Check those backplates!

[Clint Ormosen]

I know most of you guys know this. I've even read it here myself. But, I didn't take it seriously enough. Those darned plastic backplates on the OS LA series DO get loose. I had been running an LA 25 on a sport profile for some time now with no issues whatsoever. Then I pulled the motor off and installed it in an ARF Nobler for a local ARF/ARC only contest. I test flew the Nobler the day before the contest and all seemed ok except that it was kinda hard to start on the last practice. The next morning at the contest I couldnt get it to start on my first official and had to take an attempt. Eight minuets later I was up again and finally got it to run with the help of an electric starter. It just didn't seem to want to draw up any fuel. That process took way to long and I overran my time limit. Thinking it was a problem with the plastic tank I just planned to use the 'lectric starter on the next flight too. This time it was a no go at all. The engine would just run out the prime and that's it. So no second official flight at all. It wasn't untill I went to return the LA 25 to the profile model that I discovered the loose backplate. And it was REALLY loose! Sloppy loose! So now I'm a believer that the plastic plates suck. Oh, and there are no FP backplates to buy anymore.

So don't be an idiot like me. Check those stupid things once and a while.

[ray copeland]

Been working on the clunk tank for my OS 15 for awhile, thought it was the problem causing a touchy needle when i noticed the plastic backplate leaking fuel!!   

[Paul Taylor]

Would some type of gaskit seal work to "glue" the plastic back plates in place. And maybe some lock tight on the screw?

Bummer you can not get the metal ones anylonger.

Paul 

[Don Curry AMA 267060]

Most hydraulic shops have O ring material in bulk. Have an O ring made that will just go over the raised portion of the back plate. then do a small chamfer on the crank case about half the thickness of the O ring and put it together. it really helps seal the joint. I have not found a gasket cement that will stic to the plastic  or disolve in the fuel.

Don

[don Burke]

I recently saw an article on an R/C combat site that detailed sealing the backplate on an OS15LA.  Made a lot of sense to me.

I just tried to log into the site and it's showing "under construstion" at this time.  I'll post the link as soon as it's available, it had a very desrcriptive set of pics of the process.

Here's what I remember.

-Remove backplate carefully to keep from damaging the screws, or plan on replacing them with Metric Allens.
-Clean the backplate and crankcase surface and existing gasket thoroughly with solvent.
-Apply a small bead of hi-temp silicone sealant (the orange stuff) over the gasket to the mating corner of the round part that goes into the crankcase and the cover flange.
-Use blue locktite on the screws and lightly tighten to keep from damaging the plastic.

[Brett Buck]

The next morning at the contest I couldnt get it to start on my first official and had to take an attempt. Eight minuets later I was up again and finally got it to run with the help of an electric starter. It just didn't seem to want to draw up any fuel. That process took way to long and I overran my time limit. Thinking it was a problem with the plastic tank I just planned to use the 'lectric starter on the next flight too. This time it was a no go at all. The engine would just run out the prime and that's it. So no second official flight at all. It wasn't untill I went to return the LA 25 to the profile model that I discovered the loose backplate. And it was REALLY loose! Sloppy loose!

   OH! That was the problem. I had the unhappy duty of judging while  Clint first took an attempt, then take a long time to get it started, ran overtime on a pretty decent flight, then not be able to go on the second flight either. Fuel draw was clearly the issue. I am very surprised that it ran as well as it did once you did get it started.

      I would suggest what I did over on SSW - pull out the backplate, clean it off with acetone or similar, run a large bead of silicone sealant around the flange (about 3/32 diameter in a ring right in the corner where the flange hits the "stuffer" part) and stick it back together. Wait an hour, and should be good forever.

   As an aside, the LA25, even this condition, had PLENTY of power for his ARF Nobler.

     Brett

[Clint Ormosen]

   OH! That was the problem. I had the unhappy duty of judging while  Clint first took an attempt, then take a long time to get it started, ran overtime on a pretty decent flight, then not be able to go on the second flight either. Fuel draw was clearly the issue. I am very surprised that it ran as well as it did once you did get it started.

      I would suggest what I did over on SSW - pull out the backplate, clean it off with acetone or similar, run a large bead of silicone sealant around the flange (about 3/32 diameter in a ring right in the corner where the flange hits the "stuffer" part) and stick it back together. Wait an hour, and should be good forever.

   As an aside, the LA25, even this condition, had PLENTY of power for his ARF Nobler.

     Brett

Thanks for the "decent flight" comment Brett! I was so rattled by the time I actually got the thing in the air, I'm surprised I even remembered the pattern.
But I agree, and even a little surprised, that the little LA .25 with the APC 10-3 did a pretty good job hauling that Nobler around. Not a bad combo, actually.

[Larry Cunningham]

I was expecting to read about a crankshaft rubbing the back plate, perhaps due to
use of an electric starter. But then I realized it's a plastic backplate..

L.

"I know what pleasure is, for I have done good work." -Robert Louis Stevenson

[wmiii]

 Check out the classifieds on Stuka Stunt, back plates are being offered at 12.00ea

 Walter 

[don Burke]

Found the link with the backplate prep pics.  There's other stuff pertaining to the airplane being sold by these guys but still useful info.

http://www.treneffrc.com/LA-15%20Clunk%20Tank%20Secrets.pdf

[Clint Ormosen]

Check out the classifieds on Stuka Stunt, back plates are being offered at 12.00ea

 Walter 

Perfect timing! I just sent Curtis an email and ordered some. Thanks for the heads up Walter.

[Brett Buck]

Found the link with the backplate prep pics.  There's other stuff pertaining to the airplane being sold by these guys but still useful info.

   Gee, and here I was thinking I thought it up myself!  Just as an aside, I don't think you need any form of "trick" automotive silicone sealant. It doesn't get very hot anywhere on a 2-stroke glow motor, particularly not at the backplate (which cools below ambient when it's running), and plain old Dow Silicone II bathtub caulk will work just fine.
 
 just to prove my sincerity, this year I sealed my header to the engine with some silicone caulk left over from a tube that came with a  $6 toilet valve repair kit! It was already open and it was going to dry out soon if I didn't use it.  It's been there for about 7 months of hard flying no issues. Paul Walker used to use 5-minute epoxy, which burns up at about 300 degrees.

     The automotive header stuff (Permatex Ultra Copper is the kind I carry around) can stand MUCH more heat and needs to because a car header can get to 1000 degrees very easily. I would be amazed if any stunt motor header got to 500.

      Brett