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Engine basics => Engine set up tips => Topic started by: rich gorrill on August 02, 2014, 11:03:12 AM
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I just did a compression check on one of my .46 LA engines. I added a small amount of fuel in the ex. port, rotated the prop to TDC and noticed a small amount of bubbles on the left side of the piston-liner. It holds for quite a while before totally losing all compression. This engine was bought used but the P&L look fine, no scratches or score lines. Should I run it on a test stand and see what happens. I would rather replace the parts now before I put it in a plane. How much air leakage, if any, is acceptable.
T.I.A
Rich
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It doesn't seem that your engine is in the prime of youth, but it certainly sounds as if there is enough compression left to run for a goodly time. LA46s are not the best engines for longevity, I would fly it until the power output is insufficient to satisfy your needs. Then put in a new P/L from Towers.
Regards,
Andrew.
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Sounds pretty OK. I have a Cox .049 that has almost no compression unless primed and flipped hard. It starts and runs very well most of the time. When it is acting up it is not the fault of the engine, it is the operator or dead batteries, which I guess is still on me...
Static compression on high speed engines is not completely meaningful. If the bleed down takes time, then at 11k rpm there is not enough time to loose compression in the first place!
With ABC or ABN (as OS uses) construction the piston and liner change size as the engine heats up. A static test while cold is also not very meaningful. It might be more beneficial to pop the head and carefully examine the liner for the nickel wearing through as a determination of if the engine needs parts or work. With ABN the piston and the cylinder have similar life spans.
Phil
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Static compression on high speed engines is not completely meaningful. If the bleed down takes time, then at 11k rpm there is not enough time to loose compression in the first place!
Many Team Race fliers may disagree with that.
And I would think that a better static compression in a lapped engine would result in a stronger running in all cases.
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Put it in a plane and fly it. You'll like it a lot! Read the pinned setups for the .46LA at the top of the page. H^^ Steve
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I favor bench running with a tach.
For any size engine pick a tach prop and a tach fuel and start collecting data.
For example:
LA15 - 7/4 prop and 10/10/10 fuel
LA25 - 8/6 prop and 10/10/10 fuel
L40 - 10/6 prop and 10/10/.10 fuel
After you gather some data you can decide which units are healthy. Then you can go up the next level - hot starting.
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As Steve said, go out and fly it, it will probably work fine. A lot of LA engines can wear in the P/L dept, but keep running well enough to fly. It doesn't take much effort to put in a new P/L if you have to.
Go and give it a whirl, chances are it will keep running for a long time, so what if you have not got the last 5%, you probably would not notice that anyway.
Andrew.
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Andrew - is there a Tower replacement p/c for an LA46? For which Tower engine? Might need to know this one day.
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Andrew - is there a Tower replacement p/c for an LA46? For which Tower engine? Might need to know this one day.
NO there is not
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Andrew - is there a Tower replacement p/c for an LA46? For which Tower engine? Might need to know this one day.
Ok, just some crazy talk...maybe...but these pictures look impressively similar
http://www3.towerhobbies.com/cgi-bin/wti0005p?&I=TOWG0146&P=PU
http://hobbyking.com/hobbyking/store/__27128__INC_46_Glow_Engine_with_Muffler_ABC_piston_sleeve_assembly_.html
http://hobbyking.com/hobbyking/store/__39659__INC_46_Glow_Engine_Cylinder_Piston.html
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJB07&P=PU
The carburators are both pinch-on as pictured in the first two links. The liners in the second 2 links are very similar looking with a heavy groove under the lip.
I could very easily be completely wrong as pictures are just pictures.
Phil
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Hello Ian,
Just to put the record straight. I meant buy a standard OS p/l set from Towers. Even with the postage it is a cheaper bet than buying in the UK unless you are near a model shop that stocks them! Towers don't do a p/l set of their own as Randy says. Sorry for the confusion.
Andrew.
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Ok, just some crazy talk...maybe...but these pictures look impressively similar
http://www3.towerhobbies.com/cgi-bin/wti0005p?&I=TOWG0146&P=PU
http://hobbyking.com/hobbyking/store/__27128__INC_46_Glow_Engine_with_Muffler_ABC_piston_sleeve_assembly_.html
http://hobbyking.com/hobbyking/store/__39659__INC_46_Glow_Engine_Cylinder_Piston.html
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJB07&P=PU
The carburators are both pinch-on as pictured in the first two links. The liners in the second 2 links are very similar looking with a heavy groove under the lip.
I could very easily be completely wrong as pictures are just pictures.
Phil
Hi Phil
NONE of those links are the same as a OS LA 46, and they are also not plain bearing , those are dual ball bearing engines, with hugely different piston / sleeves , as compared to a LA plain bearing 46
Regards
Randy
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Hi Phil
NONE of those links are the same as a OS LA 46, and they are also not plain bearing , those are dual ball bearing engines, with hugely different piston / sleeves , as compared to a LA plain bearing 46
Regards
Randy
I misread Andrew's question. I thought he switched it to asking about the TOWER branded 46, which is not an OS engine rebranded, but some other engine rebranded. Tower lists the 46LA parts in stock currently.
http://www3.towerhobbies.com/cgi-bin/WTI0005p?&I=OSMG0047&P=Z
My brain must have misfired, OS parts are easy to get from many other venders too...
Phil
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I think some are confusing "compression ratio" with "compression integrity". The CR is a constant, regardless of the engine wear (as long as it is running and leakage not a factor). Compression integrity is all about leakage, best observed when slowly turning over. Many worn engines will start easily with an electric starter.
F.C.
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Compression ratio is a theoretical constant that assumes that there are no losses, but in a less than perfect world we are forced to deal with this.
So respectfully I disagree, true comp ratio does regard engine wear.
The closer you can get the engine to run to its mathematical comp ratio the stronger it will be.