The Cessna 120-140 Association Forum

Hello all. My name is Pat. I have a question id like to throw by you guys. I have a 1946 c140. Recently had engine rebuilt. Time for run up and test flight. We cant seem to get the rpm’s up past 2200 rpm. Even in flight. Magnetos seem to be ok. It is getting fuel. The pilot who flew it thinks its a carburator adjustment. ( he is the previous owner of this airplane). Also it does have a brand new Sensich prop. A/P thinks it may be the right mag. Any suggestions would be greatly appreciated. Thanking you.
Pat

Welcome, Pat

Has it ever worked correctly since the overhaul? If not, you might check the cam timing. Also, any parts that have been replaced, especially the cam, carb and intake spider. (Are they the right parts for an O-200?)

What is the length and pitch of the prop?

You should be able to achieve much more RPM in flight than on the ground. Is that not the case? (Effective pitch of the prop goes down as airspeed increases.)

Were the carb and mags overhauled at the same time? What is the mag timing? Why does the A&P suspect the right mag?

I have experienced low reading tachometers. With a little use they get more accurate. I usually cross check them with a model airplane tach reader which reads the blade rotation.
Did it seem sluggish in flight?

Thanks for responding guys. Sent pm. Thanks Pat

Thanks for the replies gents. First let me start out with the fact that im a TYRO TAILDRAGGER. Green as they come. I bought this airplane for a trainer. Theres alot to learn and alot of different lingo im not familiar with. After getting on the brakes and having a prop strike i had the engine completely overhauled. New crank and bearings, new prop. Replaced all hoses. Even those to intake spider. The slick mags are fairly new. 2 years. The pilot that flew the airplane is the man i bought it off of. Says the engine runs very smooth. He fly it in ground effect to see if rpms would come up and they did not. Because it was running so smoothly he took her up to elevation trimmed her up. And still the rpms would not exceed 2200rpm.the carburator was not overhauled. The AD That was out awhile back on the venturi had been corrected

The prop is a mccauly 1A90/CF7144.
Thanks to all.
Pat

8263 wrote: ↑Sun Apr 07, 2019 12:43 pm Also it does have a brand new Sensich prop.

8263 wrote: ↑Sun Apr 07, 2019 7:04 pm The prop is a mccauly 1A90/CF7144.

Seems there is some confusion about the prop...

Randy: is the McCauley approved for the O-200?

Pat: Are you sure the engine is an O-200?

If it is true that the engine makes 2200 RPM static (standing still) and 2200 RPM in flight, then I'd guess the tach sticks at 2200 RPM even if the RPM doesn't. As Randy stated, first thing to do is check the tach.

That is a prop for a C-85. McCauleys are approved for my O-200 STC, but not the 1A90 or 1B90.I also have a Sensenich approved. It is seeming like the engine is an 85 with an O-200 crankshaft. The prop Pat has should get near 2500 RPM.

Yes sir. Positive on the 0200. Thank you.
Pat

8263 wrote: ↑Mon Apr 08, 2019 5:39 am Yes sir. Positive on the 0200.

What is the basis for approval of the McCauley 1A90-CF on that engine? Not to beat a dead horse, but does the engine dataplate say O-200? There is often confusion between a true O-200 and a C85 with an O-200 crankshaft installed under STC.

Of course, none of this addresses your concern. Again, if the engine cannot accelerate as your airspeed increases, something is really wrong. There is nothing in the engine itself (like a governor) that would cause it to stop at 2200 RPM regardless of load. As airspeed increases, your RPM should will also increase.

Randy's right (again), an O200 should be able to spin that prop up just fine, heck, a C85 will probably turn it past the red line of 2575.