I bought a used 46 LA from someone getting out of the hobby.  This is the first of these types of engines (FP/LA) that I've messed with and I'm wondering if it might be a bit tired.  The piston and sleeve seem to seal when the engine is cold but after a run and when hot, the fit is nothing to write home about.  EDIT: There is nothing obviously wrong inside the engine (peeled liner, etc).  When perusing the 46 LA engine setup thread, I came across the following:

".272 venturi
ST needle assembly ( or Randy)
Powermaster 10 22 GMA fuel
good thourough break in!!!!
and the key,, an APC 12.25 x 34.75 prop
Ground setting is typically right around 9800 rpm"

I've run this engine for bit on the bench now.  The details are as follows:  Stock internals; spraybar is 3.5mm (instead of the 4mm one listed above) and I've tried both 6mm and 7mm venturi sizes.  I'm using the same APC 12.25 x 3.75 props, my fuel is 10/10/10 (so slightly less oil than above), hot plug (OS6 and Enya 3) and I'm using the stock OS 3030 muffler (with baffle). 

My understanding is that the 6mm venturi/ 3.5mm spraybar is close in intake area to the .272 / 4mm spraybar listed above.  I'm only getting 8900-9000 'Peak' RPM this way.  With the 7mm venturi, I get approximately 250 RPM more so a max of 9250.  I'd probably back off at least 200 RPM from peak to fly so  I'm down more than 10% when compared to the numbers above.  My best numbers came during reasonable weather, so I don't  think that was the issue.

So....does this point to a tired engine?  I've owned/used higher performance OS ABN stuff....Italian ABC engines....even a few 'squeaky' AAC Henry Nelson creations.  Compared to those engines this 46 LA feels used up, but I don't really know how these budget engines were supposed to fit. 

There is no mention of the muffler used above...I'm not sure if that is the difference.  I did get a few flights on the engine and it behaves nicely, I just wonder if it's making all the power a 'typical' 46LA would be making.
   

There are tired LA 46 engines out there.  My test is by feel.  Cold, with no prop, if you can grasp the thrust washer and turn it over, it is worn out.

being a Supre Tigre type ' I think the LA is gutless anyway . in comparison. Blather blather . BUT , " LA 46 " see , to cheap to even use a hyphen .       

THE LA - Like other things , The trick ?? is how it HOLDS .
Compression.

Ove T D C / Compression . A Magnificen engine , put at T D C - The Next DAY , when turned with thumb & finger , Will Push Down , having held its compession .

SOME will only hold TWO SECONDS - and might run o.k. , good even . metalurgy - expansion rates - running temperatures - oils . blather blather blather .
But I figure Yours Dont , it goss pssst , inside a half second  ? ?

( Both LA new & ST new , on similar area intake , the Tigre Tourques allong dragging 60 ounce , if required . More Drivle to follow  >: )

CAN YOU GET A Gradner P/L set , for it .  Can everyone send me all their Magnum G P 44 Pistons / Sleeves cetra . Or the lot . Willtrade .

OS being AVAILABLE , you might be o.k. . SEEing everyone talks of them SO HIGHLY , being offered one new at a considerate price by a kind chap , I got it .
Further tough bargaining at a pile of radio junk ( oooppss  ) Gotta SF 46 , FSR 45 & LA  46 for more than that . GOOD sleeve in the SF ( they interchange with LA SO THATS THE SALIENT POINT . as does Tower & clones)
Hiddeous ROT , bearings shot , crank & wrist pin Just ' within service ' salvaged . FSR 45 Matbe hadda good liner . Had to saw head bolts ( 2 ) Wanna Fn good wrench / key  sometimes . Most Peculiar . NOW FOR the LA .
Id thrown a new FP crank ( the fancy one ( into the new L A  ))  THIS had a JUNK rotted CRANK , think .o5 mm undersize big end . or thou. 5.2 insrteda 5.5 Dia . From NITRO ROT , Wrist pins go black & mangey . o.k. ? !

SO THE POINT WE'RE GETTING TO ,
Have you whipped the back plate off ?

5 seconds to strip a LA . Nuthe fing'll buket , SEIEZED wrist pin . THIS is more a Supre Tigre malady , But OS's are NOT Immune. Tickly the FSR series  . You wanna TUBE to push out the wrist pin . or the PADS are GONE
stuffed No Longer ANY USE . Trash Awol . IN NEED OF REPLACEMENT .
So watch it with the wrist pin pads .

THIS LA 46 crank was black gungety & mildly pocked From Sitting years unflushed . Theres so self nitro to acid molecular progression - So ' S H  engines are 50 / 50 TROUBLE usually . Bearings , Cleaning , repplacement obsolette parts , To FLY the snots . A N.i.B. GP 44 with No Good pistonb fit . How about TWO . bugger .

OS Cylinders , some are acid etched from fuel ' and ROT the chrome of the sleeve at a piston port . Some it falls off adjacent the port edge . A flashlite up the port , youll see the transfer ones - Gold Colours the sleeve
where the chrome ( NICKLE PLATEING / Nikasil ) has gone bye bye .

So . OFF with the BACKPLATE . if its not semi shiny in there = Off with the head .Use a old newspaper sheet - tho it hasnt got Wrist Pin Circlips to trouble you , like the FSR & SF .

TOM SEE if its salvageable - Worth fitting New Sleeve - the bits should fit with no slack / wobble . Turkeys on You Tube , toseehow . THEN youll KNOW . They Dont Last Forever .

A good GP 44s as good sleee is same as FSR but PISTON is NOT got boost port drilling - channel . A few early FP's did . at a angle of course . Denny says early ones the best . Garner sleeves for them to , thatll go in FSR 40

Whip off the head  look if the chromes peeling off . you cant miss it .

whip of the backplate , if it looks like a shipwreck in there - strip it & clean it .

Ive SEEN big expensive stunt engines go ga ga the same . even oiled . so havea look .

o.k. . Im barking up the wrong tree .

These Here SF 46 , have the same dimensions for the P & liner set up , but with a boost port ( only differance - so they interchange . The SF Ive got flying a 80 Oz Pattermaster & a 76 Oz S6B , on a 12 x 6 .


DAN obviously KNOWS the LA , so HEED His advice . Par Tickly seeing he is AT HAND , Directly . and youll get it A1 .

Me n dan 'll have to have a Shoot Out .  21/46 Vs LA46 .      Never seen a test of the LA , I was babying mine , on a 12 x 5 T F prop . wasnt winding it up . Pity theyre NOT a LA 45 or theyed go in the deH 88 .
The OldemOS Max H 40 - S is a lot lighter though , with S T 46 liners , theyd be 45's . 

Go To It . Its not a abandoned relic barn find , by the sounds of it .

Steve though I speak heresy here to many,  I've never been impressed with the engine.  I have to say I've only had one and perhaps there was something unusual about that one.  It WAS the most difficult to break in engine I think I ever had.  VERY tight.  After more than two hours on the bench I put it on an airplane

   That is absolutely not normal, there should be nearly no to negligible break-in. I have seen them fly official flights after one run on the ground, that is, box to airplane, run for 3-4 minutes, fill the tank, signal for an official. I have done official flights with the 20FP with no break-in at all, that is, the first start was for the first official flight. Not ideal because the fuel consumption dropping drastically an making it go rich toward the end, but successful enough.

   Also note this thread where I gave on a some bench tests with no prior running:
https://stunthanger.com/smf/engine-set-up-tips/some-engine-tests/msg584779/#msg584779

    This one was clearly getting better but easily out-turns any 40FP with stunt props, but the very first start out of the box it started instantly and ran a Top-Flite 11-5,3 (really a 11-6) at 10400 within a few seconds of running and would hold any of these test points indefinitely.

    I am not aware of anyone around here who ever did more than the most cursory ground running and it is much more powerful with stunt props than a 40FP, and should handle far better.

       Brett

It's hard to say without knowing the run time history but sometimes when they are kind'a new they will get more compression as you put more run time on them and they'll start better when hot. You can take it apart and see if there's any brass showing in the bore. That's a pretty good indication you need a new piston and liner. I would take the baffle out of the muffler. I don't run that big heavy APC prop. Much better props out there imho. I would think it should peak out better than 9k. There might still be some new P/L on ebay if you can find them.

MM

In reading some of the 'how much oil is too much oil' type threads, I saw mention of engines getting so tight they would squeek due to varnish buildup.  With that in mind, I've put a bit of time on this one on my bench (full gallon in total).....alas, no improvements.  My past experience with OS ABN engines has been that the P/L is as good as it will ever be on day one....from there it's just down hill (like my eyesight...LOL).  This engine seems to be following that trend as well.

  If this is the engine that was in that P-40, you didn't see me needle it to over 9600 that day while you walked out to the handle, and it wasn't peaked.  Hard to old the model, the tach and needle it at the same time. We are talking about an engine that is more or less disposable to a lot of people. I don't know if it's possible to have made that series any more cheaply than they did. But they are more than good enough for what they were intended for. It is quite normal for the LA series engines to loose a bit of compression when hot in between flights. I didn't see or hear anything out of the ordinary about it that day, and once it cooled the pinch was back to normal. I usually only static run a LA engine for one or two runs, check the engine mounting bolts, then fly the model at an easy setting, but not too rich. If you want we can put it in one of my old models and I'll fly it just so you can see it in it's element. Keep in mind that this is a stunt engine, not anywhere near the kind that you are used to dealing with. If the crash didn't harm anything, and I doubt that it did, I have no doubt that it will fly this 60 ounce model I have and will do the pattern. It's not a Rossi race engine, it's an entry level R/C-Stunt engine intended for people that don't know spam from shoe polish about running model airplane engines.
  Type at you later,
   Dan McEntee

I think that your tach and my tach need to get together and talk things out because they do not agree.  LOL   

This is, indeed, the engine that doubled as a Jart in the P-40.  Luckily, no change in performance was noted post crash.  The tall grass and soft ground seemed to save this engine from any real damage.  I tested this engine on the same test stand when I first got it, and the numbers today are the same as they were prior to the subterranean encounter.

...THE LA - Like other things , The trick ?? is how it HOLDS .
Compression.

Ove T D C / Compression . A Magnificen engine , put at T D C - The Next DAY , when turned with thumb & finger , Will Push Down , having held its compession .

SOME will only hold TWO SECONDS - and might run o.k. , good even . metalurgy - expansion rates - running temperatures - oils . blather blather blather .
But I figure Yours Dont , it goss pssst , inside a half second  ? ?

Thanks for chiming in, Air Ministry.  There's lots of info to digest here but one of your first points is the one that I first noted as deficient in this engine.  As you suggested, this engine doesn't 'hold' compression...even when cold.  Some of the more exotic engines that I've had in the past would do well on this type of test even right after a run. 

I edited my first post to specify that there aren't any obvious 'problems' internally.  No stuck wrist pin...no peeled liner.....no scratches or rust where you'd not want them to be.  I think that the fit between piston and liner is simply worn at this point.  It still runs...and I will use it, but I would expect a fresh engine to make a bit more power, and perhaps be easier to start when warm.

Thanks for linking this thread, Brett.

Something that struck me from that thread was the following statement:
"The APC 11.5-4 is the original 11.5-4 "narrow" that Billy asked APC to make for the OPS-40, and that I ran and qualified at the 94 NATS on my 40VF. "

Of the props you tested, the APC 11.5 x 4 was the only one that i had, but I'm not sure that I have the save 'narrow blade' version that you used.  The 11.4 x 4 APC prop I have(purchased recently), looks very much like the APC 12.25 x 3.75 in blade shape (wide blades....especially towards the hub).  Is this the same prop or is there a newer/wider version being sold today?  I could post a pic if that would be useful.

   As I recall, it didn't make much difference in the ground RPM. It definitely flew the airplane differently.

     Brett

As for the HOT STARTING problem...pretty normal for ABN and ABC engines. You choke the engine, get the piston wet with fuel, it shrinks, you lose compression. Either let it cool down or use an electric finger.

   No. Hot starts are far easier than on iron-liner engines. If you have this problem routinely, you are over-choking it. Depending on the engine, you might not need any choke, or only one pull-through. It needs much less choke when hot, overdo it and you do get "shrinky piston syndrome".

   If you do get this, don't wait or use a starter. Take off the battery, flip it through forward a bunch of times (like, 20 times) to distribute the fuel and heat. You will feel the compression come back.  No choking, attach battery, bump backwards.

    Brett