Morris Minor Owners Club

after putting the engine back together it was running fine for a few miles but then started losing power, when I got to where I was going it wouldnt start at all, replaced the coil, and it started, but only running on 3 cylinders, ive now replaced the rotor arm and distributor cap, swapped over ht leads and spark plugs to other cylinders and they are ok, but any spark plug in the 3rd cylinder does not fire. what else can I check? only thing i can think of is if the spark plug is being insulated from the cylinder head by some dirt in the thread. any suggestions welcome, its currently at a friends house im getting a bus there tmorrow afternoon, prefer to drive home on 4 instead of 3!
Picky

If the spark side is as you say, then do a compression test.

Maybe the sprk plug itself has failed try taking it out and laying it on the block to see if you get a good spark

Maybe the sprk plug itself has failed

It sounds like the plug and the lead has been tested

swapped over ht leads and spark plugs to other cylinders and they are ok,

This is why i suggested a comp test, or another thought. maybe a rocker arm has moved or broken.

i know the spark plug is ok because i swapped two of them over, and still the same cylinder didnt fire, but the plug that was in the non firing one was running ok on another cylinder. i will check if the compression is different from any of the other cylinders. any other ideas what could be the cause??

rocker arms are all ok, as in not broken, will turn the engine over by hand to check valves are being opened and closed.

HT lead failed ? Oh I see you have swapped them over. Seems like blown head gasket or piston/ring failure causing total loss of compression.

Is the replacment dissy cap a new one? if not, then it sounds like above.

replacement cap was new from esm. compression sounds only probable answer, ill try a compression test

Hmm - remind us what was being done to the engine ??

confession of being a complete idiot: I left the ignition on, its been on for about 24 hours, all the wires to the coil and distributor look fried as is the condensor contact points and the coil. Will it be better to replace the whole wiring loom? I know i could just cut out the wires that have melted and fit new ones, but im thinking fitting a new loom might be less hassle in the end. had to be towed home The ignition is very easy to leave on, it only needs a very slight movement to get to the on position, and any key works in it, will replace this aswell..
how come no fuse blew? is there any way of preventing this from happening again, if the ignition gets left on?

Regards,
P***** off Picky

No fuse in ignition circuit. Was this after the 3 cylinder running episode? Yes better to get new coil/points/condenser. But it would only be current of 1 or 2 amps - can't see how the wiring would be damaged by that.

well all the insulation on the wires to the coil and the distributor are all melted, and the contact points the plastic bit has melted aswell. dont know why there was so much current there. Ive bought an 8 way fusebox, going to have everything on its own fuse. Yes this was after the 3 cylinder thing, that is still not sorted, but as its not running now i cant test compression.

Back on the original problem, it would be a good plan to check your tappets have adequate gaps.

At a guess the coil got so hot as a result of being left on without the engine running that the winding insulation broke down and caused an internal short. If as BMCEcosse says there is no fuse in the ignition circuit then a very large current would flow through it and the wiring would burn out. Just be thankful the car didn't catch fire. Whether it's worth replacing the rest of the loom depends on whether the insulation was damaged on the other wires that ran alongside the ignition ones.

alex, probably right with the coil...the wiring loom is quite tatty round the whole car as a general rule, so I think to fit a new one will be a good investment against future electrical problems. When I fit the new loom I will incorporate the new fusebox which can hold 8 fuses, so that I know everything runs through a fuse. might take a while looking at the wiring diagram but worth the effort.

I still need to still sort out the non firing cylinder, which i think must be a blown piston ring, just noticed that the breather pipe on the tappet chest has been belching out oil.. is this because the pressure from the dodgey cylinder is ending up in the crankcase? im hoping one day i will be able to get somewhere and back again in this car...

Yes -sounds like serious pressurisation - rings gone or even hole in piston. For that sort of current to flow - something in the igntion circuit has failed first - maybe the condenser. Normally would only be max 2 amps through points and coil to ground. Ignition circuit is never fused on older cars - and i suspect not on newer cars either.