Engine cowl (Cutting to fit)
09-03-2009, 07:38 AM
#1
Thread Starter
Engine cowl (Cutting to fit)
Hello all:
I am in need of some expert advice on how to fit and cut my cowl. I recently purchased a Hangar 9, RV8. I installed an OS max 75AX and need some direction on how to cut/fit the cowl over the "Box" muffler (The stock muffler that caame with the engine). I need the following.
1. Muffler cut out direction.
2. Glow plug hole.
3. Needle valve hole
4. Fuel dot cut (where to position). ( I might just refuel the plane by removing the canopy, but like the idea of have a fuel dot as well.
Please e-mail me with any tips, help advice.
Regards
Glenn Williams
[email protected]
I am in need of some expert advice on how to fit and cut my cowl. I recently purchased a Hangar 9, RV8. I installed an OS max 75AX and need some direction on how to cut/fit the cowl over the "Box" muffler (The stock muffler that caame with the engine). I need the following.
1. Muffler cut out direction.
2. Glow plug hole.
3. Needle valve hole
4. Fuel dot cut (where to position). ( I might just refuel the plane by removing the canopy, but like the idea of have a fuel dot as well.
Please e-mail me with any tips, help advice.
Regards
Glenn Williams
[email protected]
09-03-2009, 10:28 AM
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RE: Engine cowl (Cutting to fit)
Use card stock to make templates of the cut outs, with the engine in place align the cutouts to fit and tape them to the fuse. Carefully remove the engine so as not to disturb the card stock. Install the cowl and trace the openings on to the cowl. Use a Dremel tool to make the holes in the cowl.
09-03-2009, 08:48 PM
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RE: Engine cowl (Cutting to fit)
This takes time, don't rush it!
Start with the muffler off. Place rolled paper towel in exhaust port, carb intake, over needle valve fitting if/when you remove needle and cover/plug all fuel lines. Install the prop drive washer and hold it in place with the propnut and a homemade spacer if necessary. If you will be using a spinner, the backplate of the spinner will rest against the drive washer, so now is the time to determine clearance between spinner and cowl. Measure from slightly behind the front of the drivewasher to the center of GlowPlug. Transfer this measurement to the cowl and drill a 1/8" hole.
There! Doesn't that feel better? You finally made a hole in the blasted cowl!
Measure the diameter of the cylinder head, then center and mark accordingly on the cowl. Using a hardwood block to "Buck" under the drill bit, drill a series of 1/8"holes at least 1/8" INSIDE and all around your mark for the cylinder head. You want to drill undersize and bring it up to fit with a Dremel sanding drum. (Or hand file and coarse sandpaper). Before you sand up to fit, you will need to "connect the dots" with a # 11 exacto blade, then sand.
Line the cowl up by eye looking down from the top of the fuselage and from the side. You can determine where to place a starting hole for the engine crankshaft. Again, open it up a little at a time until the hole is in the correct spot and of the correct size.
Measure, mark and continue for anything else that the cowl has to clear. Remember that you need access to the low speed mixture screw also.
After you get the cowl over the engine, place the muffler up to the cowl. You can then eyeball where to place your beginning 1/8" hole, then open it up a little at a time until the muffler fits. Usually, when the cowl clear's the cylinder head properly, room is there to install the muffler mounting bolts.
By beginning with smaller holes as compared to big ones, you can adjust the position of any opening as you test fit the cowl, so that when you're done, it all lines up!
Be careful about the dust you create...it's not good to breath it. Good Luck!
Start with the muffler off. Place rolled paper towel in exhaust port, carb intake, over needle valve fitting if/when you remove needle and cover/plug all fuel lines. Install the prop drive washer and hold it in place with the propnut and a homemade spacer if necessary. If you will be using a spinner, the backplate of the spinner will rest against the drive washer, so now is the time to determine clearance between spinner and cowl. Measure from slightly behind the front of the drivewasher to the center of GlowPlug. Transfer this measurement to the cowl and drill a 1/8" hole.
There! Doesn't that feel better? You finally made a hole in the blasted cowl!
Measure the diameter of the cylinder head, then center and mark accordingly on the cowl. Using a hardwood block to "Buck" under the drill bit, drill a series of 1/8"holes at least 1/8" INSIDE and all around your mark for the cylinder head. You want to drill undersize and bring it up to fit with a Dremel sanding drum. (Or hand file and coarse sandpaper). Before you sand up to fit, you will need to "connect the dots" with a # 11 exacto blade, then sand.
Line the cowl up by eye looking down from the top of the fuselage and from the side. You can determine where to place a starting hole for the engine crankshaft. Again, open it up a little at a time until the hole is in the correct spot and of the correct size.
Measure, mark and continue for anything else that the cowl has to clear. Remember that you need access to the low speed mixture screw also.
After you get the cowl over the engine, place the muffler up to the cowl. You can then eyeball where to place your beginning 1/8" hole, then open it up a little at a time until the muffler fits. Usually, when the cowl clear's the cylinder head properly, room is there to install the muffler mounting bolts.
By beginning with smaller holes as compared to big ones, you can adjust the position of any opening as you test fit the cowl, so that when you're done, it all lines up!
Be careful about the dust you create...it's not good to breath it. Good Luck!
09-08-2009, 05:53 AM
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RE: Engine cowl (Cutting to fit)
RC-Sport and Safetwire are both right. After drawing the cut lines from the template, I use a Dremal and grind it with the round dowel sander all the way near the line. Then I hand sand using sanding sticks or round dowels with sandpaper glued around it so I can sand a nice curve if I want to, until I get right up to my cut line on the cowl. Take your time and keep trial fitting until everything fits right.
Make sure the cowl doesn't touch your muffler, give it at least 3mm clearance around the muffler. I've had a plane or two with a cowl that started to burn and melt because I had it touching the muffler, or it was too close to it.
Pete
Make sure the cowl doesn't touch your muffler, give it at least 3mm clearance around the muffler. I've had a plane or two with a cowl that started to burn and melt because I had it touching the muffler, or it was too close to it.
Pete
09-08-2009, 08:56 AM
#5
RE: Engine cowl (Cutting to fit)
All sound techniques offered by the first posts! Main thing is to be patient and don't be aggressive with the rotary tool. I bet I trial fit my cowl 10 times as I get the main cylinder hole cut to final size. I use the metal bit that is shaped like a cone to rough cut the holes, and then the sandpaper drum bit to finalize the large holes. I normally turn on my central vac and have the pointy nozzle a few inches from the rotary tool business end. I wear the ear muff hearing protectors to save my hearing from the vac and rotary tool noise. It's actually a lot of fun when it turns out right! Jon
