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O.S. - OSMG1621 OSM13951 13951 531028021365 4531028021365
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O.S. 21XZ-M 3.5cc Inboard Marine Engine
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O.S. 21XZ-M 3.5cc Inboard Marine Engine
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Instruction Manuals: Manual 1 (1.6 MB)
Tower Catalog Page: 170

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Tech Notes
This is the O.S. 21XZ-M 3.5cc Inboard Marine Engine.

****** Because of the competition nature of this engine,******
******it is NOT covered by the O.S. 2 Year Warranty.******


Designed expressly for 21 class boat racing
21D big bore carburetor allows use of high nitro fuel
Blue anodized water cooled head


O.S. 21XZ-M 3.5cc Marine Engine with 0.2mm Head Gasket, Silicone
Exhaust Seal, RP7 Turbo Glow Plug, two Dust Caps and Instructions


Glow Fuel: Boat blend with 10-30% nitromethane content, use 20% for
Exhaust system depending on boat
Glow plug igniter


Displacement: .21 cu in (3.5cc)
Bore: 0.640" (16.27mm)
Stroke: 0.661" (16.8mm)
Practical RPM: 4,000 - 45,000
Power Output: 2.75 PS, 2.71 HP @ 33,000RPM
Crankshaft Size: 1/4-28
Carburetor Settings:
Needle Valve; 1.5 turns from fully closed
Mixture Control Valve: Turn clockwise 10 to lean mixture or
counterclockwise to richen mixture, adjust in steps of no more
than 45-90
Distance between mounting hole centers same side: 0.83" (21mm)
Distance between mounting hole centers opposite side: 1.4" (37mm)
Distance/mounting tab to center of exhaust: 1.1" (28.5mm)
Distance/mounting tab to center of cooling inlet: 2.2" (55.6mm)
Distance from exhaust center to mounting flange bottom: 1.1" (28.5mm)
Width not including mounting flanges: 1.2" (31.6mm)
Width including mounting flanges: 1.8" (45mm)
Height bottom of crankcase to top of intake:
Height bottom of mounting flanges to top of intake: 2.6" (66.1mm)
Length from backplate to end of crankshaft: 3.4" (86.5mm)
Length from backplate to front bearing: 2.5" (64.5mm)
Length from crankcase center to front bearing: 1.7" (44mm)

jxs 05/24/11

– If you need more information, use these O.S. resources –
Click Here: Manufacturer's Product Web Page
Email: enginesupport@hobbico.com
Web Site: http://www.osengines.com/
Phone: 217-398-8970
  Postal Address:

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Accessories Needed
This is the O.S. 21XZ-M 3.5cc Inboard Marine Engine. FEATURES: Designed for 21 class boat racing, RP7 turbo glow plug, blue anodized cooling head REQUIRES: Boat blend fuel with 10-30% nitro content, exhaust system and shore equipment

Accessories for the O.S. 21XZ-M 3.5cc Inboard Marine Engine

Primary Accessories   Building & Field Equipment Optional Accessories
  Special Stock Number Product Description Parts Saver Eligible Tower's
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 LXK129 Great Planes Silicone Fuel Tubing Standard 3'
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2.99   In Stock
 LXRXC4 Tower Hobbies TOWER Power 10% Airplane Fuel Quart
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9.19   In Stock
Subtotal for this Group of Accessories: 12.18  
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Primary Accessories   Building & Field Equipment Optional Accessories

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