OS LA .46 Replacement

I am afraid i might have ruined one of my .46 LA's today.
After some nice lean 4 stroke/rich 2 stroke runs today, it suddenly went wild. Screaming away , using 9 minutes on a 6/12 to 7 minutes tankfilling.
When it finally stopped, the nice blue top had turned nasty brown/black. When i examined it at home, the top screws were loose.
After taking off the top and cleaning off most of the burnt stuff around the gaskets, i put it together again. It seems to have lost a little bit of the compression.
So: If it is gone, i am looking for a replacement.
I would like to get one that fits the mounting holes, as i have 3 planes and i would not like to redo the motor mounts.
The dimesions are: 1.59" & 0.69" for the bolt holes.

Tower Hobbies, OS parts shipping is free, it'll be there by Friday.

I can think of a lot of causes for this to happen. Leaky backplate, leaky glowplug seal, leaky tank, leaky fuel tube, loose muffler (if you were running muffler pressure), clogged NVA. Maybe loose head screws? Did you replace the plastic backplate with an aluminum one, and the cheezy phillips head screws with socket heads, or were you possibly negligent on preventive maintainence?

First, figure out what caused the problem. None of these would cause me to buy a different engine. Instead, I would take steps to carefully setup my new .46LA so that there would be no repeat of whatever it was that caused the problem. Steve

I agree!

Far and away the best and cheapest replacement for a LA 46 is........an LA 46......... Follow Steve's advice.

Get another LA 46, it's the best motor for the money, available.

One thing to remember is that an ABC/ABN shouldn't mind (too much) a lean run. The reason is that the sleeve will expand away form the piston. So I would be surprised if you really lost compression due to this run. Running too rich will cause you to eventually lose compression, since in this state the engine is running cooler than "normal". I also assume you were using a stunt friendly 50-50 castor/synthetic 20% oil fuel.

Maybe when you cleaned the engine up, you inadvertantly removed some castor "goo", which was giving you a seal or actually removed carbon which was boosting the compression.

This isn't to say a lean run might not cause problems, but I would look at the wrist pin and crankshaft area to see if clearances still look ok.

I also agree with others, a replacement LA46 is the cheapest alternative (other than buying new parts--if you know which parts to replace), and it certainly fits the mounts! I would only do this after I saw that the engine really has problems.

Having two OS .40 LA and two OS .46 LA engines, I have learned the hard way that there are three very important things you absolutely must do to them. 1. replace the plastic backplate with an aluminum one. The OS .35/.40 FP are the same. 2. replace the plastic back plate. and 3. replace the plastic back plate. Mine kept going lean, running very fast, running out of fuel, and getting hot. I replaced all the back plates, no more problems of that nature. Now to remember to put on the right size fuel tank. Oh, and not fly so low to the ground when inverted.

Ty- you hit it on the head!

I would like to add one thing, replace the plastic backplate!

John Teosawki

It has a metal backplate from Leonard.
Will give it a test run later today to see how it works.
Thanks for all advices.

I have ordered a Stalker .51 from Kaz Minato.
(Was high on the wishlist before this happened anyway.)
I will redo the motor mounts in one (the best) of my planes.

>Ty- you hit it on the head!
>
>I would like to add one thing, replace the plastic
>backplate!
>
>John Teosawki

I keep thinking, Tower has got to be wondering why so many people are buying replacement cover plates (back plates) for their Tower 40 engine, as well as the 35/40 FP. This is the one part that just doesn't break in a crash or wear out.

But that plastic back plate--yes, get rid of it. It was a "brilliant" idea gone wrong.

LAST EDITED ON Oct-25-04 AT 10:46 AM (CDT)
 

Wonder why no one thougt of balsa glow plugs. Would save weigth.

Btw. Leonard: Did you send the backplate for my second .46 LA ?

Norvald Olsvold

Tower lists the back plate as "Tower Hobbies Cover Plate .40 ABC," costing a whopping $2.99, but out of stock til "early Nov."

Does anyone know if the "Tower Hobbies Screw Set .40 ABC (12)" would include correct size socket head replacements for the phillips cyl head screws on the LA?

Since the Tower .40 itself is discontinued, I wonder if a time will come when it is harder to replace the plastic backplate on LA .46?

Kim Mortimore
Alameda Aeronuts

>
>Tower lists the back plate as "Tower Hobbies Cover Plate .40
>ABC," costing a whopping $2.99, but out of stock til "early
>Nov."
>
I'm the guy who put these out of stock (my bad). I did manage to get one more for Norvold and put a batch more on order. It might be good for others to put orders in, too, if you want one.

>Does anyone know if the "Tower Hobbies Screw Set .40 ABC
>(12)" would include correct size socket head replacements
>for the phillips cyl head screws on the LA?

I need to check that, myself, but was thinking of putting together a set of replacement bolts for this engine. Bolts and prop nuts are two items that are definitely over priced on replacement parts. I do have hardened prop nuts

>Since the Tower .40 itself is discontinued, I wonder if a
>time will come when it is harder to replace the plastic
>backplate on LA .46?

Well, they are still supporting the FP and there are Thunder Tiger alternatives out there as well. This is still a production engine in both the 40 and 25 size, so these should be available for a while as well.

>
>Kim Mortimore
>Alameda Aeronuts

Hi, Kim:
I want to make sure I'm reading your post correctly. The Tower Hobbies Cover Plate .40 ABC fits the LA 40 and 46, right? They also list a screw set with it, so I assume this could be used to replace the phillips head screws, right? Just want to make sure I order the right thing. Thanks.
Glen

Hi Glen. Yep, in fact the first backplate I used was a spare for my Tower .40. It is an OS .40FP in Tower markings. The head has that cute Tower arrow cut into the head fins. Also I mentioned earlier that some one mentioned on this forum that the back plate gasket for the OS .35/.40FP.46LA series also fits the Super Tigre .46 like it was made for it. I was very happy to replace the gasket on an ST .46 I recently aquired. A win-win situation.

>I keep thinking, Tower has got to be wondering why so many people are buying replacement cover plates (back plates) for their Tower 40 engine, as well as the 35/40 FP

Tower 40 backplates $2.99 but out of stock until "early November" Free shipping. OS 40/46 plastic backplates $7.49 plus $3.49 standard shipping(I understand free shipping offer is only for Tower engine parts)

I put some fuel in the engine last night.
When i turn it now, it has this 'dry' feeling between the piston and cylinder.
I think maybe the 'castor layer' has burnt off.
Maybe running it on some 20-22% oil will help.

Ty,

I have two models with .46LA. They have lot of hours and I did not replace bacplate. One of them have even integrated remote NVA still in. I do not know if it leaks or not, because I NEVER dismounted them from model. But may be I had to replace them, it could be reason why I placed only 10th on WC 2002 in Sebnitz

>Hi, Kim:
>I want to make sure I'm reading your post correctly. The
>Tower Hobbies Cover Plate .40 ABC fits the LA 40 and 46,
>right? They also list a screw set with it, so I assume this
>could be used to replace the phillips head screws, right?
>Just want to make sure I order the right thing. Thanks.
>Glen

Glen,
I'm not an authority on this, but our host is. I was repeating what he said. He also said that Thunder Tiger is another alternative, so one of their backplates is a fit. (I was about take a guess which one, but edited it out to avoid possible confusion). I too was asking about the screw set as phillips replacement, so don't know.

Kim Mortimore
Alameda Aeronuts
Dept. of Uninformative Clarification

Thanks, Kim:
I'll just keep on doing research. I'm not in a great big hurry, as the plastic backplates SEEM to be OK for now.
Glen

LAST EDITED ON Oct-25-04 AT 10:16 PM (CDT)
 
Yep, my thought too. Hey that stuff only happens to the "other" guys. Wrong. Yours will get warped, but only in flight at 30,000 with 4 Zeros on your tail, and your wingman going down in flames. Then you can join me as the king of inverted landings. All my rudders have a thin ply cap. I also go through needle valves like crazy. LOL

The screws for the LA 40/46 are standard metric sizes.

Use 3mm x 12 for the head and 3mm x 8 for the backplate. DuBro carries these in stock.

You can also find them at any hobby shop that caters to the RC car racing guys. I found them in stainless steel, anodized aluminum (in various colors), and some in titanium.

Tower runs out of the backplates because guys like me buy them by the dozen

Oh yes, before I forget: Replace the backplate. LOL

Ron King

LAST EDITED ON Oct-26-04 AT 08:13 PM (CDT)
 
Awright, I just measured the screws of a NIB Tower .40 that I have apart in a cookie box. They are M3mm-.5, 8mm and 10mm long. So, everything is correct except the length of the head screws is 2mm too short. The Magnum XL .25 > .53 or XLS .32 > .52 screw sets are exactly what you want, Tower should have them in stock. Or, like Ron ****KING**** wrote, get DuBro stuff from the pegboard at about any LHS.
Steve

I ordered the '10's' for the head screws. They didn't list the '12's'. Guess I lucked out.
Thanks.
Glen

3mm x 10 will work fine as long as you don't add too many head shims.

The cylinder pressure is not so high that 2mm difference will cause a failure.

Ron King

>3mm x 10 will work fine as long as you don't add too many
>head shims.
>
>The cylinder pressure is not so high that 2mm difference
>will cause a failure.

One caution here. The case on these engines is very soft cast material. In other words, it is very easy to strip these bolts out. I have seen this done already using the stock bolts. And you only have four head bolts so you want to make sure they are snug. I would be very careful to not skimp on the length.

Hi Igor. I had a series of very short engine runs and had a rash of inverted landings, making me a very frustrated flyer. I tried different fuel, settings, props, tanks, fuel lines, with and without filters. Ad infinitum. Then at the Marietta contest on my second official, my pit man noticed fuel spraying in his face. Hard not to notice this,eh? Just as he released the model he could see it coming out the back plate. Changed it and got longer flights, only to find in the tank swap I actually replaced it with a longer but narrower tank. Fooled myself by only looking for a longer tank. Oh well, fixed that too.

You see? You have to use better cowled engine

But seriously, I just wanted to write that the leaking is not "for must". I know about lot LAs and no one leaks. But I do not say it can not. OS goes with price to edge of usefull product, so if there is ANY small reason to leak, it WILL leak. I heard also about peeling in the past. Also bearing gets free play very soon. But typically those engines work well as they are.

It was on a TEOSAWKI, a profile. I agree, the OS LA series is a great inexpensive engine for stunt. But with one leaking very obviously, I decided to fix them all and end any chance of it happening again.

Back to the theme that started this active discussion.
Yesterday i put some after run oil into the engine and let it rest overnight. Now, it seem to have regained its good feeling again. Seems to hold compression again quite well. (Not as good as the Rustler Merco 61, but that one is something special in that area).
I wonder if the overheating was caused by overloading. I ran it with a Bolly 11.75 x 4.75 carbon for the first time. Balanced by Randy Smith. It should be able to run that prop without trouble though.