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53cc TOC 3mm gas engine- 2 props to choose from

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Old 07-19-2014, 04:09 PM
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Default 53cc TOC 3mm gas engine- 2 props to choose from

Trying to decide which prop would be best for the engine's health. Weeks Special biplane 73" span 18lbs.

I have a 22x8-14 and a 20x10 both wood props Zinger and Zoar.
Someone told me the 22x8-14 would be too much prop for a 53cc and the 20x10 would be to small.

I mounted the 20x10.
After setting needles I got 7300 RPM max and idles about 1800 pulls 20lbs on a digital scale strapped to the tailwheel bracket.

I then mounted the 22x8-14 and had to change low and high adjustments accordingly, the max RPM was just 6000 (1300 less) and idles about the same 1800 RPM. Surprisingly it pulls about the same 20lbs on digital scale.

All the info I've found on the TOC 3MM 53cc engine from Cermark indicates props from 22x8 on up to 24x8 but between the two props I've tried the 20x10 feels best, more responsive to high end adjustment. The 22x8-14 feels like it's overwhelming the motor high end adjustment not as responsive and RPM's down.

It's the only two props I have to choose from at this time and I'm wanting to get airborne, I feel the 20x10 and just avoid full throttle to not ring it out would this be acceptable for a prop a tad on the small side? Thanks.
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Old 07-19-2014, 09:15 PM
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As you say, neither prop is ideal for the airframe or the engine. I've had that engine for some time and though not flown a lot, I find a 22-8 to be about the limit of its ability and that would be my choice in your case. But ..... you don't have a 22-8 so I'd just bolt on one of the props you have and go for it. See how it flies the plane then try the other one to repeat the test. Use the one that pulls the airplane the best. Not much else you can do. My bet is the 22 x 8 - 14 will be way too much prop, especially for a high drag biplane so you'll end up using the 20-10.
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Old 07-20-2014, 04:44 AM
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Thanks yea I'm leaning towards the 20x10, I know either one will make the plane fly, how well She flies I don't care, I'm not that good.
I'm mainly conncerned about the health of the engine, it was an E'pay purchase and I don't know it's history and I'm treating it as if were needing broke in.so I'm thinking the last thing I would want to do is overprop it, don't want to underprop either but have to choose the best of two evills.
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Old 07-20-2014, 05:52 PM
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If I had no choice I would use the 20x10 and lower the throttle endpoint so as not to over rev the engine in flight
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Old 07-21-2014, 10:13 PM
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Thats a lot of RPM for the 3MM53. I have 1 in my Pitts12, swigging a 22x10 Hawk. We use thses engines in tugs for aero towing. Best results is the 22x10. The newer TMM53, I use a 23x8. Diffrent porting and only using 2 bearings.
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Old 07-24-2014, 04:13 PM
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I have that engine and run the 23x8 bunny prop on the edge 540 88" and it turns it well never have tached it but the plane is unlimited
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Old 07-25-2014, 04:23 AM
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Quote:
Originally Posted by KenLambert View Post
I have that engine and run the 23x8 bunny prop on the edge 540 88" and it turns it well never have tached it but the plane is unlimited
HI ken,
I have a few ST parts,do you want them,no charge.Just shipping.
BCCHI
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Old 07-25-2014, 06:27 AM
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Hi how are you doing these days? Yes I can always use parts for them . Just let me know the cost and I will send the money.
address--
Kenneth Lambert
10000 San Leon Dr #7
Dickinson, TX 77539

Thanks Kenneth
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Old 07-27-2014, 07:02 PM
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Quote:
Originally Posted by KenLambert View Post
I have that engine and run the 23x8 bunny prop on the edge 540 88" and it turns it well never have tached it but the plane is unlimited
What is a "bunny prop" I am still learning. Capt,n
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Old 07-27-2014, 07:07 PM
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Tom sold props for those planes and engines he sold and they were called bunny props because they have a bunny graphic on them. Next time I get out I will send you a pic.
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