I found a reference to this modification at Mini Mania message board and since a friend of mine had an allegedly locked distributor in his turbo Mini we decided to try this modification. He located a Metro turbo dizzy that was practically new and I did some measurements. Turns out the pre A+ and A+ dizzy are quite similar in the critical dimensions so swapping them to either block is quite straight forward. Basically fitting the Metro turbo (or any other A+) distributor requires only the older pre A+ drive dog and one hole drilled to the dog.
The photo on the left shows the Metro turbo electronic dizzy 65DM4 and an older 25D4. The bodies and drive dogs are different. The photo on the right shows the drive dogs removed from the shaft.
The vital dimensions (the shaft and body diameter and the length of the body that enters the block) are the same on both dizzys. So, when the drive dog is fitted to the A+ dizzy it locates in the exactly correct position depth-wise. The dog will engage to the dizzy drive shaft. The only difference in the both dizzys is the shaft length. On older dizzy the shaft is longer and it protrudes from the drive dog. This helps the drive dog to fit centrally on the drive shaft and prevent possible wobble at high revs. Whether this is a problem in real life is unknown.
The drive dog is loced on the shaft with a pin. The size of the pin is different, A+ dizzy has a smaller diameter pin. Again, hole on the older dog and the A+ shaft do not line up. I chose to drill a new hole to the drive dog and use the existing hole in the shaft. So, a 3,2 mm diameter hole was driller to the older drive dog. The new hole is 90 degrees at the old hole. This means that the dizzy orientation will be different once fitted to the engine. This is a simple question of rearranging the spark plug order.
After the new hole is drilled then the dog is secured on the shaft with the pin. Remember to fit the bearings on the shaft before the drive dog is fitted. To ensure that the distributor lines up with the drive shaft I turned a short spigot in a lathe. I then drilled and tapped the distributor shaft with M6 thread and fitted the spigot with Loctite and Allen head screw. An old A series distributor base blate was modified by grinding the ID to 40 mm diameter. The distributor is locked in place exactly as the older dizzy.
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| Updated November 20, 2001. |