Distributor Curves and testing machines

[euro911sc]

I was interested in how to test a distributor outside of actually pluggin it into the engine of a running car so I looked for some testing machines on eBay. One or two come up every now and then, but they are about 25 years old...

So I got to thinking about how to build my own machine (I used to build machines for a living once upon a time). The spinning of the distributor and the noting of rpm is simple... after that measuring timing is easy once I can pick up the spark firing... which seems to be an interesting issue for me since I am primarily a Mechanical Enginerd and not an EE.

I'm interested in hearing about how some of you experts test and re-curve a distributor and which machine you use to do it. I do not want to steal your work, just very curious about how the thing works and can be tuned and measured.

Best regards,

Michael

[Steve@Rennsport]

I have a Sun 504 for this job.

One adjusts stops, alters weights, and changes springs to achieve the desired results.

[304065]

Michael,

Warren and I were discussing this a long while ago.

You need the following.

3500 RPM motor with speed control, you could use a Variac on an industrial motor, or even something like a cheapo Harbor Freight electric drill would suffice;

Chuck or clamp to grab the distributor shaft. I was thinking of using a dril-mounted drum sander with a piece of rubber hose that fit over the sanding drum glued in place and the free end of the hose over the drive gear. This is enough to turn the distributor but not enough clamp to bugger the drive gear.

Some sort of a frame to mount the above in. Ideally you would mount the distributor in the same orientation that it sits in the car (measured with a magnetic protractor in two axes). This could be made from 2x4s and a wood boring bit used to fabricate the hole for the distributor.

Ok, now you need a tachometer for the shaft. You can use the car's tach for this, mount one in the frame also, or you could use a digital tach from the cheapo FLAPS, or you could use an optical tach from the aircraft supply people. That will tell you precise speed.

Now you need a way to measure advance. The best way to do this is with a cap, rotor, plugs, points, CDI and some way to ground the plugs. Set it up identical to the car and make sure you don't fry yourself with the high-tension current.

Next, a timing light. You would need to mount some kind of trigger wheel on the distributor drive shaft to give you a TDC reference mark. This could be fabricated out of cardboard and affixed between the chuck and the drum sander and glued to the drum.

Ready, go!

[Henry Schmidt]

To do the job right, you need the right tool.

[911parts]

I know this is an old post but:

Does the Sun 504 work on distributors with electronic pick-up or just point?

[Steve@Rennsport]

Originally Posted by 911parts

I know this is an old post but:

Does the Sun 504 work on distributors with electronic pick-up or just point?

Both, if you have a Pulse Amp for breakerless units. It won't do Hall Effect ones.
.

[florio]

Hi, I did it with a drill and an oscilloscope: It's very easy, you just need one of those little de-multiplier things you put on the drill to turn it into a screwdriver, attach it the wrong way round (so that the drill turns faster, should reach 3000 rpm) and set it into a rig to hold it connected to the distributor (this was a marelli S125).

For the timing, you pick up one signal from the points, and one from the spinning rotor (anything without too much jitter works, I used an optical pickup). The oscilloscope give you the rpm very precisely and you can read the advance from the delay between the two signals.

The only issue I found is the lack of vibrations from the engine which "helps" the springs respond to the change in rpm.

Let me know if you want more details.

Dario

[Amstaff]

Originally Posted by Steve@Rennsport

Both, if you have a Pulse Amp for breakerless units. It won't do Hall Effect ones.
.

What do you charge to set up a distributor? I have a 3.0 that I need the vacuum deleted and set up for carbs and 964 cams.

[Trackrash]

I have re-curved a couple of distributors over the years. Yea, the Sun machine is nice. I don't have access to one now, however.

I went through all the options recently. Like clamping it in my lathe and using a strobe?

I decided it made more sense to just put it in the car and use a timing light. Not that hard to R&R a dizzy. Got it right on the second time.

[911parts]

So will the Sun 504 work on 77 and earlier (point) distributors as well as SC electronic distributors? Where are the rebuild as well as different weights and springs supplied?