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2SI 690 use it?

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DaveK

Well-Known Member
Joined
Apr 21, 2007
Messages
357
Location
Northern California
I am contemplating buying an unassembled kit that comes with a supposedly unused 2SI 690 engine with reduction box. If this thing really is unused and can be cleaned up (new gaskets, hoses, etc) is it worth using it? I figure if I can get a couple hundred hours out of it I’d be happy. But, I don’t want to waste time it if it will just be an issue. I don’t know much about the 2SI engines, except they stopped selling the aircraft versions of their engines.
 

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,300
Location
AMES, IA USA
I would replace all Gaskets & Seals, Carb Boots, Fuel Line, Fuel Pump, Fuel Filter.

2si 690

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2si 690
Type
Two-stroke aircraft engine
National origin United States
Manufacturer 2si
The 2si 690 is a family of in-line three cylinder, liquid-cooled, two-stroke, dual ignition, aircraft engines that were designed for ultralight aircraft.[1]

The basic engine was originally designed and produced by JLO-Motorenwerke of Germany and was later acquired by the AMW Cuyuna Engine Company of Beaufort, South Carolina and marketed under the Cuyuna brand name. Later the engine was marketed by Cuyuna under the Two Stroke International (2si) brand. Cuyuna no longer markets engines for aircraft use although the 690 is still in production as an industrial and marine engine.[1][2][3][4]

Contents
Development[edit]
The 690 is a conventional three-cylinder engine that weighs 89 lb (40 kg) in its L70 aircraft and marine versions. The aircraft engine features dual capacitor discharge ignition (single in the marine and industrial versions), reed valve porting, tuned exhaust system, three slide venturi-type carburetors, liquid cooling, fuel pumps, a cast iron cylinder liner, ball, needle and roller bearings throughout. The aircraft version was offered with an optional gearbox reduction dive system and a centrifugal clutch. The current industrial and marine version has an available gearbox with ratios of 2.04, 2.65 or 3.06:1. Starting is electric start only.[1][3]

Variants[edit]
690-L70 aircraft engine
Gasoline aircraft engine with triple carburetors, 70 hp (52 kW) at 6250 rpm, weight 89 lb (40 kg), out of production.[1]
690L-70 industrial and marine engine
Gasoline industrial and marine engine, triple carburetors, 70 hp (52 kW) at 6250 rpm, weight 89 lb (40 kg), electric starter mounted on the accessory cover end. Still in production.[3][4]
690AL-70 industrial and marine engine
Gasoline industrial and marine engine, triple carburetors, 70 hp (52 kW) at 6250 rpm, weight 89 lb (40 kg), electric starter mounted on the power take-off end. Still in production.[3][4]
Applications[edit]
Aircraft
Specifications (690-L70 aircraft engine)[edit]
Data from Cliche[1] & 2si[3]

General characteristics
  • Type: Three-cylinder, two-stroke aircraft engine
  • Bore: 69.5 mm (2.74 in)
  • Stroke: 60 mm (2.36 in)
  • Displacement: 684 cc (41.7 cu in)
  • Length: 21.6 in (549 mm)
  • Width: 19.05 in (484 mm)
  • Height: 13.9 in (353 mm)
  • Dry weight: 89 lb (40 kg)
Components
  • Valvetrain: reed valve porting
  • Fuel type: Minimum 92 octane
  • Oil system: premixed oil and fuel at 50:1
  • Cooling system: liquid cooled
  • Reduction gear: optional gearbox
Performance
  • Power output: 70 hp (52 kW) at 6250 rpm
  • Fuel consumption: 5.1 US gal/h (19.3 l/h) at 75% power
 

Monty

Well-Known Member
Joined
Jul 15, 2010
Messages
1,294
Location
Fayetteville, AR / USA
I have a good friend that flies a PPC with a 2SI motor. He swears by them and has been using them for at least 20 years. Lower output, but reliable. Parts are still available, and they are easy to rebuild. I'd go through it, break it in properly and run with it. Make sure you understand how to operate it properly. Make sure the carbs are balanced and EGTs are close together. The biggest problem is people chopping the throttle abruptly when the engine is hot at full throttle...though water cooled engines are not as susceptible to that problem. Still good practice not to do it.
 

DaveK

Well-Known Member
Joined
Apr 21, 2007
Messages
357
Location
Northern California
I have a good friend that flies a PPC with a 2SI motor. He swears by them and has been using them for at least 20 years. Lower output, but reliable. Parts are still available, and they are easy to rebuild. I'd go through it, break it in properly and run with it. Make sure you understand how to operate it properly. Make sure the carbs are balanced and EGTs are close together. The biggest problem is people chopping the throttle abruptly when the engine is hot at full throttle...though water cooled engines are not as susceptible to that problem. Still good practice not to do it.
Exactly what I needed to know. Thanks!
 

Protech Racing

Well-Known Member
Joined
Jul 10, 2020
Messages
86
I used a 440 2SI for 150 HRs or more. Synthetic oil and check the rings through the exhaust port evry 20 hrs.
 
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