Electric Motors, Engines & Accessories > Engines Glow Fuel > Engines R/C Glow Fuel Helicopter 2-Stroke - .52 & Up Bookmark this Page

O.S. - OSMG1974 OSM18650 18650 531028020535 4531028020535
Manufacturer Stock#
A Closer Look at This Product
  Tech Notes

Accessories Needed

Replacement & Optional Parts

Easy RC: Engines

Browse O.S.

O.S. 91HZ Ringed Helicopter Engine
Click for parts for this item
O.S. 91HZ Ringed Helicopter Engine
View Larger Picture

Tower Catalog Page: 198

Stock Number
Stock Status

Tech Notes
This is the O.S. .91HZ F3C Competition Helicopter Engine.


Designed specifically for F3C aerobatic competition
Rectangular heat sink allows engine to be enclosed entirely inside
cooling shroud
61-E carburetor with thermal insulator to block heat and a needle
valve control lever to control mixture from transmitter, carburetor
has three adjustment controls that enable independent adjustment at
idling, hovering and high speed
Five holes in the top of the piston route gases to the piston ring
from within to form a tighter seal with minimum blow by
Ball bearing supported crankshaft
Heat sink type backplate
Two year limited warranty through Hobby Services beginning at date of


O.S. .91 HZ F3C Competition Helicopter Engine with #8 glow plug,
needle control lever, extra 0.2mm head gasket, cap screws and
instruction manual


Fuel: 10%-30% nitromethane with at least 18% lubricant. Lubricants
may be either castor or synthetic oil or castor/synthetic blend.
Field Equipment: glow starter, fuel bulb, fuel can filter, fuel pump
hexagonal starting shaft (depending on brand of helicopter)
electric starter, battery and fuel tubing
Muffler-Depending on heli


Displacement: 0.91 cu in (14.95 cc)
Bore: 1.09" (27.7mm)
Stroke: 0.98" (24.8mm)
Output: 3.4 PS, 3.35 HP @ 15,000 RPM
Practical RPM Range: 2000-16,000
Weight Without Muffler: 1.36lb (618g)
Crankshaft Size: 5/16-24
Height from crankcase bottom to top of cylinder head: 3.9" (99mm)
Height/bottom of mounting tab to top of cylinder head: 3.2" (81.2mm)
Distance between mounting holes same side: 0.98" (25mm)
Distance between mounting holes opposite side: 2.04" (52mm)
Distance between muffler screw holes: 1.6" (42mm)
Distance/bottom of mounting tab to muffler screw holes: 1.7" (42.8mm)
Length from front bearing to backplate: 3.3" (84mm)
Length from backplate to end of crankshaft: 4.9" (125.6mm)
Width of crankcase below mounting tabs: 1.7" (43mm)
Width between mounting tabs: 2.4" (61mm)

Carburetor Needle Settings:
High Speed: 2 turns out from fully closed
Mid Range: 2 turns open
Mixture Control (low speed): indentation on screw head straight up
and down (vertical)

jxs 10/14/10

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

Click here for Units of Measure Conversion Calculators

Accessories Needed
This is the O.S. .91HZ Heli Engine with 61E Carburetor. FEATURES: 61-E carb w/needle valve control lever, ball bearing supported crankshaft, #8 glow plug, 0.2mm thick head gasket REQUIRES: 10%-30% nitro with at least 18% castor or synthetic oil or castor synthetic blend, glow starter & field equipment

Accessories for the O.S. 91HZ Ringed Helicopter Engine

Primary Accessories   Building & Field Equipment Optional Accessories
  Special Stock Number Product Description Parts Saver Eligible Tower's
Low Price
Click to Order Quantity Needed In Cart? Stock
 LXK129 Great Planes Silicone Fuel Tubing Standard 3'
Qty Discount Available
2.99   In Stock
 LXK134 Great Planes Ultra Precision Fuel Filter
Qty Discount Available
3.79   In Stock
 LXL387 Hobbico 4-Way Wrench w/Plug Storage
Qty Discount Available
4.99   In Stock
Subtotal for this Group of Accessories: 11.77  
Click to Order all items listed in this Group of Accessories    Buy This group of Accessories

Primary Accessories   Building & Field Equipment Optional Accessories

Tower Hobbies Has Been Serving Hobbyists Since 1971 • Call 800-637-6050 or 217-398-3636
See Tower Hobbies Reviews at Bizrate.com
Hobbico, Hobby & Model Construction Supplies - Retail, Champaign, IL
We accept the following: We accept the following payment methods: Discover, MasterCard, Visa, American Express, Diners Club International, JCB, China UnionPay, PayPal, and BillMeLater.
Unauthorized use of any materials presented here is prohibited. Copying or reproducing any elements from this page is not permitted. All prices, descriptions and availability subject to change. Displayed within some areas of our web site, the Retail Price is suggested by the manufacturer or supplier, or estimated in keeping with standard industry practice. It may not represent the prevailing price in your area or a price that Tower Hobbies has ever offered for the item.
Copyright © Tower Hobbies All rights reserved. Do not duplicate or redistribute in any form.