NGH 9CC running in

[Brian Dorricott 1]

Hello all , I am fairly new ( last 2 years ) to IC engines and thought I would replace some of my SC/ASP with NGH 9CC petrol . It promptly arrived from Just Engines and had the usual almost comical instructions on setting up but it did say should run on settings as supplied and it did. Okay so far couple of tanks through and it starts to ease a little doesnt stop much now at low revs and can be taken up to about 10500 rpm for a few tens of seconds and holds it nicely . Tickover can get down to around 2500rpm but i notice quite a delay when you open the throttle wide it doesnt hesitate as much as build slowly to full revs over several seconds but appears happy there . Its got a normal range prop on (11x6) and is on 20:1 oil/petrol . Do i need a: a few more tanks through it or b: do i need to adjust slow running needle and high running needle to balance it out , if that being the case what is the procedure please ?. With glows I never touch the slow running screw once set only the main needle , so was wondering if the procedure is different for petrol . I know i might be told bin it and buy OS but not got OS money at moment. Any pointers appreciated thank you.

P.S. only had 4 tanks through it yet but starts and runs reasonably cool but is even with Just Engines quiet silencer is still quite loud , a lot louder than a SC46 glow with the same silencer.

[john stones 1 - Moderator]

Have a read of the tweaking bumf on this Brian, it'll help understand how to do, what. Page 13.

Edited By john stones 1 on 19/10/2018 14:58:18

[Jon H]

Slow run needle adjustment is required on every engine fitted with one. I know many people advocate never touching it from the factory setting but this is not a good idea. Slow run needles should always be adjusted to suit the model you have the engine mounted in as they will always be different to the factory bench.

In this case specifically, i would lean off the slow run a bit and see how the performance changes. petrol engines tend to be sensitive to needle changes so use 1/8 turn incriments and see how you get on

[Brian Dorricott 1]

Thanks John I'll print that off and try it again , I don't think I'm far off being correct but would rather do it on the bench than in the air . Am I right in thinking being petrol that once it's set up it shouldn't need to altered to often ?

[john stones 1 - Moderator]

Like Jon says, they need occasional tweaks, but they're sensitive on needles, don't be scared of tweaking it, you can always go back to factory settings and start again.

[Brian Dorricott 1]

Thanks also Jon just noticed your post , as relative newcomer I need to get that knowledge that some of the more expierenced guys take for granted . i.e if it does x then it's lean or vice versa so just getting my head around it .

[Rich too]

Brian, yes, once setup you should be able to leave it alone. Good luck 👍

[Brian Dorricott 1]

Just an update on the NGH 9GT , I have 2 of then one older with pump separate and blue head , the other a new one silver head and carb and pump all in one . The older one has been a nightmare to setup and the newer one piece carb job is a pussycat to setup. So you guessed it out went the old carb and pump in went a new carb from Just Engines and hey presto it's much easier to tune and transitions nicely now. The only problem is both engines run on Just Engines quiet silencers but are still very loud , anyone any ideas on how to get them quieter ? Just to set the scene on the test bed I run them whilst wearing ear defenders otherwise my ears ring . Saw a suggestion somewhere to drill and tap the outlet pipe to M4 and adjust to suit noise wise , does this work ? My SC46 glow sounds positively Rolls Royce quiet next to these 2.

[Bob Cotsford]

I had an Evolution 10cc petrol, that also made a fair racket. I used the quiet silencer off an ASP52 and found that I needed to run 13" props to get within limits. I think that petrol igniting seems more like an exposion whereas methanol burns more slowly giving a softer sound that is less offensive. I tried the Evolution in one model but decided it was too much trouble so stuck to four stroke glows after that.

Edited By Bob Cotsford on 29/11/2018 22:50:02

[alex nicol]

To get back to the original question of slow pick up, if your idle setting is a little rich, it'll idle ok, but when you whack it open it'll take a second or two to burn off the excess fuel as the revs increase. I agree with above, if you adjust the idle, small increments at a time

[cymaz]

With petrol engines the needle adjustments are fractions of a turn...1/16 or less. The needle taper is finer than that of a glow and ,of course, uses far less fuel. Once you’ve done with the running in and finalised the needles, they really shouldn’t need touching again.

As for quietening the noise, try some pepper pot end caps that slip over the exhaust outlets with silicone tube.

Edited By cymaz on 30/11/2018 06:23:28

[Ron Gray]

The only way you will be able to get it to run a lot quieter is by having a large volume silencer. The JE ones just aren’t large enough. I’ve got a NGH 38s and really struggled with it to get the noise levels down. In the end I’ve given up with it and it sits on the shelf.

[Philflyer]

Brian - sorry but this is going to be long! I have the original NGH GT9, now over 3 years old but the carb supplied was useless. I bought a Just Engines J'En 52 carb and used an old extra quiet silencer from one of the .40 glows it had replaced. It's as quiet as a new ASP .46. I use an 11x6 prop. To cut a very long story short it was much improved but not perfect. If the slow running and WOT were correct then acceleration was iffy and mid-range was rough. If mid-range and WOT were ok then slow running had to be kept no lower 3K rpm or it would stop when the throttle was closed quickly. After taking advice from a Dutch marine engineer who has made many glow engines run on petrol (Brutus 1967 writing on RCGroups. com) I changed the throttle barrel cam profile with my Dremel, much easier than it sounds, and achieved another step change in smooth throttling, even dumping the pump as well! BUT - there was still hesitation or even a dead stick if I opened the thottle fast, particularly in high g manoeuvres. Brutus answer to this was - don't do it. The fuel scheduling in our small gassers is very primitive and the very lean mixtures, compared to a nitro engine, means that if you have a correct slow running mixture then as soon as you slam open the throttle the air will rush in far quicker than the petrol and it will stop. Every car carburettor I have come across has an acceleration pump to overcome this. The answer is to have a servo delay in the throttle channel, 0.5 seconds is fine. I found one on e-bay for a few pounds. This engine flew very well and completely reliably for over a year and at least 100 hours but in July and hot weather, I had a spate of dead sticks. Finally diagnosed the cause as worn carb O-rings and a con-rod at the crank end. By now the new NGH 9cc spares were being sold by Just Engines so, like you, I bought the new carb with the pump in and a new con-rod. Very inexpensive and great service from them as always. Brutus comment was "What! A worn con-rod! what oil and what ratio are you using?" So on his advice again I changed from the 20:1 petrol to Halfords Fully Synthetic oil I was using and went first to 15:1 and now 10:1. A huge improvement now in slow running, 200 rpm more at the top end, which really surprised me, and the throttle servo slow is not necessary. Try it. The rise in fuel cost is negligible and the oil on the fus is still less than my OS 46AX was. You will have to fine tune the top and bottom end mixture for the next several flights but it is well worth it. Any change in exhaust WILL need another retune, again over quite a few flights before it is completely stable.

Edited By Philflyer on 30/11/2018 16:07:31

[Brian Dorricott 1]

Thanks Philflyer lots to get to grips with there , I thought replacing the carb was a vast improvement but who would have thought increasing the oil would give even more smoothing . I'll try it as I need to mix some fresh about now . Pity it doesn't make them any quieter as well that would be a result - thanks !

[Kim Taylor]

Posted by Brian Dorricott 1 on 30/11/2018 17:44:18:

Pity it doesn't make them any quieter as well that would be a result - thanks !

Hi Brian

I've got an NGH GT17 which I also got from J-E.

It failed the club 82dba limit quite comprehensively even with the 'pepperpot' in the exhaust outlet.

I got it through the test by stuffing the exhaust chamber with stainless steel pan scourer material, but it was marginal. I ended up fitting one of those cheap add on silencer cans off of ebay (cost about £12.50 iirc) connected up to the now unstuffed (is that a real word??) exhaust on the engine with silicone tubing. Works a treat, takes out the bark that petrols all seem to have.

If I were you, I'd also prop it down a lot, probably to around 9k rpm max - petrol motors in general are pretty 'grunty' and will spin a big prop compared to a glow motor - and you'll get an improvement in both engine and prop noise.

Interested in the outcome - I'm thinking about a GT9 Pro for my next project.

hth

Kim