This is an old thread, but it was one of the better ones that I found searching for the right dimensions for temporary spacers. Let me add one data point from my own prop, in hopes that it adds value to someone's build.
I already have my prop so don't actually need the spacers, but I thought I'd measure it to see how good that oft-quoted 2-1/4" spacer length was. My prop is a C2YR-1BFP/F74972 72" Hartzell constant speed, ordered directly from Vans.
Measured the horizontal distance between the edge of the flange that sits on the starter ring gear to the edge of the prop hub that the spinner bulkhead contacts. The distance on my prop was 2-1/2". Van's DWG C4 specifies the following stack-up against the prob hub:
- 1/4" S-604 spacer (came with the prop)
- 1/16" AN960-416 washer
- 1/16" S-602-1 spinner bulkhead
- 1/16" S-602B doubler ring
Temporary PVC spacers would go from the fwd edge of the starter ring gear to the aft edge of the spinner bulkhead (prior to trimming that bulkhead for the prop), so the correct size of the spacers should be the 2-1/2" distance, minus the S-604 spacer, minus the AN-960 washer, minus the thickness of the bulkhead =
2-1/8". I am not including the doubler ring thickness because the PVC spacers would not contact the doubler. This is 1/8" shorter than the 2-1/4" called out by Vans. Meaning if I positioned my cowling using 2-1/4" spacers, then installed the spinner on the actual prop, the gap between the spinner and the cowl would end up 1/8" too close. Glad I measured with the real prop.
At the end of the day, I think I will eventually just install the actual prop in order to properly position the front of the cowling, but hopefully this info helps someone. I'm glad I didn't just use 2-1/4" and cross my fingers.