Engine going backwards.

You can't run a four stroke engine backwards. It would compress gasses drawn from the exhaust system and push whatever back out of the inlet manifold. One with red hot sparking plugs etc might just manage a couple of revolutions.

Some two strokes can be easily reversed by altering the ignition timing. This used to be the way with some bubble cars.

I'm not saying it'll run. Just that spraying petrol into the engine compartment might not be a good thing.

If you are thinking of the later Bond 3-wheeler, it just started in reverse; no alteration to the ignition timing was made. It was in such a low state of tune that the ignition advance would have been minimal.

Electric starting was provided by a combined starter/generator called a Siba Dynastart. To reverse entailed switching off, operating an electrical switch, then restarting. All gears could then be used to go backwards!

At around the same era I owned a 125cc BSA Bantam. With the folly of youth, I tuned it, raising its 5bhp to something possibly approaching 6! These revisions meant that it would sometimes backfire on starting, and run backwards. This was something of a surprise the first time it happened; I used it to good effect later to shock/amuse passers-by :-)

Chris

So the old addage of people being found dead in a bubble car, in a garage, because they drove in too far up against the end wall is a urban legend? :o)

PDH

One of my schoolmates' dad had one, and someone pushed him up to a wall in his bubble car for a giggle. He just opened the front to push on the wall and it moved backwards and he was out. Anybody who couldn't work it out didn't deserve to get out.

Steve

Most two-strokes with no auto advance run at a very high static advance - perhaps 30 degrees or so.

;-)

Probably. Those who had one without reverse remember you turned them round by simply lifting up the back.

I once saw a Yamaha 125 single sorta try to stall with a cough while stationary at traffic lights but it didn't actually stop running and picked up rpm again. Lights went green, rider seclected 1st, released clutch and moved off backwards.

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You can persuade some diesels to run backwards, in fact it took us some effort to stop JCBs doing it.

Some Lister type 1 and 2 cylinder diesels (eg road rollers / cement mixers) will run backwards quite well if you bounce them against compression...

Tim..

On a conventionally fuelled petrol (ie not a direct injection), they can't run backwards. When you reverse a four stroke, the inlet becomes the exhaust, and the exhaust becomes the inlet, so unless the petrol can defy laws of physics and get into the combustion chambers, it won't run.

Off course, common rail diesels and direct injections could possibly just about manage it, but the timing would be that far of, they probably wouldn't.

As for pre-common rail diesels, the basic pump designs won't pump at enough pressure for injection to occur when spun backwards, plus timing will be quite a bit out.

As to weather the ECU would detect this, it would probably detect a cam/crank sensor out of phase fault, leading to the engine management operating a reduced power mode, but the engine itself is more likely to stall before the ECU does anything about it.

Yep, the hydraulic pump used to supply enough back pressure to kick them a long way back if they didn't fire. Sounded lumpy as hell but apparently that didn't stop people putting them into drive & wondering what the hell was going on.

The timings random, it depends on the cam profile, some of them work.

The D3 Bantam was 1/16 of an inch BTDC. I've no idea what that is in degrees of crankshaft rotation, but certainly nowhere near 30!

Perhaps you are thinking of a design more recent than 1948 :-)

Chris

I was thinking of a '50s Vespa. ;-)