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0 compression on cylinder 2

SwimmingDragonfly96

Well Known Member
Rv7a with a yo-360-A1a, 280 Hobbs total, purchased 2007, first start 2014.

Got some devastating news from my A&P today about my #2 cylinder. I bought this plane, had a pre buy done by an AP/DAR/RV builder, and everything looked great. All cylinders measured 79/80 cold, clean oil analysis on every single oil change.

I have now flown the plane a fun 30 hours. I’m a paranoid guy so I wanted an RV expert up in the bay to give my plane a once over. He just called and told me my #2 cylinder is showing 0 compression with air going through to the case. Didn’t even realize I had engine troubles, even my JPI data looked fine during my flight to the A&P. He cut the filter, no metal, cylinder wall looks fine by borescope, so it must be busted rings? Either way he recommended I replace the entire cylinder.

Just wanted to vent but if anyone has any suggestions or a line on a millennium cylinder kit, please let me know. ALSO, is it normal for a new engine manufactured by lycoming to have millennium cylinders?

Thanks.

EDIT: Spoke to the builder and he said he replaced the covers with the millennium covers when he switched to silicone gaskets. If it comes to a cylinder replacement (which it seems like it might), my A&P says it’s fine to mix and match cylinders. Is this true? Sorry for being a newb, I’m still in disbelief and I bought this plane due to its seemingly excellent condition low time factory new engine.
 
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Rv7a with a yo-360-A1a, 280 Hobbs total, purchased 2007, first start 2014.

Got some devastating news from my A&P today about my #2 cylinder. I bought this plane, had a pre buy done by an AP/DAR/RV builder, and everything looked great. All cylinders measured 79/80 cold, clean oil analysis on every single oil change.

I have now flown the plane a fun 30 hours. I’m a paranoid guy so I wanted an RV expert up in the bay to give my plane a once over. He just called and told me my #2 cylinder is showing 0 compression with air going through to the case. Didn’t even realize I had engine troubles, even my JPI data looked fine during my flight to the A&P. He cut the filter, no metal, cylinder wall looks fine by borescope, so it must be busted rings? Either way he recommended I replace the entire cylinder.

Just wanted to vent but if anyone has any suggestions or a line on a millennium cylinder kit, please let me know.

Thanks.



I'd try to understand the problem before I resorted to cylinder replacement.

Have someone else check the compression.

If the results are the same, it is time to pull the cylinder to see what's wrong with it.

Depending on what you see, maybe you repair it, maybe you replace it. It could be that honing and re-ringing it is all you need to do. That's relatively inexpensive.

And no, a new engine from Lycoming won't have Millenium cylinders.
 
I think I would get a 2nd opinion? Nothing in the oil and running without a massive imbalance seems odd it has zero compression. I attached a pic of my last engine that had zero compression on a cylinder. It burnt a quart every 2-3 hours and the boroscope definitely wasn't good.
 

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I think I would get a 2nd opinion? Nothing in the oil and running without a massive imbalance seems odd it has zero compression. I attached a pic of my last engine that had zero compression on a cylinder. It burnt a quart every 2-3 hours and the boroscope definitely wasn't good.

I wasn’t burning any oil but then last time I checked the oil before taking it in, I noticed it had suddenly burnt half a quart after a 3 hour flight. I also remember a faint smell of oil during that flight.

Already had a second A&P go and confirm 0 compression.
 
With the additional info regarding the increased oil consumption and most likely black colored oil, it certainly points to a piston ring/piston problem.
 
With the additional info regarding the increased oil consumption and most likely black colored oil, it certainly points to a piston ring/piston problem.

Yeah, that makes a broken ring seem more likely. I would still pull/inspect before replacing. If it still runs ok, it means it's making some compression during the stroke, so you might get lucky and be able to replace the ring, hone the cylinder and be okay.
 
I'm not personally doing the work, and it seems like the major $$$ in this is the labor to take apart and put the cylinder back together. I'll probably just go with a new cylinder and call it a day.
 
I'm not personally doing the work, and it seems like the major $$$ in this is the labor to take apart and put the cylinder back together. I'll probably just go with a new cylinder and call it a day.

Why a new cylinder? If you had a leak in your sink drain, would you fix the leak or replace the entire sink? Fix the problem. You have a very low time engine. Odds are everything else is fine in that jug. Have it inspected, but you might very well be good to go with a new piston, rings and cylinder hone. If the cylinder walls are scored or otherwise damaged beyond repair, then you would go for the new cylinder assembly.
 
Why a new cylinder? If you had a leak in your sink drain, would you fix the leak or replace the entire sink? Fix the problem. You have a very low time engine. Odds are everything else is fine in that jug. Have it inspected, but you might very well be good to go with a new piston, rings and cylinder hone. If the cylinder walls are scored or otherwise damaged beyond repair, then you would go for the new cylinder assembly.

The other consideration is availability of cylinders. There have been tales for some time of waiting lists for some (many? most?) cylinders.
 
The other consideration is availability of cylinders. There have been tales for some time of waiting lists for some (many? most?) cylinders.

You stated in your OP that the borescope inspection showed that the cylinder walls were unmanaged. So, why be concerned about the availability of new cylinders? Fix it before the exciting cylinder is damaged.
 
You stated in your OP that the borescope inspection showed that the cylinder walls were unmanaged. So, why be concerned about the availability of new cylinders? Fix it before the exciting cylinder is damaged.

I definitely am interested in the solution that leads to the smallest amount of downtime while also making a permanent fix. I’m not 100% certain they actually have it, but aircraft spruce says it has my cylinder kit in stock for $2k. If I get piston/rings/etc, it’ll probably still be pushing $1k. I figure for a $1k delta, I might as well just get the entire thing and know 100% my problem is gone. Chatted with Jneves a bit and he suggested that if I go with the new cylinder, I might as well OH this one and keep it in storage for down the road.
 
For a mechanic to recommend the cylinder be replaced without removing it and looking at it is irresponsible to say the least. He’s either someone who has no troubleshooting abilities or just flat out hoping the cylinder is good so he can sell it. Yes, strong words but someone has to say it
 
For a mechanic to recommend the cylinder be replaced without removing it and looking at it is irresponsible to say the least. He’s either someone who has no troubleshooting abilities or just flat out hoping the cylinder is good so he can sell it. Yes, strong words but someone has to say it

I can understand your point of view, however, he didn’t say straight away the cylinder needs to be replaced. He just wants the parts available before he disassembles due to unknown down time in the event I do need a cylinder. He recommended having a new cylinder or piston/accessories before he takes anything apart.

As for the A&P himself, he’s just about the most respected/recommended RV mechanic in the entire Bay Area as far as I’ve heard. Actually, no one has recommended anybody else, and at least 5 independent people recommended him. If the cylinder is replaced, I’m keeping the old one.
 
Next step

Before doing anything else, I would do a ring flush on that cylinder. Low cost, no downside. If the problem is stuck rings, that might just clear it up.
 
I agree with the OP. The A&P is not trying to take advantage of him. Sometimes money is not the determining factor to a repair, sometimes it is down time and the owner’s peace of mind. If the cylinder is repairable then it can be done when it is off and now a spare. At the same time a new one can be installed with zero down time. Either way you will need to do a break in because more than likely the old cylinder still needs new rings and a hone. Most A&Ps will have that sent out and not done in the hangar.
 
I had a broken compression ring and got a 50/80. If you are getting 0 with all air going to the case, it would have to be either at least two broken compression rings or a hole in the piston crown. I am not even sure you would get zero with two broken compression rings, as the oil rings should hold a small amount of pressure and give a >0 reading (sorry but no real world experience to back that up). I am thinking that this would have to be more than bad luck and likely some catastrophic event. I would run the engine and make the mechanic do it again to eliminate potential error. We are all human after all. Also, 0 compression should create a noticeable roughness at high power. Low compressions can often result in no noticable affect, but struggle to see that with 0 compression.
 
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At the same time a new one can be installed with zero down time.
Not sure down time is a real consideration here... The plane is essentially grounded now until it's fixed, so maybe reducing the continued downtime is a better way of thinking about it.
 
I had a broken compression ring and got a 50/80. If you are getting 0 with all air going to the case, it would have to be either at least two broken compression rings or a hole in the piston crown. I am not even sure you would get zero with two broken compression rings, as the oil rings should hold a small amount of pressure and give a >0 reading (sorry but no real world experience to back that up). I am thinking that this would have to be more than bad luck and likely some catastrophic event. I would run the engine and make the mechanic do it again to eliminate potential error. We are all human after all. Also, 0 compression should create a noticeable roughness at high power. Low compressions can often result in no noticable affect, but struggle to see that with 0 compression.

Yeah not sure what could be causing it outside of rings. Borescope showed good cross hatch and an inconclusive potential scoring. He did the compression test when I brought it in, he said it was 40 but it was the end of the night so he went home. The next day (yesterday) he repeated and it was 0.
 
I'd start it up, warm it up, do a run-up... and then recheck that cylinder.
If possible be there when the leakdown test is done, so you can confirm that you hear the air blowing at the dipstick tube, not the intake or exhaust.
If still bad, yank the cylinder and investigate.

Might be sticky rings.

A warm value of 40 and a cold value of 0... we don't run the engines cold. So ignore the 0. Get another warm/hot check.
 
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I'd start it up, warm it up, do a run-up... and then recheck that cylinder.
If possible be there when the leakdown test is done, so you can confirm that you hear the air blowing at the dipstick tube, not the intake or exhaust.
If still bad, yank the cylinder and investigate.

Might be sticky rings.

A warm value of 40 and a cold value of 0... we don't run the engines cold. So ignore the 0. Get another warm/hot check.

He said he’s going to recheck mag timing, run it hard on the ground, and retest. I’ll keep y’all posted.
 
Cylinder

You almost certainly have an undamaged cylinder with badly damaged piston and or rings. Running it hard on the ground is a good way to damage the cylinder. PULL THE CYLINDER
 
Other considerations

That was my conclusion when I recently faced a similar problem, but then I discovered that cylinders had basically doubled in price, AND the wait time to get them (around here at least) was being measured in many months, with no truly definite delivery date available at all. So I got my cylinder repaired for half the price of new, and it is now working great.

I'm not personally doing the work, and it seems like the major $$$ in this is the labor to take apart and put the cylinder back together. I'll probably just go with a new cylinder and call it a day.
 
If I went to an A&P with low compression on a cylinder, and he wanted to look at mag timing, I would go find another mechanic.
 
You almost certainly have an undamaged cylinder with badly damaged piston and or rings. Running it hard on the ground is a good way to damage the cylinder. PULL THE CYLINDER

Voice of experience . ...

If I went to an A&P with low compression on a cylinder, and he wanted to look at mag timing, I would go find another mechanic.

Sadly, yes.
 
Voice of experience . ...



Sadly, yes.

Mag timing is totally unrelated! I went in for high CHTs, didn't expect serious mechanical failure in any way. He's just troubleshooting temps while we figure out the cylinder.

Aircraft Spruce had 16 cylinder kits for my plane available and it's shipping tomorrow, so no downtime waiting for cylinders.
 
I'd start it up, warm it up, do a run-up... and then recheck that cylinder.
A warm value of 40 and a cold value of 0... we don't run the engines cold. So ignore the 0. Get another warm/hot check.

With a healthy motor, there is very little difference between cold and hot.
 
Mag timing is totally unrelated! I went in for high CHTs, didn't expect serious mechanical failure in any way. He's just troubleshooting temps while we figure out the cylinder.

Aircraft Spruce had 16 cylinder kits for my plane available and it's shipping tomorrow, so no downtime waiting for cylinders.

Maybe not. So, just how high were the cht's...

If you have any electronic ignition, make sure your mechanic confirms timing with a timing light IAW with MFG instructions.
 
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Borderline unbelievable but he warmed up and rechecked and it was 73. He had an independent IA troubleshooting with him and I had a FaceTime with them and they were both dumbfounded. Going to fly 10 hours and confirm all is well. Thanks for your replies this forum is just phenomenal.
 
well, closing the orifice and opening the main air supply to the compression tester always helps ;)
And now you'll have a spare cylinder kit for next time as well :D

PS
On a serious note, been following this thread as well, but did not need to chime in since all the experts had a go... really happy for you now all ok :) Replacing/removing a cylinder is not a major task, but no 5' job either.
 
So... to some degree my advice was sound [warm it up and re-check]. I couldn't believe that a good running engine would read 0 compression on 1 of 4 cylinders. Further, I found it hard to believe that it could measure 40 hot and then 0 cold. I also found it really hard to believe that your rings are all broken and about to totally ruin your cylinder... but yet somehow there's no particular scoring of the cylinder seen in the borescope! So the rings broke right when you shutdown at the shop? Ah, yeah, sure.

To quote Click & Clack ... 'does this guy have a big boat with a payment coming due?'
All his time on turbines?

Or, like above... turning the orfice valve off on the tester sure helps....
 
So... to some degree my advice was sound [warm it up and re-check]. I couldn't believe that a good running engine would read 0 compression on 1 of 4 cylinders. Further, I found it hard to believe that it could measure 40 hot and then 0 cold. I also found it really hard to believe that your rings are all broken and about to totally ruin your cylinder... but yet somehow there's no particular scoring of the cylinder seen in the borescope! So the rings broke right when you shutdown at the shop? Ah, yeah, sure.

To quote Click & Clack ... 'does this guy have a big boat with a payment coming due?'
All his time on turbines?

Or, like above... turning the orfice valve off on the tester sure helps....

Hah! the 40 wasn't necessarily hot. I flew it in at 11am, he probably tested at 5pm, so I'm not sure if that's considered testing while hot. He had an A&P/IA totally unrelated to his shop there with him, and they both heard the air coming out of the filler neck. I FaceTimed with both of them and they both said they'd never seen anything like this in their entire careers. It was also clear there was no compression when he was turning the prop. I guess the only real possibility is all the gaps lined up on the piston, but who knows, at least surgery has been avoided for now.

As for the A&P, I'm not naming names, but there has to be at least 10 members of this forum who vouch for him. He's the RV guy up here.
 
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Maybe not. So, just how high were the cht's...

If you have any electronic ignition, make sure your mechanic confirms timing with a timing light IAW with MFG instructions.

I hit 400s on all cylinders before 200AGL. By 300-400 if I don't nose down, the hottest will just continue to climb. It went up to 440 on a 110kt climb the other day before I nosed down. That's the hottest I've ever seen it. Usually get to about 424 and aggressively nose down until it starts trending in the other direction.

Dual slicks for me.
 
CHT

I don't mind 425 for short periods but nothing higher. That's just a personal opinion.
Backing off the timing to 22 degrees should lower the CHT and will not have much effect on power.
 
I hit 400s on all cylinders before 200AGL. By 300-400 if I don't nose down, the hottest will just continue to climb. It went up to 440 on a 110kt climb the other day before I nosed down. That's the hottest I've ever seen it. Usually get to about 424 and aggressively nose down until it starts trending in the other direction.

Dual slicks for me.

That shouldn't happen. You should get it checked out. More fuel, wrong timing, or/and really bad baffles??
 
Make double darn sure you have the right jet on the carb. The “Mooney Mod”. I was told I had the right carb when I asked, and fought high CHTs for years. Guess what? Wrong jet.
Correct jet dropped the temps significantly.

At least I never had fouled plugs!
 
Make double darn sure you have the right jet on the carb. The “Mooney Mod”. I was told I had the right carb when I asked, and fought high CHTs for years. Guess what? Wrong jet.
Correct jet dropped the temps significantly.

At least I never had fouled plugs!

Can you buy just the jet and not drill it out? Do you have the PN handy buy chance?
 
Make double darn sure you have the right jet on the carb. The “Mooney Mod”. I was told I had the right carb when I asked, and fought high CHTs for years. Guess what? Wrong jet.
Correct jet dropped the temps significantly.

At least I never had fouled plugs!

I have the 10-4164-1 carb, and I’ve been told this is the carb with the bigger jet so I don’t think I need the Mooney mod. That being said I’m at 15gph full throttle so not sure what’s up w that.
 
I have the 10-4164-1 carb, and I’ve been told this is the carb with the bigger jet so I don’t think I need the Mooney mod. That being said I’m at 15gph full throttle so not sure what’s up w that.

You need some professional help here (probably someone who doesn't get 0 compression on a good cylinder). I just cant see a qualified mechanic accepting 0 compression with no noticeable engine roughness and going to mag timing to address low compression just validates the concern. Getting to 425* CHT a few seconds after applying full power @ 15 GPH in an RV is not right. Something is causing far more heat than normal to be produced or you have a serious flaw in the cooling air flow. I left my cowl plugs in once and at 1000 AGL was just hitting 400. Sorry, but drilling out jets is not the answer unless you have proven that inadequate fuel flow is the cause of your excessive heat. Step one is always to determine the cause of the anomalous behavior and step two is to make a change to address what was found in step one. SOmetimes we have to guess at step one, but be sure it is at least an educated guess based upon experience and diagnostic evidence that points in that direction.
 
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Once Upon

In 45 years playing around with airplanes, I’ve seen only one occasion where a compression check didn’t lift the needle off zero. It was on an old, very weary and decrepit wood wing Mooney that had a number of other catastrophic problems. The owner had just bought it and was flying it home. We discussed renting a trailer the next day but when the boss got to the airport that morning he saw it climbing out, on it’s way. Never heard what happened to the airplane after that.
 
Something fishy here. I have largely quit doing long distance diagnosis, but...

Given two experienced techs independently confirmed a zero leakdown, I'm inclined to think it was true. Let's also assume they could recognize high air volume from the dipstick tube. "Inconclusive potential scoring" of the cylinder wall (post 18) is a possible clue. Toss in a reported very rapid rise in CHT at full power, which suggest a timing or baffling issue. Fuel flow, at 15GPH (90 lbs/hr, or BSFC of 0.5 for 180 HP, and >0.5 with altitude gain) should be fine.

I suspect the top rings stayed stuck in the hot position (deeper in the grooves due to aluminum piston's greater CTE as compared to the cylinder) after cooling, but later released.

Unfortunately the only way to know is per Jim Stanton's post; pull the cylinder for a look at the piston.
 
In 45 years playing around with airplanes, I’ve seen only one occasion where a compression check didn’t lift the needle off zero. It was on an old, very weary and decrepit wood wing Mooney that had a number of other catastrophic problems. The owner had just bought it and was flying it home. We discussed renting a trailer the next day but when the boss got to the airport that morning he saw it climbing out, on it’s way. Never heard what happened to the airplane after that.

Yes my mechanic said it was first time he saw 0 in 25 years. Amazing it jumped back up to 73 the next day. Textron tech support said only thing that could cause that is all the gaps aligning on the ring?
 
Something fishy here. I have largely quit doing long distance diagnosis, but...

Given two experienced techs independently confirmed a zero leakdown, I'm inclined to think it was true. Let's also assume they could recognize high air volume from the dipstick tube. "Inconclusive potential scoring" of the cylinder wall (post 18) is a possible clue. Toss in a reported very rapid rise in CHT at full power, which suggest a timing or baffling issue. Fuel flow, at 15GPH (90 lbs/hr, or BSFC of 0.5 for 180 HP, and >0.5 with altitude gain) should be fine.

I suspect the top rings stayed stuck in the hot position (deeper in the grooves due to aluminum piston's greater CTE as compared to the cylinder) after cooling, but later released.

Unfortunately the only way to know is per Jim Stanton's post; pull the cylinder for a look at the piston.

Hey Dan thanks for your comment. Do you think even though it’s back up to 73 now, I should pull the cylinder? Seems quite invasive.
 
Hey Dan thanks for your comment. Do you think even though it’s back up to 73 now, I should pull the cylinder? Seems quite invasive.

It is invasive. I'm at the other end of the country, not hands-on. Talk it over with your local guys, see what they think about the possibility, and make a decision.
 
Yes my mechanic said it was first time he saw 0 in 25 years. Amazing it jumped back up to 73 the next day. Textron tech support said only thing that could cause that is all the gaps aligning on the ring?

If the two compression rings were stuck it could be low - zero is a hard number to obtain and support the engine running.

DanH's advice is hard to beat.
 
zero is a hard number to obtain and support the engine running.

I have a cylinder which peridocially shows exact 0 compression cold but comes back to seventies hot. No visible issues on the borescope. It's been doing it for like 200 hours without any impact on running. Lycoming sez check it hot, period.
 
I have a cylinder which peridocially shows exact 0 compression cold but comes back to seventies hot. No visible issues on the borescope. It's been doing it for like 200 hours without any impact on running. Lycoming sez check it hot, period.

Thank you for this, feeling all warm inside now haha.
 
I have a cylinder which peridocially shows exact 0 compression cold but comes back to seventies hot. No visible issues on the borescope. It's been doing it for like 200 hours without any impact on running. Lycoming sez check it hot, period.

That is not considered normal. Your motor is talking to you. Ignore it, and it will leave you stranded.....:eek:
 
That is not considered normal. Your motor is talking to you. Ignore it, and it will leave you stranded.....:eek:

I guess the question is, what do you do in this scenario? Seems all noninvasive techniques are kind of exhausted, so do you pull the cylinder and open a new can of worms in terms of risk? I guess I could carry my extra cylinder around with me.
 
I guess the question is, what do you do in this scenario? Seems all noninvasive techniques are kind of exhausted, so do you pull the cylinder and open a new can of worms in terms of risk? I guess I could carry my extra cylinder around with me.

In your case, due to low hours, I would solve the high temp problems and fly it and take action if the "0" comp comes up again.

You can check average compression by (make sure mags are grounded) pulling the prop through all cylinders during your walkaround. The low (dead) one will be obvious. Historically, this was normal practice, but given up for safety reasons.
 
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