This is fairly simple question. How much spacing would I need between two #25 sprockets for the chains not to interfere. If anyone could help that would be great. I notice that the infamous 254/968 transmission has two sprockets relatively close together and if someone knew specifically how close they are that would be awesome.
A strand of #25 roller chain is a bit less than 5/16" wide across the length of the pins, so anything above 5/16" would work. I’d go with 3/8"
Just the person I wanted to respond. Thank you very much.
You might want to make it a little bigger for safety if you are not sure. I am not sure how much side ways slop you might have with the chain on the sprocket. Meaning the center of the teeth might not be the center of the chain if it can slide sideways just slightly. Also, you wouldnt want a master link or your link to snag against another chain if you didnt account for that.
Be sure there is enough clearance to get one chain off by lifting it from the sprocket if there is a second chain on the other sprocket. Otherwise you will always have to feed one chain off, which can be a pain depending on the configuration.
Perhaps some of the dimensions in this sprocket catalog would be useful. See page 77 - multiple strand sprockets. Note that I’m not sure if those are multiple individual strands or a composite single chain.
http://www.ustsubaki.com/pdf/sprocket_catalog/sprocket_catalog_L10916.pdf
Some actual chain dimensions:
to reiterate…
make sure you account for a master link on each sprocket possibly hitting each otherr
The Tsubaki chain catalog link above lists their dimensions for distance from centerline L1 and L2, which are different. L2 is the master link side, which protrudes further. That’s not to say that other chain brands won’t differ, but it’s probably representative. It may be ANSI-spec chain. The devil is in the details 
Oh, don’t forget that there will be some clearance between sprocket and chain and that the whole chain can slide laterally (axially) a wee bit. If you place the centerlines of the two sprockets less than 7/16" apart, be watchful. 3/8" might do OK… depends on which side the master link clip is on.
Hey all you math-wiz types: figure what size actual length spacer is needed on the shaft between the two sprockets to provide the correct distance. I’m too tired tonight from trying to figure out how to fix up an automated truck weighing system and a kiln position/board moisture tracking system for a local lumber company. SOmebody did some JAVA programming to tie things together and there are a few glitches…hmmm.
Most of the time when you have two chain runs driven off paired sprockets (at least from what I’ve seen) they are going to the same size sprocket on the other end. In which case, the chains will always stay relative to each other, and you can just space the master links apart and never have to worry about them hitting.
That is kinda the idea that I had. It will be same sized sprockets side by side so they should move relative to each other. This question is in reference to the west coast style drivetrain I have posted