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High Manifold Pressure


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What would be some possible causes for a high manifold pressure reading in a R-22 Beta II? lets say 28" in a hover and the usual 21-22" S/L flight.

 

Check your maintenance manual. This is another area they don't teach anymore. Some have never seen the maintenance manual for their aircraft, much less how to use it to find the information they need.

 

Your maintenance manual has vital information that was mandated for your usage by 14 CFR §27.1529 (Appendix A of part 27; A27.3). Troubleshooting information describing problem malfunctions, how to recognize those malfunctions, and the remedial action for those malfunctions.

 

However, Apiaguy’s post above cited the probable cause, leak in the MAP system.

 

 

Maintenance Manual Section 6.610 & 13.320

 

1. Ensure MAP gage indicates ambient pressure within .3 inches (engine off).

 

2. To check MAP system, disconnect MAP line at cylinder head fitting and apply suction with syringe until MAP gage indicates 10 inches Hg. Monitor gage for one minute; indication should rise no more than 1 inch Hg.

 

Verify carburetor throttle shaft bushings are not worn; check both axial and radial clearances. Intake leaks can also occur due to loose intake pipe connections in oil sump and/or cracked sump runner tubes. For 0-320-82C engines only, incorrect thin-flanged intake pipes PINs 61363, 61364, or 61365 used in place of correct PINs LW-16728, LS-16729, and LW-16730 can cause leaks in conjunction with deep-counterbore flange PIN 74360

 

R22 Maintenance Manual

Edited by iChris
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I agree RN. In a hover, that presure should have been all at was needed to sit it down and get it checked out. Anytime a hover requires MCP or more, its possible you are either over weight, blades are covered in crap,(bugs,,dirt etc..) or... A mechanical issue. Sit it down and explore the possibles.

 

One bird we have in the fleet has a way of being totally fine for 20 min, then showing higher readings for the remainder of the flight. Thats a stumper and we have explored multiple causes. But not 28"!! Lol.

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Its something that's been going through the school for a few months now, I haven't witnessed it first hand so all my information on the issue is second hand.

 

ichris, didn't think to check the low power section in the MM. The aircraft seems to "fly fine" other than a high indication.

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ichris, didn't think to check the low power section in the MM. The aircraft seems to "fly fine" other than a high indication.

 

The helicopter maybe flies fine; however, the problem could be in the MAP indicating system.

 

In a naturally aspirated engine air/fuel mixture is drawn into the engines cylinders by atmospheric pressure acting against a vacuum that occurs when the piston travels downward during the intake stroke. The MAP line at the cylinder head fitting is the input to your MAP gauge, which reads the pressure drop or vacuum pressure.

 

So, if there is a leak in the MAP indicating system, the leak represents a loss of vacuum and a return back toward atmospheric pressure, which is a higher pressure. Therefore, leaks cause a higher than normal MAP pressure reading.

 

Hence, to check MAP system, disconnect MAP line at cylinder head fitting and apply suction (vacuum) with syringe (piston) until MAP gage indicates 10 inches Hg. Monitor gage for one minute; indication should rise no more than 1 inch Hg. Again, leaks equal higher MAP pressure.

 

Your first check, easiest check: 1. Ensure MAP gage indicates ambient pressure within .3 inches (engine off).

 

In any case, in your naturally aspirated engine, actual MAP pressure won’t exceed atmospheric pressure.

Edited by iChris
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Tell the A&P to do a leakdown test in accordance with the MM and replace that cylinder that doesn't measure up. If he replaces them all and it doesn't make power the cam is worn. If A&P can't figure it out he can call an IA that's been around the block or RHC factory where there are mechanics that have serviced R22's since before you and your A&P were born. I've had students quote the MM without owning a copy and not having been to the RHC course for Mechanics like I have. You might want to weigh the pilots on a scale and not take their word for it, remove crap from under seats, check DA (does this only happen in afternoon?), wax the blades (both sides) or if it's an IFR trainer with 50 pounds of instrument gear on the nose and has an aux tank, etc., tell the A&P what the true takeoff weigh from the weight and balance is as the pilot that "reported" this might be a couple of biscuits short of max seat weight and you might be 90 pound pilot that needs ballast. . I have some R22's that weight 930 pounds with aux tank, floats and all sorts of gear but bought an early Beta in July that is a skid without aux tank that weighs 840.

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