Borescope Opinion

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delta727

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delta727
Hi Everyone,

Just received these borescope pictures following a 100-hour inspection on a T206H with a TIO-540-AJ1A. This is the first time I've seen borescope pictures so would really value any opinions on what I'm looking at.

1. How severe are these cylinder wear patterns based on what you've seen in the past? Compressions are all in the 70s but the #5 cylinder is audibly leaking air. The mechanic is advising to pull the #5 jug and to "keep an eye on the others". Does this seem adequate?

2. The mechanic pointed out some white deposits on the outside of the cylinders he thought were unusual (hot spots, or maybe just paint)? Have you ever seen something like this?

3. The engine is leaking oil from a few places (including the crankcase seam as pictured, oil return lines, oil sump) - how common are these types of leaks? This airplane had a lot of cylinder changes with a prior owner (11, including a top overhaul) so I'm sensitive to how well the case was put back together.

Thanks so much for any thoughts, greatly appreciated...

delta727

TIO-540-AJ1A.jpg
 
I definitely would not worry about oil leaking from the upper crankcase seam. That's a common leak point on pretty much all of these engines.

The pictures aren't particularly good quality but I wouldn't be worried about the bores. You mention the #5 cylinder is audibly blowing air, but where through? If it's the rings and the compression is over 70 with oil consumption still reasonable I'd ignore it. If it's an exhaust valve (you didn't include any pictures of the exhaust valves - the biggest concern) I would monitor it but with 70+ compressions that's still not much of a concern. However if it seems like it's leaking somewhere at the cylinder head to barrel connection (or cylinder head itself), then that is obviously a concern. I once saw an engine, not an AJ1A, I think it was an AE2A (Malibu engine) that ended up burning a hole between the head to barrel threads and made a hole the size of a quarter going through the cylinder. Melted the pushrod tube and the pushrod. Obviously undesirable, but the engine did run.

The white deposits look to be hot spots. The AJ1A moreso than any other Lycoming I know of is prone to hot spots, due to a combination of the top mount induction and the cooling air design of the T206H. Essentially the flow is not as even as you'd want it to be. Plus they tend to be run at power settings that make them pretty hot.

We used to have a member here who had a T206H in the DFW area. It's been a while since he participated here, but as I recall he had a significant number of engine issues on his plane. He and I talked some and I gave him some suggestions on how to run his plane LOP, which he started doing. After doing that his CHTs dropped significantly, and fuel burn went down a ton. I can't remember how long he flew the plane after we'd talked about it but I think his engine issues did go away. Of course by that point he'd done a full top overhaul on the plane as I recall, so you'd hope that he'd be good to go for a while.

Bottom line - nothing I wouldn't expect from a T206H based on what you've shown/described at this point.
 
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Ted - thanks for your reply! Yes, I believe #5 is leaking past the rings (the mechanic said he could hear the hissing through the dipstick). Oil consumption is 1 quart every 5-8 hours, so not too bad. I've been doing a lot of reading on LOP and agree that feels like the best recipe for this engine. I'm guessing there's nothing to do about the hot spots, other than checking the baffling and making sure the CHTs stay below 380F?
 
One quart every 5-8 hours is on the high side. I forget the exact oil consumption that Lycoming allows (it's in a lb-oil/hp-hr - in other words how much oil you can consumer per horsepower you're producing in an hour, not per rated horsepower) but I think that's towards the high end of the limit.

If the CHTs are high and there is a cylinder that's starting to leak past the rings, then that's probably your primary cause. That said, if the compressions on that cylinder are still above 70, it can't be in too bad of shape. AJ1A cylinders aren't cheap and I've never been a fan of overhauling cylinders, but on those it can make some more sense. How many hours on the engine?

Regarding hot spots and keeping things cool - yes, make sure the baffles are in good shape (especially look in the nose inlets with a flashlight and make sure the baffles are firmly seated against the top cowl, not scalloped or sagging), and then also get RTV to fill in any gaps around the baffles. Try to keep CHTs at or below 380F.

Did you find what sort of power setting and mixture is being run on it currently?
 
I wouldn't worry about the oil leaks or useage. Lycoming allows up to a quart per hour on the big bore engines. The cylinder wall scaring is a little concerning. Hard to tell from the pictures but could potentially be a stuck wrist pin which is known to happen in Lycomings. I would run it to the next oil change and be sure the check for metal real closely and do another compression test on that cylinder.
 
Grum.Man said:
I wouldn't worry about the oil leaks or useage. Lycoming allows up to a quart per hour on the big bore engines. The cylinder wall scaring is a little concerning. Hard to tell from the pictures but could potentially be a stuck wrist pin which is known to happen in Lycomings. I would run it to the next oil change and be sure the check for metal real closely and do another compression test on that cylinder.
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Fair point on the wrist pin, that could be a possibility if the markings are only where the wrist pin plugs would be and so that might warrant an investigation if they are seen to get worse and, again, only be in that area.

I looked up the formula for maximum oil consumption:

0.006 x BHP x 4 ÷ 7.4 = Qt./Hr.

So on the AJ1A rated at 310 HP, that's right about 1 quart per hour like you said. However it's worth noting that limit is based on running rated power not just for takeoff, but all the time. So if you mostly run at 65% power, then that'd be 1.5 quart per hour.

However if you're really burning anything close to that much, your engine needs attention. Limits are not goals.
 
My 2 cents. Do a compression check and pull the prop before or after TDC and see what the compressions read. If those are actual scores in the cylinder walls see what happens when the rings get to the scores. My bet, down to 20 or so.
 
The 2 pistons I see look clean. New engine/overhaul? Or is this what LOP looks like on the inside? I’m used to seeing absolutely medieval looking coal type stuff on top of pistons, presumably ROP operated engines; Have no idea what LOP looks like.

Also, the lower portion of cylinder 3 is mirror-like. Glazed cylinder?

Lastly, isn’t wrist pin wear usually in one up & down spot? If the pic of 1 is in front or back of the cylinder, then it’s wrist-pin likely.

5 almost looks like it’s ring related, because it’s so wide. If it goes to near the top of the cylinder, it’s probably rings.
 
Thanks for everyone's replies - very much appreciated! To answer some of the open questions, the engine has about 1,250 hours but had a top overhaul 400 hours ago. As this is an aircraft I'm looking to lease I don't have good information into how it's been flown in the past, but I believe the current owner flies it ROP at 75% power. He is having GAMIjectors installed along with this servicing to even out the mixture distribution and plans to fly LOP in the future.
 
To me the Cylinder 1 marks look like the split on one of the rings rubbing up and down. A stuck wrist pin you’d have one single mark up and down at the 3 and 9 o’clock position. Cylinder 3 is probably the piston skirt riding along the barrel and it’s most likely only on one side. This can happen due to long periods of sitting.
 
delta727 said:
The engine is leaking oil from a few places (including the crankcase seam as pictured, oil return lines, oil sump)
Click to expand...

Lycoming has a service bulletin on using a shop vac to draw a vacuum on the interior of the case, and using a specific Loctite to seal the leaks, allowing the vacuum to draw it in.

I sealed the spine of my Cardinals' IO360A three years ago... still oil tight. Works cool!
 
PaulMillner said:
Lycoming has a service bulletin on using a shop vac to draw a vacuum on the interior of the case, and using a specific Loctite to seal the leaks, allowing the vacuum to draw it in.

I sealed the spine of my Cardinals' IO360A three years ago... still oil tight. Works cool!
Click to expand...
I couldn't find that SB - could you post the number?
Thanks!
 
the maximum allowable oil consumption limits for all Textron Lycoming aircraft engines can be determined by using the following formula: .006 x BHP x 4 / 7.4 = Qt./Hr. About 1 qt. per hour for 300 HP if my calculation is correct
 
PaulMillner said:
Lycoming has a service bulletin on using a shop vac to draw a vacuum on the interior of the case, and using a specific Loctite to seal the leaks, allowing the vacuum to draw it in.
Click to expand...
Very interesting concept! Seems like there is no reason this wouldn't work on a Continental engine. Would you mind sharing some of the details, including the Loctite type referenced in the documentation?
 
PaulMillner said:
Lycoming has a service bulletin on using a shop vac to draw a vacuum on the interior of the case, and using a specific Loctite to seal the leaks, allowing the vacuum to draw it in. I sealed the spine of my Cardinals' IO360A three years ago... still oil tight. Works cool!
Click to expand...
My first thought was 'he's joking' but would be interesting if true.
 
Rob58 said:
Very interesting concept! Seems like there is no reason this wouldn't work on a Continental engine. Would you mind sharing some of the details, including the Loctite type referenced in the documentation?
Click to expand...

Pirep on Lycoming Case Leak Repair Technique
12-14-2017, 19:55

Folks,

As recommended by Ed Kollin of Camguard, and further amplified by CFO member Vince Endter who learned of this technique during his recent Lycoming engine school in Williamsport, we put a vacuum on the case via an industrial vacuum duct-taped to the oil filler tube.

We then removed the case-half bolts along the spine of the engine where we had a BAD oil leak (1/2 quart per hour). Then, the area, including the bolt holes and along the spine, were cleaned with MEK to get rid of any oil.

We then used kind-of-pricey Loctite 290 to seal the area. Applying the Loctite to the spine, we could see it wicking down past the open bolt holes. We made roughly three passes with the Loctite, then turned off the vacuum cleaner. We then reinstalled the hardware, and left the plane to sit overnight.

On ground run up, and now after a dozen hours or so of flight operation, the entire area is as dry as a new engine. Amazingly good results! Thank you Ed, Vince, and Lycoming for letting us know about this new technique... we were really surprised by how well it worked!

I'll keep you advised as time progresses, but for now, I'm going flying!

Paul

Pirep on Lycoming Case Leak Repair Technique

Back to 2020: And today, it's still oil tight and clean, 400 engine hours later... even survived a total top, replaced all four cylinders in May last year... due to exhaust valve guide wear.
 
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