Manifold Pressure Fitting - 0-320

Hello all!

What type of fitting does the manifold pressure tap on an 0-320 require at the cylinder head? Is it the same as a primer tap? ANxxxx?

I was performing some MX when I noticed the manifold pressure line had completely severed at the tap that screws into the cylinder head (#4 in my instance). There is currently a solid line from the panel into the engine bay; it stops short ~6" which then went to a flexible hose. The flex hose was attached to the hard line with a standard automotive screw type hose clamp that continued to the cylinder tap. Mine looks to either be crimped around the flexible hose but it could very well be a 'factory' fitting.

I think I'm just not using the right search terms! I edited the thread cause I think I'm on the right track with just needing to know the correct ANxxx fitting.

Thanks!

My plane is not close-by, but ...

... I recall that being a 45 fitting, probably an AN823. I have a SS braided hose that goes from that engine fitting to the f'wall. Hose is small; no bigger than a #4.
To avoid the clocking problems of a 45, you could put a straight fitting in the engine and put the 45 in the hose. Oh yeah, I do recall my vacuum hose is 14.5 " long flare to flare ... I ordered it from Bonaco.

Have have a 1/8npt x AN3 (tiny) adapter in the threaded port on one cylinder (2 I think) connected to 1/8" copper tubing and routed to the firewall mounted transducer. has worked fine for 13.5 yrs. Need a couple of movement loops where it transitions from the engine to the mount.

Mine was definitely a straight fitting and with continued research, looked quite similar to that shown below; with the exception that the rubber flexible hose filled the void around the inner 'core', possibly crimped as I mentioned but hard to say without it in front of me (doh!)



The flexible hose was severed right at the fitting; I'm wondering if keeping it flexible or extending (running new?) the solid copper tubing would be better. One would think solid would be better and the primer lines are solid so vibration shouldn't be a large issue? On the other hand, maybe it's flexible for a reason (clearly I'm not the builder!)

Brass DOT push lock fitting. For use with NYLON/PLASTIC tubing, not rubber.
1/8 NPT thread. Some guys use -2 copper tubing (YUK), some use -3 teflon hose, some use -4 teflon. I normally use a 45* or 90* hose ends at the engine, to route the hose inboard, so it doesnt rub on the cowling.
Tom

Whatever fitting you end up using, it is a good idea to have a restrictor in it.

The restrictor will do two things you will be happy with, first it dampens the pulses from the vacuum and the gauge will not be jittery, and second if the line should fail, it minimizes the leaning effect of introducing a fresh air leak into the cylinder.

ACS and others sell restrictor fittings just for this purpose.

Good advise on the restrictor especially if using the hose connection and 45 deg fitting arrangement. Had to placed a restriction in the AN 45 deg fitting at the cylinder head to get my Dynon 180 to settle out on a MP reading.

Restrictor

My UMA MP gauge is connected with 3/16 line: solid from gauge to firewall; then rubber flex to a 45 AN fitting on the cylinder. Gauge filled with gas after a couple of hours. Filled pipe side of AN fitting with solder, drilled tiny hole (pressure, not volume....). Has worked perfectly for 27 years...

You guys are great; this should help me order what I need. Thanks!