Haflinger engine failure after running backwards

[101RRS]

Not my engine thankfully but a contact has had engine failure after it fired up and ran backwards.

The Haflinger engine is a normal 4 stroke engine with carbs and distributor - the only odd bits is that it is air cooled and a flat twin.

This guy connected the power leads to the starter the wrong way around so when started it turned the wrong way and fired up backwards and soon self destructed. One piston impacted the exhaust valve putting a hole in the piston - the valve did not break but as it was pushed sideways the valve guide was damaged, I noticed the valve spring was broken and the pushrod was bent. I am told there was no other damage. All to be expected when a valve impacts with the piston though a broken spring is not expected - did it break in the incident or is it the result of the incident.

Now the lobe profile on the camshaft is the same in opening the valve and closing the valve so there is no reason why the camshaft could not open and close the valve as per normal if going in reverse.

Now the owner is adamant the failure is because the engine ran backwards - I am not so sure because if it fired up why isn't there similar damage in the other cylinder (it is totally undamaged). Also I turned my engine backwards for over 50 revolutions by hand and there was no issue.

I suspect that there could have been a sticky valve allowing the impact to happen but more likely (as there is a broken valve spring) the spring broke and was no able to fully close the valve (maybe sticky as well) and as the engine is a "hemi" when the piston hits the valve instead of simply pushing it closed it is hit on the side and into the piston.

The guy has ordered new pistons, valves and a pushrod but did not realise he had broken valves so he needs to get them as well.

So what do the engine gurus think? If the lobe profile on the camshaft is suitable - should an engine be able to run backwards if accidently fired up?

Thanks

Garry

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[PhilipA]

You do not talk about how the timing chain is tensioned or its length, but it is conceivable that if the timing chain was old the timing backwards could be quite different to the timing forward allowing a valve to hit the piston.
Regards PhilipA

[101RRS]

Its a basic design so no timing chain -the cam shaft lives in the bottom end and is geared to the crankshaft then pushrods to the rockers on top of the heads which operate the valves - all these are not adjustable with the exception of the tappets.

Garry

[Graeme]

Turning backwards would be expected to slacken the timing chain if the tensioner was spring or oil pressure operated as the pull would be against the tensioner rather than against the camshaft. A fixed tensioner would maintain normal valve timing.

[justinc]

I'm suspicious of the ability of the starter to even engage the ring gear in opposite rotation. Normally a starter has a one way clutch / Sprag on the drive pinion to help it disengage after the engine kicks. Do these starters operate like any other?

[101RRS]

Hi Justin - there is no flywheel gear or throw out gear etc on the starter - the starter/generator is a combined dynastarter connected to the engine via a twin V belt to the crankshaft pulley. Power is applied to the starter which turns the engine via the belts and when it is running the starter being driven by the engine is then the generator.

The dynastarter is between the fan and the carb. It drives the fan and the pulley on start turning the crankshaft and when running the crank drives the fan and the generator. All DC so can go the wrong way if connected incorrectly.

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[JDNSW]

I wonder if running backwards loosened a nut on either the camshaft or crankshaft and resulted in a sheared key followed by mistiming?

[Blknight.aus]

not buying it...

sticking valve meeting piston I'm buying.

being a carbed engine it should be incapable of running backwards.

Being rolled over backwards maybe but not running.

[justinc]

Hi Justin - there is no flywheel gear or throw out gear etc on the starter - the starter/generator is a combined dynastarter connected to the engine via a twin V belt to the crankshaft pulley. Power is applied to the starter which turns the engine via the belts and when it is running the starter being driven by the engine is then the generator.

The dynastarter is between the fan and the carb. It drives the fan and the pulley on start turning the crankshaft and when running the crank drives the fan and the generator. All DC so can go the wrong way if connected incorrectly.

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Wow, thanks Gary what a great set up, learn something every day!!😊

[101RRS]

being a carbed engine it should be incapable of running backwards.

As Pauline would say - please explain [bighmmm]

Suck, squeeze, bang and blow still happens - I can see how the crank can go the wrong way and spark occurs when it should but I am not sure about the valves - valves will be closed at the right time but I have a suspicion that because the cam is turning the wrong way then exhaust valve might be open when it should be closed and likewise the inlet open when it should be closed - so not fuel/air mix gets into the engine but I am am having trouble to conceptualising this.

We know that an engine can fire backwards but can it actually run - without understanding the action of the inlet and exhaust valves I am not sure. However some ships I have been on actually fired their engines in reverse to go astern.

When I had the tappet covers off my engine - I should have checked what was happening with the valves when I manually rotated it in reverse.

Cheers

Garry

[101RRS]

Wow, thanks Gary what a great set up, learn something every day!!😊Though the engine has nothing in common parts wise with the early VW flat 4, think the same design but with only 2 cylinders.

[justinc]

Though the engine has nothing in common parts wise with the early VW flat 4, think the same design but with only 2 cylinders.

Yes, I was looking at those pics, remarkable similarity

[Tins]

Suck, squeeze, bang and blow still happens -

No, it doesn't. It becomes blow, bang, squeeze and suck. Anyone will tell you this doesn't achieve the required result. :redface:

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.

[Blknight.aus]

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....)

[gromit]

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

[JDNSW]

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".

[Tins]

(go on ask....)

Don't need to. 6V72 would get close if you seriously ****ed up.

I didn't know about the Mog thing.

Blow, Bang, Squeeze and Suck says it all for petrol, carburetted engines though. Won't work.

[Tins]

a single cylinder two stroke petrol engine -

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.

[101RRS]

Suck, squeeze, bang and blow still happens - I can see how the crank can go the wrong way and spark occurs when it should but I am not sure about the valves - valves will be closed at the right time but I have a suspicion that because the cam is turning the wrong way then exhaust valve might be open when it should be closed and likewise the inlet open when it should be closed - so not fuel/air mix gets into the engine but I am am having trouble to conceptualising this.


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)



Thanks for that Dave - you articulated what I was trying to conceptualise.

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

[101RRS]

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?


No John it is just a standard layout with dizzy, points and a coil - same as any old series LR.

However I can run my engine without a dizzy cap or rotor.

Here is my engine running

YouTube (https://www.youtube.com/watch?v=0dZghmByvHU)

Garry

[Tins]

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.



Pretty much what I was trying to say about people being inaccurate. They cannot deal with having their beliefs challenged. You'll see it every day on this forum, and please, I include me in this assessment, unlike some others.

[Milton477]

I have my doubts as to whether you could persuade a Dynastart to run backwards.

[Tins]

However I can run my engine without a dizzy cap or rotor.

Here is my engine running

YouTube (https://www.youtube.com/watch?v=0dZghmByvHU)

Garry

OK, that's fascinating.

Couple of questions.
1; Will it start like that?
2; What happens if you open the throttle?

I'm tipping the answers will be;

1; No, and
2; It will stall.

I have seen engines "diesel" before, and I suspect that yours is doing just that. Happy to be proven wrong, as I love to learn.

One thing though; will it do that backwards? I'll bet not.

[101RRS]

OK, that's fascinating.

Couple of questions.
1; Will it start like that?
2; What happens if you open the throttle?

I'm tipping the answers will be;

1; No, and
2; It will stall.



1. Yes it will start (how do you think I got it started [thumbsupbig]) [bighmmm] - answer turn the ignition key so the starter motor cranks the engine.

2. When you open the throttle it will rev fine and the car drives fine - have driven it like that - and no it is not dieselling.

[bigwhistle]

[thumbsupbig]

Garry

[101 Ron]

Haffie motors will run and last fine if not driven to their limits all the time,
They are well known to drop valves if driven hard .
Not possible for a Haffie motor to run backwards for any lenght of time.
Raising a rocker cover oil return pipe and therefore the oil level in the rocker cover reduces valve trouble under duress.
Think of early Volkswagon Kombi vans..........people would load them up a drive them over the Nullabour in 35 degree heat at 100 kph and they would drop a valve.
Same motor in a Volkswagon beetle never had the dropped valve issue.
The little motor in the Haffie works hard.
Every time I have seen one driven hard sooner or later goes bang.
Ex aussie army ones with the little belt driven governor on them and working with the extra air flow and oil cooling would last forever if the oil level and changes were kept up to it.
The motor design If memory serves me correctly as standard is 643cc and 24 bhp single thoat carby and 27 bhp dual thoat carby at about 4600 rpm which is about as hard as you really want to go on a 1950s design push rod engine meant for a scooter when designed and that horse power was never meant to be sustained on a scooter, let alone later uses for that motor in a
Puch car and Halfinger.
If driven as designed.......great motor.........if driven to its limits or hotted up its not so good.
The haffie motor wass designed in the 1950s ,in the haffie was governed and only had a 30 odd mph road speed.
That never happens these days as the haffies are driven to suit more modern times in countrys with hot climates and more open spaces than Austria.
Govenors were fitted to the haffie motors so they could not go bang
How many owners run the belt on the govenor?...............none.
Aussie army testing for our climate suggested the cooling mods for aussie army models.

[101RRS]

Good background - the car in question is not on the road and is undergoing a rebuild and the engine was just being started in the vehicle in the workshop. The owner is in denial on what occurred - also a concern the owner has not looked for, nor found the bit from the broken spring. Hopefully it fell out when the rocker cover was taken off but he did not realise the spring was broken.

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