This is my newly acquired refurbished Sun 400 Distributor Tester. This machine enables fast and accurate testing, troubleshooting and calibration of the distributor mechanical and Vacuum (if fitted) ignition advance mechanisms. An engine oscilloscope can also diagnose distributor faults quite easily while the distributor is still fitted to the engine but not all faults can be located with pin point accuracy. An example would be erratic timing movement which can be caused by several distributor related problems but can also be caused by mechanical faults in the valve train assembly. The beauty of a distributor tester is that all valve train components are removed from the equation leaving only possible distributor faults to blame. If the erratic timing still exists after a distributor re-calibration then the distributor is instantly ruled out as the suspect.
Setting centrifugal advance while the distributor is still in the engine can be extremely difficult if not impossible on most cars. With this tester the advance springs can be easily accessed and adjusted to specifications. Custom graphing an advance curve is easily achieved, sometimes in minutes rather than laboriously stopping and starting the engine to make adjustments. Within seconds any high rev problems will show up during testing. This machine is capable of spinning the distributor at 4000 rpm which equates to 8000 engine rpm. If there is even a small problem at that rpm then engine performance will suffer. That's taking it to the extreme of course as most engines only operate in the maximum area of 5500 to 6500 rpm for most mild engine set-ups.
A full distributor test with points ignition will take about 5 minutes using this tester. Once the distributor is serviced/rebuilt, a re-calibration back to standard specs usually takes about 10 minutes. A custom set-up may take up to half an hour depending on the distributor layout.
A full test with electronic distributors take a little longer because the trigger box must be disconnected and a special pulse amplifier connected to trigger the Sun tester.