Stratus and OS SZ / YS91 Instead?? - **The Result!**

[Aviation addict]

Guys,

Can a Stratus work with a Pumped SZ? I seem to be having a lot of vibration issues - indicated by a foaming tank (once again) which I'm putting down to 'engine alignment'. I've wasted gallon after gallon trying to get it right.

I'm also suspecting that either the pump or regulator are not functioning properly now on engine settings that were fine a few weeks back.

Could anyone lay out the symptoms and how to fix either a pump or regulator that is not performing 100% please.

There seems to be a lot of fuel all around the main base plate and it's very hard to tell where exactly it coming from, but I think it's more than just fuel spitting out of the carb. In addition, I've richened up my settings (half a turn) but the engine seems to be displaying signs of lean running.

In one climb out to do an Auto the engine faulted enough that I thought it wouldn't just be a practice Auto. Once safely on the ground, I packed up for the day.

Any help as always would be gratefully received.

PS How reliable are the Pumped SZ's? I'd consider selling this engine and replacing it with a YS91 if they are smoother running engines.

(PPS At 1800 - 1850 headspeed, the tail seems to kick and there's almost a metallic morse code type noise (sounds like gearing/clutch/fan). The fan is dialed to 1/2 a thou by the way and the clutch gap 0.030. Any ideas?)

[WayneBrown]

There are people experimenting with this motor/chopper combo, and for the moment the consensus is that the crankshaft is improperly balanced for the stratus.
Not saying the crank is so far out that other machines are having trouble, but it appears the stratus mounting method and the SZ are incompatable.
FWIW: fuel foaming introduces air to the fuel, and causes a lean-out.
Models that have a conventional mounting block are not seeing these issues to this extreme.

[Zilly]

Hang on :badair: is this now official I have just bought a stock SZH which I am having clined by OMI should I not bother ?

I thought there were a lot of people running the SZH without any problems?

z

[Aviation addict]

Thanks Wayne.

Can I ask how many Stratus owners have tried SZ's and how many have YS91's? Does the YS91 really run smoother than the SZ?

I've had nothing but trouble with 'my' SZ, but have been putting it down to something I've done wrong. If on the other hand I'm up against it and unlikely to ever get a smooth running heli I may as well stop wasting fuel and make the change to YS.

Should the Stratus only be fitted with a YS or say C-Spec?

[WayneBrown]

call it 'back channel' information.
Many are choosing to hold on to the old C-Spec's.
My personal preference is YS because I HATE tuning. SZ's with OMI upfits still are running inconsistant, the opinion is foaming issues.
If someone were to implement a different mounting method to the SZ in a Stratus, we could define further what's going on. (hint, hint)

[bob00]

Aviation addict:

Yes, the YS 91 is a MUCH smoother, consistent running motor than the OS SZ - always have to be touching needles on the SZ. The SZ does produce WAY more power though.

- R

[Aviation addict]

Is the power difference between the SZ and YS that noticeable?

I've been looking (just out of interest - at the moment) at the YS91 ST4. Could anyone tell me how the power output compares with the SZ and at what RPM this max power occurs.

Would I have to change my 8:18 ratio?

[ChrisLaFollette]

The YS would probably work with 8.18 gearing if you ran a little higher headspeed to put the engine in its RPM range. The 8.45 is usually best for the YS 91 engine... it allows it to recover faster because the gearing is steeper.

[Jaguar]

I've read about this problem a lot but still can't understand i have 2 stratus a fury tempest and a fury extream all have the OS 91 szh except for the extream NONE of the heli's vibrate the extream has a ys91 in it and may be a little smoother but just a little i don't know your building skills but everyone of the vibe problems i've fixed in other X-Cells for people has been either fan bal, runout, or alignment. O 1 of them had a bad auto hub the bearing had very small pits in it it was'nt oiled properly

[Rada70]

This is not good news for me. I just pulled out my YS, and replaced it with SZ w/cline in my stratus.

[NolanManley]

This is not good news for me. I just pulled out my YS, and replaced it with SZ w/cline in my stratus.

From what I've heard the Cline setup cures the OS problems and that's ALL the OS 91 current engine models

[goitoibayvoi]

check your regulator . ( see leaking ) i have 2 os 91 szh ps..
they all leaking .
just now replace the whole thing ..
with carb and reg ... now working ok

[Aviation addict]

i don't know your building skills


I balanced the fan on a high point balancer / dialed the fan onto the engine to 1/2 thou / balanced the T/R assembly and followed the manual exactly. Through faffing with the engine alignment I have managed to get the tank to stop foaming vigerously (in the past) and reduce to a light foam but I've not yet seen my heli fly as well as friends of mine Fury Experts. Do your Strati with SZ's do any foaming at high headspeeds?

[Aviation addict]

If my Regulator is leaking - can I just replace the reg or its internal parts (rather than the whole Carb? I haven't dare take it apart - so don't know whats in there.

[Rada70]

Mine produced so much foam in the new tank I installed. However, when I increased the thikness of the double sided tape, it reduced the foaming.

[Gary O]

I have Stratus' with YS, C-Spec/OMI, and one with the OS SZ/OMI. The YS Stratus and the C-Spec OMI Stratus are the ones I fly the most because even though the OMI is on the SZ it still needs tweaking when I go to fly it. I hate that. For me, the power difference isn't worth the trade off for ease of use. No, the YS doesn't have the pop that the OS has, but I can't fly like the top pilots in the world so I don't notice it nearly as much as they would. If you're trying really hard loading 3D a foot off the deck, then you need that extra pop of the OS to help recover the heli. While I fly low, I don't fly that low so I don't notice it.

[Jaguar]

No I have no fomming in the tank when mine are idleing you can put your hand on the head and barely tell their running when i built my first one i had a lot of problems with vibes and tail twitches i worked with it a lot and got them all out that is why i said fan balance, runout, and alignment are very importent my problem happend to be alignment so what i now do is after it's all built and ready for 1st hover i loosen the 4 screws on the slide mount start the engine bring the motor to a high idle to seat the ball and cluch driver shut it off and tighten the screws in an x pattern then i remove them 1 at a time to loctite them i've now built 4 stratus using this method and it seems to work well the gap is .020 all the way around but it is true that the ys is a little smoother i run my stratus at 1920 by the way

[Aviation addict]

Is it worth buying the OMI Viperhead for the YS, as I'd be looking for ultra smooth running (if I decide to go that route)? I've read that while the Viperhead does not really make much difference to the SZ, it seems to further smooth and give more power to the YS.

Got the heli in bits AGAIN (all I ever seem to do) having another inspection of everything. Haven't spotted anything wrong though. Run out still just over 1/2 thou.

[Alfred]

YS91, Hatory 937
I have just installed the new Stratus tank.
Before I had slight fuel movement but not foaming. As the engine has had just 7-8 tanks through it at a very rich setting, my guess was that it was caused due to the engine not being run in yet.
But since carefull installation of the new tank, the fuel is now dead calm.
I have to guess the rpm but used both normal and idle up.
Best guess was the range to be around 1650-1800rpm.

[Aviation addict]

What is the correct headspeed to put the YS in its powerband with the 8:45 ratio?

Would an SB18 work well, and fit the YS?

[Zilly]

I run about 1850 in idle 2

about 1700 in idle 1

and about 1600 in normal

[Alfred]

John
Why do you want to use a SB18 that requires 30% Nitro?
Use the 937 and run 20% unless you are a 3D Expert that requires every bit of availeble horse power.
Install the new tank carefully, run the YS91 in gentle and after 15-20 tanks start tuning the engine properly and you end up with one hell of a combo.

[DavidH]

SB 16 is the muffler for the YS 91.
SB 18 will not fit the YS. SB 17 and 18 only have bolt pattern for the OS in the header.

David

[david.read]

John,

I have an SB 16. But i'm not sure your 18 would be good on my OS 70 :dontknow

L8R

David

[heliroller]

I have two Stratus's with OS SZ91's running muffler pressure. Both run great now and smooth. Initially, the first Strat was foaming the tank and breaking various bolts(mostly during tic tocs). It did appear to vibrate a bit looking at the tail. It took about 2+ gallons of fuel for this engine to settle in. I had thought maybe there were balance issues but kept working with the engine to smooth it out. I run a fairly high head speed(1900-1925) and this combo seems to like it very well. If there is a crank balance issue, it may require varying the headspeed a bit to get the best rpm range on the engine. The new SZ does tune differently than the C-Spec and break in is different. Just my opinion.