An odd "Pinking" experience. Not tickled pink!

[svenedin]

I set my ignition timing about 6 months ago when I had a Lucas 25D4 overhauled. I set the timing using a strobe and used the workshop figure of 6 degrees BTDC at 600 rpm, vacuum disconnected. I have Pertronix electronic ignition in this distributor.

Yesterday I was driving up some fairly steep hills probably in a gear that was a bit too high, 3rd rather than 2nd. I heard odd rattling which went away on the flat and then recurred on hills. I scratched my head. What could this odd noise be? Was it something loose, it sounded like it was definitely coming from the engine. Timing belt maybe I thought but why only in such specific circumstances. I stopped the car, no rattle at idle, no rattle revving the engine with the car stopped. Very strange.

We parked to go for a walk with the dog. During the walk I decided that this odd noise might be pinking because the circumstances in which it arose are the test to try to provoke pinking. On the way back we avoided hills and the noise did not happen but I was determined to check the ignition timing before the car was driven again.

I got the strobe on the car, vacuum disconnected and blocked, revs at 600 rpm. At first I could not understand what was going on. I could not see the timing mark at all. Then I discovered to my horror that the timing was so far advanced that the timing mark on the pulley was not where I was looking for it. At a guess the timing was something like 30 degrees advanced!! The was no kick back on the starter motor with this ridiculous advance so I had not realised.

All is now back at 6 degrees BTDC. I cannot explain how this happened. All I can think of is the distributor clamp bolt was not tight enough and somehow the distributor got pushed in the advance direction, rather a lot, when I was doing something else.

Whilst sorting this out I took the opportunity to fit a new O-ring on the distributor sleeve that goes in the block. There was an oil leak there.

Anyway, don't ignore new strange rattles! It may not be what you think.

Stephen

[myoldjalopy]

That is odd but I had a similar experience myself recently. Car had been running without issues for years. Then, at service time, I noted the points looked a bit worn and fitted a new set, together with a new condenser. The car ran rough on starting up, so I re-checked the points installation, gap etc. but no change. I fitted another set of points, and then another condenser, as I had touched nothing else but, although driveable, still very rough and exhibiting what I thought were symptoms of retarded ignition (lack of power, occasional misfire, poor fuel economy). To cut a long story short, it seemed that the timing was out and so the dizzy was turned clockwise a bit, and this improved things but then the vac advance unit was blocked by the dynamo and it was impossible to turn the dizzy further. So the dizzy had to come out and the drive removed and turned back a bit, allowing the timing to be set properly with plenty of space to rotate the dizzy further clockwise and then the car was back to normal performance.
But I can't see how this happened when all I did was fit a set of points and condenser Any thoughts, anyone?

[svenedin]

That is odd but I had a similar experience myself recently. Car had been running without issues for years. Then, at service time, I noted the points looked a bit worn and fitted a new set, together with a new condenser. The car ran rough on starting up, so I re-checked the points installation, gap etc. but no change. I fitted another set of points, and then another condenser, as I had touched nothing else but, although driveable, still very rough and exhibiting what I thought were symptoms of retarded ignition (lack of power, occasional misfire, poor fuel economy). To cut a long story short, it seemed that the timing was out and so the dizzy was turned clockwise a bit, and this improved things but then the vac advance unit was blocked by the dynamo and it was impossible to turn the dizzy further. So the dizzy had to come out and the drive removed and turned back a bit, allowing the timing to be set properly with plenty of space to rotate the dizzy further clockwise and then the car was back to normal performance.
But I can't see how this happened when all I did was fit a set of points and condenser Any thoughts, anyone?

Well, here is a look inside on of my Lucas 25D4 distributors with a new set of (Remax) points. All I can think of with your experience is that there is a difference between the design of the points you had originally fitted and the new set.

The design specifications of the plastic heel that contacts the cam is going to have an effect on exactly when the points open. The length and curve of that heel, if changed, could advance or retard the ignition. Usually as the heel wears, the ignition becomes retarded because it needs a higher part of the cam to open the points. Perhaps your new points have a longer heel or a different shaped curve that had the effect of advancing your ignition significantly? It is normal to have to reset the ignition timing when fitting new points but unusual that it is a big adjustment......

This is the same concept as one of my other hobbies, clock and watchmaking, where a cam and its lever determine exactly when a clock will strike. Subtle changes can make a significant difference.

Stephen

IMG_9094.jpeg (1.82 MiB) Viewed 6065 times

[myoldjalopy]

Interesting theory but I don't believe that was the issue, Stephen. The old points and the new both came from the Dizzy Doc. I even tried a set of new Lucas points I had knocking about. Its a mystery....

[svenedin]

It’s very strange. Did you also replace the distributor cap and install the HT leads rotated from their original position? That would require a significant rotation of the distributor to compensate. Btw I think that it is much easier to rotate the leads in the cap than to alter the distributor drive.

[myoldjalopy]

No, I only replaced points and condenser. The only thing I wonder about is that when I turned the starter handle to set the heel of the points, I found I had carelessly left the car in reverse with the brakes on, so there was some resistance before I realised my error . But I can't see how even that would have caused the timing chain to slip, or anything else that might upset the timing.

[oliver90owner]

But I can't see how even that would have caused the timing chain to slip,

If your timing chain can slip, you would soon be in deep mire. The timing chain alters the valve timing.

[myoldjalopy]

He he! Well, I'm grasping at straws now because I just can't think what happened - nor does anyone else I've mentioned it to.......
Like Stephen and his car experience, I wonder if the dizzy clamp loosened somehow, but I don't think it was that....

[liammonty]

He he! Well, I'm grasping at straws now because I just can't think what happened - nor does anyone else I've mentioned it to.......
Like Stephen and his car experience, I wonder if the dizzy clamp loosened somehow, but I don't think it was that....

If you are seeing far more advance than you used to, and are confident that the points gap (I suppose even better is dwell angle) is correct, I suspect you are looking at weak or broken springs in the distributor, leading to the distributor advancing far faster. I suspect this could also be the case for Stephen.

[myoldjalopy]

Yes but in my case, the timing was a bit retarded and it was necessary to turn the dizzy clockwise to get it right.....having repositioned the dizzy drive so that the dizzy could be turned far enough without hindrance from the dynamo, the car has run perfectly ever since (about a month now). It really was something that happened 'out of the blue' and Is till can't think why

[kevin s]

As above, 30 degrees is pretty much all the mechnical advance, I'd guess something has broken or seized in the distributor.

[svenedin]

As above, 30 degrees is pretty much all the mechnical advance, I'd guess something has broken or seized in the distributor.

I will check again with the strobe tomorrow. I would find this strange because the distributor was completely rebuilt by Distributor Doctor just 6 months ago. I will check the timing marks with the strobe at idle and then ascertain whether the timing advances as expected (vacuum disconnected) when the engine revs are increased. This should tell me whether there is a problem with the mechanical advance. If this is what has happened I would expect the car to feel very flat indeed when driven and that is not the case......

I think I did not tighten the pinch bolt properly and then bashed the distributor in the advance direction when I fitted a new fan belt and was lifting the dynamo to tension the belt but I do not remember actually disturbing the distributor so it is only a guess.

Stephen

[svenedin]

The timing is now "correct" as checked with a strobe. I had an assistant operate the throttle whilst I watched the timing marks and the ignition does advance (mechanical advance is working) as expected. However, on a test drive the car felt hesitant and the engine was not keen to run with the choke completely in. I examined the plugs after the test run and they were white. Mixture too weak. I have adjusted that now too. Given that it was such a big adjustment of the timing (it was so wrong) it is not surprising the mixture needed adjusting too.

Stephen

[oliver90owner]

Given that it was such a big adjustment of the timing (it was so wrong) it is not surprising the mixture needed adjusting too.

That statement frankly baffles me. Do you have any documented evidence of this? The engine will run hotter if the mixture is weak, but fuel:air ratio is a function of carburettor settings and air flow - nowt to do with timing.

Strikes me that there was quite a lot of wrong settings involved with the poor running.

[svenedin]

Given that it was such a big adjustment of the timing (it was so wrong) it is not surprising the mixture needed adjusting too.

That statement frankly baffles me. Do you have any documented evidence of this? The engine will run hotter if the mixture is weak, but fuel:air ratio is a function of carburettor settings and air flow - nowt to do with timing.

Strikes me that there was quite a lot of wrong settings involved with the poor running.

Indeed the mixture setting is a completely different issue and changing the ignition timing of course does not alter the mixture in any way. However, if you alter when the spark is delivered it is going to alter how the mixture burns and a tweak of the mixture may be necessary.

I am very puzzled by it all. I know that everything was set up absolutely fine but then I find it is not. My car was at a classic car show on 1st July. The bonnet was up and I did wander off several times. It seems bizarre but perhaps somebody had a good fiddle…..Wicked pixies? I find that hard to believe though but I did notice the pinking on a hill the day after the show.