New cylinder or no

[kaweeka]

I have an IO 320 with 730 hours. The plane has run well and shows no change in power or oil consumption. Last Blackstone analysis from November noted an increase in Chrome and iron along with increased blow by. Something that was notably different from the previous oil change. (I send every oil change to Blackstone). I started my annual early this year due to my upcoming extended trip through the Caribbean. I ran the engine for about 15 minutes to get the oil temp to 100F and about 2 hours later, did my compression check. Cylinder #1 would only get 62/80 where last year it was 76/80. All the other cylinders were about the same as last year, 76-78/80. The cylinders are Superior Millennium steel cylinders. I checked the compression several times. I could clearly hear air from the oil filler tube. Soooooo, what to do? If I was staying around the area, I think I would wait a bit since I am home and can replace at any time. However, I'm flying about 8,000 miles and away from home for 3 months. I took everything off around the cylinder to remove it but stopped, thinking I should listen to people with experience rather than yield to my " if it's not right it's wrong" mind set and replace just from a knee jerk reaction. I need some advice please.

Thanks,
David

[wilddog]

Fly it another hr and test again. How do the spark plugs look?

[kaweeka]

Uppers look fine, lowers have some carbon buildup but still pretty good. I'm using the Denso iridium auto plugs recommended by Klaus with his Lightspeed ignition.

[Girraf]

Originally Posted by wilddog

Fly it another hr and test again.

I would never pull a cylinder based on a single compression test. And yes, multiple compression tests in a row isn't the same as doing a compression test after another hour of flight

[Flyhud]

May just be a stuck ring, you can try the Rislone trick, get the cylinder on the compression stroke with the bottom plug in, pour about 12 oz of Rislone down the top plug hole, replace the top plug and apply pressure to the propeller in the direction of normal rotation, this will liquid lock the cylinder and force the Rislone around the rings. Let it sit overnight and drain the Rislone from the cylinder. Run it fly it or whatever and recheck compression. I?ve seen this work well with stuck rings and you have nothing to lose other than a little time and 8 bucks for a bottle of Rislone.

[erich weaver]

Borescope to see what the valves look like

Erich

[lr172]

best guess based upon metallurgy detail, timing and comp results would be a broken ring. If you have already prepped it, might make sense to pull it. a quick hone and new ring set as all that would be required, if that were the case. The hone may not fully remove all scratches but would be quite serviceable for a 700 hour cylinder. A borescope would also help to better narrow down the issue.

One broken ring lowers compression some, but not a lot, as there are two. The edges of the broken ring (now floating in the ring land instead of compressing against the cyl wall) scrape against the cylinder wall and produce the metal debris shown in your oil analysis. If you look in the spark plug hole with a flashlight, you should see vertical straight lines on the cylinder wall for this. These would be the scratches from the ring halves.

A stuck ring would likely show something like 60 on the compression test and account for the new blowby, but doesn't explain the new metal debris.

Larry

[kaweeka]

Narrative from the oil analysis 20 hours ago in November:

"Compared to the engine's history, chrome and iron are a little high. There isn't so much metal we'd
sound any alarms just yet, but the up-trend in wear is something we'll keep an eye on. Maybe it's due to a
change in use (e.g. flight pattern, power settings) or just a temporary departure from the norm. Blow-by
increased as well, but it's not close to being out of line. Fuel is the only contamination, and a trace is mild
(nothing like the 1.3% we found back in the 03/27/18 sample). Check back at the next service for another
look at trends"

This is why I get analysis every oil change. It is a definite break from every other analysis since the engine was new. I appreciate the advice from everyone. What a great resource and even greater people. Thank you, sincerely!

[BillL]

Originally Posted by kaweeka

. . . I'm flying about 8,000 miles and away from home for 3 months.

David, I think I would do another leak check on that cylinder. And wiggle it with the prop at TDC to see if it settles better. If not with your comment, I would agree with you and pull it.

I would also do a bore scope if you have one.

Keep in mind that Vlad flew his 320 with a broken ring for more than a 100 hours (maybe a lot more) with a broken ring. He can tell you exactly how many and what the indications were in that period.

Also, the Voyager engine (around the world plane) had a broken top ring, and it had run over a 100 hours with zero indication of an issue. It was only taken down to modify the case for a CS prop after it broke the wood prop in testing. I was on hand for observation. Meaning: not the end of the world immediately if you have a broken ring. It will be a progressive thing.

On the surface, all of your listed indicators point to something, but it is usually the degree of each. How much did the chrome and iron shoot up in the oil sample? How much increase is the blow-by? Did you find any tiny particle increase of iron or aluminum in the oil filter. My filters now at 100 hrs are absolutely clean of metal flakes. If there is a corresponding, visual, note if metal in the filter, no doubts.

[mahlon_r]

So, if the cylinder is already to the point of un bolting it from the engine, why not just go ahead and do that. Check things visually and if nothing abnormal sticks out like a sore thumb, change the base o-ring and just slide it back on. Its not smart enough to know you took it off. Undoing and redoing the valve train components isn't that much of a big deal. If you see something amiss you got that covered and if not, you spent an extra 1 1/2 hours removing and reinstalling it and will sleep better at night know you saw nothin major wrong..
Just my thoughts...
Good Luck and Happy New Year,
Mahlon