64' C 172E engine compressions

Flybo01

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Flyby30
Looking to buy a C172E, engine at TBO 1900hr (0-300) but its last compressions check was done 3 months ago and it shows:
1)72/80
2)76/80
3)68/80
4)76/80
clean spark plugs, no oil leaks no defects on the muffler. will I need a new engine right away?
 
will I need a new engine right away?

If it has been inspected and certified as airworthy, legally no.

Physically, with what has been given, maybe/maybe not. What did the last oil filter examination look like? Does it make rated static RPM with the correct prop installed? What does the history say of how it has been run and looked after? What is the oil consumption?

I would be finding a mechanic you can trust to look at it and give a proper hands-on analysis.

PS You are missing a couple of cylinders there!
 
Isn't an O-300 a six cylinder engine? :confused:o_O:p
 
Besides the missing two... Can't Continentals go much lower in compression readings than Lyc's before there is an imminent rebuild typically? At least with compressions but compressions is not the only thing to look at... Jaws is right, you gotta have more info.
 
Thank you all for the replies.....sorry about the missing info....somehow I thought I wrote all compressions....the other 2 are

5 72/80
6 74/80

Flew it just recently and she did great. started right up and engine sounded and felt very smooth. Oil looked clean and it showed no sign of leaks under it. My mechanic is doing a thourough inspection for corrosion and borescope the engine. I will probably overhaul the engine anyway if the sale price is right.
 
Looking to buy a C172E, engine at TBO 1900hr (0-300) but its last compressions check was done 3 months ago and it shows:
1)72/80
2)76/80
3)68/80
4)76/80
clean spark plugs, no oil leaks no defects on the muffler. will I need a new engine right away?
No that's very typical of a TBO 0-300-D, with this compression it has had cylinder work.
I'd continue to fly it until it gives signs of needing an over haul.
 
Flew it just recently and she did great.

Then leave it alone, go fly.
The hours you get now are free engine hours, the overhaul will cost about $22-25k.
You don't know if that crank can be re-used. add $12K for another one. So get as many hours out of this one as you can.
Then buy a mid life used 0-300-D from a salvage yard.
 
Theres no reason, safety or otherwise, to rebuild an engine thats performing well, and is checked well to be in good condition... there are plenty of failures on fresh or newish rebuilds...
 
Continental publishes the instructions for that: https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiTk_zE_ureAhVEITQIHbvoBoMQFjAAegQIAxAC&url=https://www.jerrytemple.com/assets/Uploads/templesTips-page/pdf/Continental-Service-Bulletin.pdf&usg=AOvVaw3kKorvXv-8MuNnr_IkuObx

Scoot down to pages 14 thru 17. The master orifice test will establish the minimum compression for that day at the prevailing atmospheric conditions. We used to see mid-40s on that test, so that was the minimum required by Continental. Pretty low. I wouldn't want it that low, myself.
 
Continental publishes the instructions for that: https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiTk_zE_ureAhVEITQIHbvoBoMQFjAAegQIAxAC&url=https://www.jerrytemple.com/assets/Uploads/templesTips-page/pdf/Continental-Service-Bulletin.pdf&usg=AOvVaw3kKorvXv-8MuNnr_IkuObx

Scoot down to pages 14 thru 17. The master orifice test will establish the minimum compression for that day at the prevailing atmospheric conditions. We used to see mid-40s on that test, so that was the minimum required by Continental. Pretty low. I wouldn't want it that low, myself.
The master oriface test was brought out to enable the big bore TCM engines to pass a static compression test.
For the 0-300-/0-200 50 CI cylinders the regular old static test is all you need. Any reading below 70/80 you will hear where the air is going.
You don't need to get fancy to know what's happening :)
 
From past issues, here is what I recall on the question of "What does the future hold for this engine?"
Do these things:
Observe it starting; and running during all phases of flight. (sounds, vibrations, power)
Oil analysis history
Oil filter inspection
External appearance of engine (corrosion, leaks)
Comp testing (done correctly).
Cylinder scoping (barrel, piston, head, valve head/face/seat valves in motion)
Take off valve cover, observe for stem wobble
Where able, bottom end scoping (cam lobes, lifters)
Pull cylinder, if able pull lifters - in any case look at cam & lifters
Oil consumption
How fast oil gets watery or dark
Spark plug appearance (oil stained? burned, cracked insulation? etc)
Exhaust stack inner surface appearance
Logs - work done and age of components
Stored in high corrosion area or not (Miami or Phoenix?)
(Add yours here)

Once you have all this info, go straight to the Ouija Board and there will be your answer.
(mostly j/k on the this last point - however must say that - b/c on many of these engines, tests or observations will not tell you what is going to happen in 6-12 months Ie you will see people correctly quote "It's a crap shoot!")
 
The master oriface test was brought out to enable the big bore TCM engines to pass a static compression test.
For the 0-300-/0-200 50 CI cylinders the regular old static test is all you need. Any reading below 70/80 you will hear where the air is going.
You don't need to get fancy to know what's happening :)
On that Continental SB, it says, under Models Affected, "All Teledyne Continental Motos (TCM) engine models." Not just big bore engines.

And it's not intended to isolate the leaks; as you say, your ear does that. It's just a calibration standard to compensate for varying atmospheric conditions. Altitude, temperature and humidity all affect the readings. The Master Orifice is made by TCM to let you know what they think is an acceptable level of leakage.
 
On that Continental SB, it says, under Models Affected, "All Teledyne Continental Motos (TCM) engine models." Not just big bore engines.

And it's not intended to isolate the leaks; as you say, your ear does that. It's just a calibration standard to compensate for varying atmospheric conditions. Altitude, temperature and humidity all affect the readings. The Master Orifice is made by TCM to let you know what they think is an acceptable level of leakage.
Do you understand why TCM brought that master oriface test out?
When you do, you'll understand why the 0-300/0-200 doesn't need it.
 
Do you understand why TCM brought that master oriface test out?

https://www.aviationpros.com/articl...compression-testing-subject-to-interpretation

"In 1984, TCM determined that the calibration methodologies for various compression testers in the field were not consistent due to the lack of a uniform airflow requirement. To correct this, the master orifice tool was created to properly identify the pressure corresponding to 25 percent leakage. TCM's field experience has identified compression testing systems where the master orifice readings for 25 percent leakage are less than 50 psi. In simple terms, you probably wouldn't even look at these cylinders until the reading was less than 50, not 60. Make sure your facility has and is using this tool for your differential compression test."
 
Thank you all for the replies.....sorry about the missing info....somehow I thought I wrote all compressions....the other 2 are

5 72/80
6 74/80

Flew it just recently and she did great. started right up and engine sounded and felt very smooth. Oil looked clean and it showed no sign of leaks under it. My mechanic is doing a thourough inspection for corrosion and borescope the engine. I will probably overhaul the engine anyway if the sale price is right.
Oh, for corn sake. I had a '64 172 with those compressions for nearly 15 years before I pulled it down for sucking a quart of oil every three hours. That sucker will fly with those compressions until the rings become bubble gum. Go get yourself an airplane.

Jim
 
It doesn't have a filter, unless aftermarket. The screen can only catch stuff with a serial number on it.

Jim
Actually Jim, if you have a screen, and change oil at 25 hours, your engine is being cared for better than those running oil to 50 hours.

Think about it.. you're checking for metal every 25 hours, and having a fresh additive package
 
https://www.aviationpros.com/articl...compression-testing-subject-to-interpretation

"In 1984, TCM determined that the calibration methodologies for various compression testers in the field were not consistent due to the lack of a uniform airflow requirement. To correct this, the master orifice tool was created to properly identify the pressure corresponding to 25 percent leakage. TCM's field experience has identified compression testing systems where the master orifice readings for 25 percent leakage are less than 50 psi. In simple terms, you probably wouldn't even look at these cylinders until the reading was less than 50, not 60. Make sure your facility has and is using this tool for your differential compression test."
TCM wrote that propaganda when they were required to rationalize to the FAA why they could allow their cylinders to go to 40 or lower.

I have a beautiful bridge I'd like to sell ya ... :)
 
Actually Jim, if you have a screen, and change oil at 25 hours, your engine is being cared for better than those running oil to 50 hours.

Think about it.. you're checking for metal every 25 hours, and having a fresh additive package
No argument from me there. I was just answering the person who didn't know that the O-300 came out with screen when he suggested that they cut the filter and look for pieces.\

Jim
 
How often shes flown is a more serious issue, if its been 8 years id worry its more imminent than if those hours been added right along too. In my hunt i looked for regularly flown since rebuild as much as i did TT... i will take my continental as far as shell go with safe compressions, good oil analysis, filter inspections, and oil consumption and general performance when she says its time its time, 1400 hours or 3400 hours...
 
Again thank you all for your inputs on this....huckster79, she is flown regularly I just don’t know how often. Hopefully my mechanic doesn’t find anything that will make me walk away from her like bad corrosion etc...does anyone know what is the normal oil temperature at low cruise altitude flying 500ft for about an hour sea level...surface temp 29C (had to do it because ATC) He had a digital meter and at one point it reached 220 degrees...gauge needle still showed on green....
 
What then were you going to examine? The color of the can or the condition of the threads?

Jim

I wrote "oil filter examination". Maybe that is the original screen, maybe that is a remote filter, maybe it has both (I have heard that can occur). I don't really care what form the oil filtration unit comes in. I apologize if I was not clear.

What I was trying to convey to the OP is that good compressions and lack of oil leaks are only part of the story when determining if an engine needs an overhaul. Static RPM, oil consumption, logbook history, oil filter examination, off the top of my head, are also factors. These are the things I would be looking at.
 
What I was trying to convey to the OP is that good compressions and lack of oil leaks are only part of the story when determining if an engine needs an overhaul. Static RPM, oil consumption, logbook history, oil filter examination, off the top of my head, are also factors. These are the things I would be looking at.
All the symptoms that have been mentioned can be cured with new cylinders. Most of the engines I see for overhaul don't need the lower end done.
Inspect the cam and lifters when you have the cylinders off, then make the decision.
 
Again thank you all for your inputs on this....huckster79, she is flown regularly I just don’t know how often. Hopefully my mechanic doesn’t find anything that will make me walk away from her like bad corrosion etc...does anyone know what is the normal oil temperature at low cruise altitude flying 500ft for about an hour sea level...surface temp 29C (had to do it because ATC) He had a digital meter and at one point it reached 220 degrees...gauge needle still showed on green....
That temp is no worries.
 
Again thank you all for your inputs on this....huckster79, she is flown regularly I just don’t know how often. Hopefully my mechanic doesn’t find anything that will make me walk away from her like bad corrosion etc...does anyone know what is the normal oil temperature at low cruise altitude flying 500ft for about an hour sea level...surface temp 29C (had to do it because ATC) He had a digital meter and at one point it reached 220 degrees...gauge needle still showed on green....
According to the TCDS for that engine, the max oil temp is 240°F. It will hit that easily in your airplane if the ambient temps get higher or you have a long climb. Most likely the baffling and seals need fixing, and the blast stubes from the rear baffle down to the oil screen housing might be out of alignment or missing altogether. I have found the bottom front baffling missing on one old 172; it directs the air from the small inlet hole (under the prop) along the oil pan to cool the oil. That missing part not only leaves the pan uncooled, but the tremendous leakage to the underside of the engine drastically reduces the pressure differential that the entire cooling system relies on.
 
According to the TCDS for that engine, the max oil temp is 240°F.
That temp number was written long ago, when we had a simple 50 weight oil. todays oil will tolerate much higher temps.
Many 0-200/0-300 will run higher temps, for a long time.
 
Looking to buy a C172E, engine at TBO 1900hr (0-300) but its last compressions check was done 3 months ago and it shows:
1)72/80
2)76/80
3)68/80
4)76/80
clean spark plugs, no oil leaks no defects on the muffler. will I need a new engine right away?

As an owner, not a mechanic: a slightly low compression on one cylinder is not in and of itself a cause for worry unless there are other signs, like increased oil consumption, fouled plugs, exhaust valve leakage, etc. I'd keep an eye on cylinder 3, and R&R only that cylinder if needed. A good mechanic will be able to assuage any concerns about that cylinder on pre buy. I've flown cylinders in Lycs with that compression a long time without other symptoms.
 
Buy it and fly the paint off it and that low cylinder will probably come back up close to the other ones. It may be a leaky exhaust valve that needs to be lapped. Either way, buy it. Those numbers are solid for a Continental.
 
I have owned my '64 172E now going on 12 years. It has the original 0300 engine with approx. 1600 hours on the engine now. Very clean well maintained ac. Total airframe is approx. 3400 hours. It runs and flies great. Always has. Was a CAP pilot for 7 years and flew their 172's with the 180 horse engines. Quite frankly I like mine better. Lighter on the controls and smoother engine. Always starts after two prop blades go past the cowl. Flies at about the same speed as a 152. But I'm not in a hurry to get back on the ground anyway! Love that little airplane.
 
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