Building 4-stroke gas boxer - need your help
12-06-2010, 06:42 PM
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Building 4-stroke gas boxer - need your help
Hi everyone,
I am new to this forum and somehow new to RC engines. Nevertheless engines are my passion and profession. Recently Istarted to build my own 4-stroke 60cc opposed twin (boxer) which I probably end up giving away to someone who can really fly as oppose to me who can only crush planes. Ijust enjoy building engines...
Since RC engines are very unique, I definitely need your advice in what accessories to incorporate or other tips you can share that would keep me out of trouble.
Let's start with some engine info. Cylinders, pistons,and valve train are based on a Troy-Bilt 4-stroke. That's all as far as production ready parts. I will not lubricateengine by oil in the crank case, but by fuel-oil mix. It will be scavenged like a 2-stroke, from carb into the crankcase and then into intake valves.
My immediate questions to you are:
1. What carburetor to use? I think that a diaphragm Walbro type carbs may not be the best in RC planes. If yes - which one do you recommend? If not diaphragm - what other type and make should I use? I red somewhere that 2-needle carb is best... if so which one?
2. Do you know of a small reed valve assembly for this size engine?
3. Ignition. I don't believe the original heavy ignition is the way to go. Especially that it has fixed ignition timing. What ignition would you like to see in your plane?
4. Bolt pattern mounting: engine to plane. Is there a standard or preference?
Thanks for your help!
I am new to this forum and somehow new to RC engines. Nevertheless engines are my passion and profession. Recently Istarted to build my own 4-stroke 60cc opposed twin (boxer) which I probably end up giving away to someone who can really fly as oppose to me who can only crush planes. Ijust enjoy building engines...
Since RC engines are very unique, I definitely need your advice in what accessories to incorporate or other tips you can share that would keep me out of trouble.
Let's start with some engine info. Cylinders, pistons,and valve train are based on a Troy-Bilt 4-stroke. That's all as far as production ready parts. I will not lubricateengine by oil in the crank case, but by fuel-oil mix. It will be scavenged like a 2-stroke, from carb into the crankcase and then into intake valves.
My immediate questions to you are:
1. What carburetor to use? I think that a diaphragm Walbro type carbs may not be the best in RC planes. If yes - which one do you recommend? If not diaphragm - what other type and make should I use? I red somewhere that 2-needle carb is best... if so which one?
2. Do you know of a small reed valve assembly for this size engine?
3. Ignition. I don't believe the original heavy ignition is the way to go. Especially that it has fixed ignition timing. What ignition would you like to see in your plane?
4. Bolt pattern mounting: engine to plane. Is there a standard or preference?
Thanks for your help!
12-06-2010, 06:55 PM
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RE: Building 4-stroke gas boxer - need your help
I'd start by using bigger type for us older guys.[
]
WT 76 or HDC Walbro
RC Excel Ignition
I could probably help you out with a cheap Chinese reed valve assembly and carb.
I'd use the DA 50's bolt pattern, you can get it from their site and it's the standard.
]WT 76 or HDC Walbro
RC Excel Ignition
I could probably help you out with a cheap Chinese reed valve assembly and carb.
I'd use the DA 50's bolt pattern, you can get it from their site and it's the standard.
12-07-2010, 05:13 AM
#3
RE: Building 4-stroke gas boxer - need your help
Welcome to the RCU forums, Makary!
Do you know of this website?:
http://modelenginenews.org/index.html
These are some examples of commercially available four stroke engines:
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GCH
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GCI
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GCJ
http://www.osengines.com/engines/airplane.html
http://www.saitoengines.com/
Regards
Do you know of this website?:
http://modelenginenews.org/index.html
These are some examples of commercially available four stroke engines:
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GCH
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GCI
http://www3.towerhobbies.com/cgi-bin/wti0093p?&C=GCJ
http://www.osengines.com/engines/airplane.html
http://www.saitoengines.com/
Regards
12-07-2010, 06:03 AM
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RE: Building 4-stroke gas boxer - need your help
Thanks Lnewqban! I knew most of those sites but I am not into buying but building my own beast…
Didn’t know of Modelenginenews.org – really nice with a lot of stuff. Will take me a while to go thru that all.
12-07-2010, 06:17 AM
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RE: Building 4-stroke gas boxer - need your help
Thanks Soarrich!
My search showed many HDC carbs… any particular in mind for my 60cc 4 stroke?
And sure – if you can help me out with the reeds and carb that'd be great.
So what about those traditional rc engine carbs? Why some prefer them over diaphragm carbs?
12-07-2010, 07:53 AM
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RE: Building 4-stroke gas boxer - need your help
ORIGINAL: Makary
>So what about those traditional rc engine carbs? Why some prefer them over diaphragm carbs?
>So what about those traditional rc engine carbs? Why some prefer them over diaphragm carbs?
12-07-2010, 08:19 AM
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RE: Building 4-stroke gas boxer - need your help
ORIGINAL: Makary
I'm rethinking the HDC, they all my be too big for a 30cc cylinder. I have a WT263 with a choke that might work better. I'll sell you a reed assemble, carb mounting block, and the WT263 for $45 to your door.
Thanks Soarrich!
My search showed many HDC carbs… any particular in mind for my 60cc 4 stroke?
12-07-2010, 08:45 AM
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RE: Building 4-stroke gas boxer - need your help
Thanks a lot Soarrich! I'm fine with the price. Let me know what info you need from me to get it going.
You are absolutely correct about the carb size. I was about to post it, but you were faster... it's a twin throw crank. Howover, since I will have one original pumper carb for that engine (for 30cc), I'd also like to try one that is sized for a bit largerdisplacement - say around 40cc.I'm not sure how the"supercharging" from crankcase to a single cylinder will work, so need to try both. I'll rely on you recommendation...
The original carb isthe AC4 type MTD #: 753-05676. I have not seen it yet so don't know if it's made by Walbro. It'd be best if the larger one has same body or mounting, but I can make an adapter.
How about the RC Exelignition? If you don't have one, can you point me where to look?
Thanks
You are absolutely correct about the carb size. I was about to post it, but you were faster... it's a twin throw crank. Howover, since I will have one original pumper carb for that engine (for 30cc), I'd also like to try one that is sized for a bit largerdisplacement - say around 40cc.I'm not sure how the"supercharging" from crankcase to a single cylinder will work, so need to try both. I'll rely on you recommendation...
The original carb isthe AC4 type MTD #: 753-05676. I have not seen it yet so don't know if it's made by Walbro. It'd be best if the larger one has same body or mounting, but I can make an adapter.
How about the RC Exelignition? If you don't have one, can you point me where to look?
Thanks
12-07-2010, 09:13 AM
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RE: Building 4-stroke gas boxer - need your help
Since you are making a 4 stroke, how do you propose to make the Walbro Carb work? The crankcase must be vented thereby killing your pressure pulse for the carb. If you sealed the crankcase, made solid pistons to increase the compression forces and added a Disc rotor to allow for the compression of the intake charge, you could supercharge it like a YS 4 Stroke.
YS uses the downward stroke of the pistion to compress the intake charge. The trick is to use a disc rotor valve to hold the charge for compression. It seals the crankcase, the piston will compress it, and then the disc opens sending a compressed charge to the intake tract. I think it compresses on the power down stroke. I am not sure what happens on the exhaust down stroke, maybe they are compressing a charge twice per intake/exhaust cycle??
YS uses the downward stroke of the pistion to compress the intake charge. The trick is to use a disc rotor valve to hold the charge for compression. It seals the crankcase, the piston will compress it, and then the disc opens sending a compressed charge to the intake tract. I think it compresses on the power down stroke. I am not sure what happens on the exhaust down stroke, maybe they are compressing a charge twice per intake/exhaust cycle??
12-07-2010, 10:02 AM
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RE: Building 4-stroke gas boxer - need your help
You are right JeffH, I'll supercharge it from the cranckase. This is the reason I am building a twin throw crank boxer (opposed twin), and this is the reason I am going with a fuel-oil mix (no oil in cranckase). Carb will draw into the crankcase.
I don't think there will be a lot of supercharging because of the large dead volume, but there will be some.
I'll try both: first rotor valve, than reed valves. That was the plan. We'll see which one works better. I think reeds will give it more torque at lower rpm, but the rotor valve will yeld more power at high rpm.
Thanks for your input!
12-07-2010, 10:03 AM
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RE: Building 4-stroke gas boxer - need your help
ORIGINAL: Makary
Thanks a lot Soarrich! I'm fine with the price. Let me know what info you need from me to get it going.
How about the RC Exel ignition? If you don't have one, can you point me where to look?
Thanks a lot Soarrich! I'm fine with the price. Let me know what info you need from me to get it going.
How about the RC Exel ignition? If you don't have one, can you point me where to look?
The carb sizing I don't think will be to critical, reed valve engines aren't too picky, you're better off with a slightly smaller carb than I too big carb though IMHO.
@JeffH
He's treating the crankcase as a two stroke, but using it as a 4 stroke's supercharger at the same time, that was the reason for is it a twin throw or a single throw crank question.
