by JCS » Sun Jul 28, 2019 5:40 pm
Ok Guys,
First we will let Orlando have a chance with the next question on another subject, after this one.
I am not surprised that no one knows the answer, it is one that very few mechanics know, and as years roll by even less people are able to answer.
Even from the 60’s onwards successive engineers have forgotten the lesson. The problem appears not to have been known, at least in automotive circles until the 50’s. Bentley seemed to be unaware when he designed the Lagonda engine subsequently fitted to the Aston Martin DB2, engineers designing the RR V8 scored no better. Surprisingly Jaguar engineers did take action and I well remember the plaited HT leads within the sleeve in the new Mk X’s in 1963. If we dare straighten out the leads we had about 30 secs before we were looking for another job……..but hey today even main agents can sell HT lead organisers obviously they need some education!
The fault in the images is that the HT leads are fitted with the leads running parallel to each other for a considerable distance. This results in induction when unwanted cylinders fire when the leads are paralleled for somewhere exceeding 5 to 6 inches. In fact in this case the problem is so severe that the ignition IS suffering from induction problems. The leads should be crossed over each other, preferable every 6 inch or so.
A few decades ago I attended Technical College for many years and subsequently taught part time in automotive engineering. Throughout that time we used to invite the local technical representative of Champion to bring along their special induction rig to demonstrate HT lead induction. This demonstration was as follows:-
The engine used was a single cylinder test petrol engine rigged up to show this phenomenon in action. It was the single cylinder Caterpillar engine normally used by oil companies as the standard test engine to evaluate oils for piston ring sticking.
The engine had a H.T ignition lead of around six to seven feet long which was cut across at its centre that is the cable had been sliced so that the
lead was in two parts. One section connected to the magneto, one to the sparking plug. The engine was started by holding the two ends close
together, but so that any observer could see the H.T spark jump between the leads. The two sections of lead were then stretched out parallel with each other for about three feet and the cut ends separated. In this situation there was no direct link between the plug and magneto. The engine continued to run, up and down its normal revolution band from idle to full throttle without any misfire, and without a direct H.T lead connection.
When the room lights were turned out, it was equally obvious that no spark was jumping between the leads and the engine was operating only by induction of H.T across the lead. This proved that an engine could be operated, and H.T induction did occur when the H.T leads remained parallel for some distance within an ignition H.T harness.
Many years ago I purchased two cars that had faults that the factories and local dealers could not rectify. One was a 1987 Mini that could not be driven above 55 mph, the other about 1992 was a 1400c Vauxhall Astra with odd misfires. These cars were less than 12 months old and offered at very generous discounts. After looking under the bonnets of both cars, establishing the leads were paralleled, I was parted with my money and soon made my fortune after repositioning the leads.
Take note there is no physical jumping of the spark when this problem exists, the feeling is that the acceleration is being restricted.
Ok Guys,
First we will let Orlando have a chance with the next question on another subject, after this one.
I am not surprised that no one knows the answer, it is one that very few mechanics know, and as years roll by even less people are able to answer.
Even from the 60’s onwards successive engineers have forgotten the lesson. The problem appears not to have been known, at least in automotive circles until the 50’s. Bentley seemed to be unaware when he designed the Lagonda engine subsequently fitted to the Aston Martin DB2, engineers designing the RR V8 scored no better. Surprisingly Jaguar engineers did take action and I well remember the plaited HT leads within the sleeve in the new Mk X’s in 1963. If we dare straighten out the leads we had about 30 secs before we were looking for another job……..but hey today even main agents can sell HT lead organisers obviously they need some education!
[i][b][u]The fault in the images is that the HT leads are fitted with the leads running parallel to each other for a considerable distance[/u][/b][/i]. This results in induction when unwanted cylinders fire when the leads are paralleled for somewhere exceeding 5 to 6 inches. In fact in this case the problem is so severe that the ignition [b][i][u]IS[/u][/i][/b] suffering from induction problems. The leads should be crossed over each other, preferable every 6 inch or so.
A few decades ago I attended Technical College for many years and subsequently taught part time in automotive engineering. Throughout that time we used to invite the local technical representative of Champion to bring along their special induction rig to demonstrate HT lead induction. This demonstration was as follows:-
The engine used was a single cylinder test petrol engine rigged up to show this phenomenon in action. It was the single cylinder Caterpillar engine normally used by oil companies as the standard test engine to evaluate oils for piston ring sticking.
The engine had a H.T ignition lead of around six to seven feet long which was cut across at its centre that is the cable had been sliced so that the
lead was in two parts. One section connected to the magneto, one to the sparking plug. The engine was started by holding the two ends close
together, but so that any observer could see the H.T spark jump between the leads. The two sections of lead were then stretched out parallel with each other for about three feet and the cut ends separated. In this situation there was no direct link between the plug and magneto. The engine continued to run, up and down its normal revolution band from idle to full throttle without any misfire, and without a direct H.T lead connection.
When the room lights were turned out, it was equally obvious that no spark was jumping between the leads and the engine was operating only by induction of H.T across the lead. This proved that an engine could be operated, and H.T induction did occur when the H.T leads remained parallel for some distance within an ignition H.T harness.
Many years ago I purchased two cars that had faults that the factories and local dealers could not rectify. One was a 1987 Mini that could not be driven above 55 mph, the other about 1992 was a 1400c Vauxhall Astra with odd misfires. These cars were less than 12 months old and offered at very generous discounts. After looking under the bonnets of both cars, establishing the leads were paralleled, I was parted with my money and soon made my fortune after repositioning the leads.
Take note there is no physical jumping of the spark when this problem exists, the feeling is that the acceleration is being restricted.