Though the engine has nothing in common parts wise with the early VW flat 4, think the same design but with only 2 cylinders.Quote:
Originally Posted by justinc
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Though the engine has nothing in common parts wise with the early VW flat 4, think the same design but with only 2 cylinders.Quote:
Originally Posted by justinc
Yes, I was looking at those pics, remarkable similarityQuote:
Originally Posted by 101RRS
No, it doesn't. It becomes blow, bang, squeeze and suck. Anyone will tell you this doesn't achieve the required result. :redface:Quote:
Originally Posted by 101RRS
You mention a broken valve spring. Could it have dropped a valve? Seems far more likely than the running backwards scenario.
Otto cycle engines. which make up the vast majority of four stroke petrols, shouldn't be able to run backwards, as the "suck" stroke in your analogy becomes blow, which would give a blowback through the carb, rather than through the exhaust as normal. Running backwards happened on old engines on shut down due to carbon build up and also due to badly timed engines, but this was due to a hotspot in the combustion chamber and never lasted more than a second or two on petrol engines, as the fuel/air mixture was quickly exhausted. Seriously, how does a combustible fuel/air mixture come through a carburettor backwards? It flies in the face of all carburettor science.
I'm with Dave ( Blknight ) on this. It should be impossible. Of course, a DC starter would turn the engine backwards if the polarity was reversed, but what would that mean? Everything that clears going forward will also clear going backwards. It's simple engineering, and doesn't change with direction.
People often describe situations inaccurately. Ask any cop about eye witness reports. I don't mean to insult you or your contact, but it is true.
Without further evidence I'm going for a dropped valve.
a combuastion chamber injected diesel or a 2 stroke will happily run in either direction..
as there are very few 2 stroke petrols with valves I'm assuming its a 4 stroke.
anyway...
for a four stroke, normal operation starting at TDC with both valves on the rock.... (end of exhaust stroke)
1. the exhaust valve finishes closing and the intake valve opens, the piston moves down and draws in a fresh air/fuel mix. thats intake (suck)
2. the inlet valve closes, the piston swings past BDC and begins to compress the fuel air mix on the way up. Thats compression (squeeze)
3. approaching TDC the ignition system (points, mag, reluctor, coil pack) lights off the fuel air mix and as the piston over centers the burning mix raises the pressure and shoves the piston down, near the bottom the exhaust valve begins to open. thats power (bang)
4. as the exhaust valve opens the piston moves up the cylinder forcing the exhuast gasses out the exhaust and near TDC the exhaust valve begins to close and the inlet valve begins to open. Thats exhaust (blow)
Lets do that backwards...
1. the exhaust valve opens and draws in an air mix (no carby so no fuel, and while it would be nice we havent worked out how to appease the hippies by unburning things) near BDC the exhaust valve closes and the piston continues up into the power stroke.
2. the air is compressed and after TDC a spark turns up (wont work with some reluctor or electronic ignition systems)
3. the air expands and helps move the piston down the cylinder (but entropy means you dont get as much effort out as it took to squeeze the air in the first place)
4. near BDC the inlet valve opens and as the piston rises forces air out the inlet valve through the carby (which if its a very simple carby means you now have a flammable mix in the air intake and air filter)
now...
on a diesel.....
some (especially centrifuge blown and oiled 2 strokes) can run backwards (if you know someone with a unimog 1700 or 1750 that you dont like too much ask them to lend me their mog for a demo...) because a diesel only compresses air and then the fuel turns up. If the engine is warmed up enough and you can fling it fast enough the combustion chamber will be hot enough to light off the fuel even though its turning up late for the party.
IF you really work it hard you can set fire to the air filter...... (go on ask....)
The only 4-stroke I've seen run backwards was a N/A diesel dumper truck in the UK years ago, 3 reverse and 1 forward gear !
If he'd 'flooded' it to get it started it might run backwards very briefly, I tend to think it was the spring failing that caused the problem.
Colin
A couple of points - some two cylinder engines have a single coil, no distributor, with a spark every turn of the crankshaft in both cylinders. If Haflinger has this, could this allow the engine to run backwards?
In the distant past, a relative had a boat with a single cylinder two stroke petrol engine - reverse was engaged by throttling back to an idle and rotating the magneto 90 degrees (lever provided for the purpose), whereupon the engine would run in the opposite direction. The engine was, from memory, a "Blaxland Pup".
Don't need to. 6V72 would get close if you seriously ****ed up.Quote:
Originally Posted by Blknight.aus
I didn't know about the Mog thing.
Blow, Bang, Squeeze and Suck says it all for petrol, carburetted engines though. Won't work.
I have no knowledge of that particular engine, but two stroke, no cam no valve engines can run backwards. It's not so easy with 4 stroke, camshaft engines. Everything is against it, as Dave points out. It still requires a fuel/air mixture to be drawn through the carburettor. Doing it in reverse simply won't work.Quote:
Originally Posted by JDNSW
Quote:
Originally Posted by 101RRS
Thanks for that Dave - you articulated what I was trying to conceptualise.Quote:
Originally Posted by Blknight.aus
The guy is still claiming that the engine ran backwards but clearly not possible - seems a strange coincidence though that it drops a valve, most likely caused by the broken valve spring just as the starter is trying to turn the engine the wrong way but I guess these things happen.
Has solved my curiosity on this but I am not game to go back to the guy as he is already dirty on me for suggesting the damage was caused by a broken valve spring or sticky/dropped valve.
Cheers and thanks
Garry
No John it is just a standard layout with dizzy, points and a coil - same as any old series LR.Quote:
Originally Posted by JDNSW
However I can run my engine without a dizzy cap or rotor.
Here is my engine running
YouTube
Garry