Morris Minor Owners Club

First road testing after re-build of the engine was fine, but after a few miles a problem has appeared.

The engine idles fine...
The engine drives fine...

but, as soon as the car is put into drive & the rpm drops a bit, it starts misfiring
Accelerate & drive off & all is good again.

I have discovered that it is not firing on cyl no. 2 when under load at low rpm, so only firing on 3 cyls effectively.
The plug is fine (substitute made no difference) same with the plug lead & there is a spark at the plug when removed & engine running.

Baffled!

Can anyone help please?

Chris

Update..further investigations (colortune etc) seem to show that No' 2 plug is NOT sparking at low rpm

Question is, why not?

Distributor??

Chris Edgar wrote:Update..further investigations (colortune etc) seem to show that No' 2 plug is NOT sparking at low rpm

Question is, why not?

Distributor??

My money's on the rotor arm.

My money's on the rotor arm.

Interesting...During the course of the engine re-build, the rotor arm was "lost", so I had to get another PDQ, which I did from a local factor.
Trouble was, my dizzy is a 45D, not the original 23D which was fitted to the Marina engines. To cut the story short, the rotor arm I got may not be exactly right for the dizzy
There was also the high possibility that the dizzy took a clout during the time the engine was out.

Anyway, I have just swapped back to the original 23D dizzy & the problem is solved

So, you may just be exactly correct!

Thanks,

Chris

could have been the dizzy cap. if it had a clout the cap could have been damaged. if it was the rotor arm, why would it always only miss number 2?

Indeed & the cap looks fine.
But, the cap was removed for most of the time that the engine was out.
Seems too much of a coincidence that there would be a prob with the dizzy not related to the engine job, but having said that, all was good for the first couple of miles after the engine re-fit.

Seem bizarre to me, why it only missed cyl 2, but that's how it was...OK at 800rpm & up but when the revs dropped 100 or so lower as in when I engaged "drive", no. 2 simply "switched off".
Every traffic light or hold up in traffic & it went down to 3 cyls! unless I took the car back into neutral or park

Shame though, it was a nice shiny new 45D with a vacuum unit...but the replacement with the original 23D dizzy has fixed it.

How odd! Is this a simonbbc dizzy? Or accuspark ?? Does there seem to be play in the shaft ? But a 45D needs a longer rotor arm (it's a bigger cap) - and the smaller rotor arm from a 25 D will mean there is a HUGE gap for the spark to jump to each terminal inside the cap. Maybe it was 'just too far' to the #2 terminal. I suggest getting a new rotor arm for the 45D and try again.

It is an Accuspark.
The does seem to be a lot of slop in the shaft, but remember I had to get a new rotor locally & although it is clearly longer than the 23D r/arm it may not in fact be the correct one. So it could be that.
Odd that only no. 2 is affected..
I dare say I will get a new rotor from Accuspark sometime & try again as you say. Just at the moment I am happy to take a break, seem to have spent every minute working on that car lately...

I had thought to give myself one less job to do & left the dizzy in place when the block went in to be seen to. With the benefit of that wonderful thing, hindsight, I should have removed it...easily could have been bumped or whatever.

Just thinking about it now...if the end of the shaft has been bumped, & bent a little, that would result in the rotor going around eccentrically & maybe a long way from terminal 2 as it goes past...too far for the spark to jump.
How's that for a theory? I will have to take a hard look at the rotation of the shaft..easy now it's on the bench.

What next, I wonder?


Chris

If you want non standard bits it's no good telling the motor factor the model and year of the car you have, even if that's what they ask you for.

Much better to describe what you need, even better to take the old part in and match it up.

Surprised to hear there is play in the shaft as I'm guessing the dizzy hasn't done 100,000 miles.

That is the worry - because I suspect these are Chinese(or maybe Indian!!) copy dizzies - and if they are going to develop wear that quickly....... But a bent shaft would perhaps explain.

Well, I could not take the old rotor arm in to the factors, since the reason I needed a new one was that the original had gone adrift during the re-build.
Best I could do was research & produce a list of cars (such as Triumph 1300 & others) which had 45D as original equipment.

In all likelihood, the rotor they sold me was correct one ( it did fit) & in all likelihood the dizzy had been damaged in some way while the engine was out.

Be surprised if it had done 1000 miles, never mind 100k.
The cap mountings for the copy are no where as substantial as the Lucas original, BTW

Teach me to try & save a few minutes work!
Know better in future.

regards
Chris