The most common cause of
combustion problems such as pinking in MG engines is not fuel as usually
assumed (provided the engine is running on minimum 95 octane), but
distributors not performing to spec, especially wear in the centrifugal
advance mechanism of the distributor.Ford corteco oil seals . This slackness results in the distributor giving too much advance too soon with obvious results.
Often this is “tuned out” by simply retarding the whole distributor, a move which certainly stops the pinking but also leaves insufficient advance at mid to high engine speeds – leaving the engine well down on power and sluggish. Even setting the advance to the correct spec using a timing light at idle doesn’t solve it, as the distributor has already used up most of its advance at idle when worn like this and so will end up well short of where it should be at mid-high speeds.Ford corteco oil seals .
In the following example to illustrate what to do, I have used pre-73 MGB’s as an example as they are one of the worst culprits. However, all cars with old distributors will experience wear changes the advance rate and adversely affects both power and economy. Although what follows is for the early B, the principle is the same for most distributors – only the actual advance specifcations will vary, the procedure remains the same.Ford corteco oil seals .
The specifications you will need are the static, idle, maximum and intermediate advance figures. These can be found in the workshop manual. Key points in interpreting this data are:
Remember to identify whether the specs are referring to crankshaft or distributor degrees – timing figures are usually crankshaft degrees, but advance figures can be given in either.Ford corteco oil seals .
The advance figures given in the manual are the amount of advance caused only by the distributor. To get total advance you need to add to this figure the static advance. In our example, the MGB manual lists:
static advance as 10 degrees
maximum advance as 20 crankshaft degrees
-so the total maximum advance is 10 (from the static setting)+20 (from the distributor) = 30 degrees. The total intermediate advance figures are worked out in a similar way. In our example, the book lists the advance at 1500 RPM as being 15 degrees, so the total advance at 1500 RPM will be 25 degrees.Ford corteco oil seals .
Start off confirming the problem by first checking the advance rate of the distributor as it is. Using our example, we set the advance at idle to the factory speified 14 deg, then checking the advance at 2500 RPM with a timing light (vacuum disconnected) – it should be 30 degrees total. It should drop steadily through 23-24 deg @ 1750 RPM to 14 deg at 700 RPM. If it doesn’t meet this within a degree or so at each speed (many can be 10 deg or more out) the only cure is to strip the distributor and rectify the advance.Ford corteco oil seals .
Often this is “tuned out” by simply retarding the whole distributor, a move which certainly stops the pinking but also leaves insufficient advance at mid to high engine speeds – leaving the engine well down on power and sluggish. Even setting the advance to the correct spec using a timing light at idle doesn’t solve it, as the distributor has already used up most of its advance at idle when worn like this and so will end up well short of where it should be at mid-high speeds.Ford corteco oil seals .
In the following example to illustrate what to do, I have used pre-73 MGB’s as an example as they are one of the worst culprits. However, all cars with old distributors will experience wear changes the advance rate and adversely affects both power and economy. Although what follows is for the early B, the principle is the same for most distributors – only the actual advance specifcations will vary, the procedure remains the same.Ford corteco oil seals .
The specifications you will need are the static, idle, maximum and intermediate advance figures. These can be found in the workshop manual. Key points in interpreting this data are:
Remember to identify whether the specs are referring to crankshaft or distributor degrees – timing figures are usually crankshaft degrees, but advance figures can be given in either.Ford corteco oil seals .
The advance figures given in the manual are the amount of advance caused only by the distributor. To get total advance you need to add to this figure the static advance. In our example, the MGB manual lists:
static advance as 10 degrees
maximum advance as 20 crankshaft degrees
-so the total maximum advance is 10 (from the static setting)+20 (from the distributor) = 30 degrees. The total intermediate advance figures are worked out in a similar way. In our example, the book lists the advance at 1500 RPM as being 15 degrees, so the total advance at 1500 RPM will be 25 degrees.Ford corteco oil seals .
Start off confirming the problem by first checking the advance rate of the distributor as it is. Using our example, we set the advance at idle to the factory speified 14 deg, then checking the advance at 2500 RPM with a timing light (vacuum disconnected) – it should be 30 degrees total. It should drop steadily through 23-24 deg @ 1750 RPM to 14 deg at 700 RPM. If it doesn’t meet this within a degree or so at each speed (many can be 10 deg or more out) the only cure is to strip the distributor and rectify the advance.Ford corteco oil seals .
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