What is this threaded hole for?

[jackn]

While removing my pressurized mags for 500 hr inspection, one mag's bleed orifice had this screw hole tapped into it. My jpi930 rpm pick-up is a gasket style which is located under this. I am assuming there was some sort of pick-up screwed into it, but what? Was that how Mooney connected the panel RPM gauge? I'm going to replace it, but was curious.

[N201MKTurbo]

They might have been using it as a mag lock to hold the mag in place when it is installed. Other then that it might have been for a sensor. People do strange things.

[jackn]

Yup. That little cover was somebody's idea of a good solution. I guess ordering a new part was too difficult. 

[N601RX]

The cover and threaded hole are standard on an unpressurized slick mag. 

[jackn]

31 minutes ago, N601RX said:

The cover and threaded hole are standard on an unpressurized slick mag. 

Thanks! That helps clear up the mystery. This is why I do my own maintenance, with the help of an A&P. The bleed hole WAS covered up, therefore all the excess pressure was being vented through the other mag. 

[takair]

18 minutes ago, jackn said:

Thanks! That helps clear up the mystery. This is why I do my own maintenance, with the help of an A&P. The bleed hole WAS covered up, therefore all the excess pressure was being vented through the other mag. 

I haven't delt with a pressurized mag in a long time and I'm not sure I'm following the thread, however, it seems that the assembly might be there to keep the mag pressurized?  Wouldn't removing this prevent it from maintaining pressure?  Do you have access to the manual for this specific mag?

[kortopates]

From memory, that all looks normal to me for pressurized slicks. The JPI RPM sensor does not change the original slick hardware - it just adds the washer and sensor underneath the original screw in cover. You can and should verify the correct hardware in L-1363

[jackn]

19 minutes ago, takair said:

I haven't delt with a pressurized mag in a long time and I'm not sure I'm following the thread, however, it seems that the assembly might be there to keep the mag pressurized?  Wouldn't removing this prevent it from maintaining pressure?  Do you have access to the manual for this specific mag?

True, but you can't block the calibrated orifice hole(to the lower left of the screw hole). In this case, it was. 

[jackn]

14 minutes ago, kortopates said:

From memory, that all looks normal to me for pressurized slicks. The JPI RPM sensor does not change the original slick hardware - it just adds the washer and sensor underneath the original screw in cover. You can and should verify the correct hardware in L-1363

Thanks Paul, you cleaned it up. Yes indeed it's supposed to be there. The bottom of the cap has a small offset to keep the orifice hole clear, but in this case it was flattened out, so it was partially obstructing it. 

[kortopates]

Not the parts list, but this picture shows the hole is covered. But the cover does not make an air tight seal, air still bleeds out.

 

[Guest]

Normally the small domed cap with the screw has a small ridge in the centre through which the screw passes.  This allows the vent to be open while being protected. Blocking or partially blocking the vent would have no meaningful effect on pressure within the magneto or the opposite magneto.  Both are pressurized by air from the upper deck system.  

The vent would allow any moisture within the mag to drain out the bottom of the mag, or not if it were blocked.

Clarence