Author Topic: OS LA engines - Sealing the PLASTIC BACKPLATE (Read 3384 times)

Bob Zambelli · « **on:** March 13, 2007, 06:43:41 AM »

I know there have been many problems with LA backplates leaking but here is a fix that I've been using for years, on the LAs and ALL my engines:

I remove ALL of the paper gaskets and apply Loctite Anaerobic Gasket Maker.
It is part number 51817 and available from most auto supply stores.
I do this on all mating surfaces except cylinder heads - on those, I either keep the soft aluminum gaskets or use Hi-Temp Silicone.
I have used this method for the last ten years on spark, glow and Diesel engines and NEVER had a leak.
The .20 ounce tube is good for around 50 engines.

Note that this product is not a gasket cement - parts can easily be separated with a thin blade.

Here's how it works - when applied to a surface, it will remain in its gel form indefinitely.
After assembly when air can no longer get to it, it sets up semi-hard and it expands very slightly, filling in small voids.
Parts must be absolutely clean and oil free.

Give it a shot - it really works.

And, it sure beats trying to cut paper gaskets.

Bob Z.

Steve Kientz · « **Reply #1 on:** March 13, 2007, 10:48:10 AM »

Would this work between the engine and muffler?

Thanks
Steve

Bob Zambelli · « **Reply #2 on:** March 13, 2007, 10:59:04 AM »

Hi, Steve - I would use Hi-Temp silicone in that area.

Bob Z.

Leo Mehl · « **Reply #3 on:** May 11, 2007, 12:48:31 AM »

Bob, I have been running my OSLA46 with the plastic backplate fot three years now an have never had a problem, hopping this does not come back to haunt me.

Jerry Bohn · « **Reply #4 on:** May 11, 2007, 11:47:09 AM »

Leo, Have you ever taken the plate off for cleaning purposes?
I have read that when removing and reassembling is when leaks start to occure.

Bill Little · « **Reply #5 on:** May 11, 2007, 01:03:22 PM »

Quote from: Jerry Bohn on May 11, 2007, 11:47:09 AM

Leo, Have you ever taken the plate off for cleaning purposes?
I have read that when removing and reassembling is when leaks start to occure.

Yes, that's what I understand. Also, be careful if oyu have a prop out of balance r get a prop strike that doesn't *kill* the engine. Vibration can very easily loosen the screws with the plastic backplate for some reason. I saw this at a meet last year, and once the screws started coming loose, they continued. Three flights and screws came out each time.............. Some "Lock Tite" helps, I understand. I simply changed to metal backplates to start with. They are cheap, and why not if we know there can be a problem??

Leo Mehl · « **Reply #6 on:** May 11, 2007, 09:57:07 PM »

Jerry, Have never done anthing to this model but clean engine and tank compartment and have also had a broken prop that shook everything pretty good. This plane is built with only a balsa doubler which I have always said gives a better engine run than a too solid of a front end. The main fusalege sides are on the inside and the doubler is on the outside. This helps dampen the motor vibration and is old technolegy.

Jerry Bohn · « **Reply #7 on:** May 12, 2007, 03:08:40 PM »

Leo. Fine lookin plane.
I have been forced to clean a few of my LA's due to using the engine as landing gear. After cleaning the first LA with the plastic back plate it didn't run right, Eventually replaced plastic backplate with metal and switched all other LA's with a metal one. Problem solved.
I did try the sealing compound mentoined in thread on the first LA problem but found it a slight pain to re-apply. I clean all my engines with metal back plates for winter storage. No muss, no fuss.
Sounds as if your plane is built well and is flying good. Iv'e always believed in the old saying "If it works, good, don't fix it" However cleaning the engine after the flying season has always sounded like good preventative medicine to me.
Good idea about dampning the nose for vibraton. Thanks for adding another trick for my C/L learning experience.

Bill Little · « **Reply #8 on:** May 12, 2007, 07:03:09 PM »

Leo, you and I seem to work on the "Blind Hog and Acorn" principle..........

Jerry Bohn · « **Reply #9 on:** May 12, 2007, 09:17:13 PM »

Bill, I need to learn that principle, never heard the term. Waasss it mean?

Bill Little · « **Reply #10 on:** May 12, 2007, 09:25:34 PM »

Quote from: Jerry Bohn on May 12, 2007, 09:17:13 PM

Bill, I need to learn that priniple, never heard the term. Waasss it mean?

Hi Jerry,

"Even a Blind Hog will grub up an acorn every now and then".

Jerry Bohn · « **Reply #11 on:** May 13, 2007, 09:53:19 AM »

OK Bill, Good one. I never heard that but I think I fit in the group.

Bill Little · « **Reply #12 on:** May 13, 2007, 12:22:48 PM »

Quote from: Jerry Bohn on May 13, 2007, 09:53:19 AM

OK Bill, Good one. I never heard that but I think I fit in the group.

Well, Jerry, my grandfather was an old Southern Gentleman, and he raised me. His two phrases he left me with were that one and:

"Don't worry about the mule going blind until you get the cart loaded."

Some don't understand that one either.............pretty simple though!

Bob Disharoon · « **Reply #13 on:** May 18, 2007, 06:17:31 AM »

Heres one from my grandmother...."You never know how long a blacksnake is until its dead".....I have no idea what that means....H.D.

Ron Merrill · « **Reply #14 on:** May 18, 2007, 02:08:05 PM »

Here's another "too much honey for the scent"

Ron.

Leo Mehl · « **Reply #15 on:** May 20, 2007, 10:37:37 PM »

Here is my saying You can't teach realy old people new tricks because we stopped learning a long time ago.

Old flyer from the past-coined by Joe Dill.

Bob Disharoon · « **Reply #16 on:** May 27, 2007, 04:03:53 PM »

Bob..I just received a new LAS-25 and am putting some threads out for any pertinent info on the engine that might be good to know before I start messing with it.
1. any particular tank and pressure setup?
2. Is the remote needle workable?{ have seen statements of ST replacements}
3. Plastic backplate OK?..if not,where to buy metal replacement?
4. Optimum prop for an ARF Flight Streak?

guess thats all for now..you guys are really great for providing the correct info!..thanx, Bob

Ken Deboy · « **Reply #17 on:** May 27, 2007, 10:57:55 PM »

Hi Bob,
I'm not Bob Z but I have some experience with the LA 25 you may find useful.

1. any particular tank and pressure setup?
I get good runs using a Brodak 3 oz. standard vent tank with muffler pressure. Without pressure, it would lean out about half way through the tank. Same thing with non-stock (tongue) muffler with or without pressure... about half way through, goes lean, lap time jumps from 5.3 to 4.5

2. Is the remote needle workable?{ have seen statements of ST replacements}
Never tried running the remote NVA, but the ones I've seen that do stutter and burp for quite a few laps before quitting. I use a stock NVA through the venturi, when it lets you know it's going to quit, it quits within 1 or 2 (at most) laps. ST costs more than OS unit and maybe requires enlarging hole in crankcase. I haven't had any problems with the OS NVA.

3. Plastic backplate OK?..if not,where to buy metal replacement?
YMMV on plastic backplate, Tower Hobbies has FP 20 backplate which fits the LA 25 (they also have FP 35/40 backplate that fit the LA 40/46) if you don't like plastic.

4. Optimum prop for an ARF Flight Streak?
APC 9x4 works nice on a Skyray, similar wing area to Flight Streak so may be a good starting point.

cheers,
Ken

Bill Little · « **Reply #18 on:** May 28, 2007, 08:26:27 PM »

Can't really add to what Ken said. But, (there's always a "but" ain't there?) I wouldn't even risk having the backplate trouble when the OS FP backplate fits. And the standard OS NVA works just fine in the LA 25, so ditch the remote needle. APC 9-4. Just emphasising what Ken said!

Leo Mehl · « **Reply #19 on:** June 02, 2007, 10:29:48 AM »

After three years I rplaced piston and sleeve which requires taking backplate off. Again no problem. Also put socket head bolts in the head. Still runs good and as good as Super Tigre. Man, what a nice engine.

Steve Helmick · « **Reply #20 on:** June 02, 2007, 12:07:23 PM »

One of our club members has a Tigercat twin with two .15 LA's. One engine ran fine, the other would run for two or 3 laps and shut down. After several frustrating outings with this plane, I suggested he put FP or TT .15GP backplates on it. That cured the problem for him. I don't think there is anything terribly wrong with the plastic backplate, but I'd put flat washers under the screw heads, and use some LocTite. Silicon sealer would sure help. Still, I think you might find some plastic (or even aluminum) backplates that have some porosity and will never work right. I'd rather put an FP backplate on them and be done with it. A few minutes at home in the shop vs. screwing around at the field...no question, I'd rather fly than fiddle with a problem. If the LA's didn't run so good, I might not be inclined to bother...but they are sweet runners, blue or not.

Steve

Bill Little · « **Reply #21 on:** June 02, 2007, 12:25:03 PM »

Quote from: Steve Helmick on June 02, 2007, 12:07:23 PM

One of our club members has a Tigercat twin with two .15 LA's. One engine ran fine, the other would run for two or 3 laps and shut down. After several frustrating outings with this plane, I suggested he put FP or TT .15GP backplates on it. That cured the problem for him. I don't think there is anything terribly wrong with the plastic backplate, but I'd put flat washers under the screw heads, and use some LocTite. Silicon sealer would sure help. Still, I think you might find some plastic (or even aluminum) backplates that have some porosity and will never work right. I'd rather put an FP backplate on them and be done with it. A few minutes at home in the shop vs. screwing around at the field...no question, I'd rather fly than fiddle with a problem. If the LA's didn't run so good, I might not be inclined to bother...but they are sweet runners, blue or not. Steve

Hi Steve,

My thoughts, exactly. If there CAN be a problem, and there sure can be, I've seen them, then why even bother? An aluminum backplate is available, not too expensive, and saves one area that can go wrong.

Of course there are exceptions in every case, but I don't have time to mess around when I DO get to go flying! Nothing is more exasperating than an engine giving trouble on a day at the field.

Mark Scarborough · « **Reply #22 on:** June 02, 2007, 12:37:18 PM »

With regards LA 25, I have had awesome experience with the APC 10x4 prop on this motor. It didnt have any trouble at all turning this prop and it seemed to behave better than with the smaller prop. FWIW I was fling on a profile with uniflow venting tank. Plane was a P-40,, not sure of the origin I built it years ago, as in say 1985? never got to fly it until I got back in the hobby last year. Also used same engine combination on a Ukey with the 520 sauare inch wing, great flyer.

Steve Helmick · « **Reply #23 on:** June 02, 2007, 12:58:21 PM »

Hay, Mark...you must be running a stock or OS NV assy. When I put my usual .156" spraybar in mine, it lost a lot of suds. I finally drilled out the venturi to .272". This is really large for a .25, but I was going to fly it at Reno and I took along both fine and course Bruline air filters, which would equate to .252" and .262". I think the 9.5 x 4.5 APC will be better than the 10-4, but I haven't tried it yet. My lines are .012" braids, 60' eye to eye, which I am certain is a bit long, but I don't want to cut them until I find the prop that works best. By then, I will need a new set of lines, anyway (if I'm lucky!). The 10-4 Power Point works surprisingly well, tho I did work on the front side of it a bit. I'm thinkin'

about a Skyray with a Flite Streak wing.

Steve

Author Topic: OS LA engines - Sealing the PLASTIC BACKPLATE (Read 3384 times)

Steve Kientz