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24 Jan 2020, 04:18 [ UTC - 5; DST ]





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 Post subject: CHT probes for a C310
PostPosted: 21 Jan 2020, 21:19 
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Company: Flag-Williams DevCorp
Location: Grand Canyon
Aircraft: C310J
1965 Cessna 310-J with IO-470-U engines. The engine instruments have changed so much in the last 50+ years that Im having difficulty finding the right part number for the CHT probes.

On the Bayonet fitting is a Cessna number S2497439, but that doesnt correspond to anything in the IPC. Back in the day, it was referred to as a temperature 'bulb'. Not a Thermocouple or an RTD.

I still havent pulled the unit as Im waiting on weather to cooperate.

Is any one familiar with this PN S-2497439? Im thinking it may be an RTD because of the gauge behavior. It reacts normall from cold up to about 300dF (during runup). Then, after runup, when I reduce RPM, the temp rises (as it should with lower airflow); it begins to dance between 310 and 400. up and down.

At first, assuming it was an RTD, this would mean an intermittent Break due to thermal expansion. Im guessing the resistance jumps up on either an open circuit or possibly a short.

If this were a thermocouple an open would result in "0" milivolts and the gauge would drop to 0. If it were a short, it may/may not go full scale depending on the resistance to ground and which side of the lead was shorted.

As I understand it, Barons with this engine use an RTD with a bias resistor. Is this similar? Any information is better than guessing.

Thanks.

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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 03:30 
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Location: NC
Aircraft: C310F
I pulled the left engine on my C310F (IO-470-D) last fall to repair a cylinder and had to disconnect everything, including the bayonet CHT probe. It had yellow and red wire leads, which are characteristic of a K type thermocouple. I too have an OEM CHT gauge that flips out from time to time in cold weather. I haven't had time to swap the plugs on the gauges to see it is a gauge or probe issue yet. My 3 in 1 engine gauges, which house the CHT, are adjacent to each other but I don't know if the harness will allow a plug swap easily.

Thinking back, I recall one of the leads from the probe was grounded to a rib, below the intake riser on cylinder #2, in the nacelle. This is not typical wiring for a millivolt thermocouple, as it introduces a third dissimilar metal junction. Usually both leads run directly to the gauge.

I am currently away from shop but when I get back, as curiosity has gotten the better of me, I'll do some research with a heat gun and a DVM to see what I observe about the probe.


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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 12:09 
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Company: Flag-Williams DevCorp
Location: Grand Canyon
Aircraft: C310J
Thanks Gary. If the temp in the hanger gets above 40 today, Ill start the removal process.

I also ordered a bag of grommets and fiberglass sleeves for the wire's within the engine bay.

The prop cable and CHT seem to run along the lower engine support below the induction tube. I'll see about re-routing and securing it better. I've been practicing my hand using Lace-cord as it looks and lasts better than zip-ties. We'll see if I can get my hands in there.

-Bud

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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 12:34 
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Location: NC
Aircraft: C310F
I happen to have the IPC for the C310 F thru K on my traveling laptop. The part number for the CHT probe is 0813601-4 as illustrated by item 10. (don't ask me how I managed to find it :) )
Attachment:
24-30-00-03P1.jpg
Attachment:
24-30-00-03P2.jpg



Cessna Direct says this has been superceeded by 0813601-6 which sells for the obscene price of $1,181 :bugeye:

I pretty sure this is a common part which can be cross referenced given some research. It's not like they were using spare rocket parts from NASA in the early 60's to build these planes.


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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 12:43 
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Company: Flag-Williams DevCorp
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Aircraft: C310J
Gary, and thats not the list price. ~$1,415!! Another vendor will give me a break at $1,273.

yeah, if its a type K thermocouple, we may be looking for a brand X replacement.

Thanks.

-Bud

ps. Looks like Aircraft spruce has them for $999.95. Almost an AMU.

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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 13:08 
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Aircraft: C310F
At the risk of :deadhorse: the only way I'll know for sure what this probe is, will be by hands-on measurement. Heck, I have two to test and my right engine ain't misbehaving. The descriptions in many of the cross-references that I've found say "resistance". (see example below). I'll post my findings when I get back to the shop in February.
Attachment:
SpencerCHT.jpg


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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 17:15 
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Company: Flag-Williams DevCorp
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Aircraft: C310J
Well, I was able to remove the suspect part and get it under a magnifying glass.

It turns out the "Part number" is actually a Patent Number 2497439. Issued in 1947 To Tomas A. Edison. The patent ran out in 1967; two years after my aircraft was built. It is the original 0813601-1 the current dash no. is -6. 55 years for an electrical sensor is pretty good. It lasted through 4 engine and several swaps. Cant say much for the installation job as the failure mode is clearly the lack of the grommet used for strain relief.

Cheapest replacement with FFA-PMA is ~$400 through Aircraft Spruce; tho Im still lurking in the rabbit hole for a while to see what the alternatives are.

The "Tell" in diagnosing this thing was to disconnect the leads and use a multimeter to measure the voltage. A thermocouple will have a self generating voltage in the microvolt range. None present. When I turned the ships power on, the gauge went Full Scale. When shut off, the temperature reading slowly returned to 0 indicating an RC circuit was in play and not a simple voltage reader.

Wife says I should clean it up and mount it in a shadow box with the Edison Patent cover page and illustration. Try to get $400 on ebay.. :)


https://patents.google.com/patent/US249 ... =us2497439

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 Post subject: Re: CHT probes for a C310
PostPosted: 22 Jan 2020, 22:00 
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Joined: 01/18/13
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Company: FedEx
Location: Tampa, FL
Aircraft: 1961 U-3B Cessna 310
Texas Air Salvage has some used parts.

Doesn’t say the price.

https://www.texasairsalvage.com/main_vi ... id1=228619

Try preferred air parts and White Industries, I’ve had good luck with both.

Butch


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