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f2cf1g

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You have described the classic symptoms of an under-compressed glow engine, i.e. stops when plug disconnected and unwilling to 2-stroke. Try skimming the head 0
 

c_mario

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Thanks to all the suggestions I achieved a run without glow starter. The Glow plug was 5mm from the top surface of the cylinder head so I machined 5mm off the plug recess to get it flush with the top of the cylinder head. I also purchased an OS needle valve. I replaced the plug and achieved running without glow starter attached.
Firefly46 Running
Another
Firefly46Run
 
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ZebDog

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congrats on getting your engine running without the aid of the glow lead nice job very well done :D
 

stackerjack

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Well Done Mario, It runs well doesn't it. The RPM might be a bit low. What size prop are you using?
Jack
 

c_mario

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Well Done Mario, It runs well doesn't it. The RPM might be a bit low. What size prop are you using?
Jack
Yes Revs are a bit low but as UK member f2cf1g said it is probably under compressed. I will probably skim the head as he suggested. The prop is only 8 X 6. Since I got this one to actually run I am going back to Engine number three and redo the cylinder liner and piston since I have a better handle on the Lapping process. Hopefully I can get that one to run to.
 

Tim Wescott

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Remember that if you skim the head and overshoot, you can always make head shims. I'm not sure where you fly or availability of fuel, but getting it working on 5% nitro, or even 0%, shouldn't be hard. Then, if you want to fly on higher nitro (or find you need to adjust the compression for the weather) you can add or subtract shims as necessary.
 

f2cf1g

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Well done on getting it running, it sounds strong, revs sound OK to me. The motor is on the boundary between 2 and 4-stroking in the second video. If you can lean it out to pure 2-stroking, the compression ratio is OK (though you might get more power by increasing it). If it won't 2-stroke continuously but stops instead as you lean it out, then the compression ratio is definitely too low.
 

Tim Wescott

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So, curiosity here since I seem to be in the company of folks with more glow expertise than I possess -- and possibly way more throttled glow engine experience, because I've been flying mostly control line for the last decade.

I know that there's a mantra in the US at least "more nitro will make needling easier". If you're going for zero or low nitro, is there a compression setting that'll make needling easier? Or are you just doomed to a fussier engine?
 

f2cf1g

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I'm a control line and free flight man too, don't know much about throttles! What I've found in doing Nelson glow head conversions is that getting the compression ratio right can be difficult and often takes a bit of experimentation. When it's in the right ball-park, setting the needle shouldn't be a problem whatever the amount of nitro, i.e. more nitro is not a solution if the CR is wrong. That's on the bench of course, getting the needle setting right in a competition control line model is another matter, many factors come into play then, maybe tipping the can is a benefit then to easier operation in some circumstances.
 

bluejets

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I know that there's a mantra in the US at least "more nitro will make needling easier". If you're going for zero or low nitro, is there a compression setting that'll make needling easier? Or are you just doomed to a fussier engine?

Rarely ever used nitro in everyday flying over the last 50 years or more.
Found the OS and Enya engines and similar will run quite well on standard 4:1 methanol/castor/castrolM.
Reason initially was cost of nitro and secondly, the residue (nitric acid) attacks any internal steel components including ball races.
Nitro does broaden the needle setting quite a bit but the ratios of nitro don't make that much difference.
It allows four stroke engines to idle down to next to nothing but then again they were the early air bleed idle type carbies, not the 2 or 3 needle type in some of the later 4 strokes.
Since I didn't like the way it attacked the steel parts ( 4 strokes have plenty) I tended to use an on-board single nicad cell and a micro switch on the throttle servo that switched in the battery at around 1/4 throttle and downwards. A D cell (4000mAh) would last for a month or more between recharges.

Where we did use nitro was in the 049 cox and in our K&B marine engines, the latter of which were high performance engines.
In those, we found ratio's like 10% worked a bit, 15% was a tad better and 20% was a nice performance mix.
Over that it was just a waste in our opinion.
049's can handle quite a bit more but they use next to zero fuel anyhow so 40 to 50% wasn't uncommon.
The larger engines (primarily 40 size in pylon) needed quite a bit of playing with to get increased compression just right on straight 4:1 mix.
Even then, a high moisture day could see a need for change from say a previous dry day's pylon racing.

Another aspect to consider is the methanol.
In the early days of pylon, we were caught out as home setups were never the same as at the field.
Whether we were on standard head/plugs or Nelson buttons and plugs, always the same.
The only difference was, racing fuel was supplied on any given day by the race organisers.
Penny dropped and finally we found our standard methanol was in fact 95% methanol and 5% acetone.
When chucking that lot and asking for 100% methanol at the local fuel depot, all the problems disappeared.
 

Tim Wescott

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Woo hoo!

Looking at the carburetor on that engine, the throat looks undersized. That would explain why I was saying that the last one sounded slow (assuming you're using the same carb).

If that's the carb that the designer intended, then you may want to stick with it -- small-bore carburetors certainly draw fuel well & make needling easier, and it is the designer's intent.

On the other hand, if the induction hole in the crankshaft is significantly bigger than the carb and you don't like the power you're getting, you could try a different carburetor. You'll open yourself to the possibility of either reducing the engine life, or finding out that some other aspect of the engine isn't up to the power level.
 

c_mario

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Hi Tim,
The engine was not designed with this carb . The carb is a different one from the other engine, its a Rupnow design I thought might work on this engine.
I have another run video below.
SecondRun
 

bluejets

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Hi Tim,
The engine was not designed with this carb . The carb is a different one from the other engine, its a Rupnow design I thought might work on this engine.
I have another run video below.
SecondRun

Gees, that camera must have near collided with that prop..........:oops::oops:
 
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C Mario: I just saw your second run! - A great engine! I liked the spanner - or whatever - in the hole in the workmate, but did it jump out half-way through the video? Or did you take it away? - I didn't see it on the floor.

WELL DONE SIR!.
K2
 

c_mario

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C Mario: I just saw your second run! - A great engine! I liked the spanner - or whatever - in the hole in the workmate, but did it jump out half-way through the video? Or did you take it away? - I didn't see it on the floor.

WELL DONE SIR!.
K2
Thanks. Nice observation, I must have taken it out. Its sitting on the starter battery to the left. 2 minutes in.
 

c_mario

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You have described the classic symptoms of an under-compressed glow engine, i.e. stops when plug disconnected and unwilling to 2-stroke. Try skimming the head 0
You were absolutely correct. I skimmed the head and achieved high revving two stroking.
Thanks to all for all suggestions. I now have two running, two stroking engines.
 
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