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Author Topic: Is the OS MAX LA .40 timing the same for the RC and CL engine's  (Read 1819 times)

Offline Dennis Holler

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I was thinking the timing and porting was the same between the RC and CL versions, but wanted to double check. 
I Need to do some homework and look through the info stuck up top cause the answer is probably in there lol.  I have one LA46 control line engine NIB and just found a couple of LA40 RC engines for fairly cheap.  Got a new never run LA40 RC for  about $40 so I figured that was a no brainer. Figured I could either buy the venturie or I might take a couple of shots at turning one on my Lathe for fun since I have the venturi from the 46 to reference.

Maybe my question should be, any other things to consider when reworking and LA40 or 46 for that matter from the factory RC versions for use with wires and a handle?  Any changes in Comp ratio or anything like that? H^^ H^^
I've started plenty...would be nice to finish something!!!

Offline Dan McEntee

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #1 on: April 09, 2022, 08:54:46 AM »
    The LA.40 and .46 are essentially the same engine. R/C and C/L versions the same except for carb and venturi . The information pinned to the top of the list is useful for both. The main difference is that you can't run the bigger props on the .40. The .40 tended to be looked down on for some reason when they first came out, and everyone loved the .46, but I find they both handle about the same. The .46 is actually a touch lighter due to the bigger bore, but is essentially the same engine. Crankshafts, rods and back plates interchange, and the .40 might take a smaller venturi depending on the airplane. No real "rework" needed on either one. I've been using both more or less box stock. Maybe play around with venturi size and mufflers a bit, and of course, props.
  Type at you later,
   Dan McEntee
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Offline Dennis Holler

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #2 on: April 09, 2022, 09:35:29 AM »
Thank you Dan!
Yes, I foudn the Venturi info in the Pinned topic above that will work.  Imight see if I have any Al round in the shop and mess around a little bit.

Is there a school of thought on preference with style of spraybar and needle? Seems like the remote needle would add some weight.
I've started plenty...would be nice to finish something!!!

Offline Dan McEntee

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #3 on: April 09, 2022, 10:23:50 AM »
Thank you Dan!
Yes, I foudn the Venturi info in the Pinned topic above that will work.  Imight see if I have any Al round in the shop and mess around a little bit.

Is there a school of thought on preference with style of spraybar and needle? Seems like the remote needle would add some weight.

   Remote needles work fine, and serve the purpose they are there for, to keep your fingers away from the prop. You need to choke the engine a bit more to start cold, and they sometimes do not cut off cleanly at the end of a tank and tank position is a bit more finicky. You have to remember that you are setting the fuel mixture way back behind the engine, and the distance does affect how it flows up to the venturi. I'm not a fan of the O-ring type that OS used on these, and have seen lots of flat, distorted, and down right stuck and gummy O-rings on these, leading me to believe that it's just a quality issue with the )-rings and just replacing those with quality O-ring helps a ton. Remember that the spray bar for a rear needle valve set up is a different diameter because it doesn't have a needle going in and out of it, so the venturi may be smaller, and OS factory venturis can vary a bit in size. The standard OS spray bar and needle valves are fine, but I also think that the last generations of those were just some old stock that was pushed to get it out of the warehouse. The needles aren't and finely tapered and the diameters of the spray bars are smaller than the original FP-20/.35/.40 NVAs. I checked the last ones I got against the OS.15s that I have and they look the same to me. I chuck the needled up in a drill chuck and work the taper to a sharper point than what they are and they work much better. If you can find the old metal OS rear needle brackets like what came with the FPs and the NVAs  for them , they are much more user friendly I think. Look for old OS 3 and 3A R'C carbs and the NVAs that are in those are the same thing. Prop selection is the important thing, with 4 inch pitch being the standard. Lots has been written and is available on props on this forum. Get several brands and test fly them all to see what will work best with you plane and engine combo. And also remember that you can't run these like a Fox .35! They need to get up on the RPM band to run correctly, but will still have a more subtle break sometimes depending on how it it loaded with prop, airplane weight and size.
   Type at you later,
  Dan McEntee
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Offline Dennis Holler

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #4 on: April 09, 2022, 11:32:07 AM »
On those O rings, the engineer in me wonders if they are made of an appropriate material for the intended fuel, or is it just a lifespan and material with the heat/ fuel/ UV affect building up over time.

I'll learn on the 46 I have with the remote needle and for the other two will make due with the style I can locate the easiest when I swap the carb for a venturi.

Btw, there are several good threads on the question of RC versus CL some of which you had some good comments in. 

All very helpful!  H^^
I've started plenty...would be nice to finish something!!!

Offline Dan McEntee

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #5 on: April 09, 2022, 02:22:59 PM »
On those O rings, the engineer in me wonders if they are made of an appropriate material for the intended fuel, or is it just a lifespan and material with the heat/ fuel/ UV affect building up over time.

I'll learn on the 46 I have with the remote needle and for the other two will make due with the style I can locate the easiest when I swap the carb for a venturi.

Btw, there are several good threads on the question of RC versus CL some of which you had some good comments in. 

All very helpful!  H^^


     In all of them I have seen, any that were black in color were either flat , distorted or sticky, and most on pretty low or zero hour engines. I have seen one or two that were a brownish color that seemed  OK, and on the OS.70 four stroke in Walt Brownell's Typhoon, it had a white O-ring that may have been Teflon. In all of these less than stellar examples were engines that just never got a steady needle setting. Another SH member here reported finding one that was stuck so bad he needed pliers to turn to get the needle out, and so have I. I suspect , like you, that they just don't like alcohol. The LA series rear needles that are a molded in part of the back plate have obvious limitations, and the later versions of it still have a plastic back plate but the needle valve body is mounted on a metal bracket that has several position options to get it out of harms way , and this is much more desirable. If I find them with broken brackets at swap meets for a buck or so I'll pick them up and cut the nub for the NVA off.  The worlds supply of metal back plates for OS .35/40/.46 engines has dried up with everyone chucking them for suspected leaks, but I have found that they are actually pretty serviceable as long as you use the correct screws in them and don't over torque the screws. The originals are a truss head style, but if anything else is used, just make sure you use a flat washer under the head. I tiny dab of silicone sealer around the edges helps ensure a good seal.  There are a couple guys that make metal replacements if you really gotta have metal. But above all else with the LA series of engines, I just wonder who's idea it was to paint them blue??!!
  Type at you later,
    Dan McEntee
AMA 28784
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Offline Brett Buck

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #6 on: April 09, 2022, 04:50:49 PM »
I was thinking the timing and porting was the same between the RC and CL versions, but wanted to double check. 
I Need to do some homework and look through the info stuck up top cause the answer is probably in there lol.  I have one LA46 control line engine NIB and just found a couple of LA40 RC engines for fairly cheap.  Got a new never run LA40 RC for  about $40 so I figured that was a no brainer. Figured I could either buy the venturie or I might take a couple of shots at turning one on my Lathe for fun since I have the venturi from the 46 to reference.

Maybe my question should be, any other things to consider when reworking and LA40 or 46 for that matter from the factory RC versions for use with wires and a handle?  Any changes in Comp ratio or anything like that? H^^ H^^

     The timing on either is the same, and that is what you want. DO NOT rework anything, grind anything, change anything, do not adjust the compression, in fact, do not take it apart other than to put in a venturi and spraybar. Make a stock-like venturi with a choke area around .019 square inches. Start with a Thunder Tiger 11-4.5 or APC 11.5-4.  Use the stock CL spraybar/needle from OS, used on the 20FP -46LA. If you don't have a stock one, do not drill a hole in the case to fit an oversize spraybar (ST, ST Clone, PA, RO-Jett, etc.), get the spraybar and needle assembly here:

https://www.ebay.com/itm/293139719059?hash=item44407d2393:g:M8sAAOSw5eBcolX7

   so as not to ruin the case for the next guy when it doesn't work.

       You are already in the danger zone of "modifications", I strongly urge you to run it as stock as possible, with appropriate props, then make the necessary slight adjustments (like the venturi size) - rather than jump into grinding and adding head gaskets, as, even if it "works", you have lost most of the power.

     Brett

Offline Dennis Holler

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #7 on: April 10, 2022, 07:50:01 AM »
I didn't mean to suggest I was going to go hacking cluelessly.  I'm good with the solid responses I have in addition to the pinned stuff and search function results.  All I will do is to replace the carb with a venturi and proper needle assembly.
I've started plenty...would be nice to finish something!!!

Offline Brett Buck

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #8 on: April 10, 2022, 04:04:30 PM »
I didn't mean to suggest I was going to go hacking cluelessly.  I'm good with the solid responses I have in addition to the pinned stuff and search function results.  All I will do is to replace the carb with a venturi and proper needle assembly.

   Good!  I am pretty sensitized to the problem at this point, having dealt with people calling me various names when they try my engine suggestions (some tested extensively over decades) and they "don't work". The common theme in every single one of these cases is that they modified the engine or did something differently. Almost always a "better" spraybar (like the ST -  there goes 25-30% of the power and permanently-damaged case) and in many cases stacks of head gaskets. Occasionally, "stunt timing numbers" instead of "radio numbers". The solution to date in all cases is to put it back the way it came, if possible.

   So forgive me if I overreacted, asking about the timing sets off the rotating red light.

   
     In this case, I don't have anything like as a solid setup for the 40LA - just giving some advice to *start out stock*, *discard the "How I came in 6th at the 1954 Podunk Stunt Criterion" ideas that seem to be the basis for most of the engine modifiers*, and then make small adjustments only as necessary.

     If you get a stock-sized venturi, you might want to consider getting  (or making) 3 of them - stock size, one .005' smaller and another .010" smaller. The stock unit is about as big as you would likely want to go. Depending on the size of the airplane you might need to make it smaller, or even much smaller. The 40LA has a reputation of being a bit "wilder" than the 46LA, but both are *much more powerful* than a classic baffle-piston 35 or 40 from the ancient days.

  Most people get into problems trying to run these sorts of engines in older "35-sized" airplanes based on the Fox 35, and come to grief when it goes like a bat out of hades. The traditional solution is to try backing off on the needle, which seems like it will work at first, until, at some point, it takes off like a bat of of hades again, no matter how rich you set it. The essence of the problem is that the engine is so much more powerful than you need, that you have to back it off far more than it can tolerate. The needle is not a throttle. The solution is to reduce the power available, then run it where it is comfortable running, that is, a medium 2-stroke, by changing the venturi (closing the throttle).

     Brett
« Last Edit: April 24, 2022, 05:08:11 PM by Brett Buck »

Offline Peter in Fairfax, VA

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #9 on: April 13, 2022, 09:07:26 AM »
Brett,

Curious as to why the case drilling "makes a problem for the next person."  Will the O.S. NVA not install well on a drilled case?

As far as the Super Tigre NVA, I've run one for several seasons in an LA 46, as well as a Fox 35.  I like the result.  You are likely correct the reduced choke area limits performance, but that reduction also boosts fuel economy and fuel draw, perhaps.

Overall, I appreciate that your experience with the ST NVA may differ from mine.

Peter 

Offline Brett Buck

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Re: Is the OS MAX LA .40 timing the same for the RC and CL engine's
« Reply #10 on: April 13, 2022, 01:27:44 PM »
Brett,

Curious as to why the case drilling "makes a problem for the next person."  Will the O.S. NVA not install well on a drilled case?

  Correct - you drill the hole in teh case and venturi out to fit the 4mm spraybar, and the 3.5 mm cannot be installed without rattling around in the hole, and it will not retain the venturi properly. To get around it, you have to sleeve the 3.5 mm spraybar., but only on the ends when it engages the case and venturi, because the entire point is to have it be 3.5mm in the choke section.

    You can make the sleeves from brass tubing, install that on the smaller spraybar, and then use JB-Weld or something to hold it. With all that you still have to drill out the venturi holes because you still have to fit the 4mm sleeves through it. All this in order to *return it to the stock configuration* - which could also have been accomplished by leaving it alone entirely from the start.

  So, this scenario which has occurred to me repeatedly:

 " Hey Brett, I tried the 20FP and it's gutless and it won't fly my Twister in any sort of wind, you don't know what you are talking about!"
<<looks at spraybar - ST Clone>>"I told you not to use the ST spraybar"
"But it's better"
"It's 25-30% of the power off the top"
"Oh..."
"I have got stock parts in the van you could use - but they won't fit any more!"
"Oh..." <<walks away>>

   A more practical alternative is to get larger venturis to use the ST spraybar as is but still get the same choke area. OF course, now you are headed down the modification rathole, and your system cannot compare to anyone else's  -there's no baseline. So, back to random.

    As always, it's just advice, no one has to follow it. I would prefer to avoid any more exchanges like the one above, having already experienced it 20 times, but it's entirely up to the pilot.

   Brett


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