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Home✈️Aircraft🚁HelicopterFuel-Helicopters New or Limited ActivityNext D › Another OS 105 installation question...
12-25-2014 09:59 PM  5 years ago
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mikeangiulo

rrApprentice

Bellevue, WA - USA

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Another OS 105 installation question...
The 105HZ comes with a flared venturi (like a horn shape that extends the air intake on the carb) but when i try and install the fan shroud it interferes.

Should I just leave the venturi off? I guess the other option is to cut a hole in the fan shroud but that would make the cooling less efficient. Without the venturi in place everything fits perfectly and the fan spins without interference.

Thanks!
-Mike

P.S. I noticed another strange thing about this engine - the piston shroud comes down into the back case area where you would normally use a crankshaft lock to tighten the prop nut. I managed to work around that (i used the crank tool at top dead center instead of bottom and mostly torqued the prop nut against the fan collar which was secured with the clamping screws). If I hadn't noticed that I would have jammed the nylon crank lock tool and then torqued away at the nut and probably bent the piston (!)
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12-25-2014 11:12 PM  5 years ago
Steve Graham

rrApprentice

Denver, CO

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I'd dremel out the fan shroud. I doubt you'll notice any loss in cooling efficiency. Thats what I did on my N7 anyway. You do need to be careful with the 105. I'm sure you noticed that the backplate also can only be removed with the piston at TDC.
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12-26-2014 12:45 AM  5 years ago
mystar60

rrVeteran

Clifton, NJ

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Mike, just remove the fan shroud halves then install one side and trim until it fits around the Venturi then repeat on the other half. I like to have a small gap left between the shroud and carb Venturi or else it rubs thru eventually.
Kevin
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12-27-2014 06:05 AM  5 years ago
mikeangiulo

rrApprentice

Bellevue, WA - USA

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Thank you. I got it all back together just to learn that I'm going to have to carve out a little more of the fan shroud to clear the attachment for the Hatori.

On a related question I see a number of different setups for the fuel plumbing - I get the check valve and the use of a T fitting to relieve pressure when filling. I think I use the crankcase pressure tap to pressurize the fuel system so I shouldn't install the pressure nipple on the pipe. Is that correct? Any other tips for setting up the fuel system? I haven't set up a nitro heli since gyros actually spun

Thanks in advance!
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12-27-2014 01:10 PM  5 years ago
mystar60

rrVeteran

Clifton, NJ

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Correct, with the HZR engine you do not use the muffler pressure tap. I tend to use a small amount of JB Weld on a screw I use to plug the muffler tap.
As far as plumbing goes I just follow the diagram on page 21 in the manual.

http://manuals.hobbico.com/osm/105hz-r-manual.pdf
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