AmigOne Posted February 11, 2012 Report Share Posted February 11, 2012 I am installing an EDM 700 in my 1968 M20C and I will be replacing the existing CHT bayonet probe in cyl# 3 with the JPI probe but I want to retain CHT information in the factory EGHT gauge. Does anybody know if the factory probe is a J or K type? Thanks Jose Quote Link to comment Share on other sites More sharing options...
Cris Posted February 11, 2012 Report Share Posted February 11, 2012 I am reasonably certain that the factory probe is the earlier J type. If you have a pre owned JPI 700 it might have the J type probes which are identified by red & white leads. The latter 700's switched to the K probes. The K probes can be identified by the leads which are yellow & red. Mixing the probes will give you erroneous readings-ie high/low. There are several options for you to consider assuming the factory probe is a J type. 1) Install a spark plug J probe for the factory probe & a standard CHT JPI probe in lieu of the bayonet probe. Make note of the temps before & after switching to the spark plug probe and prior to installing the JPI 700 to verify accuracy. Modify the JPI 700 with an JPI adapter for a Gem 602-610 which uses the J type probes and go to all J type probes. If this is a new unit JPI might be willing to switch out your probes and/or modify the 700 to accept J CHT probes retaining the K EGT probes which is/was an option. 3) Replace the JPI 700 with a GEM 610 or better still the new G1-2. BTW I have a brand new JPI bayonet K type Part # 5050 if for some reason you find you need it or someone reading this needs it. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted February 11, 2012 Report Share Posted February 11, 2012 You can also use a 10mm (3/8") washer type J sensor under the factory bayonet probe. Or use the JPI bayonet and the washer sensor for the factory guage. Quote Link to comment Share on other sites More sharing options...
AmigOne Posted February 11, 2012 Author Report Share Posted February 11, 2012 My question was no complete. I was thinking on splicing the existing factory probe and connect it to an under the plug probe so I could retain the factory gauge operational. However I did not want to buy the JPI probe for $120 and instead wanted to buy a generic one for $35. They come on J & K types and I did not know which one would be the correct one to use. In practice the EDM 700 new bayonet probe (which will be located where the old probe was) will be giving me the more precise EGT so I was not very concerned about the precision of the factory gauge but nevertheless I wanted to buy the correct probe. I just did not want to put an 'inop" label on the factory gauge. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted February 11, 2012 Report Share Posted February 11, 2012 I dont think you can INOP a factory CHT guage unless the JPI is certified as primary for that function. We have a different engine monitor, and placed the 3/8" CHT thermocouple under the factory CHT probe on #3. the factory guage is undisturbed and the engine monitor reads the 3/8" washer probe. It is about 40 degrees low on the engine monitor but we have full functionality. here is the 3/8" type K washer thermocouple. http://www.overnitesupply.com/wtk38-2424typekwasherstylethermocouplegrounded38studsize24stainlesssteelbraidedleadssplitwithspadelugs.aspx type J is here: http://www.overnitesupply.com/wtj12-24typejwasherstylethermocouplegrounded12studsize24stainlesssteelbraidedleadssplitwithspadelugs.aspx I have an extra brand new K in spares. The minimum order is 25$ plus shipping there. Works great. Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted February 11, 2012 Report Share Posted February 11, 2012 I have the same problem and am thinking about going with either the 3/8 washer type probe, or the spark plug one. Do either of you know the identification of the J type spark plug thermocouple. I see one at Aircraft Spruce, but it does not seem to be identified as a J or K. Thanks Quote Link to comment Share on other sites More sharing options...
jetdriven Posted February 11, 2012 Report Share Posted February 11, 2012 Don, I have the J in mine. But overnitesupply has both. I think you can call a thermocouple not required as primary a standard part. This one from Spruce is a type K. http://www.aircraftspruce.com/catalog/inpages/chtTanisProbe1.php It is 90$ but AFAIK its the same as the one I got for 13$ Quote Link to comment Share on other sites More sharing options...
DonMuncy Posted February 11, 2012 Report Share Posted February 11, 2012 I looked in the Overnight catalog listing inder J type sensors but did not see one for the spark plug. Is it someplace else. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted February 11, 2012 Report Share Posted February 11, 2012 Skip the spark plug It gets torn up from plug replacements plus it is too far from the actual place to measure an accurate temp. The factory CHT probe is closer to where a bayonet probe goes. Quote Link to comment Share on other sites More sharing options...
AmigOne Posted February 11, 2012 Author Report Share Posted February 11, 2012 Quote: jetdriven Skip the spark plug It gets torn up from plug replacements plus it is too far from the actual place to measure an accurate temp. The factory CHT probe is closer to where a bayonet probe goes. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted February 11, 2012 Report Share Posted February 11, 2012 Use a 3/8" ring terminal CHT probe, Type J or K as you need. Hook that to your factory CHT guage. Put in the bayonet probe for your JPI. Put the 3/8" ring terminal under the bayonet probe. Ours is the reverse of this. Quote Link to comment Share on other sites More sharing options...
Cruiser Posted February 11, 2012 Report Share Posted February 11, 2012 does your OEM CHT probe have one wire or two wires connected to it? Most of the OEM sensors I have seen are resistive type single wire and will not work with a J or K temp probe. JPI has/had a threaded bushing type probe that allows the OEM sensor to thread into it and then it threads into the Cylinder head. This is the closest setup you can get. I don't see this type of probe listed in their online store perhaps you can call and ask them for it. I have this combination but it still does not read the same as the bayonet style probes. Technically you cannot remove or replace the OEM sensor with anything else or even move it from it current location without approval since it is a required piece of equipment for airworthiness. Quote Link to comment Share on other sites More sharing options...
testwest Posted February 11, 2012 Report Share Posted February 11, 2012 Jose wrote: "I am installing an EDM 700 in my 1968 M20C and I will be replacing the existing CHT bayonet probe in cyl# 3 with the JPI probe but I want to retain CHT information in the factory EGHT gauge." So, the only way to legally do this is to install the JPI piggy-back CHT probe, it is JPI part # 5050A. Just remove your factory probe from the cylinder. The 5050A screws into the cylinder at that same boss, and then your old factory CHT gauge probe screws into the back of the piggy-back adapter, hence the name. The piggy back has wires coming from it (type K) and an engine ground, hook those to the JPI and the engine case, respectively. Your factory CHT will work just like always, all four of your JPI CHTs will be accurate too, and you won't use your poopy language when changing the #3 spark plug. These were about $75 from JPI but I am not seeing them on their web site right now. But, Jose, you are in luck. I have a 5050A that is now surplus to my needs, since we are installing a JPI 930 that has primary certification. I'll sell it to you for $50 plus shipping. Or, if you have not bought your EDM-700 yet, I have a complete EDM-700 with the latest factory refurbishment, fuel flow and the entire complement of BRAND NEW probes. $1000 for everything and I'll throw in the 5050A for free. Don't try to splice your factory CHT probe, don't inop the gauge or try any other substitutions listed above. There really are only two correct ways to do this with a CHT advisory instrument, that is the spark plug probe on #3 while retaining the factory CHT probe, or the piggy-back. Also, by way of education, make sure you know what is meant by primary indications versus advisory indications. I'll leave that as an exercise for the reader....but not knowing this and simultaneously contemplating some of the alterations to the factory CHT outlined above could easily lead to making your airplane unairworthy. Quote Link to comment Share on other sites More sharing options...
AmigOne Posted February 12, 2012 Author Report Share Posted February 12, 2012 Norman, thanks, that was a good explanation of the proper option. I will contact you directly to arrange for purchase of this part. Originally I thought that such part existed but like you said it is not listed at this time. I already have the EDM 700. Jose Quote Link to comment Share on other sites More sharing options...
testwest Posted February 12, 2012 Report Share Posted February 12, 2012 You are welcome! Glad to help. If you read some of the posts over in the Modern Mooney section, you'll see I'm payin' it forward, several great people over there bent over backwards to help me out with some strobe info. Edit: Here is a picture of the CHT piggy-back probe! Quote Link to comment Share on other sites More sharing options...
jetdriven Posted January 7, 2019 Report Share Posted January 7, 2019 On 2/11/2012 at 5:16 PM, jetdriven said: Use a 3/8" ring terminal CHT probe, Type J or K as you need. Hook that to your factory CHT guage. Put in the bayonet probe for your JPI. Put the 3/8" ring terminal under the bayonet probe. Ours is the reverse of this. New link for the 3/8” cht ring probe to put under the factory Rochester sender. https://www.tcdirect.com/deptprod.asp?deptid=180/40 Quote Link to comment Share on other sites More sharing options...
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