Fitting a Bosch Distributor, how and why

- by Ron Hayhurst

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For those wanting a sound automatic advance to their ignition, a popular modification is to fit a Bosch distributor – available from our A7 Cherished Suppliers. This is often the case where the moving parts on the later Lucas advance mechanism, are found to be worn.

There are two or three good articles on how to make this modification to be found on line. Contributors include Mike Davies and Geoff Howe of the Cornwall Club and Terry Griffin who is a Bristol Club member.

Both Clubs now have in their web pages some very good technical advice. If you go to , select “Technical” in the menu and scroll down to “Ignition Timing and Bosch Distributor” you will find the article by Terry Griffin describing how he modified the Bosch unit and set up the timing to get the right advance. As you may know, Terry is the Club’s top racing man having won trophies on many occasions in recent years. He knows how to get peak performance out of our meagre 748ccs ! However, he concedes that he is “not too bothered” about lack of torque at low revs – as when flogging up hill in an overweight Box Saloon ! ! This is not his experience of A7 life ! !

Hence the article “Ignition Timing and Bosch Distributor – further” which is found by scrolling down to the next item to the one quoted above. In it Geoff Hardman describes how the range of advance with the Bosch distributor is such that when set up for maximum advance (which suits Terry) it will be far too retarded at low revs and there will be a big fall off in torque. He goes on to describe the mod that fixes this which is to place a spacer over the back stop where the moving parts “rest” at low revs and this reduces the range to that found in the original Lucas unit.

Geoff includes a picture which shows a spade terminal slipped over the back-stop to act as the spacer. If you have a Bosch distributor this is almost a requirement for those seeking automatic advance; the only concession being for those who have retained a hand control option as wel!

A Cautionary Tale (technical tip if you like!) :

During a partial strip-down of my Bosch distributor to check all was well lubricated (source for another tip here) I discovered that the terminal on the back-stop had taken a bit of a battering. The blue insulation had gone and the rest was hammered down to less than a mm of thickness. It was easy enough to fix once the distributor was removed, the bits of blue shaken out and a new terminal fitted. I estimate it had taken about 5,000 miles to reach this stage, so you can add this to your 5,000 mile service check ! !


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