I need 16+ lbs thrust, which engine?
07-04-2003, 01:28 AM
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I need 16+ lbs thrust, which engine?
Ok. I need your honest opinions. For a 16-20 pound biplane, which engine conversion will make for the best combination of power against cost? If cost were no object, I would of course buy a brand new ZDZ or Brison or Sachs, etc. Money IS a concern, so we are looking at conversions. What do you think?
Tommy
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07-04-2003, 03:54 PM
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I need 16+ lbs thrust, which engine?
Depending on you power requirement, you can get a brand new G26 or G38 for around $275.
The cost of a conversion engine depends largely on how cheap you can buy your chainsaw/weedwacker. Watch the internet for bargains, then decide whether you want to keep the magneto ignition or convert to electronic CDI. Poulan 46cc is a polular conversion and is probably the most likely to give you the max bang for the buck. You do need a new intake manifold, since the factory unit is a rubber sleeve press-in type.
If you want to convert to electronic CDI, Poulan 42cc is slightly easier conversion, since the engine already has a bolt-on carb manifold. It's reportedly very close to the 46cc in power.
Beyond that, you might consider Redmax/Zenoah/Echo chainsaw engines. Redmax and Zenoah are both made by the same Komazu company in Japan. Echos are made by Kioritz of Japan, and they make a 50cc chainsaw, which is what the BME 50cc is based on. If I were to pick the best candidate for absolute max power-to-weight in this category, that would be it. It is, however, not a popular conversion and so parts are not readily available. If you don't have the ability to produce your own parts, having them made for you will likely cost as much as buying a BME.
BTW, I would think all of us here give nothing but honest opinions, if not always unbiased.
The cost of a conversion engine depends largely on how cheap you can buy your chainsaw/weedwacker. Watch the internet for bargains, then decide whether you want to keep the magneto ignition or convert to electronic CDI. Poulan 46cc is a polular conversion and is probably the most likely to give you the max bang for the buck. You do need a new intake manifold, since the factory unit is a rubber sleeve press-in type.
If you want to convert to electronic CDI, Poulan 42cc is slightly easier conversion, since the engine already has a bolt-on carb manifold. It's reportedly very close to the 46cc in power.
Beyond that, you might consider Redmax/Zenoah/Echo chainsaw engines. Redmax and Zenoah are both made by the same Komazu company in Japan. Echos are made by Kioritz of Japan, and they make a 50cc chainsaw, which is what the BME 50cc is based on. If I were to pick the best candidate for absolute max power-to-weight in this category, that would be it. It is, however, not a popular conversion and so parts are not readily available. If you don't have the ability to produce your own parts, having them made for you will likely cost as much as buying a BME.
BTW, I would think all of us here give nothing but honest opinions, if not always unbiased.
07-05-2003, 01:31 AM
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I need 16+ lbs thrust, which engine?
Ahh, yes. Thanks Adam. I always get the two confused:
Poulan 46cc: coil mounts on engine, carb needs adapter manifold.
Poulan 42cc: coil mounts on chainsaw case, carb already has bolt-on manifold.
So the 46cc is easier for keeping the magneto, and the 42cc is easier for electronic CDI. I will correct my post #4.
Poulan 46cc: coil mounts on engine, carb needs adapter manifold.
Poulan 42cc: coil mounts on chainsaw case, carb already has bolt-on manifold.
So the 46cc is easier for keeping the magneto, and the 42cc is easier for electronic CDI. I will correct my post #4.
07-05-2003, 03:08 AM
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I need 16+ lbs thrust, which engine?
Thanks guys. Of course your opinions are honest ones! I appreciate the help!
Tommy
Looks like I will be hunting a new Poulan 46 or 42 ;>)
Tommy
Looks like I will be hunting a new Poulan 46 or 42 ;>)
07-05-2003, 03:29 AM
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I need 16+ lbs thrust, which engine?
After looking at Lawnstation the 46cc seems to be available in several different saws. Does it matter which saw I purchase, or is the engine the same in each one? Also, they appear to have a shaft on each side of the engine, will I need to cut this off? Any input on how to get it ready for a/c use would be good, or maybe a website to visit (besides this great one) for more info. You guys have been a great help, thanks a ton. Even if I buy this engine, convert it, and put a good CDI and muffler I am still money ahead of buying a G-45 or 62! Awesome!
Tommy
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07-05-2003, 10:37 AM
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I need 16+ lbs thrust, which engine?
Check a couple of the threads on Poulans. Some guys are buying just the motor from Lawnstation without all the "saw" stuff.
You dont have to cut the extra shaft off, some do and some dont. If you do cut it off with the crank still in the saw, just dont get it so hot it melts the seal :stupid:
Adam
You dont have to cut the extra shaft off, some do and some dont. If you do cut it off with the crank still in the saw, just dont get it so hot it melts the seal :stupid:
Adam
07-05-2003, 04:11 PM
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I need 16+ lbs thrust, which engine?
I cut the rear shaft off on mine. It makes for easier mounting and saves about an ounce. I use a air cut-off saw, and, yes, do take your time with it and don't get it too hot.
07-05-2003, 06:04 PM
#13
Cutting the shaft off
I took my Poulan 54cc apart first. I put the crankshaft in a vise with some old rags to keep from scratching it.
By removing the crank from the engine- I was able to use a portable Milwaukee (sp?) bandsaw to do the cutting. After you get the clutch assembly off- you will probably notice a groove in the crank. On my 54cc, the groove was about 1/4" away from the oil seal. Thats a perfect spot to cut the crank. The grove is a nice spot to get started with your saw- because it helps to keep the saw from wondering around and it will leave you just enought sticking out when you reassemble the engine.
Contact RCIGN for your ignition system. He makes a good unit and it works flawlessly. He can probably set you up with everything you will need to convert the motor to electronic ignition.
As for the muffler; measure your exhaust bolt pattern on the Poulan 46 first. Then try to find a commercially made muffler that is close enough to work with. On my 54cc Poulan; I found that a BCM muffler for the Moki 180 was only 1mm off on the bolt pattern. I bought the muffler and used a small rat-tail file to move the centerline of the holes out 1mm. The muffler comes with 8/32 holes in it; on 34mm centers. I needed a 36mm center with a 1/4" hole for my Poulan. I just used a 7/32" drill bit to enlarge the holes first- then I used the rat-tail file to finish it off. It works perfectly.
I had $230 in my 54cc Poulan before I bought the muffler. Thats with a Synchro-spark ignition system too. Not a fix timing unit. I went all out and bought only the high end conversion parts. I could have saved myself $30 and bought a fixed timing unit- but I had an axe to grind with a friend who is a BME fanatic. He uses synchro-spark ignition systems on his BME engines. I wanted to set our engines side by side and compare them----apples to apples. I get almost the exact RPM's as he does with the BME 50cc engine. I actually got about 100RPM MORE than the BME 50. I don't know if it's becaue I got a 54cc engine of if maybe because I have a used engine thats broken in and his is almost new. The BCM muffler was $60 with shipping. Total investment for my engine was under $300. Pretty cheap for that size gasser. Expecially when you consider that a BME or DA will run you at least double that without a muffler and ignition battery. And my engine is turning a 22-8 prop at almost 6800-6900RPM with 40:1 oil mix.
My conversion engine weighs about 3 or 4 ounces more than a BME. I can live with that. For those guys who want to spend $800 on a BME; my question is......Why would you want to pay $200 an ounce for aluminum?? Is it really worth $500 to get an engine that weighs 4 ounces less than a chiansaw? They were all chainsaws at one time or another.
Good luck with your project.
By removing the crank from the engine- I was able to use a portable Milwaukee (sp?) bandsaw to do the cutting. After you get the clutch assembly off- you will probably notice a groove in the crank. On my 54cc, the groove was about 1/4" away from the oil seal. Thats a perfect spot to cut the crank. The grove is a nice spot to get started with your saw- because it helps to keep the saw from wondering around and it will leave you just enought sticking out when you reassemble the engine.
Contact RCIGN for your ignition system. He makes a good unit and it works flawlessly. He can probably set you up with everything you will need to convert the motor to electronic ignition.
As for the muffler; measure your exhaust bolt pattern on the Poulan 46 first. Then try to find a commercially made muffler that is close enough to work with. On my 54cc Poulan; I found that a BCM muffler for the Moki 180 was only 1mm off on the bolt pattern. I bought the muffler and used a small rat-tail file to move the centerline of the holes out 1mm. The muffler comes with 8/32 holes in it; on 34mm centers. I needed a 36mm center with a 1/4" hole for my Poulan. I just used a 7/32" drill bit to enlarge the holes first- then I used the rat-tail file to finish it off. It works perfectly.
I had $230 in my 54cc Poulan before I bought the muffler. Thats with a Synchro-spark ignition system too. Not a fix timing unit. I went all out and bought only the high end conversion parts. I could have saved myself $30 and bought a fixed timing unit- but I had an axe to grind with a friend who is a BME fanatic. He uses synchro-spark ignition systems on his BME engines. I wanted to set our engines side by side and compare them----apples to apples. I get almost the exact RPM's as he does with the BME 50cc engine. I actually got about 100RPM MORE than the BME 50. I don't know if it's becaue I got a 54cc engine of if maybe because I have a used engine thats broken in and his is almost new. The BCM muffler was $60 with shipping. Total investment for my engine was under $300. Pretty cheap for that size gasser. Expecially when you consider that a BME or DA will run you at least double that without a muffler and ignition battery. And my engine is turning a 22-8 prop at almost 6800-6900RPM with 40:1 oil mix.
My conversion engine weighs about 3 or 4 ounces more than a BME. I can live with that. For those guys who want to spend $800 on a BME; my question is......Why would you want to pay $200 an ounce for aluminum?? Is it really worth $500 to get an engine that weighs 4 ounces less than a chiansaw? They were all chainsaws at one time or another.
Good luck with your project.
07-05-2003, 07:43 PM
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I need 16+ lbs thrust, which engine?
Volfy, I figured that this would change the balance of the engine. How did you check balance?
Originally posted by Volfy
I cut the rear shaft off on mine. It makes for easier mounting and saves about an ounce. I use a air cut-off saw, and, yes, do take your time with it and don't get it too hot.
I cut the rear shaft off on mine. It makes for easier mounting and saves about an ounce. I use a air cut-off saw, and, yes, do take your time with it and don't get it too hot.
07-05-2003, 08:44 PM
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I need 16+ lbs thrust, which engine?
Cutting the crank off doesn't change the balance of the engine...
No way to check it anyway, and even if you could you would have to know what percentage of the weignt of the rod, crank pin, big end bearing, piston, rings, small end bearing, wrist pin, bearing, and clips you wanted to use for balance...It's a physical impossibility to balance a single cylinder engine without using a balance shaft rotating with the crank..... You can get close at some rpms, but no cigar...
No way to check it anyway, and even if you could you would have to know what percentage of the weignt of the rod, crank pin, big end bearing, piston, rings, small end bearing, wrist pin, bearing, and clips you wanted to use for balance...It's a physical impossibility to balance a single cylinder engine without using a balance shaft rotating with the crank..... You can get close at some rpms, but no cigar...
07-06-2003, 04:19 AM
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I need 16+ lbs thrust, which engine?
Ralph is correct. There is no way to balance a single cylinder engine perfectly. You can try to balance it statically yes, but dynamically, no. They don't call them thumpers for nothing. 
I've heard claims of a good rule of thumb is to balance all the weight of conrod plus 10% of the piston (or something like that), but that's probably an estimate of a good compromise considering the normal operating RPMs.
In any case, cutting off the rear shaft doesn't alter the balance at all, since it's just a round shaft. These dual counter-balance, dual BB supported cranks are usually better at suppressing parasitic vibrations due to non-perfectly rigid members and clearancing/tolerances.
BTW, BCM now has the patterns for a wrap-around style muffler for the Poulan 46cc. It will also work for 33cc-42cc, I think, since they all share the same exhaust bolt spacing. I had ordered two of these and will post pics when I get them if anyone is interested.
I've heard claims of a good rule of thumb is to balance all the weight of conrod plus 10% of the piston (or something like that), but that's probably an estimate of a good compromise considering the normal operating RPMs.In any case, cutting off the rear shaft doesn't alter the balance at all, since it's just a round shaft. These dual counter-balance, dual BB supported cranks are usually better at suppressing parasitic vibrations due to non-perfectly rigid members and clearancing/tolerances.
BTW, BCM now has the patterns for a wrap-around style muffler for the Poulan 46cc. It will also work for 33cc-42cc, I think, since they all share the same exhaust bolt spacing. I had ordered two of these and will post pics when I get them if anyone is interested.
