Failed # 5 cylinders on a C145

[dentistpilot]

I need some advice and insight into why the #5 cylinders on my C145 engine seem prone to failure, displaying low compression, (60), much too soon in their lives. The other five cylinders are OK.
More detail:
The engine, a C145, serial no. 5904-D-1-2, is installed in my 1951 Cessna 170A, serial no. 20107. Its total time is 1914 hours, same as the airframe.
It was overhauled by Mattituck at 1297 hours, on 9/24/96.
The #5 cylinder was removed at 1379 hours and returned to Mattituck, on 11/14/97, for valve reseating, cylinder honing, and new rings.
#5 compression was down to 71, (others 78-79) at 1432 hours, on 10/5/98, but passed annual.
#5 compression was down to 60, (others 75-76), at 1454 hours, on 6/1/99, but passed annual.
Subsequent annuals, at 1499, 1609, and 1659 hours, saw compressions in the 74-76 range.
#5 compression was still good at 1703 hours, on 3/3/05, but the cylinder was removed for exhaust valve grinding, (valve and seat).
#5 was down to 60 again at 1795 hours, on 4/6/07. This time an entire new Superior cylinder assembly was installed.
Fast forward:
#5 was down again, to 60, at 1914 hours, on 6/11 10, with a stuck intake, and burned exhaust valve. New cylinder assembly installed. This is now 617 hours since overhaul. Five cylinjders doing OK, #5 always in trouble. Why?
#5 should run cool, since I can see it right in front, with no baffles out front of it.
I lean agressively during taxi to prervent plug fouling, and modestly in cruise, usually about 65%, plus or minus.
Thanks for any help any of you can offer.
Jim Heidere

[Brad Brady]

Like you say #5 should run cool cuz it is in front......Not necessarily so. if the baffles aren't correct, the air movement isn't what the engineers had in mind. And will not work the way they are supposed to.....check the baffling...especially the rear...you might be surprised. I'm not making recommendations at this time, cuz I have seen to many issues on the right hand side of the engine. others here may have a better concept of what you may be looking at.

[buzzlatka]

Replaced our #5 Cylinder at 500 hrs due to low compression also.

[GAHorn]

I need some advice and insight into why the #5 cylinders on my C145 engine seem prone to failure, displaying low compression, (60), much too soon in their lives. The other five cylinders are OK.
More detail:
The engine, a C145, serial no. 5904-D-1-2, is installed in my 1951 Cessna 170A, serial no. 20107. Its total time is 1914 hours, same as the airframe.
It was overhauled by Mattituck at 1297 hours, on 9/24/96.
The #5 cylinder was removed at 1379 hours and returned to Mattituck, on 11/14/97, for valve reseating, cylinder honing, and new rings.

Overhauled at 1379 hours SMOH???? or did you mean to say in 82 hrs SMOH?

#5 compression was down to 71, (others 78-79) at 1432 hours, on 10/5/98, but passed annual.
#5 compression was down to 60, (others 75-76), at 1454 hours, on 6/1/99, but passed annual.
Subsequent annuals, at 1499, 1609, and 1659 hours, saw compressions in the 74-76 range.
#5 compression was still good at 1703 hours, on 3/3/05, but the cylinder was removed for exhaust valve grinding, (valve and seat)..

So all that seems fairly ordinary, actually...varying compressions...all within specification....and then, a slightly leaky exhaust valve, I take it? Not due to compression but perhaps hearing some hiss? (This could have simply been a bit of carbon and might have disappeared all on it's own....and of itself, would not be indicative of a repetitively-failing-cylinder, as you seem to fear.

##5 was down to 60 again at 1795 hours, on 4/6/07. This time an entire new Superior cylinder assembly was installed...

Why? 60/80 is not a failed cylinder unless an exhaust valve leak is obvious.

Fast forward:
#5 was down again, to 60, at 1914 hours, on 6/11 10, with a stuck intake, and burned exhaust valve. New cylinder assembly installed. This is now 617 hours since overhaul. Five cylinjders doing OK, #5 always in trouble. Why? ..

This could be due to happen-chance, considering that no definite failure has actually been repetetive. (It appears that much unnecessary removals may have have occured.) Or, it's possible that a perforated/leaky intake/induction is causing that cyl to run excessively lean. Do you have an EGT probe on #5 so you can compare it to other cyls?

###5 should run cool, since I can see it right in front, with no baffles out front of it....

Only as regards CHT would this be likely. Do you have a CHT probe on #5? (in order to observe it comparatively?)
Cooling due to airflow is a seperate matter than heating/cooling due to fuel-mixture and combustion irregularities. One cannot assume that a front cylinder will run cooler than those farther aft, either. The blast that hits the cyl at it's front radius, is not the primary source of cooling.... it is the air which is forced DOWNwards between the cooling fins, which only occurs as the result of a buildup of high-pressure air forward of the air-dam/aft baffle (or airbox in your A-model.) This downward cooling is evidenced by later designs which actually placed a baffle in FRONT of the front cylinders. (And it's also possible that an improperly-baffled front cylinder might develop valve/ring problems because it runs TOO cool!)
But again, simply because it's a forward cylinder does not mean it will be the coolest externally OR internally (due to combustion differences.)

I lean agressively during taxi to prervent plug fouling, and modestly in cruise, usually about 65%, plus or minus.
Thanks for any help any of you can offer.
Jim Heidere

It's possible that #5 cyl has seen much unnecessary maintenance, except for the possibility of a single event of a burned exhaust valve, and/or temporarily aligned ring end-gaps, which may have led to unnecessary removal.

While the re-telling of the number of times #5 has been removed/replaced/etc. seems excessive.... in accordance with the statements made (and unless there is additional info) there does not appear to be an extablished reason to have performed much of that maintenance.

[Bruce Fenstermacher]

I don't have an answer. But like George I was thinking perhaps a bit more attention has been payed to this cylinder than necessary. Having said that, I personally probably would have done the same type of maintenance because I do my own work and cleaning exhaust valves is not that big a deal.

I think the continued issue with the Superior cylinder could be nothing more than bad luck. While I doubt I'd do it I might be curious enough to rotate the #5 cylinder with another to see what happens.

[GAHorn]

Here is an afterthought...
It's possible the pushrod on the exhaust valve of that cylinder is too long and preventing full seating of that valve. Have your mechanic check the length of that pushrod versus valve-lift.

The stuck intake valve is likely unrelated, and some operators seem to experience that upon startup from time to time, although it is usually an exhaust valve which sticks. (I.E. "Rope trick" is not an unheard-of procedure, but others get all the way thru life without ever experiencing it. I have some personal opinion about the cause of the stuck-valve on startup, but it's largely anecdotal:)

Ten reasons/causes of stuck valves:

10: Fractured valve guide (almost undetectable unless keepers/springs are removed)
9: Use of automotive engine oils. (metallic detergent deposits on valve stem)
8: Excessive priming in cold weather (excessive washing of lubrication from valves/stems)
7: Improper/long-term storage (lack of regular use achieving normal operating temps leads to corrosion & deprives lube)
6: Shock cooling (this is not the high-speed/low power descent, ... but the operation into heavy rain with min clearance guides. Personal experience on this one in a C140)
5: Incorrect rocker arm installation (insufficient lube/lacking squirt-hole, especially on exhaust valve)
4: Weak, old, or re-used valve springs during cylinder re-build.
3: Valve guides with insufficient I.D. (lack of proper reaming during installation)
2: Dirty valve stems/guides due to coked oil/carbon (contributory: improper cooling prior to shut-down)

and the number ONE reason for stuck valves:

1: Use of leaded gasoline without proper-leaning and accompanying TCP/Decalin (allows lead buildup on valve stem during low-combustion temps/excessive idling..sometimes related to improper shutdown.)

[dentistpilot]

Thank you all very much.
Jim Heidere

[alaskan99669]

For what it's worth, my #5 cylinder has come in at the low 60's the last 4 annuals. This year it was high 70's like the rest! I didn't do anything thing different this year than the other years. This is on my '53 170B.

[hilltop170]

Some people have installed baffles in front of #5 and #6 cylinders to direct air flow down across the cooling fins instead of direct impingement from the front which may be a stagnation area with little or no useful cooling flow. The pictures are of stock baffles installed on a C-172.

It is also very important to make sure there are no large gaps in the baffles and baffle seals anywhere in the pressurized area above the engine. I have been told by engine experts any hole larger than a dime will pass enough air to disrupt cooling and should be plugged.

Without a multi-cylinder engine monitor, you really cannot tell what is happening to each cylinder and they all behave differently. The third picture is in cruise with cylinder baffles in front of #5 and #6. The CHT is the dark bar superimposed on the lighted EGT bars on the monitor.

Click on pictures to enlarge.

#5 Cylinder baffle

#6 cylinder baffle

Note cylinder head temps on engine monitor

[mit]

Crips Richard, I would get a nose bleed if I ever got that high and I would be scared!

[hilltop170]

Tim-
If you ever fly across Kansas on a summer afternoon, you have to fly that high if you don't want to get beat to s#!t by turbulence. It's always nice and cool and no turbulence up there!

I can just imagine when these planes were new and there was no air conditioning, nobody would want to come back to earth to 100°F humid heat after flying a trip in smooth, dry, 65°F air. It must have felt like heaven to them.

Later that afternoon we finally topped out at 9500msl