Cylinder Head Temp Instl - looking for authorization data

[Baker]

Greetings,
I installed a cylinder head temp gauge in my Stinson (Westach) just prior to my annual and I am now in my annual. My IA has correctly asked me for some authorization for the install. From previous forums I understand that we did not have CHTs installed in our Stinsons and it is not on the type cert. All indicators are telling me I need to do a field approval. Has anyone done a CHT field approval before and if so can I copy the supporting data so I might have a fighting chance of passing this through on a FAA form 337. If I can not get this support info to push a 337 through, I will have to remove the CHT and try another avenue. THANKS Dean 770-494-0824

[lawheelock]

My suggestion: Get another IA. Remove it for this annual. Don't ask, don't tell.
Personally, I would consider it a minor modification with a log entry as long as it is a TSO'd aircraft quality instrument, It is not a required instrument. And, in my opinion, is unnecessary because in almost 44 years of flying behind a Franklin, it has never run hot even in Arizona heat. There are STC approved CHT/EGT combos in the digital form from EI and others.
Larry Wheelock, IA

[Baker]

Thanks Larry, good input. I installed it for engine break-in but I do agree, after that event, it stays rock solid and oil temp is a better check of overall engine temp. If the money is available, I am looking at a digital guage as you mentioned to be used for checking trends to see if I have a cylinder starting to get out of wack but for now, I already have a CHT and since I have it, I would like to keep it in. I agree that it is such a no brainer install that it should be a minor install. Thanks for your input db

[lawheelock]

If you want to save a few bucks, a 6 point EGT is much more useful for troubleshooting than a CHT, even a multipoint CHT in a Stinson, in my opinion.
I have a 6 point manual EI digital EGT in my Stinson. It is great for trouble shooting, but not much help for leaning. The ear method works best for me for leaning even though I do not hear well. In all 3 of my unscheduled landings when the engine started running bad, but always got me to an airport, the EGT immediately identified the offending cylinder which in all cases was due to a broken rocker arm due to a stuck Exhaust valve due to running 100LL.
Biggest problem is getting all 6 probes installed exactly the same distance from they cylinder exhaust port to try to get even readings. However, it really is not possible because carbureted engines always have poor fuel distribution.
Larry

[Baker]

greetings,
First, I installed a CHT gauge for the breaking in of a new cylinder. NOTE: it is a good idea to get a back up thermocoupler lead to reach the furthest cylinder if it is the break-in cylinder.
Here is what I put in my log book for the addition of a CHT gauge:
THIS IS WHAT I WROTE IN LOG BOOK: minor mod installation of FAA TSO-c43a approved (westberg Mfg Inc.) Model K29PX, s/n 25257 (gauge) & p/n 713-7D, s/n 4308 (sensor lead) using the following parts:

(4) MS21919WCJ-12 adel clamps, (5) MS21919WCJ-2 adel clamps, (2) grommets AN931-2-4, AN931-2-13; (4) AN3-3 bolts; (5)AN960-10 washer; (5) AN3-11 bolt; (5) MS21044N3 nuts; 7/16 elec standoff; (2)11-04425 raychem red buttsplice; jumper wire - MS22759 / 16-18; (2) MS25036-102 ring terminal

Acceptable data: Installation was performed per gauge manufacturers instructions (form # 17780Z, dated 2/90) and advisory circular 43.13-1b/2b. Installation of cyl head temp gauge is approved per aircraft type certification, reference: Full Blind Flight Instrument panel kit installation. This is a minor mod per FAR 21.93a. Light load calculated per 43-13-1b chapter 11. wire clamping also per 43-13-1b chapter 11

WORK COMPLETED:
Minor mod installation of Westach K29PX CHT gauge and 713-7D sender. Installed CHT gauge FAA TSO-c43a approved (westberg Mfg Inc.) Model K29PX, s/n 25257 (gauge) & p/n 713-7D, s/n 4308 (sensor lead). Insatlled Bayonett style thermocoupler lead installed on #2 (aft RH) cylinder. CHT guage is marked w/ red line @ 445 degrees(per Franklin Engine type certificate, NOTE 1). Updated Flight Manual, weight & balance and equipment list with gauge specs. Light wire picked up at light wire junction for pwer and grnd.