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-   -   Need help with SJ cowl!!! (https://vansairforce.net/community/showthread.php?t=79319)

vmirv8bldr 11-25-2011 04:55 PM

Need help with SJ cowl!!!
 
I need some assistance from anyone who has an SJ cowl on their 8. Specifically, Measurements along the cut line from FW to inlet on both sides. If you happen to have a Whirlwind RV200 and a Barrett IO-390, you're my new best friend.

Long story short, after getting the horizontal hinges installed on the bottom cowl, I put it on the plane and the hinge eyes are in contact with the valve cover on Cyl #2, front LEFT. Cyl #1 (front RIGHT) has about 1/4" clearance. Theoretically, Cyl #1 should be the tightest fit since it is the forward-most cylinder.

Obviously, this cowl is unusable but I need to figure out what caused this before starting over. Any ideas?

Details:
RV-8
Barrett IO-390
Whirlwind 200RV (CS) prop and spinner
Sabre 2.5" Prop extension

Thanks,
Bart

vmirv8bldr 11-26-2011 10:06 PM

Pictures
 
This may help explain what I'm seeing...

I checked my engine mount at the fuselage and it is symmetrical and centered. All bolts are torqued. 2.5" prop extension is installed as required by the SJ cowl for the RV-8.







In the pic below, I used a long level to extend the fuselage forward to the engine and then measured these values from the edge of the level to the center of the valve cover of each cylinder.







Bruce 11-27-2011 05:03 PM

Bart,

Do you have pics from the front of the cowl around the spinner.
I would like to see the spacing there.

With some help just remove cleco's on the long side and push
back a 1/2 inch or so.
I thought I had the same problem with mine and adjusted more
after I had the spinner side gap perfect.

Thanks and I hope it helps.
Boomer

koda2 11-27-2011 07:42 PM

engine mount
 
Bart,
I am no expert but my first impression is that your engine mount is not only canted right side down but is also pointed to the right of center. I would get some measurements of the mount itself and compare it to some others.

It would also seem impossible for the engine mount to be made improperly or bent but I had some weldments that were simply not acceptable in my kit. I threw away the copilot stick base and had to totally redo the landing gear mounts.

It would also be very unlikely that the firewall installation is crooked but,... is that possible?

Double check your engine mounts to make sure one side is not reversed on the top or bottom.

Don't throw away the cowl; I know one builder who had his engine/mount on improperly, fitted the cowl, corrected the mount problem, and had to rebuild the cowl. It was accomplished with not to much difficulty.

Dave A.
6A build

vmirv8bldr 11-27-2011 08:22 PM

Engine cant
 
The engine on the 8 is supposed to be canted. The VS is put on perfectly straight and the engine is canted to overcome P-Factor. I originally thought about the mount, but with the firewall holes lining up pretty well and the back of the spinner centered, I believe it is right. I posted the pics to see if anyone else could verify theirs is about the same.

I also thought maybe the 390 jugs were slightly wider than the 360, but I understand they are identical. (Will confirm with Barrett tomorrow morning.)

I have a few ideas on making the cowl work. While I use a 1/4" spacer for fitting, it measures about 3/8th now, so I can fill and drill the rear of the cowl and pull one side out like Bruce mentioned. Someone else suggested placing a spacer and applying some heat, then letting it cool. I may also be able to remove some materials from the spinner holes and smash it down in the center to bow the sides out.

I'm still interested in confirmation of my engine mounting measurements and will call Van's in the morning also.

Keep the ides coming.

Bruce, as I said, spacing is about 3/8" back from the spinner and centered. Though centered actually leaves about 1/8 to 1/4 on the sides to play with.

Stretch 11-28-2011 04:53 AM

A friend of mine put the engine bolts in the incorrect holes when mounting the engine in his 7. Caused misalignment of the motor with the cowl.
I am not quite at that stage myself yet but I have checked. I believe the 4 bolts that go through the Dynafocul mounts are 2 pairs of different lengths. Not much in it but I am told that if they're put in the wrong holes the motor can be canted up/down/sideways - depending which bolt is where........

Bruce 11-28-2011 02:06 PM

Bart,

Reach out for Deene Ogden.
He lives in the Austin, Tx area.
Has a 390 and James cowl.

Might be able to help.
He should be in the white pages and
is an EAA TC also.

Good luck,
Bruce

vmirv8bldr 11-28-2011 10:57 PM

Action plan
 
I spoke with Deene this afternoon. His cowl was close, but not in contact and he had a few ideas. (Actually I've spoken with him a few times now this year.)

Other info of use:
Rhonda at Barrett Precision Engines confirmed the Barrett IO-390 cylinders measure exactly the same as the IO-360A1B6 (Angle valve 200HP)

Gus at Vans confirmed my engine appears to be mounted correctly, and confirmed that Cyls #2 and #4 will be very close due to the one point something or other cant in the engine and that some point behind the spinner tip will be centered on the fuselage. (Mine is!)

Will James confirms their cowls are designed for the angle valve 360 (and is compatible with the 390.) BTW, Will has been a pleasure to work with through this, but the best suggestions came from VAF.

I understand the engine rotates on the mount rather than shakes laterally or vertically, so not much clearance is really required. According to Gus, Vans removes core material in their cowls near the rocker cover edges to allow this movement as well.

Every 1/16" of an inch counts, and I'm shooting for 1/4" to be safe.

So here's my action plan. It progresses from least rework to most rework.

1. Firm belief that this cowl is salvageable.
2. Replace horizontal hinges with quarter turn fasteners leaving a gap in the mounting strip at Cyl #2 and Cyl #1
3. Check fit. If it fits with sufficient gap, stop. If not, proceed.

4. Leaving the left side vertical hinge pin in place, pull right side forward slightly.
5. Replace right firewall hinge half with wider piece and create a scarf joint in rear cowl edge, extend with flox and glass strips.
6. Check fit. If it fits with sufficient clearance, stop. If not proceed.

7. Pull both sides out closing the spinner/cowl gap. Fill as required. (It's fiberglass!!!!)

I did some fidgeting at the hangar tonight with adjusting the cowl. I believe the first modification will do the trick and have already removed the horizontal hinge halves from the bottom cowl. The Proseal was three or four (cold) days old and was still pretty soft. After drilling out the rivets and removing the hinge half, a razor blade followed by a cleaning brush and some MEK removed about 95% of the proseal in the area than will be required to bond the quarter turn attachment strips. I'm going to go ahead and replace the top cowl firewall attach hinge with quarter turn fasteners as well.

By the way, after drilling through all this fiberglass, my #40 bit was not doing a great job on the rivet heads. I touched it up with the "Drill Doctor" my dad gave me for Christmas a few years ago and wow, what a difference!!!!!! If you don't have one of these, put it on your Christmas list! (A new bit here and there is cheaper, but if you have several bits of various sizes and use them frequently, it's nice to touch one up while you're working.)

More to come, stay tuned.

DanH 11-29-2011 07:30 AM

Quote:

Originally Posted by vmirv8bldr (Post 600879)
According to Gus, Vans removes core material in their cowls near the rocker cover edges to allow this movement as well.

The stock cowl is tight at the seam near the #3 rocker cover, but Gus probably means above the baffle mount ears.....the baffle wears or bumps the underside of the top cowl.



FWIW you can lower the baffle just a bit by filing a nice radius on the mount ears.



I seem to recall somebody mentioning low profile 1/4 turn sockets (POSTSCRIPT: it was Darwin, low-profile sockets available at Skybolt). I went with screws and nutplates on the side seam. Be cautious about skip spacing; the cowl really is a big balloon.

If you do an attach flange with glass rather than an aluminum strip it will fit better.

vmirv8bldr 11-29-2011 08:42 AM

Thanks Dan
 
Correct Dan, Gus said the core material omission in that area was for the "ears" not so much the cover, and I'm relieved to see your cowl that tight on the left side!!! Also, I went with a plenum setup, a challenge in itself. The SJ Plenum attaches directly to the rocker cover ear without baffling material and is very, very tight. I will need to lay up some flox to fill a few gaps though.

Excellent idea with the nutplate and fiberglass attach strip. I have the Milspec quarter turns already. I ordered them years ago, but decided to go with the hinges for the clean look, and to save a little time. We all see how that worked out for me. I guess advantages of the nutplates vs quarter turns is that installation is easier and lighter, there is no adjusting, and you always know it's tight enough. I assume SS screws with tinnermans. Do you have a suggestion for a requisite number of BID layers? (I have a good bit of 5.8oz S glass on hand.)

I was really surprised (and pleased) how easily the semi-cured proseal came off.

Thanks Dan!

Gonzo24 11-29-2011 11:54 AM

fiberglass strip and screws
 
Bart... I'm fighting the same fight on a -7 with SJ cowl and IO-375 right now. Was the consensus of your talk with Van's and others that 1/4" is enough clearance at the rockers? I have maybe 3/8" at #2 with hinges at present.

Also - after perusing some Lancair builder's sites... I see many elect to use the fiberglass and screw option for clearance issues on the side parting lines. After looking at their sites I didn't feel so bad about my clearances in the engine room :eek:

i would think there would be advantages to containing air leakage at the sides for cooling air drag reduction also with this method. Ah, the joys of cowling mania!

vmirv8bldr 11-29-2011 06:29 PM

1/4" should be ok.
 
From what I've learned, the engine basically rotates a bit on the mounts so the rocker covers mostly just move up and down under the cowl. One of the sources said that 3/8" side clearance is the target gap, but 1/4" should be just fine. If you have 3/8" right now and nothing's rubbing, I think you're right there with everyone else and should just move on. As for the cooling, if the baffles are sealing correctly, or you're using a plenum, then this area should be low pressure anyway and any opening would have a minimal affect on the cooling air flow.

I removed the horizontal hinges last night and put the cowl back on this afternoon. With no strap, or anything else, the sides sag out a bit. So, I'm going to make a backing strip covered with packing tape and cleco it onto the bottom cowl where the hinge was. Then use tape on the edge and outer surface of the bottom cowl to make an epoxy dam and prevent myself from gluing the halves together. Then I'll put it on the plane with the top cowl on. There's a lens shaped gap between the two cowls due to the sag that about 3/16" at the widest. I'll then fill that void with flox. After it cures, I'll sand a scarf joint and glass it over, then install the Milspecs except at the front and around rocker covers, which will get nutplates. This will get me 1/4" at Cyl #2 which will make me very happy, and I'll move on.

I'll post pics etc along the way. Seems others have had similar problems.

DanH 11-29-2011 06:53 PM

Quote:

Originally Posted by vmirv8bldr (Post 600967)
Excellent idea with the nutplate and fiberglass attach strip......I assume SS screws with tinnermans. Do you have a suggestion for a requisite number of BID layers?

Original thread here, with some good comments:

http://www.vansairforce.com/communit...ad.php?t=36697

Truss heads and nylon washers for me. I'm sure it costs me 0.1 knots ;)

Quote:

if the baffles are sealing correctly, or you're using a plenum, then this area should be low pressure anyway and any opening would have a minimal affect on the cooling air flow.
Not as a low as you think, and getting higher as you pull the exit closed.

vmirv8bldr 12-13-2011 12:06 AM

Progress
 
I have been working on a few things, but have gotten the correct fill and fiberglass strips installed on the bottom cowl. I'm pretty pleased with this really. After taking the halves apart, you can really see how much bend there is in the top cowl, and why the aluminum mounting strips would be less efficient here. Thanks to Dan H for that.

For the fill, I first sanded a scarf joint and about an inch down along the seam. I assembled the cowl in the garage and used tape (LOTS of tape!) as a release agent and mold. I taped over the edge on the top half and allowed for about 2" of overlap. Then I put a piece of tape down the seem and filled it from the back with thick flox. I squeegeed that and let it set. Then I separated the halves and sanded the back of the flox.

I then re-assembled the halves and followed Dan H's method to lay-up the mating strip. 5 plies of 2" 8oz tape. Worked like a charm. I did one on Saturday and the other Sunday. On the right hand side, all five plies run the entire length. On the left side, two plies run the full length of the seam but there is a gap in the other three plies right where the forward edge of the #2 cylinder is (you can see this in the pic.) After measuring the thickness, this was probably unnecessary, but should be ok nevertheless.

Test fit tomorrow!


thiggins 04-12-2020 06:11 AM

Carbon fiber version
 
Here's a Mike Patey video of him doing a similar process in Carbon Fiber. Took me a while to figure out how this worked, but it's very cool.

https://www.youtube.com/watch?v=BuWV5ybVX2Y

( The previous episode on cowl construction: https://www.youtube.com/watch?v=enLrRWV1bIM
)


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