Engine runs backwards

It can only happen if something inside the combustion chamber is hot enough to ignite petrol without a spark. So the water jacket might be 'cool' but that's irrelevant.

Reply to
Dave Plowman
Loading thread data ...

Yes I agree in this particular case, but you never know who else has the same problem and what they might have it with. I could have phrased it better though.

Crud in the oil filter of a newly rebuilt engine? But it has been rebuilt it so that it runs on, so you may well be right ;-)

Ron Robinson

Reply to
R. N. Robinson

That was a mistake.

The fuel is being ignited by heat instead of a spark so it must be too hot inside the cylinders, whether caused by bad timing, excessively high compression or simple overheating due to a cooling system fault. Only the last one will normally be reflected on the temperature gauge.

If you retard the timing enough you can make the exhaust manifold glow, but be ready with a cloth to shove into the carburettor because it won't stop.

Reply to
Dan Buchan

ISTR this happening to an ancient mini which became wildly advanced due to a loose nut.

Reply to
No Good Boyo

Maybe not in this case, but it's a good reason for not allowing the engine to run backwards at any time. You could have the odd bit of swarf that wasn't properly flushed out :(

Reply to
Richard Porter

I'd say there's a very real possibility of nasties in the oil filter on a newly re-built engine which has had machineing work carried out - tiny particles of swarf etc. That's why you do an oil and filter change at 500 miles.

Reply to
Dave Plowman

Just curious - how can it happen on a cool engine? I thought it was normally the result of a hot spot, thereby turning the engine into a compression/ignition thingy (i.e. Diesel).

Best bit of backwards running I ever had was on a 1927 Rolls 20. Would often bounce back after shutdown, and run quite happily for a couple of minutes, drawing air through the exhaust and breathing out through the carb until it finally died. Many years on, when I finally rebuilt the 4.2 XK engine in my Series 1 E-Type it would typically run on for about 20 secs after shutdown, then bounce back and run backwards for a few seconds before finally expiring in clouds of smoke which exited in spectacular fashion through the bonnet louvres. Turned out to be more a question of juggling fuels - FWIW I now run Shell Optimax plus Millers VSP to get the octane rating up a bit, and standard ignition timing - it now starts, runs and stops in orderly fashion.

Just thinking back to the Royce - sorry, drifting a bit off topic - a party trick was to start it without using either the starter motor or the handle. Just switch on the ignition then swing the advance/retard lever through its full arc. Four out of five times it would gently chuff into life. Hugely impressive!

Geoff MacK

Reply to
Geoff Mackenzie

That's interesting - Optimax is 98.5 ron. Where do you estimate this figure goes by further adding VSP? It's an octane booster as well as lead replacement isn't it?

I noted recently that the new BP fuel (Ultimate?) is *only* 97 ron, whereas in Greece they punt it out as 100ron!! When asked their press office mumbled about "different market requirements". I fail to see what these can be, can't imagine the Greeks are being sold cars too different to the ones in this country aside from a few ambient temperature mods. Odd.

-- Ken Davidson DocDelete

Reply to
DocDelete

It is possible, of course, but not if the build has been done properly. Depends who you go to.

But it does remind me of a while back when I was rebuilding a rather odd twin cam Ford motor (never did find out what camshafts it had) and went to Cosworth for some bits. Mentioned to them that I could do with some camshaft bearings and they produced a large box of them and said 'take your pick'. Apparently when they bought in engines from Lotus for their own conversions they changed all the bearings as a matter of course even though the unit had probably only run for a few minutes on a test bed. Looking at the contents of the box I could see why - someone at Lotus must have had a touching faith in the lubrication properties of floor sweepings. I did just about manage to put together a decent set, but it wasn't easy.

Ron Robinson

Reply to
R. N. Robinson

IIRC fuels do actually vary quite a lot from country to country. Maybe Rons do as well.

Perhaps I ought to know...

Ron Robinson

Reply to
R. N. Robinson

I don't think RONS differ from country to country. In the US, however, "pump" octane is rated as the average of its RON and MON.

The three US grades you most commonly see are 86, 89 & 93.

Reply to
Dan Drake

know! My engine was originally intended to run on five star, and the last petrol station I know of selling this quit in about 1974. For a while I ran on four star, with the ignition timing backed off a bit, but I never liked the idea.

These many years on I can now run Optimax plus VSP (used only for its octane boosting ability, not to ward off valve seat regression or other alleged problems) and can use the original ignition settings without pinking, running on, hesitation or deviation. Have to admit that electronic ignition helped a lot with starting, though.

Geoff MacK

Reply to
Geoff Mackenzie

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.