measurement needed

[pmanton]

Would someone be kind enough to take a measurement for me?
This is on a 7AC. I need a measurement from the bottom of the crankshaft along the contour of the nose bowl to the top of the airbox. My nose bowl is sitting too high and it has to be the airbox. I measure 13 ¼ inches. The crankshaft is not sitting in the center of the opening and all other measurements are off.

The engine is a C-85 with a stock Univair airbox. I’m not sure just what would cause the airbox to sit too high since everything is stock. That is Stromberg carb, stock airbox, stock Univair nose bowl, etc.
Thanks

Paul

N2426E
N1431A
2AZ1

[N86250]

I’m not sure just what would cause the airbox to sit too high since everything is stock. That is Stromberg carb, stock airbox, stock Univair nose bowl, etc.

Sounds like you have a Continental airbox as used on a Piper J3C instead of an Aeronca airbox. jrh

[pmanton]

The airbox is the stock Aeronca airbox fresh from Univair. The nose bowl is also fresh from Univair. I'm at a loss right now-----

[N86250]

You must have an aluminum airbox. I think it needs a wedged spacer to adapt it to the 7AC nosebowl opening. Bill Pancake or John Propst can help you fit the parts. My drawing of the wedge is in a dead hard drive. jrh

[jepropst]

Paul, here's a few drawings that you might want to review for dimensional information. Drawing 4-576 is a drawing of the nosebowl with all dimensions required for manufacturing. It is my understanding that the Univair metal nosebowls are dimensionally correct with respect to this drawing, but you may want to check a few dimension just to make sure. On my plane I had an old WagAir fiberglass nosebowl and the location of the airbox opening deviated quite a bit from this drawing.

Next, drawing 4-601 is the drawing for the correct airbox for a 7AC. There are a number of different airboxes for Aeroncas and also for continental engines so you may want to check and make sure your airbox is dimensionally correct with respect to this drawing. Drawing 7-446 provides a cross section of this airbox installed on the engine with the nosebowl in place. If you are using the strom. carb, the airbox should attach directly to the bottom of the carb as shown on the drawing.

If you were using a Marv. Sch. carb, you would need an adapter or other means to modify the mount so that there would be room for the accelerator pump on the bottom of the carb. From what you described, you have the Strom. carb so you should not have any adapter between the carb and the airbox. If all this checks to be in accordance with the drawings, then I would check the engine cowling to confirm that it is dimensionally correct with respect to the drawings.

When I restored my Champ, I found that the last fabrication of the engine cowling deviated significantly from the drawing, resulting in a poor fit of the nosebowl to the aircraft.

John

[pmanton]

I have checked the nose bowl and it's correct. The air box is correct and again is a new Univair unit. I don't have 7-446 but have put out a request for it on the fAA mailing list.

When I hang just the nose bowl on with no cowling it is still way too high. Looking carefully at it last night it looks like my intake manifold "spider" wants to angle the carb upward.

I'm going to investigate this further today.

Thanks

Paul

[MikeB]

Paul,
I just measured my 7AC with the A65 and it measures about 12 1/4" from the crank adapter (tapered crank) to the top of the air box. My crankshaft is exactly in the center of the Wag Aero nose bowl. This is with a Stromberg Carbureator.

On my L16 (0200) with the Marvel carb I had to make a tapered adapter as John posted above and 'dent' the airbox for the accelerator pump but that should have no bearing on your application.

Mike Berg