low compression in a TCM cylinder

Checkout_my_Six

Checkout_my_Six

Touchdown! Greaser!
Joined
Mar 4, 2007
Messages
12,490
Location
Maryland
Display Name
Display name:
Check_my_Six
OK...I have this friend who has a low cylinder in his TCM IO-550. It's lower than 50/80, but the TCM SB 3-03 allows that with a borescope inspection.

For those who have done this......what would the log book entry look like to sign that off?
 
did they use the correct gauge for test
 
Checkout_my_Six said:
OK...I have this friend who has a low cylinder in his TCM IO-550. It's lower than 50/80, but the TCM SB 3-03 allows that with a borescope inspection.

For those who have done this......what would the log book entry look like to sign that off?
Click to expand...

"Confirmed low compression on TCM IO-550, cylinder #X. Swapped engine for a Lycoming. Ground run satisfactory. Aircraft returned to service."
:D

[Yes, I know I could get reported and banned for this!]
 
Checkout_my_Six said:
For those who have done this......what would the log book entry look like to sign that off?
Click to expand...
I have not done this on this engine, but the sign off would be something like this. Inspected #X cylinder per Service Bulletin XXXX no discrepancies found. Addition compression test and bore scope inspection to be performed per SBXXXX

50/80 is not good. Were is it leaking? How many hours on the cylinder?
 
"Mediocre maintenance performed. Airworthiness to the lowest allowable standard is complied with at the time of sign-off."
 
AKBill said:
I have not done this on this engine, but the sign off would be something like this. Inspected #X cylinder per Service Bulletin XXXX no discrepancies found. Addition compression test and bore scope inspection to be performed per SBXXXX

50/80 is not good. Were is it leaking? How many hours on the cylinder?
Click to expand...
It's about 48/80 with 400 SMOH....leaking out the usual - exhaust....the exhaust valve guides are probably wearing.
 
Stewartb said:
"Mediocre maintenance performed. Airworthiness to the lowest allowable standard is complied with at the time of sign-off."
Click to expand...
Thanks...your ignorance is showing....:D

Static compression means very little to engine health when reality is dynamic....cept for regulatory compliance. The valve faces look wonderful...btw.
 
No worries. I wouldn't let you work on my planes. My mechanic wouldn't have to ask about mechanic stuff on the internet. ;)
 
Checkout_my_Six said:
Thanks...your ignorance is showing....:D

Static compression means very little to engine health when reality is dynamic....cept for regulatory compliance. The valve faces look wonderful...btw.
Click to expand...
No expert here but I agree with you. If my engine was producing rated power and the borescope came back clean, I'd have no problem operating it.
 
Checkout_my_Six said:
It's about 48/80 with 400 SMOH....leaking out the usual - exhaust....the exhaust valve guides are probably wearing.
Click to expand...

If this is the case and you know what the problem is, why not just fix it now? Or are you just doing this to prove a point?

By the way, I had one act very similar to what you describe recently. Leaking past the exhaust valve and when the valve was staked it would seal up well. It had about 400 hours on it too. I thought for sure the guide was shot but it turned out that it was too tight. A little cleaning and running a reamer through the guide fixed it. A couple of hours of my time restored differential compressions to the 70s.
 
Radar Contact said:
No expert here but I agree with you. If my engine was producing rated power and the borescope came back clean, I'd have no problem operating it.
Click to expand...

I agree. If there are no other indications of a problem I would keep flying it and keep a close eye on it.
The symptoms of heartburn and myocardial infarction share similarities; doesn't mean one should immediately book in for open heart surgery.

However, I can understand Stewartb's perspective too. What I might do here, I might think differently about flying that engine in a 185 in the remote regions of Alaska.
 
Stewartb said:
No worries. I wouldn't let you work on my planes. My mechanic wouldn't have to ask about mechanic stuff on the internet. ;)
Click to expand...
Stewartb said:
"Mediocre maintenance performed. Airworthiness to the lowest allowable standard is complied with at the time of sign-off."
Click to expand...
Hey snarky.....answer the question:

"For those who have done this......what would the log book entry look like to sign that off?"
 
Checkout_my_Six said:
OK...I have this friend who has a low cylinder in his TCM IO-550. It's lower than 50/80, but the TCM SB 3-03 allows that with a borescope inspection.

For those who have done this......what would the log book entry look like to sign that off?
Click to expand...

FYI. That, and many more service bulletins and letters, are no longer valid. TCM released a Standard Practices Manual last year and is now on revision 3. This 500+ page manual incorporates many SB's and SIL's into it. I found the language used in the manual to be very "current legalize" (CYA). I would suggest going to the TCM website and download and read through it if you are going to play by their rules.

http://www.tcmlink.com/pdf2/SIL16-2.pdf
 
Stewartb said:
"Mediocre maintenance performed. Airworthiness to the lowest allowable standard is complied with at the time of sign-off."
Click to expand...

I'm building a home built with unapproved avionics... Little to no FAA oversight, no quality system, few to no double inspections during assembly etc etc etc.
 
I've had one that has read from 44-47 over the last 3 annuals, and two different shops. It's leaking past the rings.

One shop noted that it meet the SB requirements. The other just listed each cylinder compression along with the MO.

I've put 300 hours on since the first test. It burns around a quart every 15-20 hours and the oil looks fine. I'm not pulling the cylinder for a test that meets continentals requirements.
 
dmcummins said:
I've had one that has read from 44-47 over the last 3 annuals, and two different shops. It's leaking past the rings.

One shop noted that it meet the SB requirements. The other just listed each cylinder compression along with the MO.

I've put 300 hours on since the first test. It burns around a quart every 15-20 hours and the oil looks fine. I'm not pulling the cylinder for a test that meets continentals requirements.
Click to expand...
thanks....that's what I was looking for.
 
Checkout_my_Six said:
Hey snarky.....answer the question:

"For those who have done this......what would the log book entry look like to sign that off?"
Click to expand...

Not snarky. Just a different opinion about low compression cylinders. I've had a few TCM engines and remember the years when TCM changed their honing procedures and had cylinder compression warranty claims that overwhelmed them to the point of changing the rules about compression. For myself and the guys I know the only thing that changed was who got to pay for the repairs, because nobody I know is willing to fly behind relatively new cylinders with compressions in the 40s or 50s. Mine came off for repair when they get into the low 60s. And yes, I could tell the difference after they were repaired.

Say you're doing a pre-buy inspection of a plane you intend to buy and one or two cylinders test in the 40s-50s/80. The seller's mechanic says the borescope look-see was acceptable. Do you pay full price for the plane?
Say you buy a factory reman and after 50 hours it has a cylinder in the low 50s. You followed the break-in procedures and the scope looks okay. Are you happy?
I've been in both of those situations. My attitude is consistent with my attitude about cylinders that went low on my watch. Repair them.
 
Stewartb said:
Not snarky. Just a different opinion about low compression cylinders.
Click to expand...
Do you also have an opinion bout fixing it in place?.....without throwing money and parts at it?....that increase the risk of maintenance induced failures?
 
I think that engine guru (Busch?) has had (and written about) a low compression cylinder in his twin that eventually came up in compression after 500 hours. He offered a logical explanation, but it escapes my memory. It's easy enough to find with Google.

His article did not, however, mention how to document this.
 
GRG55 said:
"Confirmed low compression on TCM IO-550, cylinder #X. Swapped engine for a Lycoming. Ground run satisfactory. Aircraft returned to service."
:D

[Yes, I know I could get reported and banned for this!]
Click to expand...

LOL. Now that is funny! Incorrect but funny.

AKBill said:
I have not done this on this engine, but the sign off would be something like this. Inspected #X cylinder per Service Bulletin XXXX no discrepancies found. Addition compression test and bore scope inspection to be performed per SBXXXX

50/80 is not good. Were is it leaking? How many hours on the cylinder?
Click to expand...

A real good start but I'd go a bit further though and make an entry similar to:

Due to compression test reading of 48/80 on #1 cylinder, performed borescope IAW TCM SB 3-03. No defects noted at this time. Retest compression at next 100 hour/annual inspection. Total time: xxx hours.

Signature. Certificate type & number. Date.

Part 43.9 details what you need in a maintenance entry.

Of course if any defects were noticed then they will have to be addressed IAW TCM tech data and a proper entry made for that as well.
 
There is only ONE reason Continental allows such poor compression readings.

To deny warranty claims!!!!!
 
Stewartb said:
Mine came off for repair when they get into the low 60s. And yes, I could tell the difference after they were repaired.
Click to expand...
This 100%. I had a cylinder that the CHT was much lower than the rest, compression was say 50/80. I replaced it and noticed a 10mph increase at cruse....:) By the way Stewart, I used a cylinder from Alaska Aircraft Engines, nice folks...
 
AKBill said:
This 100%. I had a cylinder that the CHT was much lower than the rest, compression was say 50/80. I replaced it and noticed a 10mph increase at cruse....:) By the way Stewart, I used a cylinder from Alaska Aircraft Engines, nice folks...
Click to expand...
Impossible....do you realize the HP required to increase airspeed by 10 mph? That new cylinder didn't do that. :no:
 
Checkout_my_Six said:
Impossible....do you realize the HP required to increase airspeed by 10 mph? That new cylinder didn't do that. :no:
Click to expand...
Nothing changed except the cylinder, same plane same pilot even added 1 antenna for a new used com. GPS and airspeed indicator say it happened....
 
AKBill said:
Nothing changed except the cylinder, same plane same pilot even added 1 antenna for a new used com. GPS and airspeed indicator say it happened....
Click to expand...
I'm calling that a nice 9 mph tail wind...on the GPS.:D
 
Checkout_my_Six said:
I'm calling that a nice 9 mph tail wind...on the GPS.:D
Click to expand...
To tell you the truth as I see it sitting left seat, last summer I was lucky to get 110mph in the B-19 Sport. Since I changed the cylinder this winter I see 120mph as indicated at cruse. Maybe I'm missing something please educate me...:)
 
AKBill said:
To tell you the truth as I see it sitting left seat, last summer I was lucky to get 110mph in the B-19 Sport. Since I changed the cylinder this winter I see 120mph as indicated at cruse. Maybe I'm missing something please educate me...:)
Click to expand...
the physics of that don't work.....in order to gain 10 mph there'd have to be something of the order of an increase of 30HP. One weak cylinder isn't going to provide that kind of increase.
 
Checkout_my_Six said:
the physics of that don't work.....in order to gain 10 mph there'd have to be something of the order of an increase of 30HP. One weak cylinder isn't going to provide that kind of increase.
Click to expand...
Ok, Lets say 150hp 4 cylinder that's 37.5hp per cylinder. One dead cylinder would provide the increase you speak of. Not arguing with you just trying to understand.. Do I need to get the airspeed indicator checked? Stalls at #'s in POH
 
AKBill said:
Ok, Lets say 150hp 4 cylinder that's 37.5hp per cylinder. One dead cylinder would provide the increase you speak of. Not arguing with you just trying to understand.. Do I need to get the airspeed indicator checked?
Click to expand...
unless it spit out a valve....I doubt you were down a whole cylinder (the engine would run extremely rough from the imbalance - rough enough to possibly shake the engine mounts apart). You likely might have gained a few HP....not tens.
 
Checkout_my_Six said:
unless it spit out a valve....I doubt you were down a whole cylinder (the engine would run extremely rough from the imbalance - rough enough to possibly shake the engine mounts apart). You likely might have gained a few HP....not tens.
Click to expand...
When I removed the cylinder I could not believe how scored the piston and cylinder walls were. The cylinder had less than 50 hours on it. Could not understand how the cylinder was destroyed other than having the wrong rings installed, I don't know. Just giving you the facts as I see them.
 
"Due to compression test reading of 48/80 on #1 cylinder, performed borescope IAW TCM SB 3-03. No defects noted at this time. Retest compression at next 100 hour/annual inspection. Total time: xxx hours. "

That SB is no longer valid. I would not be mentioning that in the entry. The standard practices manual has a table detailing what is to be done if the compression is above or below the minimum. Be mindful of what you are quoting, especially with something that has alternate standards, such as AC43.13, which has a 60 PSI limit.

Mike Busch's article is below if interested.

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2013-07_compression-in-context.pdf
 
AK Bill - Where was it scored? Top side? bottom side? all around? Piston head end all along, or crankcase end? If the scoring is opposite, it is a symptom of initially being to tight in the bore, where if the scoring is top side only, could be a symptom of marginal lubrication on startup or a cold start.
 
If borescope looks good, and if you're running good CHTs on same, normal oil consumption- fly the heck out of it for 20 hours and recheck compression. Using Phillips multi? You could try the rope trick lapping the valve seat with it in place, if there's any truth to that technique.
 
Jeff Cutler said:
If borescope looks good, and if you're running good CHTs on same, normal oil consumption- fly the heck out of it for 20 hours and recheck compression. Using Phillips multi? You could try the rope trick lapping the valve seat with it in place, if there's any truth to that technique.
Click to expand...
believe it or not....the rope trick works. :D
 
Jeff Cutler said:
If borescope looks good, and if you're running good CHTs on same, normal oil consumption- fly the heck out of it for 20 hours and recheck compression. Using Phillips multi? You could try the rope trick lapping the valve seat with it in place, if there's any truth to that technique.
Click to expand...

Checkout_my_Six said:
believe it or not....the rope trick works. :D
Click to expand...

Know two people who've done that. One of them, the mechanic was an older guy and wasn't scared of yanking a jug, but had never done the rope thing and wanted to try it and the owner was a friend of his, and game... and it worked great. Sticky valve. Reamed out the valve guide while they had the valve dropped down inside, too.
 
You must log in or register to reply here.
Back
Top