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HelicopterEngines Plugs Mufflers Fuel › YS 91 SR-3DS CHECK VALVE?
02-23-2014 05:59 PM  3 years agoPost 1
HeliViewAerial

rrNovice

Ormond Beach, FL

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Hey guys, kinda new to the nitro thing (or YS engines to be more precise) so please forgive me...

So this motor was broken in correctly and never "abused", VERY clean!! When I put the motor in the heli I realized there was no check valve so I bought one. NOT the YS cv, but just some "airplane" one-way check valve or something... The motor fired right up and was very smooth. My buddy who knows 3-valve nitro motors very well was trying to help me tune it. The compression was very hit/miss, flooding easily. As I took it into hover it seemed fine for about 3 minutes then started to get hot (lots of smoke still though) and shut off, auto'd down and I posted that flight on YouTube actually. I never told him it was some random RC check valve, would that be my problem? Do I need the YS Brand Check Valve or will any ol' RC nitro motor cv work? After it overheated, it wouldn't fire back up and seemed to have lost a lot of compression while def still getting fuel (cv was still "working" too). Since it was smoking fine (not too rich though) I highly doubt I fried a ring but that's not my concern at the moment. Thanks guys!!

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02-23-2014 08:01 PM  3 years agoPost 2
crflyer

rrApprentice

Maine

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You need to use the correct YS check valve for the 91
its part number - YS2510 CHECK VALVE.
The engine will run to lean with out it.

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02-23-2014 08:44 PM  3 years agoPost 3
HeliViewAerial

rrNovice

Ormond Beach, FL

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THANK YOU SO MUCH!! I just ordered three if them and new bearings, ring and gaskets just in case!! Thank u for part # by the way

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02-26-2014 09:18 PM  3 years agoPost 4
ticedoff8

rrKey Veteran

Morgan Hill, CA. USA

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Assuming the 1-way valve was okay at the start of the flight, when the 1-way check valve fails and blocks the crankcase pressure (fails closed), the pressure in the tank will drop as the fuel is consumed.

But, if the 1-way was never working to begin with, then the tank is at ambiant pressure at the start of the flight, and the engine keeps sucking fuel out and builds a vacuum in the tank.

Either way, the needle settings will go from "ok" to "too lean" as the pressure drops off and the vacuum builds.

If it fails "open", then it is like a direct connection from the backplate nipple to the tank's vent nipple. This could flood the engine's crankcase with raw fuel being sucked in from the tank on the piston's up-stroke.
This is not as bad as the "failed close". At least the tank is vented and not building a vacuum. But, you may not realize the 1-way is failed open - you just readjust the needles because suddenly it is running a little leaner than it used to.

The OS and the YS 1-way check valves are the same and interchangeable.
Keep the line from the backplate to the 1-way short - no more than 1". And use stiffer than "normal" fuel tubing - flexibility is an enemy.

Blow through the 1-way - it will open and will let air flow in 1 direction, and block it in the other (it might take a lot of "mouth pressure" to get it to open).
Remember: the air flows from the backplate to the tank, so the 1-way has to be oriented correctly.

You know you are in good shape when, at the end of the flight, you open the vent line and you hear a big "whoosh" as the extra pressure in the tank is allowed to escape.
You get used to hearing that. If you don't hear it, then stop and figure out what is wrong.
No pressure in the tank at the end of the flight means trouble.
If you had the presence of mind to check that after your engine-out autorotation, you could have known if there was good tank pressure or not and where to look for the engine failure.

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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02-26-2014 10:39 PM  3 years agoPost 5
crflyer

rrApprentice

Maine

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[quote]
Tube(C)should be set exactly at 3 15/16” or (10cm) between the engine and check valve. DO NOT use any other type of check valve.

This is from the YS 91sr engine manual.
Ive run many YS engines over the years and have never had any problems with the way YS says it should be set up.
If there is a problems with the way the engine runs with this setup most likely there is a fuel line leak some where or an exaust leak.

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HelicopterEngines Plugs Mufflers Fuel › YS 91 SR-3DS CHECK VALVE?
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