Technical What is this Sun Attachment?

I got this Sun gizmo in a box of parts a long time ago. Looks like a distributor cap would attach to it. I think it's part of a Sun distributor machine. What is it and what is it used for?

 

It is for use with the leak down tester. You pull off the distributor cap, put this in place of the rotor. Once you have number one at TDC, you line up a mark on the distributor (hold down clamp, vacuum advance, etc)and bump the starter until the next number lines up. That will put the second cylinder in the firing order at TDC. It is setup for 4, 6, and 8 cylinder engines. You can even use it to set valves.

 

Looks like differant hubs would go with it (note the six lobe shape). If so, I would guess it’s used for phasing spark to cap terminal?

 

Thanks, anyone else have any thoughts?

 

The technically correct way to check cylinder leakage was with the piston at TDC on the compression stroke with the engine at or near operating temperature. This gave more accurate readings by taking into account any taper in the bore at the top of the cylinder.

If the crank was a few degrees before or after TDC (placing the connecting rod at a slight angle) when pressurizing the cylinder with air, it tended to want to push the piston down the cylinder to BDC where there was little or nearly no wear. To some degree at least it would give you a less than accurate leak-down percentage reading. With this indicator tool used on the distributor it made it a bit quicker and easier to find TDC for each cylinder.

 

So @Moriarity is there different hubs for this indexing plate to accommodate most engines?

 

If I remember right, there was a rubber cup on the bottom that would fit most distributor shafts(you can see that in the picture). The other side of the tool was marked just like the side you see in the picture. You indexed it to line up with something on top of the engine. It seems like there were also clips that allowed it to fit the GM distributors with the advance under the rotor. I believe the screws you see hold those clips.

 

Ok I see how it would clip onto to the rotor now that you’ve explained it. Thanks.

I just slice up my balance into for big peices of pie with tic marks. Looks like this 1|6 8|5 4|7 3|2 stamped in.

 

The handful of times that I ever used one of these indicators I remember bending up a piece of coat hanger or welding rod to use as a pointer. One end was shaped to mount under a bolt head, most often somewhere on the intake manifold near the distributor. The other end was then bent to point at the indicator dial once true TDC was found. The same results could be had with a degreed damper ring or using a timing tape but was usually harder to read.

One other thing to remember when doing a CLT, especially on a hot engine. Remove or at least loosen the radiator cap and place a fender cover or a couple moving pads over the top of the radiator before pressurizing the cylinder with air. If the engine has a cracked head or blown head gasket the line pressure from your compressor may quickly try to empty the cooling system by blowing heater hoses, radiator tanks or the heater core. You don't need a hot geyser erupting under the hood.