Saito 72 vs. O.S. 70 Surpass  
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Saito 72 vs. O.S. 70 Surpass - 6/21/2004 5:31:41 PM   
jongurley



Posts: 2798
Joined: 4/24/2003
From: Goldsboro, NC, USA
Status: offline 		Hey guys I am building a seaplane and want a fourstroke engine on it, never had much experience with 4 strokes, which of these two, the O.S. vs. the Saito 70's would you get and why... thx
       Post #: 1

RE: Saito 72 vs. O.S. 70 Surpass - 6/21/2004 6:48:26 PM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Jon:

Given the choice, always take the Saito over the OS. The Saito is lighter, less expensive, and more powerful. Or you can add $5 to the price of the FS-70 OS ($250) and get the Saito FA-82 ($255) and be even more powerful, and lighter yet.

Comparison:

FS-70, 20.7oz, $250
FA-72, 16.6oz, $225
FA-82, 16.0oz, $255

As I said, the win goes to Saito.

Bill.

_____________________________

Real Airplanes have Two Engines
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       Post #: 2

RE: Saito 72 vs. O.S. 70 Surpass - 6/21/2004 11:14:04 PM   
Mighty Mouse-RCU



Posts: 597
Joined: 2/9/2002
From: Picayune, MS, USA
Status: offline 		They are both great engines. It really boils down to weight. Some airframes need a bit of weight up front, so the OS may be the ticket. I too am a Saito fan, but have the OS 70 as well. You may get a better price than saito with a coupon from Tower.

(in reply to jongurley)
       Post #: 3

RE: Saito 72 vs. O.S. 70 Surpass - 6/22/2004 4:05:02 PM   
Waco Driver



Posts: 158
Joined: 1/16/2003
From: Paris, ON, CANADA
Status: offline 		Here is another opinion based on observations I have made while servicing Saito 72 & OS 70 engines.

1. The extra 4 ounces in the OS is due to the more robust castings used, the metal backplate versus plastic, and the larger diameter, more massive crankshaft. Should you be unlucky enough to stick your engine in the ground, you will unlikely bend the shaft on the OS.

2. When it comes time to decarbonize the exhaust valve and port, you will much appreiate the removable head. Cleaning the cylinder side interior of the port on Saito engines is a chore.

3. The camshaft helical gearing of the OS is more robust than the spur gearing of the Saito and much less likely to break teeth. Also the ball bearing mounted camshaft on the OS is a class act compared to the plain bushings in the Saito.

4. The OS connecting rod is bronze bushed at both ends whereas the Saito is not. You can safely run fuels with oil contents as low as 15 % with the OS without fear of rod bearing seizure.

5. The higher compression ratio on the OS allows it to run fine on cheaper 5% nitro fuel, whereas the Saito prefers at least 10%.

If you appreciate excellence in engineering, you will spend the extra and buy the OS.

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       Post #: 4

RE: Saito 72 vs. O.S. 70 Surpass - 6/22/2004 4:45:15 PM   
Pepe J



Posts: 511
Joined: 10/7/2002
From: Canada, BC, CANADA
Status: offline 		Ditto with Waco Driver. I have both engines. They both have their pro's & con's. The O.S. has more power (500+ RPM / APC 13x6) and the only black mark is the extra 4 oz of weight.

Other engines to consider are the new Saito 82, O.S. 70 Ultimate and the YS 63.

Happy Fly'n...

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"The Lord Listens, but Money Talks."

(in reply to Waco Driver)
       Post #: 5

RE: Saito 72 vs. O.S. 70 Surpass - 6/22/2004 5:20:27 PM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Don:

A rebuttal.

quote:

ORIGINAL: Waco Driver

Here is another opinion based on observations I have made while servicing Saito 72 & OS 70 engines.

1. The extra 4 ounces in the OS is due to the more robust castings used, the metal backplate versus plastic, and the larger diameter, more massive crankshaft. Should you be unlucky enough to stick your engine in the ground, you will unlikely bend the shaft on the OS.

All this means is that the OS is built to crash, the Saito is built to fly.

quote:

2. When it comes time to decarbonize the exhaust valve and port, you will much appreciate the removable head. Cleaning the cylinder side interior of the port on Saito engines is a chore.

This can go either way. The removable head allows decarbonization without disturbing the ring, but it adds higher machining costs and another joint with its possible failure. The actual decarbonization is not an issue, a quick soak cleans either. Note that FS piston engines have the heads welded to the cylinder barrels, in effect the same as Saito.

quote:

3. The camshaft helical gearing of the OS is more robust than the spur gearing of the Saito and much less likely to break teeth. Also the ball bearing mounted camshaft on the OS is a class act compared to the plain bushings in the Saito.
The helical gear drive is "Sexier" than the spur gear set, but helical gears also have greater power losses than spur drive. Also, ball bearings absorb more power than plain bearings, they are more trouble to replace, and while I have replaced cams in Saito engines none has ever been replaced due to bearing wear or failure.

quote:

4. The OS connecting rod is bronze bushed at both ends whereas the Saito is not. You can safely run fuels with oil contents as low as 15 % with the OS without fear of rod bearing seizure.

The jury is still out on this one. Saito used bushed rods for years, only in the past couple years have they switched to unbushed rods. But there is no indication of their needing any more oil than the earlier bushed rods.

quote:

5. The higher compression ratio on the OS allows it to run fine on cheaper 5% nitro fuel, whereas the Saito prefers at least 10%.

Bad argument. Neither is really happy with 5% fuel. How many people do you know actually using 5% anyway?

quote:

If you appreciate excellence in engineering, you will spend the extra and buy the OS.

If you appreciate excellence in engineering that's even greater than OS, you will spend a little less money and buy the Saito. And if you are satisfied with OS engineering save even more money and buy the same engine with a different brand name on it. And a chromed bore instead of nickel plating.

The OS multi cylinder engines are quite different, still excellent quality. I have no hesitation in recommending them.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

(in reply to Waco Driver)
       Post #: 6

RE: Saito 72 vs. O.S. 70 Surpass - 6/24/2004 2:48:48 AM   
jongurley



Posts: 2798
Joined: 4/24/2003
From: Goldsboro, NC, USA
Status: offline 		William Robison you are the man,,,, I appreciatte the heck out of all of the info guys....

(in reply to William Robison)
       Post #: 7

RE: Saito 72 vs. O.S. 70 Surpass - 6/24/2004 6:25:11 AM   
slagburn


 

Posts: 148
Joined: 9/22/2003
From: 5000 ft ASL, CO, US MINOR OUTLYING ISLANDS
Status: offline
quote:

ORIGINAL: William Robison
Note that FS piston engines have the heads welded to the cylinder barrels, in effect the same as Saito.
Bill.



Bill, what engine type are you referring to? That's a new one to me.

Personally I dislike the Saito one piece barrel and head arrangement. Well, I guess actually I'm neutral on it, since it hasn't cost me extra money yet. But I would like the option of replacing the cylinder only in the event of grime inhalation or similar.
Of course that one piece setup adds rigidity to the engine and decreases weight.

(in reply to William Robison)
       Post #: 8

RE: Saito 72 vs. O.S. 70 Surpass - 6/24/2004 7:05:51 AM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Jon:

Standard construction of aircraft cylinders for many years, at least in America, supplies the cylinders as a one-piece assembly of cylinder barrel and head, with incorporated rocker boxes.

The head is normally cast or forged in aluminum alloy with a steel ring where it fits on the top spigot of the cylinder barrel. In the machining of the head this sleeve is given internal threads to mate with the male threads on the cylinder spigot.

The cylinder is fully machined except for any cuts that depend on its circular position, such as the holes in the base flange for its mounting, or narrowed fins to clear an adjoining cylinder in a "Flat" engine.

The spigot threads are then smeared with a bronze metallic paste, the cylinder and head are screwed together, then the assembly is "Baked" to finish the bronze welded joint. And finally, the finish machine work is done, and you have a new jug.

At overhaul time it goes back in the oven, the old barrel is unscrewed and a new one put on tthe old head.

Picture attached is a jug for a Jacobs 300hp radial, from a Cessna 190.

Bill.

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< Message edited by William Robison -- 6/24/2004 1:06:46 AM >

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       Post #: 9

RE: Saito 72 vs. O.S. 70 Surpass - 6/25/2004 12:12:31 AM   
ShempHoward


 

Posts: 1147
Joined: 12/4/2001
From: San Francisco, CA, USA
Status: offline 		All the RC Magazine tests showed the OS 70 Surpass to be more powerful than the Saito 72 and more user friendly as well but about 3 ounces heavier than the Saito.

(in reply to William Robison)
       Post #: 10

RE: Saito 72 vs. O.S. 70 Surpass - 6/25/2004 1:39:46 AM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Shemp:

Not all the mags. They got the lighter weight and easier operation right in all cases, but the power was close, with the edge going to Saito.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

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       Post #: 11

RE: Saito 72 vs. O.S. 70 Surpass - 6/25/2004 2:57:35 AM   
jongurley



Posts: 2798
Joined: 4/24/2003
From: Goldsboro, NC, USA
Status: offline 		I am really neutral, I simply like the looks of the SAITO better, but I am still torn, I have noticed the Saito82 but I don't know anything as far as ratings etc...

(in reply to William Robison)
       Post #: 12

RE: Saito 72 vs. O.S. 70 Surpass - 6/25/2004 3:33:20 AM   
William Robison



Posts: 20269
Joined: 11/10/2002
From: Mary Esther, Florida, FL, USA
Status: offline 		Jon:

Even if the power were exactly the same, the quarter pound lighter weight of the Saito would make it effectively the more powerful of the two.

Bill.

_____________________________

Real Airplanes have Two Engines
AMA 25139 - More than 40 years.

(in reply to jongurley)
       Post #: 13

RE: Saito 72 vs. O.S. 70 Surpass - 6/25/2004 7:09:52 AM   
Richard L.



Posts: 8775
Joined: 7/28/2002
From: Redmond, WA, USA
Status: offline 		In most cases, the OS 70 will pull away from the Saito 72 on the same prop and fuel, and this is based on magazine tests and real world experience. The Saito 72 is only slightly stronger than the OS 70 when higher nitro is used.

(in reply to ShempHoward)
       Post #: 14

RE: Saito 72 vs. O.S. 70 Surpass - 6/25/2004 2:47:30 PM   
Waco Driver