engine runs backward

[Rust bucket]

Checked the web and some folk say it's impossible for an engine to run backwards, well I have a running on problem with my engine when the ignition is turned off. Only does it when it's normal or above temperature, tried everything........still does it.
As i leave the car in reverse gear when parked up I use this to stop the engine running on, car will creep forwards not backwards thus must turn over a few times backward...odd.

[oliver90owner]

Wrong plugs, wrong timing, wrong fuel mixrure? Modified engine? Requires a decoke? Those are the normal culprits.

[Rust bucket]

One thing has stayed the same all along is the fitment of an electronic distributor, timing has been adjusted but still believe that's the main problem. I may go back to points and see what happens.

[simmitc]

I have seen running on with a lean mixture caused by an air leak. Think about induction - compression - power - exhaust. If it was running backwards then you would have exhaust - fire - compression - induction - exhaust etc so you would have exhausted most of the mixture and have no compression, so I don't see how it could fire. 2-strokes can run in reverse but Minors have 4-stroke engines.

[oliver90owner]

The ‘running on’ is often caused by a hot spot sufficient to ignite the fuel mixture too early. While running fast enough it just pinks and keeps running in the normal direction, but just prior to stopping, the pre-ignition is so early that the piston direction is reversed, so the engine turns backwards and stops. The pinking is bad enough for the engine components but the forces on reversal of the engine direction are worse still. Good job it only happens once each time it stops! ‘Running on’ is likely to destroy the engine bearings prematurely, as well as cracking piston rings, so the fault certainly needs addressing.

Some 2 stroke vehicles, in the past, selected reverse by changing the engine rotation. One particular example that should not have reversed, but did, was an early walk-behind tractor (that was soon withdrawn from use) as it promptly ran over its driver. There are no examples of this model in existence as they were all very quickly recovered,by the manufacturer, and destroyed!

[pgp001]

We used to occasionally manage to start our old Field Marshall tractor up backwards, it was a bit disconcerting having one forward and three reverse gears !!

It was a two stroke single cylinder diesel with a piston the size of a bucket.

Phil

[don58van]

If I am not very much mistaken, some two-stroke mini-cars had to be started with the engine running in the reverse direction when the driver wants to move the vehicle backwards. I think the Gogomobil is an example. Perhaps the Messerschmitt 3-wheeler?.

Don

[BrianHawley]

I would not have thought true backward running was possible in the a series.

I guess a pressurised cylinder reaching the top of the up stroke when you let the clutch out in reverse could slowly push back down again, but that’s just half an engine rotation. Could explain it if the forward creep is very slight.

[oliver90owner]

There have been loads of instances of broken hands and wrists with a back-fire while hand cranking an engine.

I have seen the effect of a starting handle which struck the person after one reverse revolution - it broke his arm. I also remember the crank handle of a stationary engine flying some 8-10 feet in the air when an engine, Dad was starting, fired backwards - I had to avoid it it when gravity took over - and I was standing well back at the time! I always time the magnetos on my tractors to fire the right side of TDC. One has a capacity of 1.8 litres per cylinder, so one does not want that ‘kicking back’ while hand cranking!

Engines when rotating have inertia (stored energy) - that is why the flywheel is there.

RAB

[BrianHawley]

There have been loads of instances of broken hands and wrists with a back-fire while hand cranking an engine.

I have seen the effect of a starting handle which struck the person after one reverse revolution - it broke his arm. I also remember the crank handle of a stationary engine flying some 8-10 feet in the air when an engine, Dad was starting, fired backwards - I had to avoid it it when gravity took over - and I was standing well back at the time! I always time the magnetos on my tractors to fire the right side of TDC. One has a capacity of 1.8 litres per cylinder, so one does not want that ‘kicking back’ while hand cranking!

Engines when rotating have inertia (stored energy) - that is why the flywheel is there.

RAB

Agreed.

But OP’s post refers to “creep” which sounds like something slower and less dramatic than kickback.

[oliver90owner]

The engine kick-back caused the whole car to ‘creep’ a little. That was how I read it. Not that the car continued to be driven in the apparent wrong direction. Like I said, flywheels storecenergy when in motion.

[Edward1949]

If I am not very much mistaken, some two-stroke mini-cars had to be started with the engine running in the reverse direction when the driver wants to move the vehicle backwards. I think the Gogomobil is an example. Perhaps the Messerschmitt 3-wheeler?.

Don

In the late 1950s - early 1960s Bond Minicars with 2 stroke Villiers engines had this feature ( deluxe models only, the basic Mark D which I owned had hand-start only). This meant that a brave owner could go through the gears to over 50mph in reverse engine mode
I believe the system was called Dynastart, the dynamo and starter being a single unit.

[BrianHawley]

If I am not very much mistaken, some two-stroke mini-cars had to be started with the engine running in the reverse direction when the driver wants to move the vehicle backwards. I think the Gogomobil is an example. Perhaps the Messerschmitt 3-wheeler?.

Don

In the late 1950s - early 1960s Bond Minicars with 2 stroke Villiers engines had this feature ( deluxe models only, the basic Mark D which I owned had hand-start only). This meant that a brave owner could go through the gears to over 50mph in reverse engine mode
I believe the system was called Dynastart, the dynamo and starter being a single unit.

That is a truly terrifying thought

[Sleeper]

If I am not very much mistaken, some two-stroke mini-cars had to be started with the engine running in the reverse direction when the driver wants to move the vehicle backwards. I think the Gogomobil is an example. Perhaps the Messerschmitt 3-wheeler?.

Don

In the late 1950s - early 1960s Bond Minicars with 2 stroke Villiers engines had this feature ( deluxe models only, the basic Mark D which I owned had hand-start only). This meant that a brave owner could go through the gears to over 50mph in reverse engine mode
I believe the system was called Dynastart, the dynamo and starter being a single unit.

The same as on my old Greeves M/cycle...Siba dynastart..

John

[IslipMinor]

Before I fitted an anti-diesel valve from the MG Metro to our 1380, when unknown to us, it was running on a higher than calculated CR (was supposed to be ~10.5:1, but the head supplied by a then (1990's) very well-known A-Series engine tuners meant that it was actually more than 11:1!), we would often get what appeared to be 'backwards running' when the engine was switched off, and it ran on and then appeared to change direction until it stopped. I was never completely sure that it actually did ran backwards, but it certainly sounded as if it did.

Once the mistake was identified, we swapped the head for another 12G 940, and this time getting Peter Burgess to do the head work, the CR is now actually ~10.5:1, and no run-on at all.

[oliver90owner]

Yes, Richard, it would/could have ‘run on’ until it ruined the engine, but the last firing will be when the engine is reversed in direction. That is why it then stops turning. A huge overload on the bearings takes place when the charge has detonated but the piston cannot get over TDC, but not so much less while it detonates completely before the piston reaches TDC but has enough rotational energy to keep running forwards (the duration of the ‘run on’).

Purely a matter of piston velocity dropping to zero before TDC, thus producing that final reversal of several revolutions (without any other retarding influence like letting the clutch out while in gear to stall the engine)

Regards, RAB

[philthehill]

We need to be quite clear here:-
The 'A' Series engine will not run in reverse because of the inlet/exhaust manifold arrangement, the camshaft valve timing and the ignition timing.
If it does goes backwards one ore two revolutions at the most it will be because of other factors such as those stated above.
I would be looking at the ignition timing especially the static timing.