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OS 120 Surpass : to pump or not to pump

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OS 120 Surpass : to pump or not to pump

Old 12-11-2002, 09:42 PM
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KrisG
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Default OS 120 Surpass : to pump or not to pump

I have the occasion to purchase an unused OS 120 Surpass, without the pump, or a Surpass II with integrated pump ( but used, and now on the shelf for 3-4 years). I thought the better idea was to buy the unpumped one, and add a Perry Oscillating pump, rather than buy the pumped one, with the risk of having problems with the more complex mechanics that have been resting/rusting for years now.

Any ideas, opinions or suggestions?

The Perry Oscillating pump seems like a nice alternative : if it breaks, I replace it. If the integrated pump breaks, I have expensive repair costs to pay.

Kris
Old 12-11-2002, 10:19 PM
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MinnFlyer
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Default OS 120 Surpass : to pump or not to pump

I have heard some not so good things about the 120 w/pump. I really can't elaborate, and I will repeat that this is only hearsay.
Old 12-11-2002, 10:46 PM
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LQUAN
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Default OS 120 Surpass : to pump or not to pump

Good question. I don't have any OS120FS in my inventory, yet. I am thinking of getting one for my next project. However, I have three OS91FSII w/pump. The first one I bought was almost 2 years ago. It still seem to work fine. Now, whether the pump is still working properly or not, I can't tell. The pump unit on the OS 4-stroke is setup to deliver fuel whether the pump is still working or not. The muffler on this engine has a fitting hole for the muffler pressure fitting, this hole is coverred up with screw when you buy an engine with pump. I put a fitting valve in place a the screw and ran a line to the fuel tank for my engine. This is sort of a double pump setup. The engine has a fuel regulator, so, 1 or 2 pumps won't change the fuel rate input to the engine.

The down side of buying an OS 4-stroke with pump is that you have to shell out an extra $80 for a .91 or $30 for a 1.20. The replacement pump is $60 for both. I am thinking the same way as you do; use a $25 Perry VP-30. I haven't read any complaint on the VP-30, yet. For my next OS91FS, I will get the VP-30 instead. For the OS120FS, I am still incline toward the OS pump since the price difference is only $5 and I don't have to mess around with drilling and fitting a $3 fitting valve to the engine back cover to save $2.

Both the OS pump and the Perry's pump work on the same principle. The mechanic on the OS pump is not complex, just a membrane diaphram sandwitched by the front and back cover. They all made out of polymer; therefore, no rust. The only time these pumps failed is when the flexible membrane diaphram get torn due to age. Oh, do use a filter before these pumps because you can't open them up to remove the debris.

I would never fly my $1000+ and 1000hrs+ warbird with an engine that has no pump and on-board glow driver.
Old 12-12-2002, 06:50 AM
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KrisG
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Default OS 120 Surpass : to pump or not to pump

Hi LQUAN,

Can you really install a regular Perry pump on a 4-stroke? I thought this was not possible due to the vented crankcase ( so not much pressure changes in the crankcase). I was planning to use the oscillating pump, which works with engine vibration. I used one on a 2-stroke with success for a couple of years. I was definitely planning to use muffler pressure, as I do on all my 2-strokes.

The 2nd hand pumped engine that I am considering saw very little use, but was then shelved for a couple of years. I am afraid the membrane may have gone bad on that one ( fuel on it + age).

What fuel do you use? I normally make my own mix, and was planning to make 16% synthetic + 5 or 10% nitro. All my 2 strokes run very well with 6% castor, 12% synthetic ( Castrol MSSR) and 2-3% nitro for sport flying. I am sure a 120 is quite thirsty.

What prop ( brandname and size) for this first generation Surpass, if I use it on a Goldberg Ultimate or Extra?

Kris
Old 12-12-2002, 09:41 PM
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LQUAN
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Default OS 120 Surpass : to pump or not to pump

I saw a few heli guys at my field installed VP-30 to their OS91FSs. However, I recall reading some posts on rcuniverse that it is not effective compare to the oscillation version. I will try to do more research. About the propeller size for OS91FSII, I use 14x7 and 13x8. 14x8 would work, too. For the OS120FSIII I am planning to use 14x9-3-blade. This propeller seems too large for a OS120FSIII, but I am going to mount it on a TF P-40E. In case you wonder, the TF P-40E has a 4" spinner which take off a considerable amount of propeller blades when attached. I figure the 14x9-3-blade will ended up as 13x8-3-blade when attached to a 4-in spinner, which is about the manual recommended size.
Old 12-12-2002, 11:59 PM
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rajul
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Default OS 120 Surpass : to pump or not to pump

The OS carb is not the pressure type. Isn't it better to use the VP-30 with a cline regulator ?
Old 12-13-2002, 12:18 AM
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LQUAN
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Default OS 120 Surpass : to pump or not to pump

The VP-30 has a regulator built in. You don't need a Cline regulator at the carburator. I figure the VP-30 would work on the OS 4-stroke, because the OS pump is nothing more than a flexible membrane diaphram that move back and forth as the pressure inside crankcase housing changes. When the piston moves up, it sucks the diaphram forward, when the piston moves down, it blows the diaphram backward. The other side of the diaphram would has a pumping effect that draws the fuel to the regulator. The regulator has a one-way check valve to prevent the pump from drawing the fuel back when the diaphram changes direction.

KrisG, one way to test the pump unit on your OS is to, first, remove it from the engine. Put a small clean fuel line to the inlet nipple, block off the outlet nipple with your finger, and use your mouth to blow into the inlet via the fuel line. If air comes out of the engine crankcase nipple, you'll know that the diaphram is broken.

If there is someone else who has different knowledge on the design of the OS pump, please jump in.
Old 12-13-2002, 01:53 AM
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Default OS 120 Surpass : to pump or not to pump

Originally posted by LQUAN
The VP-30 has a regulator built in. You don't need a Cline regulator at the carburator
FWIW, there's some good discussions on the perry and cline and how to get a better transition. See http://www.rcuniverse.com/showthread...ght=perry+pump]

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