Sport CARF Pitts - Engine Upgrade

[reyn3545]

I've had this Pitts finished for almost 2 years, and probably only have 6 or so flights on it. To make matters worse, it's already on its second motor!

I started with one of the Evolution 260 radials. Great looking motor, but performance wasn't dependable, and the motor leaked from every exhaust port, regardless of what I did to try and stop them. I yanked that motor off and sold it cheap before it ever went in the air.

I upgraded to a Moki 250. That was a great running motor, but like a lot of other people have found, on a 55 pound biplane with all of the inherent drag, a Moki 250 is a little sluggish for aerobatic flying. Great for buzzing the runway, but it falls off pretty quickly in the uplines. Shame.

I decided last week to sell that motor and go with a 3W 220 CS. It's a 4-cylinder, and puts out about 21 horsepower, compared to 15 horsepower on the Moki. That should solve the upline problem.

 

[reyn3545]

Now comes some new problems...

The Evolution motor had the ignition module bolted to the back side of the engine, on a set of stand-offs to make it clear the rear mounted carb. In order to get the motor mounted, I had to cut a HUGE hole in the firewall.

The Pitts came with the original motor dome and firewall already mounted on the plane. That firewall would accommodate a 4-cylinder motor. For 2-cylinder motors, there was an additional dome that fits over the first, and that created a second firewall about 2.5 inches in front of the first one.

Unfortunately, to get the Evolution mounted, I had to cut a large hole in the center of BOTH firewalls. In addition to that, I had to cut access holes in the original firewall so I could install nuts on the engine mounting bolts in the forward firewall. End result... the original firewall kinda looks like spoiled swiss cheese.

I was able to mount the Moki and work around these holes, but I'm not sure what problems they may pose for the 3W. The motor should show up in a few days, so I'll find out soon enough. I'm thinking about a metal plate on the back and front of the original firewall. that will push the motor forward another 1/8 inch or so, but that should be fine.

Here's a few photos of the firewall WITH the extension cap mounted on it (the one with the smoke pump hanging on the side), and the original firewall with the cap removed. From now on, I will swear by Aeropoxy and West Systems Epoxy. I used that to put the cap on in the first place, and it was a BIOTCH to get off of there!

 

[WMcNabb]

This should be fun to watch!

 

[reyn3545]

Lots of sanding and clean-up to do before I put the 3W on, but this should give me a good idea of how much re-work the firewall needs.

I'll remove the rudder and stand the plane on its stab against something solid (probably a deck post in the back yard). Then I can sit the motor in place, re-install the cowl, center the motor, remove the cowl, and then see just how much those holes complicate my project. Fingers crossed!

 

[49dimes]

Will watch this one. I remember that radial issue you had. I think your doing the right thing going with the dub quad.

 

[reyn3545]

yeah, why don't you tell my wife how smart I am!

 

[49dimes]

Hey now! I am NOT the kind of guy to go mess with another mans wife!

 

[dhal22]

Mike, great to see a thread on this swap out. Now to see it fly. That quad will sound sweet.

 

[reyn3545]

Yep, I hated to see the Moki go, loved the sound, but it was so boring to fly that it wasn't worth the half hour it takes to put it together.

When the motor and headers get here tomorrow, I'll learn a lot about the next challenges... Firewall, header adjustments, where to mount the throttle servo, and a common 3W problem... How do I get to the carb screws with the headers in the way!

 

[witchfingers]

Hey now! I am NOT the kind of guy to go mess with another mans wife!

Just remember, its not the stroke...it's the rpm that matters. lol. I want another bipe so bad. I love watching these builds and mods.