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Scale model Economy hit & miss engine builders wanted

I need to get my engine running

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Charles 201026/11/2010 17:49:41
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84 forum posts
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A chum of mine is designing a 555 timer strobe so that I can get a good idea as to when my engine is doing that sort of speed ..
 
If it is successfull I will let you know details via this forum ..
 
Regards Charles

Edited By Charles 2010 on 26/11/2010 18:00:56

John Wood127/11/2010 11:55:55
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116 forum posts
Well done Charles, it's certainly getting there and all credit to you.  The governor spring needs to be lighter to run slower, and indeed to get it to open in the first place, I can run mine VERY slowly indeed and much less that 400rpm although 4 to 5 is certainly a decent working speed.  I picked up a small electronic strobe off the internet, it's the type which triggers from a small piece of white reflective tape stuck onto the wheel, it all works fine and was not too expensive (about £20 as I remember). I thought about building one myself based on the 555 timer chip but felt my time was worth more to me so went for the easy commercial option.
 
Will you be trying it on gas at any time I wonder?
 
LA Services demo engine runs slowly but without hit & miss which, I agree is not the best way of demonstrating, I guess it's less likely to falter when running continuously so that's why they do it.
 
Have now moved house (at last) so no workshop yet.  Will get back into it probably in the spring.
 
All the best,  John
Charles 201027/11/2010 18:10:03
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84 forum posts
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Thanks for the comments John.
 
the strip down revealed the follow ing problems:-
1. that the main bearing had been moving in their seats - solution - the oilers have been made with M5 connection and this has been taken right into the bearings to prevent rotation.
2. the big end had slight end float  - solution - a slight filing of the end piece take up the slack
3. the speed lever did not allow operate - solution - much lighter spring used  and the minimum position noted
 
and also  the good points:-
1. that the piston is as good as new
2. that there is no wear noticed o nthe gudgeon pins and end caps
 
When all is bolted back down and photos taken it will have another run ...
 
Regards Charles
Andrew Johnston27/11/2010 20:46:33
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7061 forum posts
719 photos
Hi Charles,
 
Congratulations on getting the engine to run! Although I have already part machined the carb to the published drawings, if you don't mind I'll half inch your design instead. It's a lot simpler. Thank you.
 
Regards,
 
Andrew
Charles 201027/11/2010 21:02:27
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84 forum posts
54 photos
Hi Andrew
 
I put the design on the forum so that other can use it ..  At the air entry end I did progressively bell out the end with 20 then 30 then 40 then 50 deg cuts which i hope you can make out from the pictures.  So I bored the first angle as stated and the just went in from the end so the the edge is quite thin .. Again I hope that can be seen from the drawing ..  I have also made a choke to go on the end ...
 
the integral non return vave works a treat  but I do hope to make a bird feeder type fuel tank such that the level in the lower tank start just a small amount below the entry to the carb ...  This is just thoughts at the momnet but the carb is proved.
 
If you want more detail let me know ..
 
Rgards Charles
Video can be seen here -- follow the links on the pages to Economy engine  then video

Edited By Charles 2010 on 27/11/2010 21:03:50

Charles 201027/11/2010 21:05:40
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84 forum posts
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Posted by John Wood1 on 27/11/2010 11:55:55:
 I picked up a small electronic strobe off the internet, it's the type which triggers from a small piece of white reflective tape stuck onto the wheel, it all works fine and was not too expensive (about £20 as I remember).
 
 
 
Any more details you can give to lead me to the one you bought ...??
Charles 201027/11/2010 21:52:57
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84 forum posts
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This is an improved drawing showing the "bell mouth air entry"  angle not important but create a smooth curve ...
 

The lower unon is part of the the  non return valve, and as such has a CROSS filed into the flat to allow fuel to flow past with a lower section  that screws onto the M6 Thread with a small stainless steel ball bearing.
 
Regards Chalres 
Charles 201029/11/2010 18:09:01
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84 forum posts
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All being well I will be making up a base to bring the crank up to about 23" from ground level, then may be add 4" wheels which will bring it to about 24"  which should be a reasonable height from the gound  for starting and running.
 
It is being made from the steel angle and square section I have laying around so it will be put to good use ...
 
Still think about the fuel tank !!!
 
Regards Charles
Andrew Johnston02/12/2010 10:14:20
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7061 forum posts
719 photos
Hi Charles,
 
Thanks for the updated carb drawing. I'm not sure I understand the purpose of the non-return valve. I assume that air drawn thru the carb causes fuel to be sucked from the tank? Does the non-return valve stop it running back? At what level do you think the fuel tank should be relative to the carb? I'm planning to TIG weld an external stainless steel fuel tank, so I'll have freedom to set it at what height I want.
 
Regards,
 
Andrew
Charles 201002/12/2010 10:33:31
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84 forum posts
54 photos
According to all that I have read and been told the fuel entering a carb should be just below the exit point in the carb ( ie where the needle jet opening is.
 
So to achieve this the first way is to put a non return valve in the line so that the fuel that is sucked up stays there ready for the next entry into the cylinder.
 
An alternative is to have a float chamber adjacent to the carb with a needle to stop fuel entering when full
 
Another alternative is to use the chicken feed hopper idea where fuel only enters the feed section when previous fuel has been used and allows more fuel to enter
 

 
and lastly a small thin but long fuel tank placed at just below the level of the exit point to the carb.
 
What you want to avoid is for fuel to have to be sucked up into the carb all the time as the needle jet will need to be open further than necessary for the right amount of fuel to enter the carb and mix with air and this will lead to flooding of the engine.
 
I understand that the mix must be 14.2 to 14.9% fuel to air for ignition and this must be in vapour and not dropletts. 
 
An external fuel tank sounds a good idea but at no time must the fuel in the tank be above the exit point of the carb else it will just flow out nor too far below other wise the mix will not be right as the carb has to do too much sucking up of fuel before vapourising.
 
I hope this has been fo some help you you ..

Edited By Charles 2010 on 02/12/2010 10:42:39

Andrew Johnston02/12/2010 10:53:33
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7061 forum posts
719 photos
Hi Charles,
 
Great stuff, thanks. I think I understand what is going on now. I'm not sure what the percentage of fuel to air is, but I do remember vaguely from my thermodynamics courses that the stoichiometric air/fuel mixture for petrol is approximately 14.7, by mass, for complete combustion.

I think the best thing to do is make and fit the carb and then design the fuel tank to suit. I'm planning to mount the engine and ancillaries on a square piece of jig plate, so I also have some flexibility on the height at which I mount the engine.

Regards,

Andrew
Charles 201002/12/2010 11:17:42
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84 forum posts
54 photos
Well I was in the right ball park ..
 
I have Googled and 14.7% is right ...  well recalled !!!
 
Here is the stand I built on Tuesday before the "real" snow arrived !!!!
 
 
It is designed to bring the crank handle to about 24" from ground level. I may also fit it with wheels.
 
Regards Charles

Charles 201011/12/2010 15:16:17
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84 forum posts
54 photos
With all the modifications made to the engine the most necessary one was to the hit and miss action in that I have taken the pushing shaft back so that the push shaft does not exit the rotation shaft until the balls start to fly then as the engine speed up the shaft causes the hit and miss action to take place ...
 
All very satisfying but not caught on video as I was operating all the items my self ..
 
BUT bad engineering on my part means that a new crank is needed as mentioned before even the pinning has not held things solid so I may try welding the crank ad a temporary measure.
 
The big eng bearing is also showing slop ...  so a new one of those also required ...
 
Still progress has been made and 2011 should see the engine running well ...
 
Thanks for all who have made most useful comments on this forum ...
 
Happy Christmas and good engineering in 2011..
 
Charles
dixie11/12/2010 16:05:02
31 forum posts
Hello Charles 2010
To make a tapered fuel screw drill down the end of your threaded part then super glue a gramophone needle in job done, look on ebay for needles.
brian
Charles 201011/12/2010 20:20:05
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84 forum posts
54 photos
The needle idea sound good.
 
I am pleased to say the re-vamped carb is now working very well but now have to work out a way to stop the vibration of the engine causing it to close. Probably I will work out a stop so that is fails to an open position  and not closed position !!
 
Regards Charles
MichaelR12/12/2010 11:51:24
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528 forum posts
79 photos
Hi Charles,
You may have to think about balancing the flywheel on your engine to cut down the vibration, you can do this by removing some weight from the flywheel inner rim and diametrically opposite the crank pin, this can be a trial and error job. As in the picture

Edited By Stick on 12/12/2010 11:52:17

Charles 201012/12/2010 12:13:57
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84 forum posts
54 photos
When I have made the new crank in 2011 Then I will be able to set about trying to balance the fly wheels as you suggest. in the mean time may be I can add some weight as done with car wheels !!!
 
Regards Charles
JasonB12/12/2010 13:54:22
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25215 forum posts
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You may also want to think about some balance weights on the crank webs
 
J
Charles 201012/12/2010 21:29:58
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84 forum posts
54 photos
I have been considering why my key ways are not holding the flywheels and I have found this web site ..
 
 
Looking at the table it seems that the keyways for the Model Economy engine could take  6x6mm keys rather than as the plans suggest 4x4mm keys.
 
Am I reading the table correctly as a 6x6mm key is substantially bigger than a 4x4mm and may be the reason why I am getting s working loose.
 
Any comments please even to say I am totally wrong and 4x4mm is correct.
 
regards Charles
Keith Long12/12/2010 21:43:38
883 forum posts
11 photos

Hi Charles

My personal feeling id that if the shaft is a suitable size for a 6x6 key then you won't loose anything by going for the bigger size. From my own (limited) experience with keys in a crankshaft (on a full size car) fit is all important. The key should be a GOOD  snug fit in the shaft as any slackness will eventually lead to the key coming loose and damaging the shaft by fretting. I had this happen on a Peugeot 504 engine. Fortunately I was able to repair the shaft with stainless steel filled Devcon, and changing the pulley that was keyed to the shaft was an easy option. A new key fitted into the shaft with the Devcon, allowed plenty of time to set and 20,000 miles later all was still well. Also how are the other parts held to the shaft. If they can move against the key you are likely to end up with damage.

Keith 

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