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NGH 38CC 4 stroke

Old 11-11-2015, 08:36 AM
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Originally Posted by Erwin Z
hello,

after 3 tanks consumed on the ground I am planning to maiden my 25% Hangar9 J3 this coming weekend, my concern is the max RPM, with a MA 18x10 classic series, I get roughly 6200 rpm at WOT, it seems underpowered, is that ok? or can I do something to get more output, I will apreciate your comments

cheers Erwin
That seems about right for an 18x10. Haven't run mine on that prop I use a MA Classic 18x8 and that gives me 6600. Plenty of power to haul my 80inch Ugly Stik round. A club member runs his on a 17x8 APC. It seems very happy and gives about 6700. If you are worried try less pitch.

One thing we have both found is that the engine idles better on a heavy prop like the MA series. Originally ran them on wooden props but idle was high and inconsistent. I put that down to lack of 'flywheel' with the lighter props.

One thing - have you read back through this forum and checked all the issues others have found with their engines - timing; valve settings, carb issues etc?
Old 11-11-2015, 09:13 AM
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Originally Posted by DoctorG
That seems about right for an 18x10. Haven't run mine on that prop I use a MA Classic 18x8 and that gives me 6600. Plenty of power to haul my 80inch Ugly Stik round. A club member runs his on a 17x8 APC. It seems very happy and gives about 6700. If you are worried try less pitch.

One thing we have both found is that the engine idles better on a heavy prop like the MA series. Originally ran them on wooden props but idle was high and inconsistent. I put that down to lack of 'flywheel' with the lighter props.

One thing - have you read back through this forum and checked all the issues others have found with their engines - timing; valve settings, carb issues etc?
well it sounds reasonable based on your numbers, I saw one video on youtube where someone got 6800 or so with a 18x10 prop and mentioned he moved the timing.

I have read randomly this thread, some talk about timing issues, so I wonder If stock setup needs to be changed, I got my engine from HobbyKing more than a year ago. from the beggining seemed to be a good engine, idle is so smooth a really low RMPs, so my only concern is it's max output, gess my Cub wont need so much power to fly anyways
Old 11-11-2015, 10:44 AM
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Well... those figures do seem a little low. I was getting around 6900-7000 rpm with a XOAR laminated 18 x 8. The laminated XOAR is quite heavy. I am running a beechwood XOAR 18 x 8 on the Waco and pulling 7200 rpm on the ground. The beechwood prop is lighter, I prefer the laminated prop, but I have found them hard to get.

It may depend on environmental conditions.

Regarding timing, I don't believe NGH have made any changes to the position of the pick-up, or the programming of the electronic ignition. It is true that you will drop top-end rpm if you re-position the pick-up so that the spark is coming later (closer to TDC). I noted a drop of around 500 rpm when I moved mine, and the idle was better.

I guess differences in fuel and environments might affect the output. Honestly, without really knowing much about the MA Classic propellor, I would have thought that 6600 rpm on an 18 x 8 prop was a bit on the low side unless the spark has been retarded significantly.
Old 11-11-2015, 11:59 AM
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Originally Posted by ALFIEV
Well... those figures do seem a little low. I was getting around 6900-7000 rpm with a XOAR laminated 18 x 8. The laminated XOAR is quite heavy. I am running a beechwood XOAR 18 x 8 on the Waco and pulling 7200 rpm on the ground. The beechwood prop is lighter, I prefer the laminated prop, but I have found them hard to get.

It may depend on environmental conditions.

Regarding timing, I don't believe NGH have made any changes to the position of the pick-up, or the programming of the electronic ignition. It is true that you will drop top-end rpm if you re-position the pick-up so that the spark is coming later (closer to TDC). I noted a drop of around 500 rpm when I moved mine, and the idle was better.

I guess differences in fuel and environments might affect the output. Honestly, without really knowing much about the MA Classic propellor, I would have thought that 6600 rpm on an 18 x 8 prop was a bit on the low side unless the spark has been retarded significantly.
other than timing did you check anything else? valve gap ? I found that H needle adujst is very critical, it does not tolerate more than just a little tiny turn or the RMP drops significantly
Old 11-11-2015, 12:28 PM
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Yes, I do check my tappet gaps quite regularly. I found they needed to be closed up some after the initial runs. They need less adjustment and checking after the engine is run in. Yes, I agree, the high speed adjustment does require very small changes. I am running my high speed on the Waco a little rich (and I mean very slightly eg. approx 100 rpm drop from optimal) because the engine has stacks of power for the model, it is fully cowled (except for clearance at the bottom for the top of the head of the engine), and I want to run it a little cooler to prolong the life if possible. Is working out fine so far.
Old 11-11-2015, 05:01 PM
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Originally Posted by ALFIEV
Well... those figures do seem a little low. I was getting around 6900-7000 rpm with a XOAR laminated 18 x 8. The laminated XOAR is quite heavy. I am running a beechwood XOAR 18 x 8 on the Waco and pulling 7200 rpm on the ground. The beechwood prop is lighter, I prefer the laminated prop, but I have found them hard to get.

It may depend on environmental conditions.

Regarding timing, I don't believe NGH have made any changes to the position of the pick-up, or the programming of the electronic ignition. It is true that you will drop top-end rpm if you re-position the pick-up so that the spark is coming later (closer to TDC). I noted a drop of around 500 rpm when I moved mine, and the idle was better.

I guess differences in fuel and environments might affect the output. Honestly, without really knowing much about the MA Classic propellor, I would have thought that 6600 rpm on an 18 x 8 prop was a bit on the low side unless the spark has been retarded significantly.
The weight of the prop has nothing to do with maximum RPM. A heavier prop will spool up & down slower & allow a lower idle speed, but it will not affect maximum RPM.

Environmental conditions can have a significant affect on maximum output. I have seen as much as 150 RPM difference from one day to the next.
Old 11-11-2015, 06:43 PM
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Air specific gravit play an important hole but we must remember the propeller design, resulting i higher or lower coeficients of power and thrust. These coeficients may make more diference than variation of specific gravity of air AT SEA LEVEL.
Old 11-12-2015, 02:25 AM
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Originally Posted by PARDAL
Air specific gravit play an important hole but we must remember the propeller design, resulting i higher or lower coeficients of power and thrust. These coeficients may make more diference than variation of specific gravity of air AT SEA LEVEL.
I think the term you are looking for is Density Altitude.
Old 11-12-2015, 05:39 AM
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I said 'specific gravity of air AT SEA LEVEL' meaning air density at sea lavel. I understand environmental conditions as the fators temperature, air pressure, relative umidity... these factors determine the specific mass density or specific gravity ( as americans says ) or air density.

Last edited by PARDAL; 11-12-2015 at 07:37 AM.
Old 11-12-2015, 09:22 AM
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Altitude might be the factor in my case, I am located at 5,600 feet over sea level
Old 11-12-2015, 10:11 AM
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Originally Posted by PARDAL
I said 'specific gravity of air AT SEA LEVEL' meaning air density at sea lavel. I understand environmental conditions as the fators temperature, air pressure, relative umidity... these factors determine the specific mass density or specific gravity ( as americans says ) or air density.
Originally Posted by Erwin Z
Altitude might be the factor in my case, I am located at 5,600 feet over sea level
"Density altitude" can vary at any "geographic" altitude. It take geographic altitude (in feet above/below sea level) ambient temperature, barometric pressure as well as relative humidity into consideration for not only power output (as in drag racing) but lift. (as in flying full scale aircraft) All of those factors affect the "density" of the air & can be calculated as a relative "density altitude".

It factors in more than just "specific gravity" which is a measure of weight (density per unit volume)

Last edited by SrTelemaster150; 11-12-2015 at 10:14 AM.
Old 11-12-2015, 12:10 PM
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I operate at around 200 feet above sea level at our field. The temperatures are still quite cool as it is only now approaching summer. Humidity in this part of New Zealand is quite low. I expect I get quite good performance because of those factors.
Old 11-12-2015, 01:31 PM
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Originally Posted by ALFIEV
I operate at around 200 feet above sea level at our field. The temperatures are still quite cool as it is only now approaching summer. Humidity in this part of New Zealand is quite low. I expect I get quite good performance because of those factors.
Toss in a day with high barometric pressure & you have nature's supercharger. Low altitude means denser air. High barometric pressure also means denser air, but more importantly, it pushes more air into the engine.Contrary to popular belief, vacuum does not suck air into the engine, barometric pressure pushes the air into that vacuum. "Standard barometric pressure" is about 14.2 PSI. 0 PSI G (gauge) is actually 14.2 PSI. 14.2# of boost is 2 atmospheres, and theoretically the engine should produce 2X as much HP as a N/A engine of similar displacement & design..

With a N/A high performance automobile engine, I have seen as much as a 20% variance in HP (reflected by ET in the 1/4 mile) due to DA (density altitude)
Old 11-14-2015, 06:35 PM
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Just numbers
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Old 11-15-2015, 05:23 AM
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Originally Posted by nalby
I'm going to try to jb weld it. I did find a place for parts so I ordered a new one. http://www.austars-model.com/gf38_741.html I haven't heard of this place before so I'll have to see what happens.
Well received the intake manifold from austars on sat. took 20 days chose the standard shipping. Slow but at least I they have the parts.
Old 11-15-2015, 07:16 AM
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Hi Jim,
I ordered a new crankcase and motor mount also from Austars. My NGH38 came as the "pro" model with no lugs to beam mount it. The standoffs didn't fit that good and on a deadstick landing punched the firewall. I like the motor mount Austars has for this engine . It is tapped 5mm and ready to go for a good solid mounting.

Two problems i found when i took the motor apart after about an hour of flying.
1) Part no.F38309 rocker arm was 0.2mm undersize on one side only. Making the rocker arm very sloppy. Looks like it was manufactured like that.
2) Part no.F38301 cam has some deep gouges on the down side of the cam lobe. Looks to me like the cam profile is two steep for the tappet dia. I am going to radius the tappets a little and see if that helps. I am thinking of some way to make a roller tappet. That would solve the problem and cut the friction on the cam.
the last shot shows the rocker arm, cam and motor mount.
Looks like another order for parts. Austars seems to have all the parts and at a reasonable price.

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Old 11-16-2015, 05:45 AM
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Originally Posted by capnpaul
Hi Jim,
I ordered a new crankcase and motor mount also from Austars. My NGH38 came as the "pro" model with no lugs to beam mount it. The standoffs didn't fit that good and on a deadstick landing punched the firewall. I like the motor mount Austars has for this engine . It is tapped 5mm and ready to go for a good solid mounting.

Two problems i found when i took the motor apart after about an hour of flying.
1) Part no.F38309 rocker arm was 0.2mm undersize on one side only. Making the rocker arm very sloppy. Looks like it was manufactured like that.
2) Part no.F38301 cam has some deep gouges on the down side of the cam lobe. Looks to me like the cam profile is two steep for the tappet dia. I am going to radius the tappets a little and see if that helps. I am thinking of some way to make a roller tappet. That would solve the problem and cut the friction on the cam.
the last shot shows the rocker arm, cam and motor mount.
Looks like another order for parts. Austars seems to have all the parts and at a reasonable price.

Changing the radius on the tappet or going to a roller lifter will change the duration specifications of the cam.
Old 11-16-2015, 07:33 AM
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Originally Posted by SrTelemaster150
Changing the radius on the tappet or going to a roller lifter will change the duration specifications of the cam.

Thats a good point. What i noticed is when i hold the push rod against the tappet and rotate the engine you can feel the tappet fall off the top of the cam. This is what gouged the cam. I radiused the tappet until i didn't feel this anymore. At high rpm it will probably still jump but at least it is a little better.
The cam was very rough also and could cause chatter at high rpm. So i stoned the cam to a polish and tried to flatten out the ramp and exit of the lobe.
This cam has a very round lobe which is what they use for roller cams.
You are right the duration will be shorter. That should make the engine a little smoother or less power. I also left the gasket out from under the cylinder to raise compression. Mainly because i didn't have one but will try it and see how it runs. Little changes and one kinda offsets the other.
As been mentioned earlier i don't like sucking the dirty oil into the engine and am going to block off that tube and have the oil blow out the front vent. To me any oil and air that is being drawn into the cylinder takes away from the draw of good air and fuel cutting power. When i took the head off it was carboned up and soaked with oil. The Saito engines only have one ring and allow for a little blow by to lubricate the bottom end. Or being that this is a three ring engine do i go for a wet sump and just change the oil at the end of the day. This is my next thing to look at.
Old 11-18-2015, 10:34 AM
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last Monday I did maiden my 25% Piper Cub with the NGH, so underpowered but steady and sonds great, the motor has no adjustments except of needle carburated. next, I am going to check timing, valve gap and try with different props.

https://www.youtube.com/watch?v=DqMEz4X6mJY

excuse the bad video

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Old 11-18-2015, 11:59 AM
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Hi Erwin, what size prop are you using? It sounds very loaded down.
Old 11-18-2015, 12:12 PM
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Originally Posted by capnpaul
Hi Erwin, what size prop are you using? It sounds very loaded down.
Prop is a MA Clasic series, 18x10
Old 11-18-2015, 03:39 PM
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what rpm do you get with that prop?
Old 11-19-2015, 07:27 AM
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Originally Posted by tyor
what rpm do you get with that prop?
without the cowl I was barelly getting 6200, now with cowl installed, 5800, I guess I can get more than that, will do some adjustments
Old 11-19-2015, 07:48 AM
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Originally Posted by Erwin Z
without the cowl I was barelly getting 6200, now with cowl installed, 5800, I guess I can get more than that, will do some adjustments
Even at 6200 you aren't even making 1 3/4 HP! Way too much prop!.
Old 11-19-2015, 07:59 AM
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Originally Posted by SrTelemaster150
Even at 6200 you aren't even making 1 3/4 HP! Way too much prop!.
I started with that one because is what the manual recommends, I also have wooden props 18x8 and 17x8, will test ussing a scale, advance timing, and check valve gaps.

by the way what is the correct gap for the valves?

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