Is a 6 Cylinder Engine Monitor Overkill on a O-300A

How to keep the Cessna 170 flying and airworthy.

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GAHorn
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Re: Is a 6 Cylinder Engine Monitor Overkill on a O-300A

Post by GAHorn »

DaveF wrote:And how do we know that carbureted engines don’t run well lean of peak? Because we have engine monitor data that tells us. Without a monitor you don’t actually know what each cylinder in your engine is doing. No problem if you don’t care, but I do.
I think Mr. Busch would argue (and agree with you) that in order to reliably run LOP…one would have to have great engine monitoring instrumentation.

The problem with our airplanes is that their carburetor/induction systems are so crude that it’s impossible to get the majority of cylinders into a LOP condition even if one had such instrumentation. A calibrated torque wrench is useless on a crude pipe-thread. A vernier mixture control is of no particular advantage with a carburetor-induction system.

(And we’d have to define “run well” before we can sensibly discuss how sophisticated instrumentation might assist us. I define “run well” for these 145 hp continentals as being smooth/low-vibration, using about 7.5 gph at 2450 RPM with very small magneto-drops. That definition is not exactly the same one I’d use on a GTSIO-520 on a C-421. :wink:
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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GAHorn
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Re: Is a 6 Cylinder Engine Monitor Overkill on a O-300A

Post by GAHorn »

To further explain my previous comments: The approved carburetor for this installation is a fairly crude device which has its’ origins in 1930s farm tractors. The induction system to which it is mounted involves six “spider” tubes of varying lengths and differing shapes. Additionally, there are elbows, hose-fittings, and clamps which offer ample opportunity for air leaks which alter the possible fuel/air ratios individual cylinders may receive.
The manifold to which the carb is mounted has a divider which re-directs the air-flow left/right…that manifold being cast within the oil-sump where it is surrounded by hot oil (intended to assist atomization and fight carb-ice and cold re-start conditions)… The point being that the individual cylinders receive differing qualities of atomized fuel/air ratios. So if one is to run this engine LOP… which particular cylinder do you wish to do so…??
LOP operations requires individual fuel/air manipulation for each cylinder… OR…. if only a single-point of fuel/air manipulation is provided (such as ours and most other airplanes have in a single mixture-control)…the individual cylinders must have uniform fuel/air mixture delivered to them. As the induction system already described clearly does not do that…. leaning this engine only manipulates the fuel which leaves the carb throat… and the induction system then offers its’ adulterations of the fuel/air delivered to each cylinder. (This situation is the one which the GAMI-injector people wish to address and the resolution upon which Mr. Busch has relied to write numerous articles promoting (and deserving recognition for) the merits of LOP operations.)

However, the lack of uniformity of the C145/O300 carb/induction system makes any plan to run all six cylinders with identical fuel/air ratios virtually impossible…. and that means if one or two cylinders can be adjusted to a particular level of LOP….that the other cylinders will be either ROP or Peak… OR…ALL cylinders must be LOP with the liklihood that four of them will be TOO lean…. defeating the purpose. In some engines this lack of uniformity can result in valve damage and engine failure.

This condition DOES make good the argument in favor of accurate six-cylinder instrumentation…. if only to show the operator how impossible it will be to run all six cylinders at the same fuel/air degree of LOP…. and to help detect a leaking induction-hose or other anomaly which may develop between cylinders. This would be especially helpful if a prior record is kept, either in the devices’ memory…or by the operator by recordation of in-flight engine parameters. If you do that… keep in mind that the OAT, Pressure Altitude, Cruising Speed, RPM, etc. will also be necessary for each recordation event if any valid use is to be made of the data.
Hope this helps.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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Karl Towle
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Re: Is a 6 Cylinder Engine Monitor Overkill on a O-300A

Post by Karl Towle »

Way back in the 4th post to this thread, Dustin made mention of discovering two of his cylinders running hot during climb. I too have an Insight G2, and I discovered the same thing on my O-300D powered B model. I also discovered that pulling the mixture out to about 3/8" to 1/2" lean of full rich brings the temp down those two cylinders. This might be a sign of how crude this induction system is, as has already been eloquently elaborated upon.

That said, I really like having information in flight. Once I had the center electrode depart one of my REM40E plugs in flight. I was IFR at the time (of course) and the engine just didn't quite sound the same. An in-flight mag check revealed I had a dead plug on the left mag, in cylinder #4. About this time, I flew through a clearing in the smoke, and I spotted an airport in the clearing. Diverted, landed, knew exactly which plug to check & swap, then got my clearance back and was off again for the rest of the trip. (Electrode had squirted out an exhaust valve, and the top of the piston showed no signs of stress.) I had another such episode on the ground with a carbon fouled plug; mag check showed exactly which plug needed to be pulled for cleaning.

So, all that extra information, although maybe of questionable value while everything is working, can save loads of frustration when something breaks. And, if you fly in IMC or at night, you really want to know the instant anything goes wrong. As has already been said, the G2 allows one to discard their carb temp gauge (if installed), and adds system voltage, outside air temp, and fuel flow + totalizer. Not a bad assortment of data for in-flight monitoring and decision making.
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