79 231 -LB TIT Probe Question

[vance.k]

Howdy,

I would greatly appreciate the wisdom of the collective here.  Since getting my 231, I've been struggling with an issue related to the TIT gauge.  I had gone through a couple shops that couldn't figure it out before finding an A&P that would supervise and let me poke around on some things together.  We've fixed a bunch of other nagging stuff that the other shops didn't (largely thanks to MS), so progress is being made. 

To make a very long story short, the ship gauge and JPI 830 are wired in parallel to the TIT probe.  The gauge is unreliable and with them paralleled, the JPI reads about 200 degrees lower than when connected by itself, which is also about 200 degrees lower than the EGTs, so that doesn't seem right.  With the ship gauge disconnected (for testing), the JPI seems to read where I'd expect.

The TIT probe is the clamp style JPI probe.  Speaking with JPI, they indicated the JPI probe doesn't support the ship gauge and we need one of the factory probes and those can be paralleled to the ship gauge and the JPI.  Fine, no problem.

From the reading on this forum and looking through the IPC, it seems I need the $400 Mooney 880055-505 or Alcor 86291 or Alcor 86309.  Fine, no problem.  

Except those are all screw in probes and I do not appear to have anywhere to install that.  I spent some time tonight looking at the exhaust tubing to make sure I wasn't just missing something and it appears the only place for a probe is where the current one is installed, via the clamping mechanism, directly inside the turbo inspection door.

I'm guessing it has been this way since the new -LB1B engine was installed 10+ years ago.  What is the proper method for fixing this and getting the ship in shape, so to speak?  Is there a supported factory approved probe that works with the clamp vs a screw in?

Thanks for your help!
Vance

 

Edited November 4, 2017 by vance.k
Engine replacement period was wrong.

[MIm20c]

My experience has been the combo sensors are the first to fail / give low readings.  However, I understand you want the information on both devices because the 830 is not primary.  Not sure what to suggest but I’d probably make do with one or the other or put the $500 toward a primary unit. 

[jlunseth]

Well, just be careful with that.  I have not looked at the Type Certificate in quite awhile but I am confident the specified factory TIT gauge is required for the aircraft to be considered airworthy.  The reason is that there is a redline TIT limit, and without a gauge matching the one on the type certificate to provide a reading, on an STC'd primary substitute, the aircraft is not airworthy.  A half way smart mechanic will know that and pick it up at annual.  You have two choices.  Get the factory gauge working properly, which will meet the Type Certificate, or have a unit installed that is STC'd as primary for TIT (as well as anything else on the unit where the factory gauge no longer functions).  That would be, for example, the JPI930.  But the middle road where the JPI gauge is working correctly but is not STC'd as primary, and where the Type Certificated factory gauge is not working properly, is not airworthy.  You either have to have the equipment present and working that is on the Type Certificate, or an STC'd primary substitute.

Edited November 4, 2017 by jlunseth

[vance.k]

Appreciate the feedback. To clarify, it is absolutely my desire and intention to get the ship gauge working properly. 

The question is how?  Is there a valid non-screw in type of probe that can be used?  JPI said there's isn't it. There's no place for a screw in one that I see that is called out in the IPC.

How can I reconcile this?  Happy to call or research more, just seem to have exhausted my google foo and MS search foo. 

Thanks!  V--

[DanM20C]

My factory gauge uses a clamp type also. It appears very accurate, I’m assuming it’s approved. Who knows.

I’m installing a JPI 900 within the next month.  You welcome to mine if you can wait 4-6 weeks.  

I’m really looking forward to removing all the factory gauges.

cheers,

Dan

[vance.k]

That's good info Dan. Any chance you have the part number of the probe in use?

Thanks!

[DanM20C]

I don’t have a part number handy, l’ll swing by the airport and look for any markings on it. Should be able to later today or tomorrow.  I’ll keep you posted.

cheers,

Dan

[DanM20C]

Vance,

Mine is an Alcore  86310. 

http://alcorinc.com/index.php/products/egt-tit-type-k-thermocouple-clamp-2-35-max/

hope that helps.

Cheers, 

 

Dan

[vance.k]

Extremely helpful, thanks Dan!  I need to confirm my pipe diameter, but that looks perfect.  It is hard to believe those are almost $500.  Pfft..airplanes..  ;-)

Thanks again!
Vance

ps.  Extra thanks for making a trip to the hangar and getting that part.  Way above and beyond!

[DanM20C]

No worries, the hanger is close and I’m always looking for an excuse to head out there. 

$500 is crazy, The JPI ones are less than $200. 

Cheers,

Dan

[carusoam]

Getting one thermocouple to feed two different instruments at the same time...?

That seems to be a technical challenge.  It’s a tiny voltage, susceptible to all kinds of things... including stray ground differences.

That's why The ship's CHT and the JPI CHT use two different TCs... The never ending challenge.

And that's for something much less critical than a TIT gauge.

It wouldn't take much effort for a TC manufacturer to co-locate two TCs in one device. But, I haven't seen one...

Does the expensive TC have two independent sets of leads coming out of it?

The TIT sensor exists in a very tough environment. It may be built to a heavier standard?

PP thoughts only, not a mechanic...

Best regards,

-a-

[vance.k]

Yea, that was my first thought as well, but from what I've read, seems ok to parallel the TIT with ungrounded probes.  I believe the ship CHT probe is grounded, so perhaps that is the difference?

Also, the JPI tech said it was the correct way to do it, as well as there being installation and calibration instructions in the manual specifically for this use case, as well as this FAQ.
https://www.jpinstruments.com/FAQ/tit-calibration/

The JPI tech did say the JPI probe isn't approved for being connected to the ship gauge.  I did read somewhere that the Alcor probes are designed to produce more power to drive the ship gauge...  I guess we'll find out.

I'm curious how people with non-certified engine monitors are doing this?  Are they installing a second TIT probe or paralleling the factory probe?  Would this involve drilling a second hole and if so, I presume there are some specific location/distance requirements for that? 

Given the cost of that particular piece of pipe, I'd be pretty hesitant to let someone go drilling on it.  But I am curious how others solve the problem short of upgrading to a certified engine monitor and eliminating the gauges.  That is my end goal, but I'm just not ready to bite that bullet yet.

I appreciate all input.

Thanks!
Vance

[gsxrpilot]

I think I'd just not connect the JPI to the TIT. It still provides other value with CHT/EGT RPM/MP, etc. TIT is pretty critical information when operating a turbo and especially one as finicky as the 231.

This is just one of the many, many reasons I went with the 900 instead of the 830. I've just never seen the value in adding the 830 so one can have a second but not certifiable view of engine data.

[Guest]

5 hours ago, vance.k said:

Yea, that was my first thought as well, but from what I've read, seems ok to parallel the TIT with ungrounded probes.  I believe the ship CHT probe is grounded, so perhaps that is the difference?

Also, the JPI tech said it was the correct way to do it, as well as there being installation and calibration instructions in the manual specifically for this use case, as well as this FAQ.
https://www.jpinstruments.com/FAQ/tit-calibration/

The JPI tech did say the JPI probe isn't approved for being connected to the ship gauge.  I did read somewhere that the Alcor probes are designed to produce more power to drive the ship gauge...  I guess we'll find out.

I'm curious how people with non-certified engine monitors are doing this?  Are they installing a second TIT probe or paralleling the factory probe?  Would this involve drilling a second hole and if so, I presume there are some specific location/distance requirements for that? 

Given the cost of that particular piece of pipe, I'd be pretty hesitant to let someone go drilling on it.  But I am curious how others solve the problem short of upgrading to a certified engine monitor and eliminating the gauges.  That is my end goal, but I'm just not ready to bite that bullet yet.

I appreciate all input.

Thanks!
Vance

Because of the lack of room for a second probe, I’ve seen a 231 with two probes with their clamps screwed together.  It seems to work fine.

Clarence 

[CaptRJM]

KS Avionics makes the TIT probe for Mooney. They make both screw in and clamp in versions. It is PMA’ed and comes with all the paperwork. Best parts is it’s $200 and comes with a 2 year warranty, not $500+ from Mooney.

I had similar issues with getting my 830 and ships gauge to work consistently. My AI decided to just put in a second probe using the same clamp. No more issues. 

He did calibrate the 830 for accuracy against a known value. The ships gauge reads about 75 degrees low using the known value. As far as I know there is no way to adjust the ships gauge. 

[vance.k]

27 minutes ago, CaptRJM said:

My AI decided to just put in a second probe using the same clamp. No more issues.

This is great info, thanks.  If/when you get a chance, would you mind snapping and sending a photo of how that is done with one clamp?  Really curious about that. 

Thanks again!
Vance

[CaptRJM]

Next time the cowl is off I’ll take a few pictures. But, all my AI did was drill another hole in the clamp and turbocharger inlet pipe. If my memory is correct they are about 120 degrees apart. 

[vance.k]

Thank you, sounds good!  I'm going to focus on getting the correct probe and getting the ship gauge working and will worry about how to get the JPI happy after that.

Thanks again!  V--

[CaptRJM]

Just remember that you can calibrate the JPI for accuracy. In my case the ships gauge would read 1575 degrees when it would really be 1650 which is max TIT temperature. 

[TargetDriver]

Great thread guys. I've got a 231 that has a functioning TIT but I've bought an 830 and will put it in next month. Haven't ordered the JP probe yet but it will be waiting for me when I get back from deployment.  I'd be curious to learn more about adding the JP probe in the same proximity to the original as well.  Bear in mind I haven't begun research to actually doing it so have no idea about the details of installing the second probe.  I'll keep posted to this thread.  Thanks for all the info as always.

[vance.k]

On 11/6/2017 at 3:32 PM, CaptRJM said:

Just remember that you can calibrate the JPI for accuracy. In my case the ships gauge would read 1575 degrees when it would really be 1650 which is max TIT temperature. 

@CaptRJM, to clarify, did you use the Alcor calibration and test set to determine the ship gauge was inaccurate?  I suspect the JPI 830 with a JPI probe is probably pretty well calibrated, where I have less confidence in the ship gauge.  I've seen you can rent that Alcor test set, but I'm just curious how you determined yours was off.

Thanks!
Vance

[CaptRJM]

My AI has a test set, not sure if it's an Alcor or not.  The JPI was pretty close to what the test set said, the ships gauge was about 75 degrees colder than the test set.

[vance.k]

Just realized I hadn't followed up on this thread to close the loop.

I ended up buying the PMA'd KSAvionics A002C-30 unit for a little over $200.  Installed it and verified it worked correctly with the ship gauge.  Then we paralleled the JPI and everything is working correctly.  The JPI reads about 25F higher than the ship gauge, but I'm happy with that.

So, I guess this is confirmation that there is some technical issue with the JPI probes not being able to drive this particular ship gauge, but the PMA'd units work just fine.  And legal...so that's a bonus.  

Thanks again to all the MSers that pitched in to help with info and guidance. 
Vance

[One Whiskey Hotel]

I’ve learned in owning my K that ships gauge TIT indications are notorious for being low by as much as 75 degrees F. Keeping that in mind, I’d use your engine monitor for TIT and backup with ships gauge for redline, etc. As such, when my FF gauge laid an egg I opted for a JPI 900...seems all those ships gauges are a qualified best guess while reputable engine monitors are quantified and much more accurate.

[Cardinal767]

After all the discussion on how far off the OEM TIT indicator is, I connected(piggy back) my 830 to the OEM TIT probe. The part number on the probe installed is 3199516. Before starting the engine I checked that all CHT/EGT and now the 830's TIT temps all read the same as my aircraft OAT and the 830's independent OAT. All (15) temps were within 2*F of each other. The aircraft TIT of course was off scale too low. After takeoff I monitored both the aircraft TIT and the 830's indication as I climbed from 600 to 8,500 msl. At first, both indications were within 25*F(at 1300*F), with the 830 reading higher of the two, but that was short lived. The higher I climbed, the difference between the two increased, ending with about a 100*F split (830 highest)  . Here is what concerned me, in cruise (2400rpm, 30.0 MP @ 9.5-9.7gph LOP) the aircraft TIT read around 1525*F and the 830 read 1625*F. I tend to take the word of the one closer to the danger zone (and 37 years younger). I went ahead and continued to lean until the 830's TIT dropped below 1600*f to be safe. Being I'm new to LOP, is pushing the 1650*F max TIT normal?

Yes, I know I need to check the calibration of both indicators. Until I do, I just want to be nice to my engine.

Thanks for the help

Bob