Most of the time the problem
is only a bit of wear in the secondary spring hook and/or its supporting
pins, allowing the distributor to advance too far before the second
spring takes up. The primary spring is seldom a problem in the MGB as it
is under constant tension when the car is running (and so doesn’t
chatter around the take-up point) and is also much lighter.Honda corteco oil seals.
Check the take-up point of the heavier spring – in our MGB example: when the heavier spring takes up, the cam should have moved about 1/3 of the way to its stop when the heavy spring takes up. Typically, in most worn MGB distributors the cam will advance nearly all the way before the larger spring cuts in!Honda corteco oil seals.
For other engines, you can work out the correct take-up point of the second spring by plotting the intermediate advance figures on a graph. Where the graph line changes gradient is where the second spring should take up. Work out what proportion of maximum advance is taken up at this point, and that’s the proportion the distributor cam should have moved towards its stop when the second spring takes up.Honda corteco oil seals.
New distributor springs are not available, but the problem is not insurmountable. Although the springs do lose a bit of strength with age/use, this is relatively insignificant compared with the additional advance generated by the wear in the spring hook and post.Honda corteco oil seals.
It’s easy to fix: It can be 90% cured simply and cheaply by closing up the hook on the heavier spring a bit so that it takes up at the correct point. To compensate for the normal amount of weakness in the secondary spring of a high mileage MGB, over-tighten the spring a little further. I usually close the hook up so that it takes up after one third of the cam’s movement from fully backed off to where it hits the stop. This is a degree earlier than original and gives a good approximation to the overall shape of the std advance curve with the average high mileage distributor.Honda corteco oil seals.
Closing the hook up is a bit fiddly: I grip the base of the hook (where it joins the main coil of the spring) in the corner of a vice, then tap the hook end-on with a small hammer.
Modified engines may require stronger springs to slow down the rate of advance (refer to the page on Setting up ignition timing for modified engines.) If the distributor springs are not strong enough, a stronger spring can be obtained from another Lucas 25D distributor. All BMC cars of the period had the same basic distributor, but varied in the spring strength and the point at which the secondary spring takes up. Suitable candidates are Mini or BMC1100/1300.
Once you have attended to the springs, install the distributor, reset the ignition timing & check the newly adjusted advance with the light again, followed by any final adjustments necessary from road test. You won’t believe its the same car after that!Honda corteco oil seals.
Check the take-up point of the heavier spring – in our MGB example: when the heavier spring takes up, the cam should have moved about 1/3 of the way to its stop when the heavy spring takes up. Typically, in most worn MGB distributors the cam will advance nearly all the way before the larger spring cuts in!Honda corteco oil seals.
For other engines, you can work out the correct take-up point of the second spring by plotting the intermediate advance figures on a graph. Where the graph line changes gradient is where the second spring should take up. Work out what proportion of maximum advance is taken up at this point, and that’s the proportion the distributor cam should have moved towards its stop when the second spring takes up.Honda corteco oil seals.
New distributor springs are not available, but the problem is not insurmountable. Although the springs do lose a bit of strength with age/use, this is relatively insignificant compared with the additional advance generated by the wear in the spring hook and post.Honda corteco oil seals.
It’s easy to fix: It can be 90% cured simply and cheaply by closing up the hook on the heavier spring a bit so that it takes up at the correct point. To compensate for the normal amount of weakness in the secondary spring of a high mileage MGB, over-tighten the spring a little further. I usually close the hook up so that it takes up after one third of the cam’s movement from fully backed off to where it hits the stop. This is a degree earlier than original and gives a good approximation to the overall shape of the std advance curve with the average high mileage distributor.Honda corteco oil seals.
Closing the hook up is a bit fiddly: I grip the base of the hook (where it joins the main coil of the spring) in the corner of a vice, then tap the hook end-on with a small hammer.
Modified engines may require stronger springs to slow down the rate of advance (refer to the page on Setting up ignition timing for modified engines.) If the distributor springs are not strong enough, a stronger spring can be obtained from another Lucas 25D distributor. All BMC cars of the period had the same basic distributor, but varied in the spring strength and the point at which the secondary spring takes up. Suitable candidates are Mini or BMC1100/1300.
Once you have attended to the springs, install the distributor, reset the ignition timing & check the newly adjusted advance with the light again, followed by any final adjustments necessary from road test. You won’t believe its the same car after that!Honda corteco oil seals.
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