LA40 vs LA46

[Phil Coopy]

I was just reading a post (Twister vs Banshee) recommending an LA46 for a Banshee.  I have used both engines on a lot of profile models in the past. I usually reduce the compression by hogging out the head rather than shimming which destroys the effect of the squash band.  What I found out was that the LA46 vibrates a lot more than the LA40,  which is not too good on a profile model.  The reason for this is that when they produced the LA46 they just bored out an LA40 and inserted a larger heavier piston.  However they never increased the counter weight on the crankshaft (i.e. same part# for both).  I also tried re-balancing but the piston is difficult to lighten and the counterweight is even harder to insert a heavy metal slug in.  I also found out that for C/L the LA40's break better in the hot Florida weather and that there is not much difference in the power for a plane like a Banshee.

Just relating my experience......

Phil

[James Holford]

I have a Brodak 40 on my Banshee and it has more than enough power even in a very strong wind. Too much power really but I found a prop/venturi/muffler combo that makes it work.

The LA 40 has more power than the Brodak 40 so an LA 46 on a Banshee that was designed with the Fox 35 in mind is kind of ridiculous.

Motorman

People say the same thing bout a .46LA on a Twister til they fly one .

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[Air Ministry .]

Heres a liddle pitcher of a crankshaft or two , 



Mebee an EARLY one with all the Fancy Fandangular things .



Not So Fancy , Fandangulariclly .

Checking the OS parts thing , the 40 & 46 run the same crank ( part No. ) A 35 FP will ' 40 er ise , FP crank fits LA ?? , so ' a choice ' of cranks .

Later less fancy , less counterweighted . So comparison maybe only valid with this taken into account , perhaps .

FSR Cranks , at least in the clones , are only ' Flat Flank ' Flywheel / big end set up ,
where Some are Fully Machined on the rear face , for a more concentrated counterbalance .
Or more eliminated weight opposite counterballance .

Thus :



Just thought Id point it out , for what its worth .

[Steve Helmick]

Would any of our inspectors/machinists/engineers care venture an opinion on whether that top crank picture is of a forging or a casting? I'm of the opinion that it's a forging, but I've not seen all that many steel forgings or castings...lots of aluminum forgings and castings. That's the LA crank. The middle one should be an FP crank. I don't know about the bottom picture, but it is not an ASP/Magnum crank. The reason I'm asking is because Leonard Neumann said that the LA cranks are from a casting, which I tend to disagree with.

FWIW, I have read that the FP .35/.40 cranks interchange with the .40/.46LA cranks. I also wonder if OS changed the crank counterweight when they changed the FP's from the iron piston to ABN. I would kinda like to know what the difference would be, if any, in the static balance. And I don't know how to describe the difference. I'd figure that one would hang some weight on the crankpin to get it at 9 or 3 o'clock. The cutout for the timing port would make a little difference, but probably not a lot. Is the counterweight made offset to compensate for that? I doubt it.  Steve

[Brett Buck]

I was just reading a post (Twister vs Banshee) recommending an LA46 for a Banshee.  I have used both engines on a lot of profile models in the past. I usually reduce the compression by hogging out the head rather than shimming which destroys the effect of the squash band.

  Why would you want to reduce the compression?

     Brett

[Dave Hull]

Tilting at windmills requires reduced compression.

The top crank is cast, not forged.

Dave

PS--I tried to post a comparison photo of two cranks that highlight the difference in appearance but it crashed my answer. I will try one more time...   Ok. This time I didn't kick the klaymore. Cast part is on the left, forged on the right. You don't get a pebbled surface on a forging unless you fabricate pebbled forge dies. You don't get that from machining, so the only way is from really uniform erosion (no way), or from shot-peening the die to improve surface durability (it wouldn't be that rough relative to the size of that part.) Or, much more likely, the roughness would come from scale as the part was reheated and subjected to a series of forge steps. The pebbling doesn't look like that to me. My 1-1/2 cents worth....

PPS--Steve, regarding static balancing, there is another thread that now overlaps this one where Larry Renger asked about crank balancing. If you have not read that one, you could start there. And then add any questions that you still have.

[Phil Coopy]

  Why would you want to reduce the compression?

     Brett

Not my idea, got it from Steve?(west coast) years ago.  It makes the engine 4 cycle a lot better, transition better, and limits runaway in the hot Florida climate. Made a tool and fixture to mount the head on my lathe, and plunge cut the head retaining the hemi combustion chamber.  Bear in mind that the LA engines are timed and built for the most power at high speed....for RC.  Even tho some were sold as C/L engines, they only changed the venturi and needle. Timing and compression appear to be unchanged from the RC version.

As I say, this information is only from my experience using LA's......Phil

[Brett Buck]

Bear in mind that the LA engines are timed and built for the most power at high speed....for RC.  Even tho some were sold as C/L engines, they only changed the venturi and needle. Timing and compression appear to be unchanged from the RC version.

  OY GEVALT!  That's what you *want*, otherwise, you gain no advantage over ancient engines.

      Brett

       

[Phil Coopy]

  OY GEVALT!  That's what you *want*, otherwise, you gain no advantage over ancient engines.

      Brett

       

When I modify an LA40 for C/L I replace the stock carb with a .282 diameter venturi ....much larger that the stock carb which is only about .237(required for even operation over a wide range).

Voila..power you think you lost from the reduced compression is still there because of the better breathing.

Phil

[Steve Helmick]

I'd like to point out that there are other "Steves" on the West Coast, and Mr. Coopy must be referring to another one, and not I. I've only personally run the .25LA and .46LA, and both with stock compression. I did mess with mufflers and venturi bore sizes, and always used .157" spraybars (K&B, ST, PA) and ended up with .272" venturi on both. Mufflers were either OEM, Randy Aero's CNC Tube muffler, or the late & great MACS Muffler. All require finding the correct propeller match.  Steve

[Phil Coopy]

I'd like to point out that there are other "Steves" on the West Coast, and Mr. Coopy must be referring to another one, and not I. I've only personally run the .25LA and .46LA, and both with stock compression. I did mess with mufflers and venturi bore sizes, and always used .157" spraybars (K&B, ST, PA) and ended up with .272" venturi on both. Mufflers were either OEM, Randy Aero's CNC Tube muffler, or the late & great MACS Muffler. All require finding the correct propeller match.  Steve

Sorry Steve, remembering names at 80 gets a little tricky.....that's why the ? mark.

Phil

[Steve Helmick]

No problem, Mr. Coopy. I am 73, so I'm there with you. When I'm tired, my memory sux. Give me a good dose of caffeine and I'm good, except for the frequent and sudden trips to pee.  Steve

PS: Maybe you meant "Scott"? I'm not sure what Scott Riese did/does to the LA engines, but know he has done some reworks on them. IMO, there are a lot of ways to make an engine work for you.

[Tim Wescott]

When I modify an LA40 for C/L I replace the stock carb with a .282 diameter venturi ....much larger that the stock carb which is only about .237(required for even operation over a wide range).

I can't speak to the 40LA, but when I modify a 46LA for C/L I take it out of the box and slap it on a plane.  If it has an R/C carb I put on a right-sized venturi.  Then I go fly.  No shims, no machining -- just the right prop for the plane (low pitch), the right RPM for the engine (high), and good performance.

[Air Ministry .]

O.K. , this is what i was looking for ;

Early Crank . The Flash Machining there on the rear face , was eliminated later .
Thus COUNTERWEIGHT on earlier engines , is more .higher balance factor % number .

Though THIS is a 20 / 25 crank ,






====================================================================================



CRANKSHAFT 40-46LA.35-40FP -  OS-23302000



Which is where we started . the ' Vibes ' , crank & or abc , are relevant .

If both cranks were the same , & both were abc , there might be something else ,  .

[TigreST]

Something of a related comment, perhaps?

Was it not mentioned many moons ago that the LA-46 came in with a weight savings of a sort over the LA-40 because the LA46 engine case is bored out for the larger piston liner assembly,...or am I all wet on that one?

edit: Maybe I'll answer my own question.  Just found this listing which (if good intel) shows the weights of the different O.S. products.  The 46LA-S comes in a bit lighter then the 40LA..but in the ends it depends on which version (model number) we are speaking of.  Here's the link:

https://www.osengines.com/parts/engine-specs-discontinued.html

[Curare]

I can go weigh them both if we all feel we need some form of corroborating evidence.

[Juan Valentin]

O.K. , this is what i was looking for ;

Early Crank . The Flash Machining there on the rear face , was eliminated later .
Thus COUNTERWEIGHT on earlier engines , is more .higher balance factor % number .

Though THIS is a 20 / 25 crank ,






====================================================================================



CRANKSHAFT 40-46LA.35-40FP -  OS-23302000



Which is where we started . the ' Vibes ' , crank & or abc , are relevant .

If both cranks were the same , & both were abc , there might be something else ,  .

 

   Hello Matt
                          I think that he last crank on your post is a Tower.40 crankshaft. I bought one from Tower Hobbies way back to try on my .40 LA.

[phil c]

I'm with Tim.  The best mod is to take either one out of the box and mount it in a plane.  Mild, 10% fuel.  Use the stock muffler.  Mostly I use a 4-4.5in. pitch prop.  The 40 needs a smaller prop.  I've had good luck with the Master Airscrew 10/5 three blader on the 46, cut down to 9.5 for the 40.  The 40 likes the .265 venturi with the OS 20-46 NVA if you have one.  The 46 likes the 272 venturi.  Both like 10,300 for launching and settle down into a nice 4 cycle with a bit of 2 cycling starting around 45° altitude.  The stunt friendliest motors I've ever seen outside of a piped setup or the old OS 35S and the OS 40H stunt version.

[Dennis Moritz]

I’ve run LA46s stock on profiles. On lighter planes I was able to run them very rich. Four stroke with a touch of break in the useful places. No bad vibes. Mostly bad vibes come from an (un)sympathetic harmonic. LA 40s in my experience are just as prone to those issues, if not more so. Crank shaft balancing didn’t seem to effect Fox 35s much. At least the one high zoot crank I saw fly many times didn’t smooth the Fox out. Crank didn’t break tho. A big plus.


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