Friday, August 20, 2010


Bosch distributors, as used in Saabs with V4 engines, get old, tired and sloppy. [I've known some mechanics like that, too...]. Bosch didn't bother to put bushings at the BOTTOM of the distributor body, so over time and a lot of miles, the aluminum distributor body gets "hogged out". When that happens, the ignition point gap varies as the engine runs, the dwell changes, and the basic engine timing changes. And the engine runs like crap.

Here is my setup in that pretty blue lathe again, to machine out the bottom of the distributor body so I can install a bushing. I built a precision tool [mounted in the lathe chuck in this photo] to hold the distributor body on its exact center line. The precision lathe bit [shown in the steady chuck at the bottom of the photo] does not move. The chuck in the lathe rotates the distributor body as the steady chuck advances the bit through the body, machining the correct diameter hole as it goes.

Here I am using a larger bit in my big, commercial drill press to do a light chamfer in the freshly machined hole. This will allow the bushing to start into the distributor body easier.

I use a bolt that is machined to JUST slightly smaller than the diameter of the new bushing to guide the bushing into the distributor body. The bolt is long enough to fit through the bushing on the TOP end of the distributor body, so the bolt forms a perfect guide as I press the bushing into place. The bushing is an interference [plus] fit into the distributor body.

I use an adjustable reamer to open up the bushing to an inside diameter equal to the diameter of the distributor lower shaft, plus 0.003". I always HAND ream, and never attempt to speed up the reaming process as some might by putting the reamer in a hand drill. I ream a little, then test fit the shaft, and repeat the process until it is just right. When I'm finished with one of these Bosch distributors, it doesn't know it isn't young, vibrant and ready to go for thousands of miles once again.

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