Smooth cowl, Rotax 912, IV-1200 fit..HELP!

[GWright6970]

After exhausting all of my efforts, I can't get the top and bottom sections to be 5/8" from face of cowl to face of prop flange ON THE TOP AND THE BOTTOM to save me. (See photo) I have the aft end of the top of the bottom cowl at 17.5 inches up from the bottom longeron, etc...

The cowl came from the factory two months ago, and was already pretty much trimmed.

I even tried taking the aft end of the top cowl, and pulling it down 1.5 inches SUPER TIGHT over the sides aft end of the bottom, and even that extreme measure did not fix the angle.

PLEASE.. what am I missing gents??!! Thanks!!!

[Geowitz]

Mine was the same and I tried the exact adjustments you did without any luck. This is a problem with the mold.

What I did to get it closer was to use a cutoff wheel in the dremel and cut out a wedge behind the top flange into the top of the cowling, but still leaving the flange attached at the bottom. Then I when I pushed the top of the flange back it brought the angle closer into alignment and I hysoled the back of the flat part of the flange to the cowling. Kinda hard to explain.

It wasn't perfect, but I just ended up just going with it. Overall alignment of the cowling to the plane and windshield trumped spinner alignment. Using the adjustments you already tried will give you problems with the windshield later. Just adjust the flange with a little fiberglass work using the joggle joint to align the cowling with your thrust line and it'll be fine. No one ever notices and it functions perfectly fine.

[GWright6970]

I think I understand.... let's go for a picture!

After looking at it, did your wedge cut further down around the sides also? I'm trying to figure out how that cut blended with the air intake openings. Seems they need to be "shaved back" and new glass put in.

I just wish that we didn't have to do this!!! (Like fix the mold) You know something is up when looking at the top mold's overlap flange with the bottom joggle edge and it does not have the same match angle... a good 5-8 degrees off.... The bottom is ok.... its the top that is bad.

In any case, we need a fix... is this what you did George?

Thank you!!

[mr bill]

I mounted the engine on the fuselage before doing anything with the cowl. Then drilled and clecoed the top and bottom halves of the cowl together, before mounting on the plane. Then removed the fuel pump from the engine and centered the cowl opening relative to the prop flange and moved the cowl back 5/8" and clamped the cowl to the fuselage tubing. Then I drilled holes in the cowl to match the tabs in the fuselage, clecoing as I went along. Lastly, I trimmed the rear edges of the cowl to match the door opening. I had none of the problems you have mentioned.

[Geowitz]

Mr Bill - your cowling is slightly different. The latest mold sold for the IV's has this problem.

[GWright6970]

Bill,
I am envious!! This one is nothing like that in fit!

Thanks for trying!!
Cheers,
Grover

[cubtractor]

Mine was the same way as yours. I had to live with a little mismatch. No one really notices.

[GWright6970]

Mike, I think mine was more than just cosmetic, as I think the prop backing plate would be rubbing on the top half of the cowling. The top is a full 5/8 inch to 3/4 inch off.

After a great pair of phone calls this morning with George (Geowitz) and Lowell (Highwing) I decided to have a go at it.

Not knowing how much of a mess I am going to make cutting this, I covered the engine in 6 mil plastic. I then marked and cut out the "wedge" and also found that one has to cut further down the frontal plate to get a better rearward slope. I cut further down than George did. I then taped it aft, removed it from the aircraft, and stood it on its noose. I measured the port and starboard sides to make sure it was plumb and then anchored it in the positin with string and weights. Next step was cleaning up the inside surfaces for a good clean surface for the new fiberglass. (A small wire brush is awesome for getting the dust out before the acetone wash.) The next step was the application of the fiberglass cloth and resin on the inside of the cowling to close and secure it.

Tomorrow, when its all set up, I will remove the tape, and rough sand it, etc. I'll post the finished pictures for future builders.

Huge thanks go to George and Lowell, and to all of you who are responding!!! THANK YOU!

[Geowitz]

Man that looks great! I wish I had done mine all the way like yours.

It will go back together very easy since you left everything attached at the bottom to keep the alignment. A little filler and you're good to go.

Too bad you had to go through this.

[GWright6970]

Today, I removed the wax paper and tape. I then sanded down the slick surface with 100 grit sandpaper for an initial sanding. I will do the finer grits, etc., when it comes time to paint.

The top is 3/8" face to face, and the bottom is 3/4' face to face. I can't make the construction manual distance of 5/8" top and bottom, unless I cut the blazes out of the front of the top cowling. I can't say how darn disappointed I am. There are other issues with this poorly manuafctured cowling. Suffice it to say, that if I start, well.... moving on.... I sure hope that this fits the windshield at the other end correctly....