Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Engine keeps on running!!!

I have an 82 4/4 with a cross flow fitted. Electronic ignition replaced the points some time ago, but otherwise standard.

When I turn her off at the switch, she continues to run for several seconds, juddering and making dying sounds, before she gives a final "whir" before stopping completely.

Does anyone know why this is, and how I can stop it? It is slightly embarrassing when your car impersonates chitty chitty bang bang when stopping!!!

It sounds as if the ignition timing is too far advanced and that you are getting pre-ignition - essentially hot spots within the combustion chamber are doing the job of the spark plugs. Switching off the ignition therefore has no immediate effect.

The juddering you referr to appears to confirm the problem. When the engine does this it's actually trying to reverse its rotation. The final whir happens when the engine goes into reverse rotation and is allowed to expire.

Having an engine's ignition timing too far advanced can seriously damage pistons and cylinder heads so I recommend that you check the timing accurately with a strobe. If the engine has been tuned, consider using a higher octane fuel or use an octane additive. aside from early Ford crossflow engines, the combustion chamber is in the piston, not the head so skimming such a head doesn't alter the compression ratio.

I'd also recommend that you check the cylinder compressions as it's possible that the head has not been converted for use with lead-free petrol. Erosion of the valve seats and/or valves may be the cause of your pre-ignition problem.

Hope that this helps and good luck!

Running on - that takes me back. Usually the problem is a carbon build-up in the combustion chamber, or some other hot spot. Sounds like a de-coke (is that word still used?) may be needed. And all that Mr Cheshire says makes sense.

Many thanks David. I will check the timing. I have a strobe for use on the bike but have never used one on a car. I may let my mechanic do it to save the faf. I will also use some booster to see if that helps.

Carbon and or spark plugs getting too hot.

Standard NGK plug for a cross-flow is a BP6ES, put a set of BP7ES plugs in, ie one grade colder running. I had the same problem years ago with two different cross-flows and colder plugs fixed it.

There is a downside in that the plug is slightly too cold for a standard engine, but it's only noticeable if you spend a long time in slow moving traffic.

Redex or Terraclean?

I know that it may feel like opening a can of worms but it is worth checking the cylinder compressions. If a de-coke is required or the valves and seats are a tad moth-eaten, then being OHV rather than OHC or DOHC, it's a relatively easy exercise to remove the head. And there are enough specialists who can convert to lead-free.

Of course once off, you could get it gass-flowed to gain improved performance or even go one stage further and dump the cast iron head for a nice CNC machined and ported aluminium cylinder head.

Thanks gents. She was converted to unleaded many years ago. I will go and check the plugs when this current rain has stopped.

I was thinking of chucking some valvemaster plus in to boost the octane. The terraclean looks good, but would another brand such as redex do the same thing?

Unless you have pinking, boosting the octane rating will do little. While the engine was designed for 98 octane, I never had problems with 95, and only put Super in for competition. And that was with a seriously looney crossflow, 1840, twin 45s and a ridiculous compression ratio.

Terraclean website is big on headlines and very thin on actual facts. Probably similar to Redex. Redex is basically a thin oil with a lot of detergents dissolved in it. Produces clouds of smoke and the feeling that must have done some good.

There is a problem with any liquid through the spark plug hole on that engine as a result of the design - flat head, bowl in piston. As a result, you raise the compression considerably and can create other problems as getting the bowl contents out is very difficult.

Put a new set of BP7ES in and go for a proper thrash! At least 20 miles, wait till water temperature hits normal, and increase the revs used.

BP7ES plugs are a bit cold for a standard engine, so I'll not rule out needing to revert to 6s but give it a go.

There is absolutely no point in fitting iridium/platinum plugs to that engine other than wallet emptying as no real performance advantage exists.

I have just spoken to my local motor factor and he was telling me all about Terraclean. Apparently it is not a thing you just add to the petrol. They plug in a seperate fuel supply with the terraclean in it. They then run the car and this stuff then cleans the engine. The chap was telling me about a Range Rover which had its mpg go from 12 to 18 mpg just after the treatment. However, its about £150 a go. I might do some more research. However, I am just waiting for her to cool down before fitting the new plugs.