OS 25LA backplate

Hi there,

I finally gave up trying to keep my 30 year old engines running and bought a new OS 25LA for the Flite Streak, based on posts here. I figure if Mikey is learning to fly inverted we will be needing parts and it's easier to buy replacements from Tower than to JB Weld the old stuff together. I sanded out the crack in the piston but it's kind of thin walled now. Did you know that an OS20FS rod will fit if you relieve the case a bit? It's even bushed at both ends!

No I didn't bother ordering the controline engine, just picked up an R/C version at Hobby Shack. Rubber band kept the carb open on the test stand. I tried it out this afternoon and after a couple of runs it seemed to be broken in enough to fly. Turns the same props the same RPM's as the old baffle piston engines, but quieter with the stock muffler. 10 percent nitro 22 percent oil. Might even be able to do without the electric starter and hand start like the real roundy round pit crews do.

I haven't figured out what to do with the backplate. Do I just hack off the extension with the needle valve? Is the plastic durable enough or will it distort and leak over time? I'm going to steal the venturi and front needle from the old engine.

BTW, I was using the TNC tach and it locked on till about 5:20 PM when it got too dark to read the display. It was really too dark to be running engines safely, especially with the black plastic props I'm using. Well worth the hundred bucks.

Thanks,

John and Mikey in the PRC

A razor saw will cut the N/V off the backplate very nicely, and a sharp exacto blade will trim it to look like the other three corners.
I have two .25LA's modified this way with no problem. They're great little engines.
Andrew Raney

If you want a metal backplate, one for a 25 TT will be cheaper than the OS FP, and, again, is a perfect fit. You might even find someone with an old engine that has been pranged into the concrete. The back plates usually endure long after the rest of the engine has gone

Ask in the Classifieds?

Great little motor. I can start them with one backflip on the spinner. Flown on an Excalibur, Primary Force to 500 point patterns and soon to be in a Don Stills Stuka. No bad habits and very dependable. Install a super tiger needle valve assy. rotate the venturi 90 degrees then drill out the oversize hole for the oversize assembly. This will give you a somewhat choked down venturi which will increase the fuel draw. That way you can go back to a smaller needle valve assembly by rotating the venturi back to its original position. Also remove the baffle in the stock muffler to improve power. That should be all Unless you want to install a metal backplate.

On profiles a Hayes 3 oz plastic flop tank uniflow configuration works fine. Use a 9x4 apc prop to start. set it off at about 11,300 to 11,800.

Bob Smiley
A Lancair 360 builder/pilot trying to be a modeler.

I have four 25 LA's and all I do is chop off the remote needle bracket on the plastic back plate. I sand it smooth on a disc sander. The plastic back plates are durable and I see no reason to replace them, also I have never seen any leakage around the plate.

Great motor, reliable. I have used both 9x5, 9x6 and 10x5 props all will success.

Nice motor. I have one of Len's own SSW versions, with a Delrin venturi insert.

I use old original Y & O 10-4 props on it. Very comparible in power to a Fox Stunt. Currell

Thanks, guys. Any easy way to get rid of that blue color? Easy Off oven cleaner? Sure cleaned up the aluminum Turbo 350 trans case on my Chevy, except for the etching as I left it on too long. Antifreeze in a crock pot? Hate to disassemble a new motor.

John in the PRC