Max Cylinder Head Temp on new cylinder break-in.

[sreeves]

I have a newly major overhauled C-145 in my C-170A including six new Superior Millenium cylinders. The engine is being re-hung now so I will begin the break-in soon.

The latest Superior Service Letter L96-08D on their website says not to let the CHT exceed "original airframe equipment manufacturer recommended max cruise limit".

Anybody know what that would be? I do have a JPI engine analyzer installed in my airplane so I will have individual CHTs displayed but it uses the spark plug type gasket sensor for those readings. So it is my understanding that the spark plug gasket sensor reads somewhat higher than a CHT probe sensor would. So that clouds the picture further.

I have emailed and left a phone message with Superior AirParts but have not received a reply.

Steve

[gfeher]

On p. 5 of the overhaul manual for the C-145 (X30013), in Table VIII, it states:

“Maximim cylinder head temp ([deg] F)
(Measured by thermocouple imbedded in down-stream spark plug gasket) … 525”

[sreeves]

WOW !!! 525 seems awful hot. But thanks for that info. I will keep researching...

[GAHorn]

WOW !!! 525 seems awful hot. But thanks for that info. I will keep researching...

That is Fahrenheit

[n2582d]

Steve,
There is no CHT limit listed in the C-170 Owner's Manuals or in the AFM because a CHT gauge wasn't standard equipment on the 170. It wasn't required by CAR 3. M89-7R1 has been incorporated into the Continental Standard Practice Maintenance Manual, M-0. There you can see that for ground operations the CHT limit is 400ºF and the oil temp limit is 200ºF. For flight, the M-0 manual says,

Monitor a) engine RPM, b) fuel flow and pressure (if equipped), c) oil pressure and temperature, d) cylinder head temperature (if equipped), e) exhaust gas temperature (if equipped), and f) turbine inlet temperature (if equipped) to verify the engine is operating within the parameters specified in the primary Instructions for Continued Airworthiness (Section 1-1.1).

In Section 1-1.1 it cites the O-300 Overhaul Manual. As has been previously said, the CHT limit there is 525ºF. While I have my differences with much of what Busch writes, I agree with him here in using 400ºF as a redline for the O-300 CHT. I think 525ºF is way too high for O-300 cylinders. Regarding the spark plug gasket probe vs. the bayonet probe, EI has a good article on that here. Millennium cylinder break-in was discussed a year ago here.

[ghostflyer]

having cylinders over 400deg does break down the oil qualities , and it’s possible to have a normal oil temperatures with cylinders at over 400 degs but there are hot spots created in the cylinder assembly that do break down the oil . My info came from,Superior . My requirements are that my oil temps are at 180 deg and my cylinders are around 380 degs. One issue that I have is on a slow descent from say 12,000 ft , I reduce throttle for a 500 ft descent rate . But my cylinders temps drop to about 260 degs . My check ride examiner gets carried away about having a cold engine . He wants me to increase RPM for a couple of minutes and then return it to,my descent RPM. To me that is shock heating/cooling the engine . As I approach circuit height I slowly increase RPM to 2200 rpm for the down ward leg of the circuit.
PS. In summer here in australia due to extreme turbulence it’s best to fly as high as you can ,in cool non disturbed air .

[GAHorn]

As a point of discussion, the TCM Ovhl Manual provides the “limits” for the engine. These “limits” are exactly that: If -exceeded…the engine is considered to have been compromised. (Exceeding Limits requires Maintenance/Inspection for return to service. This is a good time to recognize why calibrated instrumentation in good condition is nice. It’s doubtful that many “original” 170s have anything better than what tractors and autos of the period. This can be “good” or “poor” depending on the viewpoint.)

It should be clear that moderate operating pressures/temperature's are beneficial to longevity and that abnormal pressures and temperatures are harmful. Generically it’s been my experience of 50-yrs of operations of many different makes/models of engines that CHTs in the 300-400 F range are “normal”.

The Owner’s Manual* for this airplane mentions only one CHT probe…the spark-plug-gasket type, for the lower spark plug on what the mfr’ states to be the hottest cylinder, No 2. (left/rearmost…LOWER spark plug)

(My own 1100-hr O300 has a CHT so-configured and my cruise CHT typically indicates 210-C (410-F), …but the gauge is of WW2 vintage and I consider it “for entertainment purposes only”. It fills what would otherwise be a blank-hole.)

* While providing useful information, Owners Manuals are information-guidelines, not maintenance manuals. To Gary’s point: A CHT indicating system is required-equipment for airplanes with cowl-flaps. (CAR3) A little-known rule also requires a CHT-indicator if the engine exceeds eng-mfr’s limits in climb above best-rate (I don’t recall where I learned that, but it suggests that we should avoid extended climbs below best-rate. You DO know what Best-Rate speed is…right?. viewtopic.php?t=1476#:~:text=(6)%2520sp ... 0trademark ) Neither requirement for a CHT applies to 170’s.