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HelicopterEngines Plugs Mufflers Fuel › O.S. MAX-91HZ > PS or not?
03-17-2009 11:34 AM  8 years agoPost 1
nwolsink

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Ruurlo-Netherlands

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I am currently running an O.S. MAX-91SZ PS in my TREX700.
Although the engine is just fine I simply want to try a different one this year. I am sticking with OS so it will be an HZ off course.

The question is do I go for the pumped version or do I take the "stock" one?

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03-18-2009 08:39 AM  8 years agoPost 2
nwolsink

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Ruurlo-Netherlands

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nobody?

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03-18-2009 12:39 PM  8 years agoPost 3
Brendan78

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NSW Australia

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can't speak about he non pumped HZ, but the OS91HZ-PS is awesome, haven't had a problem with mine and it pulls like a frieght train, easy to tune as well.

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03-18-2009 03:26 PM  8 years agoPost 4
NitroPolymer

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Southeast Florida

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My belief is that less is more in this department. The HZ is a great motor that works perfectly without a pump in virtually any flight regime imaginable. Therefore, why add complexity when you can have the same or better results with no headache?

In short: The non-pumped version is the way to go.

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03-19-2009 08:53 PM  8 years agoPost 5
nwolsink

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Ruurlo-Netherlands

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Man, I just saw the TT Hemi (Redline 106) this is one bad engine!
Might just get this one!

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03-20-2009 04:21 AM  8 years agoPost 6
Brendan78

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NSW Australia

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Same or better results with no headache? not sure what headache your refering to? mine has given me no headaches at all straight out of the box and is simple to tune, sucks every last drop of fuel without any needle changes while pulling like a freight train, so i'm more than happy with it. I had the SZ-PS as well before this engine, the SZ-PS took some initial fiddling with to get to where it should be(Correct shimming to run on 30%), but it was fine after that also, the HZ-PS definately pulls through 3D a lot stronger than my SZ-PS did, it will pull a few more degrees pitch than my SZ-PS did.

My understanding is the two engines are slightly different out of the box as well (apart from the pump). The PS doesn't come with the extra shims to run 30% as it will run it out of the box. The non pumped motor has a heat sink on the backplate, and I think possible the internals are slightly different too but someone can else can elaborate on the exact differences.

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03-24-2009 03:03 PM  8 years agoPost 7
nwolsink

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Ruurlo-Netherlands

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from what I understood the internals were the same, anyone???

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03-24-2009 04:31 PM  8 years agoPost 8
Santiago P

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South West, Ohio

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If you look at the parts list, they are the same numbers!

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03-26-2009 12:27 AM  8 years agoPost 9
Costas

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Adelaide - AUSTRALIA

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Carby internals on the pumped HZ are totally different and the combustion chamber is different on the pumped HZ as well - Note different part numbers between the 2 heads.

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03-26-2009 03:28 AM  8 years agoPost 10
Brendan78

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NSW Australia

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That's what I thought, thanks Costas.

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03-26-2009 04:40 AM  8 years agoPost 11
cdrking

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Seattle

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Carby internals on the pumped HZ are totally different and the combustion chamber is different on the pumped HZ as well - Note different part numbers between the 2 heads.
Can you list the differences?

Jeff

To hover is divine, the alternative is rather PLANE.

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03-26-2009 06:28 AM  8 years agoPost 12
Costas

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Adelaide - AUSTRALIA

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Here are the critical differences between the HZ and the HZ-PS: Note that I have both of these motors and their respective manuals. You can also download an exploded pdf view from the OS website for these two motors and have a look as well.

Heatsink Head HZ OS Pt No 29074000
Heatsink Head HZPS OS Pt no 29074020

Carby Rotor HZ 29085200
Carby Rotor HZPS 29183210

Mixture Control Valve (carby spray bar effectively) HZ 29085510
Mixture Control Valve HZPS 29181630

There are a few other minor differences but the ones listed above are the 'Mission Critical' ones.

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03-26-2009 10:36 AM  8 years agoPost 13
nwolsink

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Ruurlo-Netherlands

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@ Costas, which engine do you prefer?

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03-26-2009 10:58 AM  8 years agoPost 14
Costas

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Adelaide - AUSTRALIA

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I have not had a chance to run the non pumped HZ but have been running the pumped version in my 3D machine since early Jan this year with no problem. The non pumper has been installed in my scale machine which is not quite finished as yet.

There is another guy at our club running a non pumped HZ and that seems to be working really well out of the box but on 20% nitro.

The only area where the pumped version will be better at is pretty much where you run down the main tank and notice the engine normally run a tad lean (not a great deal though).

ATM my HZ-PS is running real sweet out of the box on 30% nitro. Definitely has more power than my previous SZH-PS.

BTW - I did forget to mention that the pump is a different pump compared to what was fitted on the older SZH-PS motors. The new pump has more screws fitted around the case (possibly sealed better?) and it is meant to flow fuel at a higher rate as well.

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03-26-2009 05:00 PM  8 years agoPost 15
cdrking

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Seattle

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Costas,

Yes the pumps are different from the SZ and the HZ pumped. The SZ has the PD-07 pump and the HZ has the PD-08 pump.

What would be interesting is to see the parts of each engine side by side. I realize part numbers are different but understanding why they are different and what they actually look like would be cool.

If you wouldn't mind taking apart both your engines and posting the pictures that would great.

I have the non-pumped HZ with a fuel magnet and it works excellent. I think I may try the HZ with the cline setup since I have the carb and back plate already. I really like not using muffler pressure.

Jeff

To hover is divine, the alternative is rather PLANE.

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03-28-2009 08:28 AM  8 years agoPost 16
Costas

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Adelaide - AUSTRALIA

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If you wouldn't mind taking apart both your engines and posting the pictures that would great.

Actually just download the exploded view PDF's to give you a basic idea.

The important bits: Bearings, Crank, Rod, Gudgeon Pin, Piston and Ring are identical (same OS part numbers) between the two.

Jeff - Give it a go without the Cline setup - Many pilots are reporting favourable feedback on both of these engines as they are out of the box.

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03-28-2009 04:06 PM  8 years agoPost 17
cdrking

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Seattle

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I'm running a stock HZ now and I may try the cline, I am a fan of a system without muffler pressure.

The stock HZ is extremely smooth and powerful.

Jeff

To hover is divine, the alternative is rather PLANE.

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