylinder!

[Bavafa]

Just curious if the source of oil leak was found?

[bkervaski]

Just curious if the source of oil leak was found?

Yep! One of those little blue aluminum elbows had a hairline crack. Only discovered after replacing the oil cooler and one of the hoses, it was the only thing left.

Note that the oil cooler manufacturer wants us to use steel fittings, although I put new Vans recommended fittings back in place.

(I didn't want to de-rail the thread, was turning into some informative stuff)

[DanH]

Originally Posted by bkervaski

Yep! One of those little blue aluminum elbows had a hairline crack. Only discovered after replacing the oil cooler and one of the hoses, it was the only thing left.

Note that the oil cooler manufacturer wants us to use steel fittings, although I put new Vans recommended fittings back in place.

Curiosity question...was the cracked elbow a real AN fitting? If not, I missed it on the TC call.