NGH GF38 Installation

[Andy J]

Installing an NGH GF38 Petrol 4 stroke in an Flair Tiger Moth and have a couple of queries.

 

Engine is in an inverted orientation which puts the crankcase breather on the top as pictured.  Should I connect up this breather and exit the tube underneath the cowl to avoid any oil entering the cowl or just leave it disconnected?

 

Second query is that I can no longer see the throttle barrel to determine at which position is wide open. So from the two pictures is there some consensus as to which is the one showing the throttle wide open as would rather verify this prior to the first start.

[Paul De Tourtoulon]

The throttle lever should have a spring on it to close it up and a stop screw to adjust the idle..

[Frank Skilbeck]

Mines inverted and I ran the crankcase breather outside the cowl on my Privateer.

 

Can you operate the choke, not sure how easy a cold start will be without the choke. On mine I put the choke on, spin the starter until it fires, let the choke off and then restart, then allow it to warm up before opening the throttle.

[Paul De Tourtoulon]

9 hours ago, Frank Skilbeck said:

 On mine I put the choke on, spin the starter until it fires, let the choke off and then restart, then allow it to warm up before opening the throttle.

That's how I start all my petrol 2 strokes.

[Frank Skilbeck]

46 minutes ago, Paul De Tourtoulon said:

That's how I start all my petrol 2 strokes.

Yep, same here, with a glow you can get away without a choke by just priming the engine, but I find that choke is needed on the walboro carb'd engines.

[Manish Chandrayan]

Andy to answer your two specific questions

1. Yes, you can run a tube from the breather and take it down to a convenient position to keep the cowl area clean. Keep it as short as possible or if it has to be longer better to use short length of fitting tube exhausting into oversize tube. That will ensure that the breather actually allows the engine to breath out the spent oil.

 

2. If you haven't removed or disengaged the throttle arm spring, and have either backed out or eliminated the big idle screw the throttle arm will come to fully closed when disengaged from servo. From this position it will move only one way, towards open. To ascertain how far the throttle butterfly is open look at the opposite side of the throttle arm to see a pawl. This will rotate and hit a stop when the throttle butterfly is in full open position. I generally set up my servo to have thin paper clearance between the pawl and the stop. That way I am sure the butterfly is opening fully and servo is not straining.

 

Now for something that you did not ask.

Please make sure that you have proper baffling and hot air exit . Moth air intake position and given our engines rotate the way they do, does not allow for very efficient air entry in to the cowl. Add to that the hotter running nature of petrol engines. So, unless we make best and efficient use of baffles to keep the engine cool we may come to grief. Have seen a OK pilot 1/4 scale model destroyed when the owner changed over to a Saito 30 petrol without adequate baffling from 120 glow and had repeated engine stoppage due to heating. He tried to overcome the issue by running the engine rich. Resulted in another engine stoppage and inability to make it back to the strip.

 

With that NGH 38 you may not have needed any dead weight , power will be adequate for a quarter scale and you can run 18" props that near the scale prop size      👍

[Engine Doctor]

If you can fit a velocity stack to the carb it will prevent blow back mist in the carb area  keeping the cowling cleaner and will also make engine even more economical. Another tip worth  try is to run the breather tube to the mouth of the carb . Any oil should then be sucked in and burnt during combustion. 

If throttle arm spring is still on there don't be tempted to remove it as it prevents the carb from chattering and wearing. Any servo worth using will hold the throttle spring load without any issues. 

Edited January 24, 2023 by Engine Doctor

[john stones 1 - Moderator]

If you don't want the throttle spring putting load on the servo, just disengage the clip and leave the spring there, if you're a bit fussy fit a plastic tube there.

[Andy J]

Removed the throttle linkage and verified that the first picture shows the closed position, so now just need to check if the servo is running in the correct direction.

 

As to the suggestion of removing the throttle spring will give this some thought, but don't recall seeing its location so will have to take a further look at the carb diagram tomorrow.

 

Like the idea of a velocity stack on the carb, so will have a look if that is possible. Is it better to have a direct connection to the carb intake?

 

Have made a custom baffle for the engine which I spent this afternoon attaching to the cowl with fiberglass, so cooling air should now be forced through the cylinder fins.

 

Cowl sides are hinged on both sides as per the full size aircraft, so there should be no problem accessing the choke.

[Jason Channing]

remove the idle screw is a must.

[Andy J]

Had miss understood as to what a velocity stack was on a carb as thought it was more a device to draw air from outside the cowl but having looked at other threads discussing this aspect I can now see what is required.

 

So my next query is does a velocity stack have to be matched to a particular engine / carb and if so what are the critical aspects required to ensure the device works as intended.

 

Have not heard of feeding the crankcase breather back into a carb before as suggested by ED. Is this not going to be an issue as assume the breather is not going to supply a steady stream of oil and hence the air intake is occasional going to see a sudden increase in air density as a glob of oil is drawn into the carb.

Edited January 25, 2023 by Andy Joyce

[Frank Skilbeck]

Andy, my experience with my NGH 38, I don't have any additional velocity stack on the carb, there doesn't seem to be aby blow back, I have also just routed the crankcase breather to outside the model, as the fuel oil content is very low (I run 32:1) and fuel consumption itself quite low the amount of oil coming out of the breather is minimal so you don't get much mess on the model and it's also very easy to wipe off (not sticky like the glow fuel oils), there's more residue coming out of the exhaust, but again it cleans off very easy.

 

My engine is out of my6 model at the moment as a lose aileron servo horn caused a bit of an arrival, but just waiting for some better weather so I can spray it up and get it back together.

[Engine Doctor]

1 hour ago, Andy Joyce said:

Have not heard of feeding the crankcase breather back into a carb before as suggested by ED. Is this not going to be an issue as assume the breather is not going to supply a steady stream of oil and hence the air intake is occasional going to see a sudden increase in air density as a glob of oil is drawn into the carb.

Hi Andy . The breather pipe allows any excess oil to blow out but this isn't very much by volume. If pipe is kept short then it will probably only be a mist. A pipe out the bottom of cowling  will work just as well . A little oil goes a long way and dirt sticks to it so it was just a suggestion to keep the model clean .

Frank informs us that his NGH doesn't blow any mist possibly due to little or no overlap cam design , unlike some of the bigger fs glow engines I've used. So a velocity stack may not benefit the NGH. I have a NIB NGH 38 to play with at sometime so will find out about its characteristics .

[Andy J]

Well I got to the stage of doing an engine run today which brings up a couple of further queries.

 

Have two starters both powered from a 11.2V lipo.  The smaller one turns the engine over fine but the soft rubber cone is already starting to fret away whilst the second larger starter which is geared fails to turn the engine over as the hard rubber cone does not bite sufficiently onto the engine shaft nut.

Is there any solution to this issue to allow me to use the larger geared starter.

 

Second issue is after the first start I found that as I increased the throttle the revs dropped so I assume this would be caused by a lean mixture. Hence I turned the fast jet anti clockwise. This improved the top end performance but a rapid change of throttle is causing the engine to cut. So do I lean or increase the mixture to fix this issue?

 

[john stones 1 - Moderator]

Use a Yellow cone, it'll shape to the spinner, carry a spare, the Black ones are a pain.

Could be either needle Andy, if your happy top ends right then yes richen L needle, let  it warm a couple of minutes before tweaking.

[Andy J]

Not usung a spinner John.  Currently all that engages with the starter is a standard engine shaft locking nut.

Have looked at what the full size aircraft uses and perhaps a JEN domed nut from JE would semi replicate it but don't think it would be any better interface to the starter cone.

[john stones 1 - Moderator]

In that case I turn the cone around in starter, you do that ?

 

[Brian Cooper]

A safety thing:  Disconnect the battery before turning the cone around. 

[Andy J]

The rubber insert on both starters are fitted such that the small hole is facing forward.

Turning the cone around would not help as the cone is then designed to interface with a spinner, which as I say is not fitted.

 

 

 

[john stones 1 - Moderator]

Then you're on a stout glove and flicking Andy, not so bad with electronic ignition.

 

[Andy J]

Did start using hand starting but given the reluctance for the engine to fire had too resort to using the starter.  At least I got the engine running but the starter cone is not going to last long.

Have charged up the ignition battery so perhaps it will be more eager to fire on the next outing.

Will look again at using a small spinner to provide a better interface to the starter.

[Caveman]

Andy, I use a J’EN 32mm domed nut on my Panic. It’s a perfect size to fit my starter cone.

 

 

[Andy J]

Yes did see those from JE but I am a bit wary about using a single nut to retain the prop as the GF-38 has a tendency to keep shedding the prop when it backfires. Certainly did it once yesterday but I hope this will reduce as the engine gets ran in and loosens up.

[Frank Skilbeck]

15 hours ago, Andy Joyce said:

Well I got to the stage of doing an engine run today which brings up a couple of further queries.

 

Have two starters both powered from a 11.2V lipo.  The smaller one turns the engine over fine but the soft rubber cone is already starting to fret away whilst the second larger starter which is geared fails to turn the engine over as the hard rubber cone does not bite sufficiently onto the engine shaft nut.

Is there any solution to this issue to allow me to use the larger geared starter.

 

Second issue is after the first start I found that as I increased the throttle the revs dropped so I assume this would be caused by a lean mixture. Hence I turned the fast jet anti clockwise. This improved the top end performance but a rapid change of throttle is causing the engine to cut. So do I lean or increase the mixture to fix this issue?

 

Only my 2pth worth, 

 

1) make sure the engine has warmed up before trying to go to full throttle, mine cuts until it's warm

2) set the high jet for top end revs, I tuned for max revs then just backed off a tad so it erred on the rich side (I found a tacho essential for this as I couldn't use the exhaust note to tell any small increase/decrease in rpm). 

3) adjust the low end jet to get a reliable pick-up.

 

As for starting I used a gear starter on mine with a 4s Life or Lipo, but my model has a 3" diameter spinner.

[Engine Doctor]

Andy . One thing to note when using wooden props is that they compress consequently the prop nut comes loose . Check prop nut regularly until the wood is fully compressed then check now an again or use a composite prop. If your NGH has half decent compression it should hand start easily once run in using a decent glove of course. 

I've found the the walbro carb or copies needs both needles adjusting until in balance. ie , once top end is adjusted adjust bottom end then re check top end etc u til it will run well on WOT , idle for long periods and transition well. Once set it should keep its tune and not need any fiddling. E10 or E5 fuel will harden the diaphragm in the carb eventually especially if left standing and it will need replacing as once the diaphragm has gone hard and cracks it won't pump any fuel. Very easy job to change . This can be overcome by using Aspen fuel or by removing ethanol from the pump bought fuel then adding your oil. Like petrol garden tool expect to change diaphragm once a year.

If you go the route of removing the ethanol yourself then an ignition additive might be needed . Apparently or so I've been told, Shells V power is ethanol free ,correct me if I'm wrong .Also BP ultimate has little or no ethanol bit more expensive but won't mess up carb .