Engine runs backwards

My BMC "A" series 1100 engine in my Sprite has just started running backwards when I turn it off - a few revs and smoke comes aout of the air intakes - does anyone know what causes this?

There seems to be a lower suction throgh one of the carbs compared to the other. I don't know if this is related.

Thanks in advance

Stephen

Reply to
Stephen
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sounds like a bad need for some decoking here.

It's probably "running on", but backwards.

J.

Reply to
Jacques Hankin

I get this with a 1380 A+. It's caused by pre-ignition just before the engine stops. If the piston is before TDC when this happens it can spin the engine backwards, sucking in unburnt fuel from the exhaust system. It is not a good idea to let this happen, so if necessary stall the engine by putting it in gear and releasing the clutch.

Probably not. It happens with single carbs too. I've fitted an electric vacuum release valve from a Metro which is supposed to stop running-on but it's not entirely successful.

Reply to
Richard Porter

It's just been re-built - has new pistons done 200 miles.

Reply to
Stephen

It's 'running on' - caused by something inside the combustion chamber being hot enough to ignite fuel without a spark. Could be carbon build up or retarded ignition for running on unleaded. The smoke is because with the engine running backwards the carbs become the exhaust. It needs sorting, as it's possible for a fire to start this way.

I'd start by checking or replacing the points, then setting the ignition timing to standard, and running on Shell Optimax or BP Super - I doubt the extra cost of the petrol is significant with the mileage you're likely to do, and the car should run better with better MPG as well. Optimax should also help to get rid of carbon if this is the problem, unless the engine is very worn and using a lot of oil.

It's also possible to fit an anti-run on valve which lets in air past the carbs when you switch off, but an A Series in good nick shouldn't need one.

Reply to
Dave Plowman

You mentioned that it was newly rebuilt: it might be an idea to double check the cam shaft and distributor timing. is everything where it should be at TDC and at every turn of the engine?

Good luck, J.

Reply to
Jacques Hankin

Several possibilities - overadvanced ignition, wrong octane level petrol, serious need of a decoke, etc. No simple fix - just go back to basics and get everything right.

Geoff MacK

Reply to
Geoff Mackenzie

My mates jag xjs did this. It was stood for a year ... and had a bit of tlc before we tried to start it. New battery, oils, filters, plugs, leads, fresh fuel ... but wouldn't start on cranking. After towing it round the block in 2nd gear it started firing. When we started it on battery it fired, stopped ... then imediatly reved up in reverse (at least 3k revs) with smoke belching out the air box.

The cause was a jammed air flow meter flap ... the reverse revving damaged the oil cooler up front (made it leak!!).

Mind you .. when it reverse revved, it didn't half pink!!!

-- Regards..... Steve.

Reply to
FEo2 Welder

It definitely needs some TLC and checking basics like valve timing with crank at TDC, ignition timing, etc. Sounds just like the death throes of my Suzuki SJ413... Never found out what was wrong, binned the 1.3 Suzi lump and put in a 1.8 Manta engine & box instead...

Simon H

Reply to
Simon H

Why does the ignition timing affect it? The ignition has been switched off so there is no spark.

This is a rebuilt engine so it shouldn't need a decoke. Has the block or head been skimmed? This will increase the compression ratio unless compensated for elsewhere (head machined out, dished pistons or thicker gasket) and make detonation more likely particularly with low octane fuel.

Reply to
Richard Porter

If the timing is retarded the engine will overheat and perhaps run on.

Reply to
Dan Buchan

*Retarded* ignition will make it run hotter - and something inside the combustion chamber is glowing red hot, enough to ignite fuel with no spark.

If the head has been skimmed, it's possible the edges of the combustion chamber weren't relieved afterwards. Shards of metal can cause this. The 'spike' between inlet and exhaust in the combustion chamber is another possible source.

Reply to
Dave Plowman

True, but if it's been overadvanced and pinking it turns itself into a diesel when you switch off - will either run on or bounce off a compression and run backwards for a while. Just a matter of luck which way it goes.

Geoff MacK

Reply to
Geoff Mackenzie

compression

As an amusing tailpiece to this thread, of the 6 A-series engines in my motoring career, the only one that did this was a 1.3 Marina. It was a company car from new, and within a few months I could turn off the ignition, get out of the car and lock it (no central locking), walk up the garden path and be inside the house before the engine stopped. Happily it didn't run backwards though! It was such an awful car in every respect, and they even made the normally exemplary A-series engine fit the ethos of the rest of the thing. Does anyhone remember certain microcars which had no reverse gears, and ran their 2-stroke engines backwards in order to reverse? Must have been fun to get into top gear backwards. Sorry to digress - I am still in holiday mood.

Reply to
Les Rose

Bond 3 wheeler with single cylinder Villiers, needed to lift bonnet to kickstart the engine.

AJH

Reply to
Andrew Heggie

If the camshaft and ignition timing is right, then this is very probably the answer. If you don't want to take the head off again and radius everything off nicely you'll just have to get into the habit of engaging top gear and letting the clutch pedal up as you switch off. Do not let the engine run backwards, I have been told it can confuse some timing chain tensioners.

Ron Robinson

Reply to
R. N. Robinson

Also DAF Variomatics, being another two stroke. However the transmission means that they are somewhat easier to get to flat out in reverse !

Reply to
Samuel Clemens

Daf 55 & 66 (all that I know of) are four-stroke water-cooled four-pots, with reversing by bevel gears and a dog clutch in the front pulley box. The little 33 was an air-cooled boxer twin, but even that was a four stroke.

Reply to
Andy Dingley

Yes but Stephen said "overadvanced". Running on is not necessarily associated with overheating. It can happen on a cool engine.

Reply to
Richard Porter

Don't forget this is an A-series engine. There isn't a timing chain tensioner. Also unless it's had a vernier camshaft sprocket fitted the camshaft timing is not adjustable. If you get the chain one tooth out you will know about it! If the engine runs backwards the oil pump will be running backwards so no lubrication, and it could suck crud back out of the oil filter.

I agree that Dave's diagnosis is a very likely cause.

Reply to
Richard Porter

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