When I designed the jackshaft brackets, I included provisions for adjusting the primary chain tension. The bottom pillow block mounting bolt hole is oval, so that the jackshaft can shift fore and aft. However, I needed to ensure that the two pillow blocks were adjusted the same distance, and I needed something more positive than bolt torque to prevent driveline torque from pulling things out of whack. I designed 4-position tension adjuster plates. The range of adjustment is pretty small—only about 3.5 mm at the jackshaft—but the primary chain is not terribly long, and #35 chain only has a 10mm pitch, so it should be fine. I had SendCutSend drill and tap each bracket for a M5 socket head screws that acts as a locating pin.
I had to buy a 6.5mm drill bit to get a slop-free fit over the screw head. Despite having a Chinese drill press that wanders more than a desert cougar at night, I actually managed to fabricate the plates out of alloy pretty accurately. One of is slightly out-of-round, but not enough to effect function. I decided not to worry about making the outside shape look pretty.
I was half expecting some sort of glitch to surface when I installed them, but they didn’t get in the way of anything else, and they function precisely as intended. It’s certainly better than no adjustment at all.
