backwards engine running

[ben hall]

can anyone shed light on this. any articles or advice . just want to hear what people think about what cures it and the reasons behind it

[John Privett]

Most modern model two-stroke engines will run backwards quite easily,  though nothing like as efficiently as they will in the correct direction.  Often a half-hearted flick, maybe a half-flooded engine causes the engine to fire way before top dead centre and the piston starts descending causing the engine to reverse direction.  If it then fires on the next stroke it may continue running in reverse.

 

Some small engines have reed-valve induction engines - like some of the small Coxes - these are equally happy to  run in either direction.  I'm sure over the years many free-flight flyers have failed to spot the engine running backwards and watched, puzzled as the model leaves their hand and sinks to the ground at their feet...

 

As an aside to this,  with Enya engines that have the front crankcase separately attached (do current Enya still have this?) it is possible to "retime" the induction for reverse running by rotating the front crankcase 90 degrees one way (don't know which way though!)

[colin watson]

IS THIS A NEW ENGINE OR AN ENGINE YOU HAVE USED ?

I ONCE HAD A IRVINE 61 WITH THE LINER FITTED INCORRECTLY

OTHERWISE HOW ARE YOU STARTING THE ENGINE AS MOST TWO STROKES WILL RUN BACKWARDS BUT USUALLY FROM HAND STARTING WHEN IT REVERSES ABOUT TOP DEAD CENTRE. USING A STARTER HELPS SPIN IT OVER TDC

[ben hall]

heli engine not new but nearly new started with a proper started ran correct way for about 3 mins as i carried it to flight line spooled up then it blipped and ran backwards . took canopy off and just hold the starter rod lightly then it ran the right way . i know why it did i was cause by the glowplug being to hot for the fuel i just wanted to hear what people thought . and how many have had this problem in the past

[Martin Harris - Moderator]

Ben,

 

You've got me wondering what your real reason for posting was.  John and Colin went to the effort of trying to help someone with an apparent problem but it feels to me that you were just testing the responders.

 

Wouldn't it have been better to simply state what you'd experienced and asked whether it was a common problem?  This would make me think twice about posting a reply to any future problem that you might post.

 

P.S. You might like to know that you can type a capital letter by pressing the shift key at the same time as pressing the desired letter.

[ben hall]

Thanks martin for you very informative engine tips . many thanks to john and colin tho. colin even went to the expense of typing with one hand while he held down the shift key 

 

was posted to see what people thought and what knowlage could be brought to light or articles uncovered . but never mind

 

[Stephen Grigg]

Hi Ben last Thursday watched an expert starting he is engine backwards.He has trouble starting it the right way so starts it backwards initially because its easier.Once he has run it for half a minute or so he stops it and starts it the correct way.Sometimes his will kick back and run the correct way.He says that OS engines sometimes start better backwards than the right way..Interesting isnt it.It must be the simplisity of the engine design..Like when an engine wont start you put your finger over the exhaust it draws fuel in the carb and atarts.Youve an engine that wont stop you put your finger over the exhaust and it stops____urgh

[ben hall]

very interesting stephen . i wonder if this is something similar happening to him as was me .

[Tim Mackey]

Please let's not go down the route of sarcasm etc now chaps TY - I'm sure Colin didn't meant to "SHOUT" ( Colin....in case you didn't know - using capitals is considered shouting when posting on the WWW )

Ben..... your posts would be a little easier to follow if you applied a little more correct punctuation and used the inbuilt spell check faciltiy ( use left click on the mouse, and highlight everything,  then right click and choose " check spelling " )

HTH

[ben hall]

Cheers Timbo . I am just poor at english thats all . Excuse my dumbness

[Stephen Grigg]

There is that possibility Ben Ive seen it happen at the strip  without people realising there engine is going backwards.They wont rev up and they stand there wondering why the engine wont rev.One guy today was holding his hand behind the prop He was checking his engine was running the correct way.I dont think its uncommon at all.You always kno.w.If when you give it throttle it heads backwards youl;l Know some thing is wrongSaw a guy the other week launch his electric.He launched it without power gave it all and it nearly took his head off.The pitts were in hysterics.Would have made a good Last of the Summer Wine episode,

[Tim Mackey]

Posted by ben hall on 21/03/2010 22:15:06:
Cheers Timbo . I am just poor at english thats all . Excuse my dumbness

 

Not dumb at all Ben.... just need a little help that's all which is why I suggested the spulchugger

[Stephen Grigg]

Ben its not our brains that cant spell its our fingers

[Martin Harris - Moderator]

Posted by ben hall on 21/03/2010 21:51:15:

Thanks martin for you very informative engine tips . many thanks to john and colin tho. colin even went to the expense of typing with one hand while he held down the shift key 

 

was posted to see what people thought and what knowlage could be brought to light or articles uncovered . but never mind

Ben,

 

Hopefully your post was made in good faith without any intent to test the responders and if that's so, I'm very glad.  My point was that it would make me less inclined to venture opinions or suggestions suspecting that a poster might already know the answer and was apparently trying to show his superior knowledge. Posing your question in the way you did just made me feel uncomfortable when I read your later reply.

 

No doubt you're totally familiar with the principle of automatic timing adjustment in the glow engine principle - as the element heats up with increasing load as a consequence of increasing speed, the ignition effectively advances, retarding as the plug cools at lower revs.

 

As can be deduced, a hotter plug will advance the ignition over the complete rev. scale therefore increasing the possibility of the piston being kicked backwards at low revs.

 

Oddly enough, although considered "shouting" in newsgroup/emailing circles, writing in capitals looks far less lazy or offensive to us "oldies" brought up to take a measure of pride in getting punctuation, spelling and grammar somewhere near correct.  Would I be correct in guessing that you're one of our younger forumites?

 

Edited By Martin Harris on 21/03/2010 22:29:29

[ben hall]

Fantasic info Martin. no i know nothing about the auto timing adjustment . You just got mee googling . thats the type of info am looking for. i like to know why things so what they do  

 

am not young am 29 but spelling is my bad point

[Tim Mackey]

Love it ...

"I am not young, I am 29 " 

[Tim Mackey]

Two posts deleted - I did ask to keep on topic and the spelling and sarcasm issue has been dealt with .

[Peter 'Ivanna Crashalot' Savage]

I do like starting my engines with a wooden stick, primarily to avoid the need for a starter and to avoid melting the spinner! I do find my OS 15LA does quite often start in reverse, its just when you bring the throttle up it falters and dies, on the odd occasion it will then pop into the correct direction. Not aggravating, just mildly annoying when your trying to start it! 

[Peter Beeney]

Ben, as other forumites have noted, some model two-stokes will occasionally start and run backwards quite easily, and indeed, often quite persistently. Model four-strokes will also do the same thing. One of my beginner colleagues had one of the earliest OS 40 four-strokes with a pressure feed to the fuel tank and it was so determined to start backwards, despite using a starter running forwards, the only way to prevent it was to remove the exhaust pressure tube and replace it once it was running. Larger petrol two-strokes will do the same thing. Royal Enfield made a 125cc motor cycle for war time use and so there were a number of these running around in civvy street later on. It was certainly not unknown for these to be ticking over, give a little cough, and then be running backward; for instance, at a set of traffic lights. That could be a touch embarrassing! The BSA Bantam, another a lightweight two-stoke of the same era, would also infrequently run backwards. As I remember, the slow running mixture was thought to be the problem, but I might be quite wrong there. In the ‘fifties this feature was in fact exploited to some extent. Some bubble cars and invalid carriages that used two-stoke engines, and also had a reverse gear, that employed an unusual technique. These were generally 197 or 250cc in size. To engage reverse you stopped the engine, put it in reverse, and restarted the engine. In reverse! Running backwards! The reverse gear simply changed all the electric's around, including the ignition timing, so it did cheat a bit. And to make matters worse, on at least one nightmare creation the dynamo, I’m sure it was a dynamo in those days, not an alternator, became the starter and vice versa. The electrical circuitry on this lot made brain surgery look easy! I don’t think they lasted too long.
Martin -  Whilst I agree entirely with you about glow plug timing, indeed it is the glow engine’s willingness to adjust the timing to suit the revs and/or load that makes it such a success, I’m not entirely convinced that’s the whole explanation here. I think Ben’s experience is unusual; invariably it seems to me they always want to run backwards from starting up. Which maybe has something to do with the heater (glow) battery being attached? Does the compression ratio also play a part? I think it might. Certainly as in Ben’s case, slowing the engine right down will ‘flip it over’ and make it run properly; I do it by pressing on the spinner. Why did Ben consider the glow plug was too hot for the fuel? Is there a subtle difference between a ‘hot glow plug’ and a glow plug that is ‘too hot’?  Having said all that, I’m now thinking this could well be another of those protracted discussions which goes nowhere anyway, so I may consider it to be a good idea to not proceed any further.

.epip tsuahxe nwo ruo pu raeppasid thgim ew esiwrehto      PB

Edited By Timbo - Administrator on 23/03/2010 12:40:50

[mal brewer]

  Re Peter  writing about two-stroke engines operating in reverse, all the engines he quoted were piston-controlled induction. In other words,side-port induction,exactly similar to early model engines,including the famous Mills engines. These engines will operate in either direction,as the timing is identical in either direction. The starter he was referring to was known as a 'Dynastart', and it was indeed a combined starter and generator.It was fitted to the Villiers engines of ,as he states, some of the weird 'economy' bubble cars of the '50's. It was also fittted,minus the reverse start facility,to some of the higher-spec motorcycles and scooters...............Mal.

                    I have also had engines starting in reverse,usually when flick-starting (i.e. not using a starter ) normally it occurs when the engine is a little too rich,or wet. It will start,then when the throtle is opened,it will usually die,but on occasion,it will give a cough,and continue running,but in the correct direction..............Mal

[Martin Harris - Moderator]

Posted by mal brewer on 22/03/2010 15:01:02:

I have also had engines starting in reverse,usually when flick-starting (i.e. not using a starter ) normally it occurs when the engine is a little too rich,or wet. It will start,then when the throtle is opened,it will usually die,but on occasion,it will give a cough,and continue running,but in the correct direction..............Mal

 I very often use this effect the other way to start engines from a reverse flick - particularly 4 strokes with a nice rich prime - although my OS91 FX loves it just as well and most of my other 2 strokes will bounce into life once they're nicely set up in warmer weather.

[Peter Beeney]

 Mal, Thanks for that. Now I remember, Dynastart!!! I didn’t get involved with these very much, it’s just that our gang had a few bubbles in those days and muggins usually got roped in when things went wrong. Talk about poke and hope………    I first found out, definitely the hard way, about the reverse gear in the invalid carriage, I was actually doing someone a favour. Took me a while to work it out and that was more by luck than judgement.  More lovely nostalgic flavours lurking here, I feel.         PB                                                                                                                                                                                                                                                                     

                                                                                                                                                   

Edited By Timbo - Administrator on 23/03/2010 12:44:10

[001]

re The bubble cars with electric reverse. They were usually fitted with a Siba Dynastart, or a Bosch unit. Messerschmitt 3 wheelers were fitted with it. My brother had a Berkeley 3 wheeler, (front wheel drive) that had a Siba Dynastart on an Excelsior twin 2 stroke engine, caused all sorts of problems caused by insulation breaking down. Villiers engines had them too.

I remember reading about a scooter owner who fitted the reversing version of the Dynastart to a scooter, I think it was a Durkopp Diana, because he had to wheel it backwards down a narrow passage to park it!

 

Also I recently, accidentally, managed to get my Enya 41 4 stroke to run in reverse.

[Brian Parker]

Reversing Dynastarts were also fitted to marine outboard engines. Oil contamination of the brush gear and CB points tended to be problem, usually at the most inopportune moment as I recall.

[John Privett]

2 strokes - no problem.  we've all "been there, done that, got the T-shirt." 

 

But I'm struggling to work out how a 4-stroke manages to run backwards.  Surely it is then sucking air in through the exhaust and exhausting out through the carb?  Maybe if there was some unburnt fuel in the exhaust it may run very briefly, and probably very badly.  Is that what people are seeing, or are they seeing more prolonged reverse running of 4-strokes?