Archive for the ‘Engines’ Category

Fuel Magnet Failure

August 3rd, 2009 No comments

Despite the poor weather lately Sunday turned out to be a great day for flying and for once all the fleet was serviceable.

I was about half way through my first flight on the Aurora when I noticed some leaning and then fuel gushing out. After landing it was clear that the fuel stopper had been ejected mid-flight. Once the heli was back on the bench I then noticed the fuel filter had changed color from red to orange? As it turns out that was the remains of my OMI Fuel Magnet. This is the first time I’ve had one completely disintegrate on me, previously they have become a bit tatted and I’ve just replaced them. This one lasted about 9 months… this clearly explains why the fuel stopper was ejected. All things considered I was pretty lucky, it could have been a low inverted flame-out and/or a toasted engine.

Align filter caked with dead fuel magnet

Align filter caked with dead fuel magnet

I’m not suggesting fuel magnets are no good because I happen to thing they function very well (when they don’t disintegrate). I would only highlight that they have a limited shelf life, somewhere in the order of 6-12 months is my guess. And that is with the correct preventative steps, such as: running off back-plate pressure and re-filling the tank for storage.

I might list this post under reviews, as you can clearly see the “Align 3 Way Fuel Filter” exceeding expectations, for that I’ll give the filter a score of 8/10.

10 Aug 09

….and here’s the new replacement fuel magnet with Hayes Medium Clunk Line (neoprene) and small sections of silicon tube used to tighten the coupling of fuel-magnet. 

New Fuel Magnet

CY MP6-90 Now Available

June 26th, 2009 No comments

MP6-90 rumored to be in stores now


Review: OS91HZ with Cline Carb Modification

June 23rd, 2009 No comments

Anyone that’s been in nitro helis for a while knows of the OMI cline regulator mod for the OS91SZ, which works pretty well. For those that are concerned about engine performance this seems to be the more robust solution, as pumped versions of the engine have been known to break down.

Normally an OS91SZ has some of the pressure redirected from the exhaust back into the main fuel tank. In turn when the carb opens and the pressure from the tank forces the fuel through the carb. The more the carb opens the more fuel flows, simple. This system works okay but wont guarantee the same fuel flow for all orientations and through out an entire tank, particularly during aggressive 3D flight.

By comparison the cline regulated fuel delivery system uses pressure from the back plate to pressurize the tank (separated by a oneway valve), which is substaintially more pressurized then a normal setup. When the carb opens it creates a “suck” which pulls a diaphragm (like a scuba regulator) which proportionately opens the cline valve to allow pressurized fuel to enter the carb. The end result is a smoother running engine at any attitude which doesn’t lean towards the end of a tank. Also you don’t have exhaust fumes in the fuel tank which can eat cluck lines and fuel magnets.

What about the OS91HZ?

The OS91HZ in general is a far superior engine to begin with:

  • Redesigned performance head
  • Carb inlet hole on the crank is bigger
  • Crank is rebalanced
  • Port timing has been changed
  • Piston is lighter with a cut on the skirt for better fuel flow
  • Piston is ported on the top
  • Carb barrel is sealed with an o-ring
  • Carb mount clamps are sealed with o-rings
  • Carb has a thermal insulator

Needless to say the NON-pumped version runs great out of the box but wont give you the 3D edge. The pumped version however is designed for 3D flight and when the pump is functional it seems to perform really well. Unfortunately there still seems to be durability issues with new OS fuel pumps, already one person at my field has had one die. A cline regulated system by contrast, is simple, effective and has less parts that could fail.

Cline HZ Flight Performance

OS Check Valve (OS 72403061)Amazingly smooth and powerful, while not being too hot. The main needle is set quite low too, just over 1 turn and the mid at about 1.5 turns. Obviously those settings are not gospel but are working for me in the current UK weather (low 20c’s). I’ve been running this setup in conjunction with an OS check valve (OS 72403061) which works great. It is note worthy that the cline needs as much of the engine pressure as possible in order for the regulator to work correctly (not lean). To give you an idea, a typical YS has a check valve with about a 6PSI thresh hold (using a spring) by comparison the cline needs a thresh hold of no more than 2PSI. I have tried a YS check valve (the smalller 2 stroke one) and the engine definately runs hotter. I have heard removing the spring works well in the smaller YS check valve or using the larger 4 stroke YS check valve.

SZ Carb

My setup uses a stock new carb from an SZ which was cline modified already and had an insulator sleeve added to the carb in order for it to fit. I have another HZ which I’m about to break in which has the stock HZ carb cline modified, which I assume will be very similar in performance, I’ll report back on that soon.

OS91HZ with OMI Cline carb modification attached

OS91HZ with cline carb mod

OS91HZ - Cline modification


This is a great upgrade for your new OS91HZ if you are a die hard 3D pilot. You get the performance of a pumped engine with out the hassle.

Rating: 9/10

New OS55max HZ Engine

June 18th, 2009 No comments

Checkout this new bad-boy from OS. I’m not running a 50 size nitro heli at the moment…maybe I should look into it. The interesting thing about this engine is that it has 3 needles like the OS91, that is a major improvement in terms of tunability.

New OS55hz Engine

New OS55hz Engine

Also see:

Categories: Engines, General Discussion Tags: ,

How to Toast an OS91 Engine

June 16th, 2009 No comments

Only 4 easy steps for complete engine destruction:

  1. Mod the engine so that it is super high performance by putting a Viper Head and Cline regulator on it.
  2. Neglect to tune the engine even after a sufficient change in weather on a hot day.
  3. Fail to do anything other than replace the glow plug after 2 have been previously eaten.
  4. Continue to 3D the hell out of it to the point where the glow plug deforms and punches a hole through the top of the piston.

OS91 Hybrid with toasted piston

OS91 Hybrid with hole in piston

Categories: Engines, General Discussion Tags: