NGH GF38 Installation

[Andy J]

Thanks for the tips ED, currently using Aspen fuel and I certainly find the engine runs far better on it than petrol and has less residue  emitted out of the exhaust.

 

Prop is wooden,  think it was purchased from HK, so probably not the best quality. Certainly the prop throwing issue has occurred every time I have ran the engine, so did ponder briefly today if I could drill the crank shaft prop driver to accept a couple of M3 bolts.

 

Did find the engine has less vibration now that I have fitted an NGK plug so that was positive item of advice from another thread specific to the engine.

 

Sure I already have a spare carb kit so will do that change as the engine has certainly sat for at least two of three years since I last played with it.

 

Despite not quite scale like for a TM, will get a spinner on order tonight to allow a better interface to the starter.

[john stones 1 - Moderator]

Some of the domed nuts a recessed Andy, it acts as your lock nut then.

[Richard Thornton 2]

On 24/01/2023 at 15:19, Engine Doctor said:

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. 

Hi Engine Doctor, interesting comment about fitting a “velocity stack”, so where do we get one of those from and what does one look like?

[Richard Thornton 2]

Andy, having fitted your engine to your moth, how did you get on with the exhaust?

I am having issues with the exhaust touching the cowl, just at the point of exit from the cylinder head, very frustrating.

[Engine Doctor]

12 hours ago, Richard Thornton 2 said:

Hi Engine Doctor, interesting comment about fitting a “velocity stack”, so where do we get one of those from and what does one look like?

Hello Richard.  A velocity stack looks like a trumpet end that fit on the carb. They are available on ebay for various engines . Search Velocity stack in toys and games . I dont know if the NGH 38 is listed. The NGH pictured at the begining of the thread shows a VS fitted although it looks too short to be of any use and just a bit of bling  , twice as long would be good for any effect.

[Paul De Tourtoulon]

There are pages on it on Rcgroups, Saito,,,

[Andy J]

14 hours ago, Richard Thornton 2 said:

Andy, having fitted your engine to your moth, how did you get on with the exhaust?

I am having issues with the exhaust touching the cowl, just at the point of exit from the cylinder head, very frustrating.

I made a custom exhaust from a oblong steel pipe Richard. First attempt was too long so had to shorten it considerably. I can post some pictures if you wish to replicate it for your installation.

[Andy J]

Picture 1 was attempt No. 1 Richard, second version was half the length and the exit exhaust stub was taken off on the lower edge.

[Engine Doctor]

Hi Andy . Did you fit anti crush tubes through silencer to stop the fixing bolts  crushing it ? also if not then silencer will continually loosen and cause damage to head .

Can I also suggest fitting a another fixing point to teh silencer that can then be fixed to the engine mount with a metal strap . Its a simple addition and helps prevent vibration taking its toll . It always seem to work  when silencers , especially on Four strokes keep coming loose. 

[Andy J]

Yes as you can see in picture 1 there are two brass tube inserted to prevent the fixing bolts causing deformation at the engine manifold interface. Also I have used spring washers on the two fixings to hopefully prevent the silencer coming lose in flight.

Entire item is silver soldered given the high exhaust temperatures but a welded construction would probably have been better. First attempt on fixing the exhaust stub had a trace of lead on its surface and that came adrift almost instantly on starting the engine.

To date I have only done ground runs on the installation but the construction seems to be holding up very well with no observable leak at the engine manifold interface.

Possibly a good idea about a second fixture as I have seen other postings on this forum that report issues about vibration causing structural failure.

Have shortened the exit pipe since the picture was taken so the lever arm caused by the rear section of the exhaust and exit pipe is I hope not significant. 

 

 

[Richard Thornton 2]

8 hours ago, Paul De Tourtoulon said:

There are pages on it on Rcgroups, Saito,,,

 

[Richard Thornton 2]

Many thanks to Paul and Engine Doctor, I have some homework to do.

 

Andy, good job on the silencer, yes, this might be the only option. Some head scratching to do now, many thanks to all

[Richard Thornton 2]

10 hours ago, Engine Doctor said:

Hello Richard.  A velocity stack looks like a trumpet end that fit on the carb. They are available on ebay for various engines . Search Velocity stack in toys and games . I dont know if the NGH 38 is listed. The NGH pictured at the begining of the thread shows a VS fitted although it looks too short to be of any use and just a bit of bling  , twice as long would be good for any effect.

Hi there, again. The velocity stack that is in the photo, now I know what the ‘blue bell shaped thing’ is called, is the standard VS fitted to the Welbro WT carb. Compared to the photos on line, it’s not very long at all, so replacing it with a longer version might improve the carb misting all round. 
 

Thanks for your help

[Paul De Tourtoulon]

I also made a couple, washers and silver solder won't do the job, they will only hold out if braised .

[Engine Doctor]

Hi Paul are you saying that silver solder failed due to the heat . Some silver solder does melt quite low compared to proper brazing . 

What i think is being overlooked is that petrol four stroke exhausts are far hotter than their glow equivalents . Now if ign timing is a little retarded this exhaust temp can get even hotter . Remember our motorbikes back in the day ? New exhaust pipes would quickly go through all the colours and burn off the cheap chroming if timming was retarded. 

Good luck and hope you get it sorted.