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3 hours ago, Rjfanjet said:

So, is using a portable tach legal?

No.

But as @jetdriven noted, the tach is required equipment under FAR. So, technically the aircraft is unairworthy without it  But, if the FAA determines (this is where the FSDO has latitude) that the flight can safely be conducted to a place where repairs can be made, it can issue a special flight permit (aka ferry permit). 
https://www.faa.gov/aircraft/air_cert/airworthiness_certification/sp_awcert/sp_flt_permit/

 

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My tach stopped working. A couple screws and I slid it out the back. If it took me 30 minutes I’d be surprised, but I’m used to working in small places. Took mine to a gyro overhauler who turned it around in a day and even corrected it. 
 

-Robert 

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Ferry permit was pretty painless when I had to fly down for engine overhaul. FSDO was great to work with but YMMV. 

If they allow it you will probably need to document a plan on how you would reasonably infer RPM and mitigate risk. Not proscribing the following or saying it is safe to go, but just offering it to the forum for feedback for thinking it through for safety:

 

Optical Tach? or...

Mag drop check - ??? 

Takeoff RPM -  achieving rated MP/FP & fuel flow for full RPM?, Risk mitigation lots of extra run way?

Cruise - lean to fuel flow/MP/TAS per OAT/smooth engine operation - as historically associated with typical, normal cruise RPM

Landing/Go-Around - Full RPM

Thoughts?

 

(I also have all my instruments that I pulled for the EDM 900... there is a MP/FF/tach in there, but don't know if it is compatible with a C model)

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Nice logic, Stephen!

The tach gets used a lot to make sure the engine is running properly before we even leave the ground...

Then to know it is producing max power while trying to leave the ground...

Best regards,

-a-

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I hesitate to post my reply for fear of encouraging someone to do something that might be illegal or unsafe for them, but I’ll worry about the flame suit later, here goes:

I don’t have much time in my Mooney, probably a hundred hours or so if I looked it up.  I’ve been a Motörhead since a small child growing up in my dads auto repair shop, so maybe I have a better feel for engines than most.  I also am capable of reliably doing most anything to a vehicle and in the case of an airplane, get it signed off.

With that preface if I can not speak to the OP’s comfort level when it comes to maintenance and repair operations.  I would find a way to repair it myself or find someone who could.  Failing that, I believe I have enough time and feel my IO360 that I could safely make that flight.  During the run up, I would lean it enough for the mag check to be able to feel that each mag is working.  Richen it for all other aspects of the run up.  After climb out. I would know about how many turns for roughly 2,500 and still have an MP gauge for the desired setting.  I would probably govern it on the low side of 2500.  
 

Now!  It’s easy for me to sit back comfortably in my chair and write such things without actually being in that situation.  It all depends on the particular circumstances, but if it were legal, I believe I could safely make a short ferry flight as I described.

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If you go for a ferry permit, I would keep it really simple: you want to go from point a to point b with an inop tach. With the FAA, you don't want to volunteer too much information. In my experience, you definitely do not want to make up procedures using unapproved equipment. Think what you are asking if you do this: You are asking someone from the FAA to approve something that they probably don't have the knowledge or authority to authorize. That's a recipe for not getting approval. The O-360 is approved for continuous operation at 2700 rpm. If the governor is working you can just fly with the prop control all the way in. It's not a big deal and shouldn't be an issue with the FSDO if you keep it simple.

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I've been flying for almost 30 years. It actually broke at an intermediate stop. I'm comfortable with flying by ear, no issues there. I just should've said nothing and flown it to my mechanic. Going to check with my mechanic today.

Thanks for all the advice.

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1 hour ago, Rjfanjet said:

I'm comfortable with flying by ear, no issues there. I just should've said nothing and flown it to my mechanic.

I'd probably still do that. 

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16 hours ago, Rjfanjet said:

Sorry, can’t figure out how to rotate....

Just pull back gently on the yoke...

;)

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MS best humor prize of the day is awarded to...

EricJ!

:)

Best regards,

-a-

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